Mitigation Assessment Team Report

Spring 2011 Tornadoes:

April 25-28 and May 22

Building Performance Observations, 

Recommendations, and Technical Guidance

FEMA P-908 / May 2012
All photographs and figures used in this report were taken by the 

MAT or developed for this report unless stated otherwise.

Aerial imagery sources (unless otherwise noted in the MAT):

•	Post-damage aerial imagery of Alabama and Mississippi: 

NOAA Imagery, http://ngs.woc.noaa.gov/storms/apr11_tornado/

(accessed August 16, 2011 through January 23, 2012).

•	Post-damage aerial imagery of Missouri: NOAA Imagery, 

http://ngs.woc.noaa.gov/storms/joplin/ (accessed August 16, 

2011 through January 23, 2012). 

•	Pre-damage aerial imagery: Google Earth Pro, 

http://www.google.com/enterprise/earthmaps/earthpro.html

(accessed August 16, 2011 through January 23, 2012). 

A special thanks to the Tuscaloosa County Sherriff’s Office and 

Emergency Management Agency for use of aerial photography taken 

after the tornado in Tuscaloosa, AL.

Any opinions, findings, conclusions, or recommendations 

expressed in this publication do not necessarily reflect the 

views of FEMA. Additionally, neither FEMA nor any of its 

employees makes any warrantee, expressed or implied, or 

assumes any legal liability or responsibility for the accuracy, 

completeness, or usefulness of any information, product, 

or process included in this publication. Users of information 

from this publication assume all liability arising from such use.
MITIGATION ASSESSMENT TEAM REPORT

Spring 2011 Tornadoes:

April 25-28 and May 22 

Building Performance Observations, 

Recommendations, and Technical Guidance

FEMA P-908 / May 2012

®

National Institute of

Standards and Technology
Members of the Mitigation Assessment Team

Executive Summary 

Glenn Overcash

Chapter 1

Amit Mahadevia

Lauren Seelbach

Chapter 2

Jason Senkbeil

Amit Mahadevia

Lauren Seelbach

Chapter 3

Erin Ashley

Samantha Passman

Lauren Seelbach

Chapter 4

Glenn Overcash

John Miller

Chapter 5

Dave Conrad

John Miller

Manny Perotin

Adam Reeder

Chapter 6

Tom Smith

John Miller

Manny Perotin

Jason Senkbeil

Chapter 7

Tom Smith

Dave Conrad

Manny Perotin

Lauren Seelbach

Laura Seitz

Scott Tezak

Chapter 8

Dave Low

Chapter 9

Scott Tezak

Larry Tanner

Chapter 10

Glenn Overcash

Erin Ashley

Dave Conrad

Dave Low

Samantha Passman

Tom Smith

Scott Tezak

Chapter 11

Erin Ashley

Dave Conrad

Dave Low

Glenn Overcash

Samantha Passman

Tom Smith

Scott Tezak

Appendix G

Glenn Overcash

Team Leader

Paul Tertell, PE, FEMA HQ

Team Manager

Erin Ashley, Ph.D., URS Group, Inc.

Team Members

John Battles, PE, CBO, ICC

Harold Colon, FEMA Region IV

David L. Conrad, PE, Atkins

Ron Cower, FEMA

Bob Franke, FEMA Region VII

Andrew Herseth, PE, SE, FEMA HQ

John Ingargiola, EI, CFM, CBO, FEMA HQ

David Javier, FEMA HQ

Neal Johnson, AIA, URS Group, Inc.

Marc Levitan, Ph.D., National Institute of Standards and Technology

Dave Low, PE, D.K. Low & Associates

Amit Mahadevia, URS Group, Inc.

Desiderio Maldonado, PE, Atkins

John Miller, PE, SE, J&M Engineering

Glenn Overcash, PE, URS Group, Inc.

Manuel A. Perotin, PE, CFM, Atkins

John Plisich, FEMA Region IV

Adam Reeder, PE, Atkins

Lauren Seelbach, EIT, CFM, URS Group, Inc. 

Laura Seitz, EIT, CFM, URS Group, Inc.

Jason Senkbeil, Ph.D., University of Alabama

Randy Shackelford, PE, Simpson StrongTie

Thomas L. Smith, AIA, RRC, TLSmith Consulting Inc. 

Eric Stafford, PE, T. Eric Stafford & Associates, LLC

Larry J. Tanner, PE, Texas Tech University

Paul Tertell, PE, FEMA HQ

Scott Tezak, PE, TRC Engineering

John W. van de Lindt, Ph.D., University of Alabama

Jeff Walker, PE, MCP, ICC

Erin Walsh, FEMA HQ

Internal Support

Technical and Management Support:

Samantha Passman, EIT, URS Group, Inc.

Technical Editors: 

Susan Ide Patton, URS Group, Inc.

Ivy Porpotage, URS Group, Inc.

Amy Siegel, URS Group, Inc.

Graphic Artists: 

Lee-Ann Lyons, URS Group, Inc.

Billy Ruppert, URS Group, Inc.

Aerial Image Creation:

Kevin McMaster, URS Group, Inc.

Advisors

Bob Bissell, Region VII

Ginger Edwards, FEMA Region IV

Albie Lewis, CEM, Region I 

Robert Lowe, FEMA Region IV

Chapter Leaders and Authors

Team Members
Dedication

FEMA and the spring 2011 Tornado 

Mitigation Assessment Teams dedicate 

this report to the memory of the 

victims of the April 25–28, 2011 

tornadoes in the southeastern United 

States and the May 22, 2011 tornado 

that struck Joplin, Missouri.

This report is also dedicated to the 

families, friends, and communities 

suffering from their loss.
Photographs that appear across the top of the first page of each chapter (from left to right): 

300-foot latticed cellular tower that collapsed during the tornado event (Tuscaloosa, AL); Glazing damage at 

patient rooms (St. John’s Medical Center, Joplin, MO); FEMA-funded residential safe room (Smithville, MS); 

Corridor designated as tornado refuge area; debris was blown into it during the tornado (Joplin High School, 

Joplin, MO); Failed steel column (Fitness Center, Tuscaloosa, AL)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT i

Executive Summary

The Southeastern and Midwestern portions of the United States 

experienced historic tornado activity in the spring of 2011.

During the week of April 18–22, 2011, the meteorological community began to discuss a potentially 

significant severe weather scenario developing in forecasted model runs for the following week. 

Several telling meteorological parameters foreshadowed the historical tornado activity that was to 

follow. The tornado outbreak that ensued resulted in April being ranked the country’s most active 

tornado month on record, with 753 tornadoes. The previous record had been set in April 1974, with 

267 tornadoes. From April 25 to 28, 2011 hundreds of tornadoes touched down from Texas to New 

York, with some of the strongest and most devastating on April 27 occurring in Alabama, Mississippi, 

Georgia, and Tennessee. According to the National Weather Service (NWS), tornado-caused deaths 

reached 364 during the month of April, with 321 people killed during the April 25–28 tornado 

outbreak. 

Less than a month later, on May 22, more than 50 tornadoes touched down across an eight-State 

area, the most powerful of which was a 0.75-mile-wide tornado that cut a 6-mile path through Joplin, 

MO. The tornado destroyed thousands of homes and caused widespread damage in the city. This 

historic tornado resulted in 161 fatalities, the most fatalities ever recorded from a single tornado 

since modern record keeping began in 1950. 
ii MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

EXECUTIVE SUMMARY

While tragic, major catastrophic events and disasters such as the tornadoes of spring 2011 often afford 

unique opportunities to research how hazards affect the built environment. The maximum winds 

associated with many of the tornadoes were well above the wind speeds used to design and construct 

many of the buildings damaged and destroyed during the tornadoes, so significant damage to the 

built environment would be expected. However, important information can be garnered related to 

building performance and tornado sheltering after such an event. Damage assessments can also be 

used to measure the effectiveness of adopted building codes, standards, and practices, and to assess 

how buildings built to design-level or near design-level respond near the edge of violent tornadoes or 

along the path of weaker tornadoes.

The Federal Insurance and Mitigation Administration (FIMA) of the U.S. Department of Homeland 

Security (DHS) is responsible for investigating the effect of such events on the built environment. 

In response to a request for technical support from the FEMA Regional offices in the impacted 

states, FEMA deployed a Mitigation Assessment Team (MAT) to investigate the damage and provide 

technical assistance to the affected communities through their Joint Field Offices established in 

response to the events. The purpose of the MAT deployment was to assess the performance of 

buildings, infrastructure, and safe rooms, storm shelters, hardened areas, and tornado refuge 

areas affected by the tornadoes. The MAT was first sent to Alabama, Mississippi, Georgia, and 

Tennessee on May 6, 2011 and then re-deployed to Missouri on June 1, 2011. The MAT included 

FEMA Headquarters and Regional Office engineers, scientists, and communication specialists; 

representatives from academia; and practicing architects, engineers, and building experts from the 

design and construction industry. 

The MAT investigated the performance of residential buildings, commercial and industrial buildings, 

critical and essential facilities, and infrastructure, as well as safe rooms, storm shelters, hardened 

areas, and tornado refuge areas. Additionally, the MAT rated building damage according to the 

Enhanced Fujita (EF) tornado scale to assess wind speeds exerted on the building. The MAT then 

developed conclusions and recommendations based on their assessments. This report presents the 

MAT’s field observations, as well as subsequent conclusions and recommendations.

Observations 

The following summarizes the observed damage and overall building performance by type or use of 

the buildings or structures. 

Residential Construction: Groups of one-, two-, and multi-family residential buildings provided 

opportunities for the MAT to compare damage to multiple buildings. Most of the residential building 

stock affected by the storms were older homes, but some were newer and in compliance with the 

International Residential Code (IRC). The newer structures generally performed well under designlevel wind loading, but the older structures with non-code-compliant construction failed under 

comparable wind conditions. Additionally, throughout the damaged areas, the MAT observed a lack 

of above-code design construction practices, which left the buildings vulnerable to damage from the 

tornadoes. 

Damage was progressively more severe with increasing winds, and revealed structural vulnerabilities 

in buildings, particularly in those subject to winds below the IRC design level of 90 miles per hour 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT iii

EXECUTIVE SUMMARY

(mph). Not unexpectedly, the damage occurred even in new, code-compliant construction in areas, 

as wind speeds were estimated to be well above the IRC design level of 90 mph (3-second gust).

Commercial and Industrial Buildings: The types of commercial and industrial buildings the MAT 

visited are normally designed by a design professional. Accordingly, the MAT assessed the design 

approaches and construction techniques observed in the context of building damage sustained when 

these structures were exposed to the design-level or higher wind speeds. Buildings designed to the 

latest edition of the building code have some capacity to resist above-code level wind speeds, but are 

not able to resist violent winds associated with extreme wind events such as EF4 (associated with 166–

200 mph winds) and EF5 (associated with winds over 200 mph) tornadoes. While failed elements 

of the building envelope contributed to damage, significant portions of commercial and industrial 

buildings were determined to have collapsed when the load path of the Main Wind Force Resisting 

System (MWFRS) was disrupted through structural connection failure. 

In general, buildings the MAT observed appeared to have been designed and constructed in 

accordance with the applicable building codes, but experienced failure of the building envelope and 

structural systems when loaded beyond code parameters.

The MAT noted several commercial and industrial buildings, particularly one- and two-story buildings 

with long-span roofs that suffered catastrophic failure when small, localized failures progressed to 

affect larger areas. In some cases, progressive collapse was the result of a lack of redundant stability 

systems or non-discrete structural systems. Another factor that contributed to complete building 

collapse was the failure of structural connections when load paths were not continuous, such as with 

unreinforced masonry (URM). 

Some of the commercial buildings had operational plans to direct people to refuge areas. While 

these operational plans were diligently activated, in most cases, people were directed to places in 

the building that were not hardened to provide life-safety protection. Further, most of these areas 

were not evaluated by design professionals to identify their vulnerability to damage and failure from 

extreme wind events.

Critical and Essential Facilities: The critical and essential facilities observed by the MAT included 

schools, healthcare facilities, first responder facilities (police and fire stations), and Emergency 

Operations Centers. Most of the buildings were damaged by winds estimated to be at or below designlevel wind speeds, and in general performed no better than commercial and industrial buildings. 

Since it is of vital importance to communities that critical facilities remain functional during and after 

tornadoes, the MAT assessed whether the observed critical facilities had areas specifically designed 

to provide life-safety protection, and if so, whether the areas met the near-absolute protection offered 

by a safe room designed to FEMA 361, Design and Construction Guidance for Community Safe Rooms 

(FEMA 2008a) or a storm shelter designed to International Code Council (ICC) 500, Standard for the 

Design and Construction of Storm Shelters (ICC/NSSA 2008). The MAT found that none of the observed 

facilities along the path or in the periphery of the tornadoes had areas specifically designed for lifesafety protection. Instead, emergency plans often directed building occupants to interior corridors 

or restrooms, areas that provided varying degrees of protection. 

Infrastructure: The MAT assessed tornado damage to communications towers, water treatment 

and distribution facilities, and one wastewater treatment facility. Communications towers not 
only support cell phone service, but are relied on by emergency management agencies and first 

responders. Disrupted operations of community infrastructure due to electrical service interruption 

or structural failure frequently delayed recovery efforts. Wind-blown (“wind-displaced”) materials 

that adhered to latticed communications towers, while presently not accounted for in tower design 

standards, likely contributed to observed tower collapses. There were numerous examples of how 

wind-displaced materials may have increased loads on communications towers. Furthermore, the 

MAT inspected the failure of guy anchors when wind-displaced materials struck the guy wires of a 

communications tower, resulting in its collapse. The current criteria and guidance for the design of 

communications towers does not address increased wind pressures when wind forces act on debris 

that has become entangled with the structure. 

The MAT observed water distribution facilities, water towers, and pumping stations rendered 

inoperable because of power interruption; this led to water loss and decreased water pressure, 

which in turn exposed communities to a risk of contamination and health hazards resulting from 

unsanitary conditions. 

Safe Rooms, Storm Shelters, Hardened Areas, and Tornado Refuge Areas: The MAT observed 

safe rooms, storm shelters, hardened areas, and tornado refuge areas in residential, commercial and 

industrial, and critical facilities, as well as stand-alone community tornado refuge areas. All residential 

and community safe rooms and storm shelters that the MAT observed were built before the adoption 

of the 2009 International Building Code (IBC) and IRC, which codified the requirements of ICC 

500, with the exception of a storm shelter constructed in Seneca, MO. Inspection of safe rooms and 

storm shelters revealed that many of them had one or more of the following deficiencies:

+ Doors and door hardware not designed or constructed to meet known wind and wind-borne 

debris impact criteria for life-safety protection

+ Inadequate ventilation

+ Inadequate anchorage of pre-fabricated units

+ Undocumented location

+ Lack of backup system to provide communications capabilities if needed 

The MAT heard numerous accounts of homeowners seeking shelter in basements or interior rooms. 

Similarly, operational plans in critical facilities often designated hallways as refuge areas. While 

building occupants often consider basements, interior rooms, and hallways as areas of refuge, the 

MAT noted many instances in which seeking cover in these areas was not a safe option. The MAT 

observed areas labeled “tornado shelter” that were used as refuge areas but that had not been 

designed or constructed to provide life-safety protection or evaluated by a design professional to 

identify vulnerability to damage and failure during an extreme wind event. Although enhanced windresistant construction may reduce damage to buildings, only safe rooms or storm shelters hardened 

to provide life-safety protection from tornadoes can truly provide protection during tornadoes. 

The amount of time between the warning and the tornado, which influences where people seek 

shelter, varied significantly. In the April tornadoes in the Southeast, warnings of the likelihood of a 

iv MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

EXECUTIVE SUMMARY
massive tornado outbreak prompted early school dismissals. The rapidly forming tornado that hit 

Joplin, however, left residents with less than 20 minutes to seek shelter. 

Recommendations

The MAT’s key recommendations in this report are presented in Table ES-1, grouped by topic area. 

Table ES-1: Summary of the MAT’s Key Recommendations

Topic Subtopic Key Recommendations

Codes and 

Standards

Residential State and local governments should:

•	 Adopt and enforce current model building codes

•	 Increase emphasis on code compliance

•	 Maintain and rigorously enforce the adopted model building code since 

amendments or lax enforcement practices may weaken the continuous 

load path of the building

Commercial 

and Industrial

•	 Include failure states and survivability in building codes and standards

•	 Change risk category for large-footprint commercial structures with 

long-span roofs to Risk Category III in ASCE 7-101

•	 Improve design approach in ASCE 7 and IBC to address risk consistently 

across hazards

•	 ASCE 7 should improve the commentary on code limitations

•	 Clarify risk tolerance in ASCE 7 and IBC

•	 Include best practices for wind design in IBC

Critical Facilities •	 Change code to require newly constructed schools; 911 call stations; 

emergency operation centers; and fire, rescue, ambulance, and 

police stations to include a FEMA 361-compliant safe room or ICC 

500-compliant storm shelter

Tornado Refuge 

Areas, Hardened 

Areas, Storm 

Shelters, and 

Safe Rooms 

•	 The ICC and FEMA should continue to coordinate standards and 

guidance for storm shelters and safe room design

•	 Improve performance of safe rooms and storm shelters through 

adoption and enforcement of the 2009 or newer versions of IBC and IRC, 

which require compliance with ICC 500 for any storm shelter 

•	 Change code to require new buildings that do not incorporate a FEMA 

361-compliant safe room or ICC 500-compliant shelter to identify the 

best available refuge area(s)

Building Type Residential •	 Implement voluntary best practices to mitigate damage to one- and twofamily residential buildings

1 A Risk Category is assigned to buildings based on the risk to human life, health, and welfare associated with potential damage or 

failure of the building (per ASCE 7-10). The assigned Risk Category, I through IV, dictates the mean return interval for a design event 

that should be used when calculating the building’s resistance to the events. In ASCE 7-05, Risk Categories were called “Occupancy 

Categories.”

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT v

EXECUTIVE SUMMARY
Topic Subtopic Key Recommendations

Building Type Commercial 

and Industrial 

•	 Install a storm shelter or safe room or identify best available refuge areas 

in large-footprint buildings 

•	 For all public buildings, install signage in a conspicuous place at building 

entrances that states relevant building design parameters and additional 

signs indicating refuge areas

•	 Place decision-making check lists or flip charts for emergency protocols 

in prominent locations

•	 Do not use URM in primary or critical support areas of a building

•	 Use screws in deck-to-joist connections instead of puddle welds

•	 Include enhancements to building connections beyond the code 

requirements

•	 Incorporate redundancy into the MWFRS

•	 Incorporate more redundancy in the design of large-footprint buildings

•	 Use discrete structural systems in large, long-span buildings

Critical Facilities •	 Perform a vulnerability assessment and identify best available refuge 

areas in existing buildings

•	 Include safe rooms in design of new buildings

•	 Enhance building design to better withstand tornadoes 

•	 Strengthen the facility to remain operational following a tornado or highwind event

Infrastructure •	 Work collaboratively to better understand the risks of wind-displaced 

materials on communications towers

•	 Work collaboratively to better understand the effects of wind-displaced 

materials on latticed structures

•	 Provide alternate electrical source

•	 Work collaboratively to better understand communications tower 

performance

Tornado Refuge 

Areas, Best 

Available Refuge 

Areas, Hardened 

Areas, Storm 

Shelters, and 

Safe Rooms

•	 Research travel time to, and use of, safe rooms and storm shelters

•	 Locate safe rooms or storm shelters close to people who will use them

•	 Identify best available refuge areas in buildings without safe rooms

•	 Perform vulnerability assessments of buildings to facilitate planning for 

high-wind events

•	 Register safe rooms with appropriate local government organizations 

and provide coordinates of the primary entrance to them

•	 Equip safe rooms, storm shelters, and best available refuge areas 

with tools to assist occupants when doors and egress routes become 

damaged, inoperable, or blocked by debris

•	 Equip safe rooms, storm shelters, and best available refuge areas with 

an alternate means of communication

•	 Provide training on tornado safe rooms, storm shelters, and refuge areas 

to professional organizations, public officials, emergency managers, 

building owners/operators and the public

Table ES-1: Summary of the MAT’s Key Recommendations (continued)

vi MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

EXECUTIVE SUMMARY
Topic Subtopic Key Recommendations

EF Scale •	 Add DIs to the EF scale guidance

•	 Increase the number of DOD categories for specific DIs

•	 Provide additional guidance for DOD assessment when only a portion of 

a large building is struck

•	 Modify EF scale DI 2 (One- and Two-family Residences) to remove DOD 

5 (“house shifts off foundations”)

•	 Provide photographs with DOD descriptions in EF scale rating guidance

Post-Tornado 

Imagery

•	 NOAA should capture post-tornado aerial photographs

•	 NWS should develop EF contours

•	 NWS should enhance the determination of EF ratings at individual 

structures by including a design professional as part of the QRTs

Definitions:

ASCE = American Society of Civil Engineers

ASCE 7 = Minimum Design Loads for Buildings and Other 

Structures (current edition: ASCE 7-10)

DI = damage indicator

DOD = Degree of Damage

EF = Enhanced Fujita

FEMA = Federal Emergency Management Agency

IBC = International Building Code

ICC = International Code Council

IRC = International Residential Code

MWFRS = main wind force resisting system

NOAA = National Oceanic and Atmospheric Administration

NWS = National Weather Service

QRT = Quick Response Team

URM = unreinforced masonry

Table ES-1: Summary of the MAT’s Key Recommendations (concluded)

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT vii

EXECUTIVE SUMMARY

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT ix

Contents

Executive Summary..................................................................................................................................... i

Observations ................................................................................................................................ ii

Recommendations.........................................................................................................................v

1 Introduction..........................................................................................................................................1-1

1.1 FEMA Mitigation Assessment Teams....................................................................................... 1-2

1.1.1 Purpose of the 2011 Tornado Mitigation Assessment Team...................................... 1-2

1.1.2 Team Composition ....................................................................................................... 1-4

1.1.3 Methodology ................................................................................................................. 1-4

1.1.4 Types of Buildings and Structures Assessed by the MAT .......................................... 1-6

1.1.5 Involvement of State and Local Agencies ................................................................... 1-9

1.1.6 Past Tornado MAT Deployments................................................................................. 1-9

1.2 Terminology and Background for Tornado Protection Alternatives .................................. 1-11

1.3 2011 Tornado Recovery Advisories..........................................................................................1-14

1.4 Organization of Report .......................................................................................................... 1-15
2 Meterological Background and Tornado Events of 2011......................................................................2-1

2.1 Tornado Prediction................................................................................................................... 2-2

2.2 Enhanced Fujita Scale...............................................................................................................2-3

2.3 Tornado Winds and Damage Patterns ....................................................................................2-4

2.4 National Weather Service Tornado Warning Strategies and Ratings....................................2-6

2.4.1 Tornado Watches and Warnings ................................................................................. 2-6

2.4.2 NWS EF Rating Assignments ...................................................................................... 2-7

2.5 Tornado Events of Spring 2011.................................................................................................2-8

2.5.1 April 25–28, 2011 Tornadoes in the Mid-South Area of the United States.............. 2-8

2.5.1.1 April 18–24, 2011........................................................................................... 2-8

2.5.1.2 April 25, 2011 ...............................................................................................2-10

2.5.1.3 April 26, 2011 ...............................................................................................2-11

2.5.1.4 April 27, 2011, 2:00 a.m. to 12:00 p.m. .......................................................2-11

2.5.1.5 April 27, 2011, 2:30 p.m. to 3:00 p.m.: Philadelphia, MS, 

Tornado #24, and Cullman, AL, Tornado #38..........................................2-12

2.5.1.6 April 27, 2011, 3:00 p.m.: Hackleburg to Huntsville, AL, Tornado #40 ..2-13

2.5.1.7 April 27, 2011, 3:30 p.m.: Smithville, MS, Tornado #43............................2-14

2.5.1.8 April 27, 2011, 3:38 p.m.: Cordova, AL, Tornado #41/#49.......................2-15

2.5.1.9 April 27, 2011: Macon County Supercell Thunderstorm, Tornado #46...2-16

2.5.2 May 22, 2011 Storms in Missouri ................................................................................2-17

2.5.2.1 Summary of Synoptic Setting and Mesoscale Environment .....................2-18

2.5.2.2 Damage and Path of the Joplin Tornado ...................................................2-19

3 Design and Construction Considerations ........................................................................................... 3-1

3.1 Effects of Wind Loading on Structures...................................................................................3-2

3.2 Wind-Borne Debris ...................................................................................................................3-6

3.2.1 Missile Types and Sizes.................................................................................................3-8

3.2.2 Wind-Borne Missile Quantity .................................................................................... 3-11

3.3 Federal, State, and Local Regulations ................................................................................... 3-13

3.3.1 International Building Code and International Residential Code ..........................3-14

x MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

TABLE OF CONTENTS
3.3.2 International Codes and Storm Shelters....................................................................3-14

3.3.3 State and Local Codes and Regulations in Areas Visited by the MAT .................. 3-15

3.3.3.1 Alabama........................................................................................................3-17

3.3.3.2 Georgia ........................................................................................................ 3-18

3.3.3.3 Mississippi.................................................................................................... 3-18

3.3.3.4 Tennessee .................................................................................................... 3-18

3.3.3.5 Missouri ....................................................................................................... 3-19

4 Observations on Residential Building Performance ........................................................................... 4-1

4.1 One- and Two-Family Residences.............................................................................................4-2

4.1.1 EF Rating Evaluation of Residential Buildings........................................................... 4-3

4.1.2 Description of Progressive Damage for One- and Two-Family 

Residential Buildings ...................................................................................................4-4

4.1.3 Loss of Roof Covering and Exterior Siding (DOD 2)................................................4-5

4.1.4 Glazing Damage (DOD 3) ...........................................................................................4-6

4.1.5 Garage Doors Collapse Inward (DOD 4) ...................................................................4-8

4.1.6 Uplift of Roof Decks (DOD 4)................................................................................... 4-10

4.1.7 Gable End Walls: Vulnerability Related to Uplift of Roof Deck (DOD 4).............. 4-13

4.1.8 Entire House Shifts Off Foundation (DOD 5) .........................................................4-14

4.1.9 Roof Structure Removed (DOD 6)............................................................................ 4-15

4.1.10 Collapse of Framed Walls (DOD 6–9) ..................................................................... 4-18

4.1.11 Wall Framing-to-Foundation Connection Failure: 

Damage Related to Collapse of Framed Walls (DOD 7–9) .................................... 4-20

4.2 Multi-Family Residences .........................................................................................................4-24

4.2.1 EF Rating Evaluation of Multi-Family Residential Buildings .................................. 4-24

4.2.2 Chastain Manor Apartments (Tuscaloosa, AL)........................................................ 4-24

4.2.3 Mercy Village Apartments (Joplin, MO) ..................................................................4-30

4.3 Summary of Conclusions and Recommendations................................................................4-35

5 Observations on Commercial and Industrial Building Performance ................................................... 5-1

5.1 Tilt-Up Precast Concrete Walls with Steel Joist Roof System..................................................5-5

5.1.1 Description of Construction Method and Load Path ................................................5-5

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT xi

TABLE OF CONTENTS
5.1.2 Typical Failure Modes Observed by the MAT.............................................................5-6

5.1.3 Home Depot (Joplin, MO) ..........................................................................................5-6

5.2 Load Bearing Masonry with Steel Joist Roof System ............................................................ 5-16

5.2.1 Description of Construction Methods and Load Path..............................................5-17

5.2.2 Typical Failure Modes Observed by the MAT............................................................5-17

5.2.3 Strip Mall – Dry Cleaner, Two Large Retail Stores, and Other Stores 

(Tuscaloosa, AL)......................................................................................................... 5-18

5.2.4 Jefferson Metro Care (Birmingham, AL) ................................................................. 5-22

5.2.5 Walmart (Joplin, MO)................................................................................................ 5-27

5.3 Light Steel Frame Buildings ..................................................................................................5-36

5.3.1 Description of Construction Method and Load Path .............................................. 5-36

5.3.2 Typical Failure Modes Observed by the MAT........................................................... 5-36

5.3.3 Fitness Center (Tuscaloosa, AL)................................................................................ 5-37

5.3.4 St. Paul’s United Methodist Church (Joplin, MO)................................................... 5-39

5.4 Reinforced Concrete Frame with CMU Infill Walls .............................................................5-42

5.4.1 Description of Construction Method and Load Path ..............................................5-43

5.4.2 Typical Failure Modes Observed by the MAT...........................................................5-43

5.4.3 Ozark Center for Autism (Joplin, MO).....................................................................5-43

5.5 Summary of Conclusions and Recommendations................................................................5-48

6 Observations on Critical Facility Performance: Schools..................................................................... 6-1

6.1 Building Performance...............................................................................................................6-4

6.1.1 Alberta Elementary School (Tuscaloosa, AL) ............................................................6-4

6.1.2 University Place Elementary School (Tuscaloosa, AL) ............................................ 6-10

6.1.3 Ringgold High School and Ringgold Middle School (Ringgold, GA) ................... 6-18

6.1.3.1 Ringgold High School ................................................................................ 6-18

6.1.3.2 Ringgold Middle School............................................................................. 6-26

6.1.4 Joplin East Middle School (Joplin, MO)................................................................... 6-29

6.1.5 Joplin High School (Joplin, MO) ..............................................................................6-35

6.2 Operational Issues...................................................................................................................6-43

6.2.1 Severe Weather Policy ................................................................................................6-45

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6.2.2 Severe Weather Communication and Decision Making ..........................................6-46

6.2.3 Changes for the Future ..............................................................................................6-47

6.2.4 Summary .....................................................................................................................6-48

6.3 Summary of Conclusions and Recommendations............................................................... 6-48

7 Observations on Critical Facility Performance: Healthcare, First Responder, 

and Emergency Operations Centers ....................................................................................................7-1

7.1 Hospitals and Health Care Facilities........................................................................................7-3

7.1.1 Birmingham Nursing and Rehabilitation Center (Birmingham, AL)...................... 7-4

7.1.2 LaRocca Nursing Home (Tuscaloosa, AL) .................................................................7-7

7.1.3 Greenbriar Nursing Home (Joplin, MO) .................................................................7-12

7.1.4 St. John’s Medical Center (Joplin, MO).....................................................................7-15

7.2 First Responder Facilities (Police and Fire)........................................................................... 7-22

7.2.1 Fultondale Municipal Complex (Fultondale, AL) ................................................... 7-22

7.2.1.1 Fire Department...........................................................................................7-24

7.2.1.2 Library and “Shelter”.................................................................................. 7-25

7.2.1.3 Building and Inspections Department...................................................... 7-26

7.2.1.4 City Hall....................................................................................................... 7-28

7.2.1.5 Summary of the MAT EF Ratings for the Fultondale 

Municipal Complex ................................................................................... 7-29

7.2.2 Tuscaloosa Fire Station 4 (Tuscaloosa, AL).............................................................. 7-29

7.2.3 Webster’s Chapel Volunteer Fire Department (Wellington, AL) ............................ 7-34

7.2.4 Smithville Police Department (Smithville, MS) ....................................................... 7-37

7.3 Emergency Operations Centers ............................................................................................7-42

7.3.1 Tuscaloosa EOC (Tuscaloosa, AL) ............................................................................ 7-42

7.3.2 Cullman County EOC (Cullman, AL) ...................................................................... 7-49

7.4 Summary of Conclusions and Recommendations................................................................ 7-51

8 Observations on Infrastructure Performance ..................................................................................... 8-1

8.1 Water Treatment and Distribution Facilities...........................................................................8-2

8.1.1 Tuscaloosa Water Works (Tuscaloosa, AL) ................................................................. 8-3

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8.1.2 Smithville Water Treatment and Distribution System (Smithville, MS) ...................8-6

8.2 WasteWater Treatment Facilities ............................................................................................ 8-11

8.2.1 Tuscaloosa Waste Water Treatment Plant and Collection System 

(Tuscaloosa, AL)......................................................................................................... 8-11

8.3 Towers (Communications and Antennas).............................................................................8-12

8.3.1 Free-Standing Towers................................................................................................. 8-13

8.3.1.1 Latticed 250-Foot EMS Communications Tower (Tuscaloosa, AL)......... 8-13

8.3.1.2 Latticed 300-Foot Cellular Tower (Tuscaloosa, AL)................................. 8-16

8.3.1.3 Solid Cellular Tower, 13th Street (Tuscaloosa, AL).................................. 8-19

8.3.2 Guyed Towers.............................................................................................................. 8-21

8.3.2.1 300-Foot Guyed Cellular Tower (Smithville, MS) .................................... 8-21

8.4 Summary of Conclusions and Recommendations................................................................8-25

9 Observations on Tornado Refuge Areas, Hardened Areas, and Safe Rooms ..................................... 9-1

9.1 Terminology and Examples......................................................................................................9-2

9.1.1 Hardened Areas: Areas Designed to Provide Some Protection ................................ 9-3

9.1.2 Storm Shelters and Safe Rooms: Areas Designed for Life-Safety Protection...........9-4

9.2 Tornado Refuge Areas .............................................................................................................9-7

9.2.1 Tornado Refuge Areas in Residences.......................................................................... 9-7

9.2.1.1 Core Remnants .............................................................................................9-8

9.2.1.2 Basement Areas........................................................................................... 9-10

9.2.1.3 Tornado Refuge Areas in Multi-Family Buildings or Complexes............ 9-13

9.2.2 Tornado Refuge in Commercial and Industrial Buildings: 

Planned Tornado Refuge Areas..................................................................................9-14

9.2.2.1 Walmart (Joplin, MO )................................................................................9-14

9.2.2.2 Lowe’s Home Improvement Store (Tuscaloosa, AL) ................................ 9-15

9.2.2.3 Home Depot (Joplin, MO)..........................................................................9-17

9.3 Hardened Structures, Rooms, and Areas Not Designed to Defined Criteria ..................... 9-18

9.3.1 Hardened Structures for Residential Use ................................................................ 9-20

9.3.1.1 Below-Ground Applications....................................................................... 9-20

9.3.1.2 Above-Ground Applications....................................................................... 9-22

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9.3.2 Hardened Structures Used as Community Tornado Refuge Areas........................ 9-23

9.3.2.1 Above-Ground Applications....................................................................... 9-24

9.3.2.2 Below-Ground Applications....................................................................... 9-25

9.4 Safe Rooms and Storm Shelters .............................................................................................9-26

9.4.1 Above- and Below-Ground Alternatives.................................................................... 9-26

9.4.2 Prefabricated versus Site-Built Alternatives.............................................................. 9-28

9.4.3 Residential Safe Rooms and Storm Shelters............................................................. 9-29

9.4.3.1 Below-Ground Applications....................................................................... 9-29

9.4.3.2 Above-Ground Applications....................................................................... 9-31

9.4.4 Non-Residential and Community Safe Rooms ......................................................... 9-33

9.4.4.1 Brookwood and Phil Campbell Community Safe Rooms (AL) .............. 9-34

9.4.4.2 Brookside Fire Station and Community Safe Room (Brookside, AL) .... 9-37

9.4.4.3 Seneca Intermediate School (Seneca, MO) ............................................. 9-38

9.5 Travel Time to Community Safe Rooms, Storm Shelters, and Tornado Refuge Areas......9-42

9.6 Compliance Issues with FEMA 320, FEMA 361, and the ICC 500.......................................9-43

9.6.1 Identifying Design Criteria Used for Safe Rooms and Storm Shelters ..................9-43

9.6.2 Accessibility to Safe Rooms and Storm Shelters.......................................................9-44

9.6.3 Ventilation for Safe Rooms and Storm Shelters .......................................................9-45

9.6.4 Toilet Facilities for Community Safe Rooms and Storm Shelters............................9-45

9.6.5 Location and Labeling of Safe Rooms and Storm Shelters ....................................9-45

9.6.6 Tools and Other Equipment within Safe Rooms and Storm Shelters ....................9-46

9.7 Summary of Conclusions and Recommendations................................................................9-47

10 Conclusions of the 2011 Tornado MAT............................................................................................. 10-1

10.1 Codes and Standards..............................................................................................................10-2

10.1.1 Residential Buildings.................................................................................................. 10-2

10.1.2 Commercial and Industrial Buildings....................................................................... 10-4

10.1.3 Critical Facilities ......................................................................................................... 10-4

10.1.4 Infrastructure Facilities.............................................................................................. 10-5

10.1.5 Tornado Refuge Areas, Hardened Areas, and Safe Rooms..................................... 10-5

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10.2 Performance of Residential Buildings ..................................................................................10-6

10.3 Performance of Commercial and Industrial Buildings ....................................................... 10-7

10.3.1 Communications and Operations............................................................................. 10-8

10.3.2 Building Performance/Building Design................................................................... 10-8

10.4 Performance of Critical Facility Buildings ...........................................................................10-9

10.5 Performance of Infrastructure Facilities ............................................................................ 10-11

10.6 Performance of Tornado Refuge Areas, Hardened Areas, and Safe Rooms ................... 10-12

10.6.1 General.......................................................................................................................10-12

10.6.2 Residential Safe Rooms and Storm Shelters............................................................10-14

10.6.3 Community Safe Rooms, Storm Shelters, and Tornado Refuge Areas..................10-16

10.7 EF Scale.................................................................................................................................. 10-17

10.8 Post-Tornado Imagery ........................................................................................................... 10-18

11 Recommendations of the 2011 Tornado MAT ....................................................................................11-1

11.1 Codes and Standards.............................................................................................................. 11-2

11.1.1 Residential Buildings...................................................................................................11-2

11.1.2 Commercial and Industrial Buildings........................................................................11-3

11.1.3 Critical Facilities ......................................................................................................... 11-4

11.1.4 Tornado Refuge Areas, Hardened Areas, and Safe Rooms..................................... 11-4

11.2 Residential Construction........................................................................................................ 11-5

11.3 Commercial and Industrial Construction............................................................................. 11-6

11.3.1 Occupant Notification and Operations .................................................................... 11-6

11.3.2 Detailing and Connections.........................................................................................11-7

11.4 Critical Facilities...................................................................................................................... 11-8

11.4.1 Existing Critical Facilities............................................................................................11-9

11.4.2 New Critical Facilities................................................................................................11-10

11.5 Infrastructure Facilities ........................................................................................................11-10

11.6 Tornado Refuge Areas, Hardened Areas, and Safe Rooms ................................................11-11

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11.7 EF Scale...................................................................................................................................11-13

11.8 Post-Tornado Imagery ............................................................................................................11-13

Appendices

Appendix A Acknowledgments

Appendix B References

Appendix C Acronyms

Appendix D Glossary

Appendix E EF Scale Summary

Appendix F Recovery Advisories for the Spring 2011 Tornadoes

Appendix G Recommendations for One- and Two-Family Residential Buildings

List of Figures

Chapter 1

Figure 1-1: NOAA SPC Storm Reports for April 25-28, 2011 tornado outbreak ............................ 1-3

Figure 1-2: NOAA SPC Storm Report for the May 22, 2011 tornado outbreak.............................. 1-4

Figure 1-3: Communities in Alabama, Georgia, Mississippi, Tennessee, and Missouri 

visited by the MAT in 2011.............................................................................................. 1-5

Figure 1-4: HMGP-funded residential safe room in Smithville, MS, that was occupied 

during the storm, but was not in the tornado path....................................................... 1-8

Figure 1-5: Cover of FEMA 320.........................................................................................................1-11

Figure 1-6: Cover of FEMA 361.........................................................................................................1-13

Figure 1-7: Cover of ICC 500 ............................................................................................................1-14

Chapter 2

Figure 2-1: Potential tornado damage pattern ................................................................................ 2-5

Figure 2-2: Map of tornado tracks associated with the April 27, 2011 outbreak in Alabama........ 2-9

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Figure 2-3: Map of tornado tracks associated with the April 26–27, 2011 outbreak 

in Mississippi ...................................................................................................................2-10

Figure 2-4: Base reflectivity and hook echo for Cullman, AL ........................................................2-12

Figure 2-5: Base reflectivity and hook echo for Hackleburg, AL ...................................................2-13

Figure 2-6: Base reflectivity and hook echo and storm relative velocity for Phil Campbell, AL ..2-14

Figure 2-7: Base reflectivity and hook echo and storm relative velocity for Smithville, MS .........2-15

Figure 2-8: Base reflectivity and hook echo and storm relative velocity for Cordova, AL ............2-15

Figure 2-9: Base reflectivity and hook echo and storm relative velocity for Tuscaloosa, AL........2-16

Figure 2-10: Base reflectivity and hook echo and storm relative velocity for Pleasant Grove, AL..2-17

Figure 2-11: Joplin, MO, base reflectivity with hook echo and storm relative velocity ...................2-19

Chapter 3

Figure 3-1: Effects of a breach in a building envelope when the breach is on the windward 

or leeward side of a building........................................................................................... 3-3

Figure 3-2: Load path continuity in CMU wall.................................................................................3-4

Figure 3-3: Building failure modes in high-wind event....................................................................3-5

Figure 3-4: Uplift pressures acting on a building.............................................................................3-5

Figure 3-5: Brick veneer blew off this high school cafeteria during the tornado in Phil 

Campbell, AL. Note that brick ties do not appear to be at the correct spacing..........3-6

Figure 3-6: Example of small- and medium-sized missiles commonly observed by the MAT 

(Tuscaloosa, AL).............................................................................................................. 3-7

Figure 3-7: Example of medium- to large-sized wind-borne missiles (Tuscaloosa, AL)................ 3-7

Figure 3-8: Medium-sized missile that struck the roof of a school building (Tuscaloosa, AL).....3-8

Figure 3-9: Large roof beam penetrated the roof of this home (Athens, AL) ............................... 3-9

Figure 3-10: OSB damaged the first floor locker in Joplin High School (Joplin, MO)................... 3-9

Figure 3-11: Small pieces of OSB debris penetrated the roof of a home (Harvest, AL) ............... 3-10

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Figure 3-12: Metal sheathing travelled 200 feet as wind-borne debris and landed next to a 

building outside of the tornado swath (Fultondale, AL)............................................ 3-10

Figure 3-13: A 2x6 missile penetrated the roof and seat of a car (Joplin, MO)............................. 3-11

Figure 3-14: Wind-borne debris consisting of wood framing members and plywood 

sheathing near the Alberta Elementary School, Tuscaloosa, AL ............................... 3-11

Figure 3-15: Large quantity of wind-borne debris covering the lawn of a nursing home in 

Joplin, MO...................................................................................................................... 3-12

Figure 3-16: Numerous missiles struck the outer wall of this non-residential building, 

including several that remained embedded (Tuscaloosa, AL)................................... 3-12

Figure 3-17: Large pile of small- and medium-sized wind-borne debris outside of Joplin 

High School (Joplin, MO) ............................................................................................ 3-13

Chapter 4

Figure 4-1: Wind-borne asphalt shingle penetrated the gypsum board on both sides of 

this interior wall at Chastain Manor Apartment Complex (Tuscaloosa, AL) .............4-4

Figure 4-2: Example of DOD 2 (loss of asphalt shingles) (Tuscaloosa, AL) [MAT EF 

Rating = 0] .......................................................................................................................4-5

Figure 4-3: Example of DOD 2 (loss of siding) (Tuscaloosa, AL) [MAT EF Rating = 0] ..............4-5

Figure 4-4: Example of DOD 2 (loss of siding) through DOD 6 (large sections of roof 

structure removed) (Joplin, MO) [MAT EF Rating = 2] ..............................................4-6

Figure 4-5: Effect of wind on an enclosed building and a partially enclosed building ................4-6

Figure 4-6: Double-glazed window with outer pane sacrificed, leaving the inner glazing 

intact (Mercy Village, Joplin, MO) ................................................................................. 4-7

Figure 4-7: Example of DOD 3 showing window with shattered double-glazing 

(Harvest, AL) [MAT EF Rating = 2] ..............................................................................4-8

Figure 4-8: Example of DOD 4 showing a wide garage door collapsed inward, while 

narrow garage door to left is intact. (Joplin, MO). [MAT EF Rating = 2] .................. 4-9

Figure 4-9: Example of damage including loss of large sections of roof (DOD 6) 

(Joplin, MO) [MAT EF Rating = 2] ............................................................................... 4-9

Figure 4-10: Example of how garage door failure (DOD 4) initiated progressive failure, 

including loss of the garage roof (DOD 6) (Joplin, MO) [MAT EF Rating = 2]........ 4-9

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Figure 4-11: Example of DOD 4 showing roof decking blown off along eaves and hip 

(Joplin, MO) [MAT EF Rating = 2] ............................................................................. 4-10

Figure 4-12: Component and cladding wind pressures ................................................................... 4-11

Figure 4-13: Example of DOD 4 showing where roof decking lifted and blew off above 

damaged soffit (Birmingham, AL) [MAT EF Rating = 2] .......................................... 4-12

Figure 4-14: Example of DOD 4 showing roof decking removed at wide eaves on hip roof 

(Phil Campbell, AL) [MAT EF Rating = 1] ................................................................. 4-12

Figure 4-15: Red circled roof deck nail not connected to rafter (Harvest, AL)............................. 4-13

Figure 4-16: Example of DOD 4 showing damage to gable end of simple gable roof

(Harvest, AL) [MAT EF Rating = 1]..............................................................................4-14

Figure 4-17: Example of DOD 5 showing residential building shifted off masonry piers

(Cullman, AL) [MAT EF Rating = 2]............................................................................4-14

Figure 4-18: Example of DOD 6 showing failed roof-to-wall connections that resulted in 

loss of roof structure (Harvest, AL) [MAT EF Rating = 2]......................................... 4-15

Figure 4-19: Example of roof-to-wall connection failure facilitated by non-code-compliant 

construction (Harvest, AL) [MAT EF Rating = 1] ...................................................... 4-15

Figure 4-20: Over-notched rafter found on ground with two toe nails withdrawn from plate 

(Harvest, AL) [MAT EF Rating = 1]............................................................................. 4-16

Figure 4-21: Example of DOD 6 showing trusses were connected to walls with small 

hurricane ties (Phil Campbell, AL) [MAT EF Rating = 2]..........................................4-17

Figure 4-22: Example of DOD 6 showing insufficient connection of single roof-to-wall 

connector (Tuscaloosa, AL) [MAT EF Rating = 2] ......................................................4-17

Figure 4-23: Example of DOD 6 showing failure of roof framing that resulted in loss of 

lateral support for the top of this wall (Phil Campbell, AL)[MAT EF Rating = 2]... 4-18

Figure 4-24: Example of DOD 6 showing pressurization of garage when failure of the 

garage door/wall removed the support (Harvest, AL) [MAT EF Rating = 2] .......... 4-19

Figure 4-25: Example of DOD 6 where most walls remained standing, but under-braced 

garage entry wall failed (Joplin, MO) [MAT EF Rating = 2] ..................................... 4-19

Figure 4-26: Example of DOD 6 showing under-braced framed sunroom wall failure 

(Harvest, AL) [MAT EF Rating = 2] ............................................................................ 4-20

Figure 4-27: Example of wall framing-to-foundation connection failure (Harvest, AL)

[MAT EF Rating = 2]..................................................................................................... 4-21

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Figure 4-28: Example of wall framing-to-foundation connection failure (Harvest, AL) 

[MAT EF Rating = 2]..................................................................................................... 4-21

Figure 4-29: Wall-to-foundation connection failure (Hackleburg, AL) [MAT EF Rating = 3]..... 4-22

Figure 4-30: Wall-to-foundation failure where bottom plate and concrete nails were pulled 

out by high winds (Hackleburg, AL) [MAT EF Rating = 3] ....................................... 4-23

Figure 4-31: Wall-to-foundation connection failure (Tuscaloosa, AL) [MAT EF Rating = 4] ...... 4-23

Figure 4-32: Aerial view of Chastain Manor Apartments in relationship to the approximate 

centerline of the tornado damage swath (Tuscaloosa, AL)........................................ 4-25

Figure 4-33: One-story Chastain Manor Apartments suffered damage varying from roof 

decking uplift to collapse of roof structure ................................................................. 4-26

Figure 4-34: One-story Chastain Manor Apartment unanchored porch column that rotated 

at top and bottom of column........................................................................................ 4-27

Figure 4-35: Example of DODs 3 and 4 showing two-story Chastain Manor Apartments with 

varying roof damage...................................................................................................... 4-27

Figure 4-36: Example of DOD 6 showing two-story Chastain Manor Apartments completely 

destroyed by the tornado with slabs swept clean ......................................................... 4-28

Figure 4-37: Two-story Chastain Manor Apartment steel porch column was blown away and 

embedded in neighboring hillside ............................................................................... 4-28

Figure 4-38: Most of the bottom plates were blown off the Chastain Manor leasing office .......... 4-29

Figure 4-39: Two-story Chastain Manor Apartment slab with bottom plate pulled over 

remaining anchor bolt and 1-inch diameter washer ................................................... 4-29

Figure 4-40: Aerial photograph showing Mercy Village prior to tornado ......................................4-30

Figure 4-41: Aerial photograph of Mercy Village after the tornado (Joplin, MO)........................ 4-31

Figure 4-42: Aerial photograph of Mercy Village after tornado (Joplin, MO) .............................. 4-32

Figure 4-43: West wall and elevator tower where brick fell off and damaged one-story roof........ 4-33

Figure 4-44: Damage to the gable end wall at south stair tower end. Note third floor wall is 

missing and second floor wall is bowed outward......................................................... 4-33

Figure 4-45: Damaged glazing on the interior courtyard of north wing building; majority of 

glazing was damaged.....................................................................................................4-34

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Figure 4-46: Nails through roof sheathing and nail plates have separated from roof trusses 

because of wind pressures............................................................................................. 4-35

Chapter 5

Figure 5-1: Location of Joplin, MO, buildings described in Chapter 5 .......................................... 5-3

Figure 5-2: Location of Tuscaloosa, AL, buildings described in Chapter 5 ...................................5-4

Figure 5-3: Location of Jefferson Metro Care medical office in Birmingham, AL........................5-4

Figure 5-4: Aerial view of Home Depot in Joplin, MO, in relationship to the approximate 

centerline of the May 22, 2011 tornado damage swath................................................. 5-7

Figure 5-5: Field east of Home Depot with roof debris....................................................................5-8

Figure 5-6: Failed puddle welds that connected the metal roof deck to the top chord of 

the joist............................................................................................................................. 5-9

Figure 5-7: Joist girder and column failure....................................................................................... 5-9

Figure 5-8: Separation at bottom chord to stabilizer plate ............................................................ 5-10

Figure 5-9: Buckled column..............................................................................................................5-11

Figure 5-10: Bolt failure at interior column resulting from shear and tension. The hooked 

anchor bolts pulled out of the slab............................................................................... 5-12

Figure 5-11: Joist support pocket at top of a precast wall................................................................. 5-12

Figure 5-12: Failure of joist-to-joist girder connection shown by broken welds...............................5-14

Figure 5-13: The joist seats came free of their bearing locations when both the seat-to-joist 

weld and the seat-to-embed plate weld broke...............................................................5-14

Figure 5-14: Example of weld plate and joist failure. The joist seat was torn from the joist 

and the anchor studs from embed plate were torn out of the concrete. ................... 5-15

Figure 5-15: The panel at the weld plate failed ................................................................................ 5-15

Figure 5-16: Example of a weld plate failure. Note the attached joist and the joist pocket at 

the top of the wall panel. .............................................................................................. 5-16

Figure 5-17: Aerial view showing the locations of the dry cleaner building, fitness center, 

retail store “A” and retail store “B” (Tuscaloosa, AL).................................................. 5-18

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Figure 5-18: Steel joist in midst of collapsed unreinforced masonry wall at the dry cleaner 

store (Tuscaloosa, AL)................................................................................................... 5-19

Figure 5-19: Solid steel hot rolled sections left in beam pockets of CMU building section.......... 5-20

Figure 5-20: Sequence of failure for CMU wall at the dry cleaner building .................................. 5-20

Figure 5-21: Global wall instability failure. The CMU blocks are lying loosely on the 

ground and many have rotated due to the complete separation of all the blocks.... 5-21

Figure 5-22: View of steel joist pockets in CMU wall where joists pulled out; the exterior 

CMU wall fell inwards ................................................................................................... 5-22

Figure 5-23: Steel joists with joist seat and bond beam on top of collapsed wall. Wall 

fragmentation shows lack of reinforcement in the wall.............................................. 5-22

Figure 5-24: Aerial view showing the Jefferson Metro Care Facility in relationship to the 

approximate centerline of the tornado damage swath (Birmingham, AL) .............. 5-23

Figure 5-25: Failed bond beam-to-structural steel connection over front windows....................... 5-24

Figure 5-26: Roof joist lifted off front and folded over rear half of building ................................. 5-25

Figure 5-27: Failed roof deck with no connections between the roof deck and the joists............. 5-25

Figure 5-28: This CMU cell was found on the ground adjacent to the structure........................... 5-25

Figure 5-29: Bar joist with embed plate and bond beam cell still attached.................................... 5-26

Figure 5-30: Embed plate with bond beam cell on roof .................................................................. 5-26

Figure 5-31: Aerial view of a Walmart in Joplin, MO in relationship to the approximate 

centerline of the May 22, 2011 tornado damage swath............................................... 5-27

Figure 5-32: The relatively undamaged west elevation of Walmart after the May 22, 2011 

tornado (Joplin, MO).................................................................................................... 5-28

Figure 5-33: Interior of the north half of the Walmart, looking east. Fallen roof structure 

shown in right side of the picture................................................................................. 5-29

Figure 5-34: Destroyed east side of north half of Walmart.............................................................. 5-29

Figure 5-35: Interior of the north half of building showing water infiltration 

collected in bags ............................................................................................................ 5-30

Figure 5-36: Interior view from the south half of the building looking toward the east. This 

shows the boundary of roof damage to the south portion of the building. .............. 5-31

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Figure 5-37: View of the south half of the building looking north showing roof damage. 

Note the missing roof membrane................................................................................. 5-31

Figure 5-38: Typical connection of two steel joists to joist girder. While the joist seat from 

one joist remains, the weld failed at the other joist seat connection.......................... 5-32

Figure 5-39: Joist girder rotated at the column; the bottom chord was not attached to the 

stabilizer plate................................................................................................................ 5-32

Figure 5-40: Collapsed column with hooked anchor bolts remains attached to the 

foundation at the base................................................................................................... 5-32

Figure 5-41: Roof structure remaining in south half of Walmart (Joplin, MO)............................ 5-33

Figure 5-42: Reinforcing steel in Walmart foundation .................................................................... 5-33

Figure 5-43: Partial collapsed wall in southern half of store ........................................................... 5-34

Figure 5-44: Area of relatively limited damage................................................................................. 5-35

Figure 5-45: Another view of the area shown in Figure 5-44........................................................... 5-35

Figure 5-46: Aerial view of the fitness center in relationship to the approximate centerline 

of the April 27, 2011 tornado damage swath (Tuscaloosa, AL).................................. 5-37

Figure 5-47: Front of fitness center building..................................................................................... 5-38

Figure 5-48: The anchor bolts of this base plate connection performed well while the weld 

along the base of the steel column failed .................................................................... 5-39

Figure 5-49: Ductile end column at southwest corner of building. The anchor bolts 

remained attached to both the foundation and the column...................................... 5-39

Figure 5-50: Aerial view of St. Paul’s United Methodist Church (Joplin, MO) in relationship 

to the approximate centerline of the tornado damage swath ....................................5-40

Figure 5-51: Intact PEMB main frames............................................................................................. 5-41

Figure 5-52: Roof system purlins intact with metal roof clip released ............................................ 5-41

Figure 5-53: Secondary framing (light gage infill walls) failed while the main 

frames survived..............................................................................................................5-42

Figure 5-54: Aerial view of the Ozark Center for Autism in relationship to the approximate 

centerline of the tornado damage swath (Joplin, MO) ..............................................5-44

Figure 5-55: East elevation of the Ozark Center for Autism showing damage ...............................5-45

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Figure 5-56: East elevation from northeast corner of building. The structural core of the 

taller building performed well, as did the CMU infill................................................5-45

Figure 5-57: Two-story extension on east side of building shown in Figure 5-56; view shows 

typical interior layout ....................................................................................................5-46

Figure 5-58: Roof of the third-story main building..........................................................................5-46

Figure 5-59: Roof section at two-story extension showing how the metal roof deck 

diaphragm is connected to the joists............................................................................ 5-47

Figure 5-60: View of roof of the two-story extension observed from the third floor. Note the 

failed decking at the corner.......................................................................................... 5-47

Chapter 6

Figure 6-1: Location of Tuscaloosa, AL, critical facilities described in Chapters 6 and 7............. 6-3

Figure 6-2: Location of Joplin, MO, critical facilities described in Chapters 6 and 7....................6-4

Figure 6-3: Aerial view of tornado track in vicinity of Alberta Elementary School. The 

center of the damage swath is approximated. ...............................................................6-5

Figure 6-4: Area shown in yellow circle of Figure 6-3. The general location of the tornado 

refuge areas for the two surviving wings is shown.........................................................6-6

Figure 6-5: View of the central core area. Refuge areas for the two surviving wings were in 

the collapsed area............................................................................................................6-6

Figure 6-6: Interior reinforced CMU wall in the central core area where rebar had 

deficient splice lap ........................................................................................................... 6-7

Figure 6-7: Center classroom wing remains standing while the wing to the right collapsed........6-8

Figure 6-8: Partially collapsed corridor wall.....................................................................................6-8

Figure 6-9: Looking down the corridor of the collapsed classroom wing ......................................6-9

Figure 6-10: The reinforced CMU walls around the restroom were left standing, but the 

rooms were littered with debris ......................................................................................6-9

Figure 6-11: University Place Elementary School after the tornado ............................................... 6-10

Figure 6-12: Aerial view of the tornado track in the vicinity of the University Place 

Elementary School. The center of the damage swath is approximated..................... 6-11

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Figure 6-13: Close-up of Figure 6-12 showing classroom wings A and B and multipurpose 

wing (cafeteria, kitchen, and multipurpose room)..................................................... 6-11

Figure 6-14: View looking south showing damage of the classroom wings and 

multipurpose wing......................................................................................................... 6-12

Figure 6-15: View looking north showing wall and roof structure damage to classroom 

wing B and damage to the multipurpose wing............................................................ 6-13

Figure 6-16: View of the second floor damage to classroom wing B............................................... 6-13

Figure 6-17: View inside the cafeteria ................................................................................................6-14

Figure 6-18: View toward the cafeteria from within the multipurpose room. The inset 

shows a multipurpose room girder supported by a concrete column.........................6-14

Figure 6-19: Multipurpose room girder. Lack of alignment of the bolt holes in the top and 

bottom plates (see insets) prevented installation of the anchor bolts. ...................... 6-15

Figure 6-20: Weld remnants where a joist was attached to the girder and weld remnants 

where a joist was attached to a bearing plate at a bond beam.................................... 6-16

Figure 6-21: A strong weld attaching a piece of decking to the joist. The photo on the right 

shows a weak deck attachment where the weld burnt through the joist. ....................6-17

Figure 6-22: Rebar extending out of the slab at the multipurpose room end wall.........................6-17

Figure 6-23: View of the Ringgold High School and Ringgold Middle School prior to the 

April 2011 tornado. NWS EF contour ratings are also shown. ................................... 6-19

Figure 6-24: Close-up view of Figure 6-23 showing the Ringgold High School prior to the 

April 2011 tornado......................................................................................................... 6-20

Figure 6-25: View of one of the portable classrooms. The red arrows indicate anchor straps. 

The strap shown in the inset had corroded through. ................................................. 6-21

Figure 6-26: View of the 2008 auxiliary gymnasium and original gymnasium.............................. 6-22

Figure 6-27: View of the two gymnasium roofs. The EPDM (black) membrane is over the 

original gymnasium. Note the displaced rooftop equipment. ................................... 6-22

Figure 6-28: View of the roof of the 2008 auxiliary gymnasium; inset shows lifted decking ........ 6-23

Figure 6-29: The loss of the roof covering shown in Figure 6-28 led to water intrusion that 

damaged the floor below............................................................................................... 6-24

Figure 6-30: View of the aggregate ballasted roof. The fully adhered roof membrane blew 

away; inset below shows broken windows. .................................................................... 6-24

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Figure 6-31: The roof covering was blown off of the 2008 art center. The metal wall 

covering and insulation was also blown off the CMU................................................. 6-25

Figure 6-32: At the wrestling facility, metal roof panels were blown off, steel framing was 

damaged, and a portion of the unreinforced CMU wall collapsed ........................... 6-25

Figure 6-33: View of the Ringgold Middle School prior to the April 2011 tornado....................... 6-26

Figure 6-34: View of the Ringgold Middle School (the inset shows the left portion of the 

school). The 2008 auxiliary gymnasium and original gymnasium are shown. ........ 6-27

Figure 6-35: This wing lost most of its roof decking, and a portion of the brick veneer and 

unreinforced CMU collapsed ....................................................................................... 6-27

Figure 6-36: View from within a classroom with the collapsed wall shown in Figure 6-35. 

The deck bulb-tees also blew off................................................................................... 6-28

Figure 6-37: Deck panels blew off the original gymnasium ............................................................ 6-28

Figure 6-38: EIFS wall failure, glazing damage, and roof deck blow-off ........................................ 6-29

Figure 6-39: Aerial view of the tornado track in the vicinity of the Joplin East Middle 

School. NWS EF contour ratings are also shown.........................................................6-30

Figure 6-40: Close-up of Figure 6-39. Major areas of blow-off of the roof membrane and 

roof deck are shown.......................................................................................................6-30

Figure 6-41: Interior rooms designated as “shelters” in the middle school’s Tornado 

Evacuation Plan. The inset shows the “shelter” signage.............................................. 6-31

Figure 6-42: View of the collapsed auditorium roof and both exterior walls................................. 6-32

Figure 6-43: View of the gymnasium. The inset shows where the truss was attached to 

the wall. .......................................................................................................................... 6-32

Figure 6-44: View of the end of the collapsed truss shown in Figure 6-43 ..................................... 6-33

Figure 6-45: Roof truss and wall debris on the gymnasium floor ................................................... 6-33

Figure 6-46: Brick veneer/insulation/precast concrete wall on the gymnasium floor ..................6-34

Figure 6-47: View of rain infiltration damage in a school corridor ................................................6-34

Figure 6-48: Aerial view of the track in the vicinity of the Joplin High School. The center of 

the damage swath is approximated. NWS EF contour ratings are also shown..........6-36

Figure 6-49: Close-up of Joplin High School .................................................................................... 6-37

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Figure 6-50: View of a corridor designated as tornado refuge area. The debris was blown 

into the corridor during the tornado...........................................................................6-38

Figure 6-51: North classroom wing. The inset shows a close-up of the opposite side of 

the wing..........................................................................................................................6-39

Figure 6-52: Collapse of the exterior brick veneer/reinforced CMU wall and roof assembly 

into the corridor at the north end of the north classroom wing ...............................6-39

Figure 6-53: Collapsed brick veneer/reinforced CMU.....................................................................6-40

Figure 6-54: View of the collapsed gymnasium. The inset shows the base plate and an 

anchor bolt that connected the girder support column to the pilaster. ....................6-41

Figure 6-55: Interior view of the second gymnasium.......................................................................6-41

Figure 6-56: North wall of the auditorium........................................................................................6-42

Figure 6-57: South wall of the auditorium, showing collapse of the masonry infill wall...............6-42

Figure 6-58: Flowchart depicting severe weather decision making process used by school 

districts in Alabama.......................................................................................................6-46

Figure 6-59: Flowchart depicting severe weather decision making process used by the 

Joplin, MO, School District ...........................................................................................6-47

Chapter 7

Figure 7-1: Location of Tuscaloosa, AL, critical facilities described in Chapters 6 and 7............. 7-2

Figure 7-2: Location of Joplin, MO, critical facilities described in Chapters 6 and 7.................... 7-3

Figure 7-3: Aerial view of the nursing home. Figure shows courtyard where residents were 

evacuated to and impact of wind-borne debris (Birmingham, AL). ........................... 7-4

Figure 7-4: Aerial view of the nursing home in relation to the approximate centerline of 

the tornado damage swath (Birmingham, AL)............................................................. 7-5

Figure 7-5: View of interior corridors that serve as the residents’ tornado refuge area 

(Birmingham, AL)........................................................................................................... 7-5

Figure 7-6: This portion of a roof from a nearby house was found across the street from 

the nursing home (Birmingham, AL)............................................................................ 7-6

Figure 7-7: The emergency generator is located near many trees that could easily have 

damaged the generator and taken it out of service (Birmingham, AL)...................... 7-6

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Figure 7-8: Aerial view of the track in the vicinity of the nursing home. Inflow damaged 

the nursing home and buildings (Tuscaloosa, AL)........................................................7-7

Figure 7-9: Close-up of the nursing home shown in Figure 7-8 (Tuscaloosa, AL)......................... 7-8

Figure 7-10: Roof structure and brick veneer were blown off the nursing home 

(Tuscaloosa, AL).............................................................................................................. 7-8

Figure 7-11: Roof structure blown off over resident rooms. The inset is a view from within 

one of the rooms. The window was broken (Tuscaloosa, AL)...................................... 7-9

Figure 7-12: Interior damage as a result of roof structure blow-off (Tuscaloosa, AL) .................... 7-9

Figure 7-13: View of the two-story wing. Most of the windows along this façade were broken 

(Tuscaloosa, AL).............................................................................................................7-10

Figure 7-14: Tree-fall damage. Note the boarded-up broken windows. The inset shows a 

close-up of the tree-fall damage (Tuscaloosa, AL).......................................................7-10

Figure 7-15: Generator at the southwest side of the facility. Note the roof structure blow-off 

and wall collapse (Tuscaloosa, AL). ..............................................................................7-11

Figure 7-16: Aerial view of the track in the vicinity of the nursing home. The center of the 

damage swath is approximated (Joplin, MO). .............................................................7-12

Figure 7-17: Close-up of Figure 7-16 showing the damaged nursing home. The inset shows 

the nursing home before the tornado struck (Joplin, MO). .......................................7-13

Figure 7-18: Aerial view of the nursing home after the tornado (Joplin, MO)...............................7-13

Figure 7-19: Only one wall remained standing at the nursing home (Joplin, MO) .......................7-14

Figure 7-20: Aerial view of the track in the vicinity of the St. John’s Medical Center 

(Joplin, MO) ...................................................................................................................7-15

Figure 7-21: Close-up of Figure 7-20 showing St. John’s Medical Center (Joplin, MO) .................7-16

Figure 7-22: View of the glazing damage at patient rooms (Joplin, MO) .......................................7-17

Figure 7-23: This parking lot was littered with 11⁄2-inch nominal diameter aggregate from 

the ballasted roof membrane (Joplin, MO) .................................................................7-17

Figure 7-24: Collapse of a portion of the exterior metal composite foam wall panels at the 

East Tower addition (Joplin, MO).................................................................................7-18

Figure 7-25: View of a missing precast concrete wall panel at the loading dock 

(Joplin, MO) ...................................................................................................................7-19

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Figure 7-26: Metal decking blow-off and glazing damage in the administrative area 

(Joplin, MO) ...................................................................................................................7-19

Figure 7-27: Exterior wall collapse (EIFS over unreinforced CMU) at an equipment room 

(Joplin, MO) .................................................................................................................. 7-20

Figure 7-28: Metal decking blow-off and glazing and EIFS damage at the medical office 

building/outpatient center (Joplin, MO) .....................................................................7-21

Figure 7-29: Aerial view of tornado track in the vicinity of Fultondale Municipal Complex 

in Alabama (Fultondale, AL)........................................................................................ 7-23

Figure 7-30: Tornado winds damaged an emergency generator and a roof, and lifted a roof.

The “shelter” entrance is shown (Fultondale, AL). ..................................................... 7-23

Figure 7-31: The apparatus bay doors of the fire department collapsed (Fultondale, AL) ...........7-24

Figure 7-32: The metal roof panels blew off the apparatus bay of the fire department. The 

panels unlatched from the clips (Fultondale, AL)...................................................... 7-25

Figure 7-33: The library is on top of the community tornado refuge area. The note in the 

window directed people to the “shelter” below (Fultondale, AL). ............................. 7-26

Figure 7-34: The roof structure of the Buildings and Inspections Department building 

blew off in one complete section (Fultondale, AL)..................................................... 7-27

Figure 7-35: Note the inadequate anchorage from the truss nailer that was nailed to the 

wall top cap block (Fultondale, AL)............................................................................. 7-27

Figure 7-36: The front of the City Hall showing damage to the metal roof covering over the 

entrance (Fultondale, AL) ............................................................................................ 7-28

Figure 7-37: Back of the City Hall. Photograph shows the generator that was disabled by a 

fallen tree (Fultondale, AL).......................................................................................... 7-29

Figure 7-38: Aerial view of the track in the vicinity of the fire station (Tuscaloosa, AL).............. 7-30

Figure 7-39: View of the fire station. The apparatus bay, the living quarters, and the nearby 

heavily damaged apartment buildings are shown (Tuscaloosa, AL). .........................7-31

Figure 7-40: View of the fire station with adjacent apartment building with unreinforced 

CMU cells (Tuscaloosa, AL) ..........................................................................................7-31

Figure 7-41: View of the living quarters of the fire station from outside. Note the amount 

and size of wind-borne debris adjacent to the walls (Tuscaloosa, AL). ..................... 7-32

Figure 7-42: View of a restroom toward the center of the fire station where occupants took 

refuge (Tuscaloosa, AL)................................................................................................ 7-32

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Figure 7-43: View of the wood-frame apartment building behind the fire station 

(Tuscaloosa, AL)............................................................................................................ 7-33

Figure 7-44: View of the Webster’s Chapel Volunteer Fire Department in relation to the 

tornado (Wellington, AL)............................................................................................. 7-35

Figure 7-45: View of the Webster’s Chapel Volunteer Fire Department after the tornado 

(Wellington, AL) ........................................................................................................... 7-36

Figure 7-46: View of the old apparatus bay of the Webster’s Chapel Volunteer Fire 

Department. The multipurpose room is indicated (Wellington, AL)....................... 7-36

Figure 7-47: View of the back of the building. The debris in the foreground is from the 

multipurpose room roof and the old apparatus bay (Wellington, AL)..................... 7-36

Figure 7-48: Aerial view of the tornado track in the vicinity of the Smithville Police 

Department (Smithville, MS) ....................................................................................... 7-38

Figure 7-49: Smithville Police Department prior to the tornado (Smithville, MS) ....................... 7-38

Figure 7-50: Smithville Police Department (close-up of Figure 7-48) showing the room 

where refuge was taken during the tornado (Smithville, MS)................................... 7-39

Figure 7-51: Smithville Police Department. Note the collapsed communications tower 

(Smithville, MS)............................................................................................................. 7-39

Figure 7-52: The office where two children and an adult took refuge under the desk 

(Smithville, MS)............................................................................................................. 7-40

Figure 7-53: View of the collapsed east wall and restroom of the Smithville Police 

Department. Note that some of the restroom walls collapsed (Smithville, MS)....... 7-40

Figure 7-54: Aerial view of the track in the vicinity of the Curry Building city complex 

(Tuscaloosa, AL)............................................................................................................ 7-43

Figure 7-55: Oblique view of Figure 7-54 showing the Curry Building .......................................... 7-44

Figure 7-56: View of the southeastern end of the Curry Building before the tornado struck. 

The inset shows post-storm conditions (Tuscaloosa, AL). .......................................... 7-44

Figure 7-57: View of a portion of the collapsed one-story area (Tuscaloosa, AL) ......................... 7-45

Figure 7-58: View of a portion of a collapsed loading dock area (Tuscaloosa, AL)....................... 7-45

Figure 7-59: View of the refuge area (Tuscaloosa, AL).................................................................... 7-47

Figure 7-60: Part of the southern portion of the building. The inset shows a metal door that 

buckled inward (Tuscaloosa, AL)................................................................................. 7-47

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Figure 7-61: The door that leads to the EOC area. The inset shows the area above the EOC 

that collapsed (Tuscaloosa, AL). .................................................................................. 7-48

Figure 7-62: An exterior view of the Cullman County government building housing the 

Water Department and the County EMA facility (Cullman, AL) .............................. 7-49

Figure 7-63: Interior view of the emergency operations room of the Cullman County EMA 

facility (Cullman, AL) ................................................................................................... 7-50

Chapter 8

Figure 8-1: Locations of infrastructure assessed by the MAT in Tuscaloosa, AL .......................... 8-2

Figure 8-2: Locations of infrastructure assessed by the MAT in Smithville, MS............................ 8-3

Figure 8-3: The approximate centerline of the damage swath in relationship to the 

Tuscaloosa Water Works storage tower and the DCH Regional Medical Center ........8-4

Figure 8-4: Representative damage to overhead electrical lines and substations along the 

tornado path (Tuscaloosa, AL) ......................................................................................8-5

Figure 8-5: The approximate centerline of the tornado damage swath in Smithville, MS ...........8-6

Figure 8-6: Smithville Water Treatment Plant and storage tower aerial photograph predates the tornado (Smithville, MS)................................................................................ 8-7

Figure 8-7: Water tower after the tornado (Smithville, MS)............................................................8-8

Figure 8-8: Destroyed unreinforced CMU building and damaged metal-framed building 

(Smithville, MS)...............................................................................................................8-8

Figure 8-9: Reinforced CMU building housing control equipment (left) and undamaged 

water treatment control equipment (right) (Smithville, MS)....................................... 8-9

Figure 8-10: Debris impact damage to Smithville, MS, water tank .................................................. 8-9

Figure 8-11: Lift pumps and controls of the Smithville, MS, water plant were exposed, but 

not damaged .................................................................................................................. 8-10

Figure 8-12: Lightly secured chlorine cylinders; some were displaced by high winds 

(Smithville, MS)............................................................................................................. 8-10

Figure 8-13: Aerial view of the Tuscaloosa Waste Water Treatment Plant in relation to the 

approximate centerline of the April 27, 2011 tornado damage swath....................... 8-12

Figure 8-14: Aerial view of the approximate centerline of the tornado damage swath in the 

vicinity of the latticed 250-foot EMS communications tower (Tuscaloosa, AL) ........8-14

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Figure 8-15: View of toppled EMS communications tower (Tuscaloosa, AL)..................................8-14

Figure 8-16: View of the collapsed EMS communications tower; the EOC across 35th Street 

is also shown (Tuscaloosa, AL) ..................................................................................... 8-15

Figure 8-17: Photograph shows the six-bolt tower base with cracks in concrete foundation 

cap (Tuscaloosa, AL)..................................................................................................... 8-15

Figure 8-18: Aerial view of the approximate centerline of the tornado damage swath in the 

vicinity of the 300-foot latticed cellular tower (Tuscaloosa, AL).................................8-17

Figure 8-19: Base for 300-foot latticed cellular tower (Tuscaloosa, AL)..........................................8-17

Figure 8-20: View of the 300-foot latticed cellular tower that collapsed during the tornado 

event (Tuscaloosa, AL).................................................................................................. 8-18

Figure 8-21: Photograph of the 300-foot cellular tower and the metal building to the 

southeast before the April 27, 2011 tornado (Tuscaloosa, AL) .................................. 8-18

Figure 8-22: View of the collapsed 300-foot cellular tower and the destroyed metal building 

southeast of the tower (Tuscaloosa, AL) ...................................................................... 8-19

Figure 8-23: Remnants of a trailer that struck the fence surrounding the 300-foot cellular 

tower (Tuscaloosa, AL).................................................................................................. 8-19

Figure 8-24: Aerial view of the approximate centerline of the tornado damage swath in the 

vicinity of the solid cellular tower (Tuscaloosa, AL) ................................................... 8-20

Figure 8-25: Aerial view of solid cellular tower left standing after event. Insert shows aerial 

view of the tower amidst destroyed buildings (Tuscaloosa, AL). ............................... 8-21

Figure 8-26: Aerial view of the 300-foot guyed cellular tower in relationship to the 

approximate centerline of the tornado damage swath in Smithville, MS ................. 8-22

Figure 8-27: Aerial photograph showing the 300-foot-tall guyed cellular tower after the 

tornado (Smithville, MS) .............................................................................................. 8-23

Figure 8-28: Guy attachment plate, turnbuckle, and anchor shaft (Smithville, MS)..................... 8-23

Figure 8-29: Collapsed 300-foot cellular tower. The triple guy in the foreground is one of 

the three supports for the temporary tower on the site (Smithville, MS). ................ 8-24

Figure 8-30: Wind-displaced building materials wrapped around the 300-foot cellular 

tower guy (Smithville, MS) ........................................................................................... 8-24

Figure 8-31: The anchor securing one guy was dragged several feet through the ground 

(Smithville, MS)............................................................................................................. 8-25

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Chapter 9

Figure 9-1: A hardened room in a residential building in Tuscaloosa, AL ....................................9-4

Figure 9-2: Above-ground residential safe room installed in a garage of a home in Joplin, 

MO, directly impacted by the tornado........................................................................... 9-5

Figure 9-3: These above-ground community safe rooms in Brookwood, AL, were used during 

the April 27 tornado outbreak, but were not directly impacted by a tornado ............ 9-5

Figure 9-4: Aerial view of tornado damage swath in Crescent Ridge, AL ...................................... 9-9

Figure 9-5: Core remnants of homes sometimes survive a tornado as shown in this 

photograph of site-built homes (Crescent Ridge, AL).................................................. 9-9

Figure 9-6: The core remnant of a home in Joplin, MO ................................................................ 9-10

Figure 9-7: Manufactured homes destroyed in Crescent Ridge, AL ............................................. 9-10

Figure 9-8: Tornado refuge area in a Tuscaloosa, AL, basement...................................................9-11

Figure 9-9: Aerial view of the Pleasant Grove, AL, neighborhood ................................................ 9-12

Figure 9-10: A hardened porch slab over this basement helped to create a tornado refuge 

area that allowed this family to survive the tornado (Birmingham, AL) .................. 9-12

Figure 9-11: An interior bathroom, often considered a tornado refuge area, was heavily 

damaged when the tornado struck (Tuscaloosa, AL)................................................. 9-13

Figure 9-12: Walmart store in Joplin, MO......................................................................................... 9-15

Figure 9-13: Close-up view of the damage at the Walmart store in Joplin, MO ............................. 9-15

Figure 9-14: Lowe’s Home Improvement building (Tuscaloosa, AL) ............................................. 9-16

Figure 9-15: Lowe’s Emergency Response Flipchart (Tuscaloosa, AL)........................................... 9-16

Figure 9-16: Home Depot after the May 22, 2011 tornado (Joplin, MO)....................................... 9-18

Figure 9-17: Tornado refuge area (training room) of the Home Depot. Note the collapsed 

tilt-up wall and the wall leaning into the refuge area (Joplin, MO).......................... 9-19

Figure 9-18: Underground shelter that survived a tornado (rated EF2 based on the MAT’s 

observations) (Smithville, MS)..................................................................................... 9-21

Figure 9-19: Below-ground hardened structure used for tornado refuge (Hackleburg, AL) ....... 9-21

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Figure 9-20: Above-ground shelter with untested door system; inset shows the inside of the 

door latch (Smithville, MS) .......................................................................................... 9-22

Figure 9-21: A family shelter with a single deadbolt (Athens, AL).................................................. 9-23

Figure 9-22: Above-ground hardened structures used as community tornado refuge areas 

(Amory, MS) .................................................................................................................. 9-24

Figure 9-23: Below-ground, hardened structure with poor door and locking system and 

damaged vent (Smithville, MS) .................................................................................... 9-25

Figure 9-24: Above-ground safe room that matches the aesthetics of the home (outside 

Tuscaloosa, AL) ............................................................................................................. 9-26

Figure 9-25: Above-ground community storm shelter (Graysville, AL).......................................... 9-27

Figure 9-26: Below-ground FEMA-funded residential safe room (Tuscaloosa, AL)...................... 9-27

Figure 9-27: Site-built FEMA-funded residential safe room (Tuscaloosa, AL) .............................. 9-28

Figure 9-28: Below-ground FEMA-funded residential safe room (Tuscaloosa, AL)...................... 9-29

Figure 9-29: FEMA-funded residential safe room (Smithville, MS) ............................................... 9-30

Figure 9-30: Below-ground garage shelter (Huntsville, AL)............................................................ 9-30

Figure 9-31: ICC 500-compliant storm shelter (Huntsville, AL) ..................................................... 9-31

Figure 9-32: Residential safe room that survived the May 22, 2011 Joplin, MO, tornado 

(rated EF4 based on the MAT’s observations) ............................................................ 9-32

Figure 9-33: Proximity of the residential safe room shown in Figure 9-32 to the 

approximate centerline of the Joplin, MO, tornado damage swath........................... 9-33

Figure 9-34: Residential safe room (Joplin, MO)............................................................................. 9-34

Figure 9-35: Community safe room with exterior and interior locking mechanism; inset 

shows the three-point interior locking system (Brookwood, AL) .............................. 9-35

Figure 9-36: FEMA-funded community safe room (Phil Campbell, AL) ....................................... 9-36

Figure 9-37: Interior of the community safe room shown in Figure 9-36 featuring seating, 

emergency lighting, and ventilation (Phil Campbell, AL).......................................... 9-36

Figure 9-38: A large site-built, below-grade community safe room is housed below this fire 

station; an unprotected generator is shown (Brookside, AL)..................................... 9-37

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Figure 9-39: Interior view of the well-furnished community safe room shown in Figure 9-38 

(Brookside, AL) ............................................................................................................. 9-37

Figure 9-40: Seneca Intermediate School (Seneca, MO) ................................................................ 9-38

Figure 9-41: Seneca Intermediate School safe room in the cafetorium ......................................... 9-39

Figure 9-42: Seneca Intermediate School gymnasium safe room................................................... 9-39

Figure 9-43: Doors and ventilation louvers in Seneca Intermediate School community 

safe room........................................................................................................................9-40

Figure 9-44: Outside doors and louvers protected by alcoves at the Seneca Intermediate 

School community safe room .......................................................................................9-40

Figure 9-45: Elevated ventilator in the Seneca Intermediate School community safe room. 

Inset shows the exterior shroud.-.................................................................................. 9-41

Figure 9-46: Emergency generator building for the community safe room at the Seneca 

Intermediate School...................................................................................................... 9-41

Chapter 10

Figure 10-1: Concrete nails used in lieu of anchor bolts on residential buildings under 

construction in the City of Tuscaloosa, AL, after the 2011 tornadoes....................... 10-3

Figure 10-2: Lack of anchor bolts on recently constructed slab foundation in Jefferson 

County, AL ..................................................................................................................... 10-4

Figure 10-3: Plywood placed over damaged glazing at this police station (Tuscaloosa, AL) .......10-10

Chapter 11

Figure 11-1: IBC/IRC covers...............................................................................................................11-2

Figure 11-2: Collapse of exterior CMU/brick veneer wall and roof collapse at the Joplin 

High School (Joplin, MO). The wall debris fell into the corridor. .............................11-9

Appendix E

Figure E-1: The EF scale is based on level of typical observed damage..........................................E-2

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List of Tables

Executive Summary 

Table ES-1: Summary of the MAT’s Key Recommendations................................................................v

Chapter 2

Table 2-1: Fujita Scale Converted to EF Scale................................................................................. 2-4

Chapter 3

Table 3-1: Wind-Borne Debris and Rolling Debris Classifications................................................3-8

Table 3-2: Historical Codes for Commercial Buildings................................................................ 3-16

Table 3-3: Historical Codes for Residential Buildings.................................................................. 3-16

Chapter 4

Table 4-1: Degrees of Damage for One- and Two-Family Residences ........................................... 4-3

Table 4-2: Degrees of Damage for Multi-Family Residences........................................................ 4-24

Table 4-3: Summary of Conclusions and Recommendations for Residential Building 

Performance...................................................................................................................4-36

Chapter 5

Table 5-1: Summary of Conclusions and Recommendations for Commercial and 

Industrial Building Performance .................................................................................5-49

Chapter 6

Table 6-1: Number of Critical Facilities Observed by the MAT..................................................... 6-3

Appendix G

Figure G-1: Load path elements and height and width limitations for residential buildings 

covered in Appendix G...................................................................................................G-4

Figure G-2: Anchor bolt installation guide......................................................................................G-13

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT xxxvii

TABLE OF CONTENTS
Table 6-2: List of School Districts Interviewed by the MAT.........................................................6-44

Chapter 7

Table 7-1: Summary of Conclusions and Recommendations for Critical Facility 

Performance................................................................................................................... 7-52

Chapter 8

Table 8-1: Summary of Conclusions and Recommendations for Infrastructure 

Performance................................................................................................................... 8-25

Chapter 9

Table 9-1: Summary of Conclusions and Recommendations for Tornado Refuge Area, 

Hardened Area, and Safe Room Performance............................................................ 9-47

Appendix E

Table E-1: Wind Speeds Used in Fujita Scale Compared to EF Scale............................................E-3

Table E-2: EF Scale Damage Indicators...........................................................................................E-3

Table E-3: Example – EF Scale DOD for DI No. 2 (Single-Family Residence)..............................E-4

Table E-4: MAT EF Ratings for Sites Visited in Alabama, Georgia, Mississippi, 

and Tennessee..................................................................................................................E-5

Table E-5: MAT EF Scale Ratings for Sites Visited in Joplin, MO..................................................E-8

Appendix G

Table G-1: Recommended Design Pressures for Doors and Windows.......................................... G-7

Table G-2: Connector Selection and Installation ..........................................................................G-10

Table G-3: Roof-to-Wall Connector Requirements........................................................................G-11

Table G-4: Roof-to-Wall Connection Loads ...................................................................................G-11

Table G-5: Anchor Bolt Spacing Guide ......................................................................................... G-12

Table G-6: Percentage of Full-Height Sheathing in Maximum Building Dimension 

(Length).........................................................................................................................G-14

xxxviii MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

TABLE OF CONTENTS
Table G-7: Percentage of Full-Height Sheathing in Maximum Building Dimension 

(Width).......................................................................................................................... G-15

Table G-8: Top Plate Splice Guide .................................................................................................G-17

Table G-9: Connection Loads at Each End of Exterior Wall Headers .........................................G-17

Table G-10: Connector Requirements at Each End of Exterior Wall Headers..............................G-18

Table G-11: Top Plate-to-Stud-Connection Loads...........................................................................G-19

Table G-12: Top Plate-to-Stud Connector Requirements................................................................G-19

Table G-13: Stud-to-Stud Connection Requirements..................................................................... G-20

Table G-14: Stud-to-Bottom Plate Connector Requirements......................................................... G-21

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT xxxix

TABLE OF CONTENTS

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 1-1

1Introduction

In the spring of 2011, a historic number of powerful and 

destructive tornadoes struck portions of the United States, causing 

widespread damage and loss of life. In response to these events, 

the Federal Insurance and Mitigation Administration (FIMA) 

of the U.S. Department of Homeland Security’s (DHS) Federal 

Emergency Management Agency (FEMA) deployed building 

science experts to assess the damage.

On May 6, 2011 FEMA deployed a Mitigation Assessment Team (MAT) to the States of Alabama, 

Georgia, Mississippi, and Tennessee to assess the damage caused by an outbreak of tornadoes 

occurring April 25 through April 28, 2011. A second MAT was deployed on June 1, 2011 to Missouri 

following the tornado on May 22 in Joplin. This report presents the observations, conclusions, and 

recommendations in response to those field assessments. The objective of this report is to provide 

information to communities, businesses, design professionals, and individuals so that they can 

rebuild safer, more robust structures and minimize loss of life, injuries, and property damage in 

future tornadoes and high-wind events. 
1-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

INTRODUCTION

1.1 FEMA Mitigation Assessment Teams

Along with responding to disasters and providing assistance to people and communities affected by 

disasters, FEMA conducts building performance studies after disasters in order to better understand 

how natural and manmade events affect the built environment. Following a Presidentially declared 

disaster, FEMA determines the potential need to deploy one or more MATs to observe and assess 

damage to buildings and structures caused by wind, rain, and/or flooding associated with the storm. 

FEMA bases this need on estimates from preliminary information of the potential type and severity 

of damage in the affected area(s) and the magnitude of the expected hazards. 

The intent of the building performance studies is to reduce the number of lives lost to future events 

and minimize the economic impact on the communities where these events occur. The MAT studies 

the adequacy of current building codes, other construction requirements, and building practices 

and materials in light of the damage observed after a disaster. MATs are deployed only when FEMA 

believes the findings and recommendations derived from field observations will provide design and 

construction guidance that will not only improve the disaster resistance of the built environment in 

the impacted State or region, but will also be of national significance to all disaster-prone regions. 

Lessons learned from the MAT’s observations are provided in a comprehensive report available 

to communities to aid their rebuilding effort and enhance the disaster-resistance of building 

improvements and new construction. 

1.1.1 Purpose of the 2011 Tornado Mitigation Assessment Team

The outbreak of tornadoes on April 25 through 

April 28, 2011 and on May 22, 2011 in the 

Southeastern and Midwestern regions of the 

country has been cited as the deadliest and 

most destructive group of tornadoes of its kind 

according to National Oceanic and Atmospheric 

Administration (NOAA) National Weather Service 

(NWS) data1 in over 50 years. In accordance 

with its mission of “supporting our citizens and first 

responders to ensure that as a nation we work together to 

build, sustain, and improve our capability to prepare for, 

protect against, respond to, recover from, and mitigate all 

hazards...,” 2 FEMA responded to the April tornado 

outbreak in the Southeastern states of Alabama, 

Mississippi, Tennessee, and Georgia, and the 

Joplin, MO, tornado on May 22, 2011 by deploying 

a MAT composed of national and regional experts 

to each of the affected areas. Figures 1-1 and 1-2 

1 NOAA NWS, 2011 Tornado Information, www.noaanews.noaa.gov/2011_tornado_information.html

2 FEMA Web site, www.fema.gov/about/

The National Weather Service (NWS) is 

one of the six scientific agencies that make 

up the National Oceanic and Atmospheric 

Administration (NOAA). It is tasked with 

providing “weather, hydrologic, and climate forecasts and warnings for the United 

States, its territories, adjacent waters and 

ocean areas, for the protection of life and 

property and the enhancement of the national economy.” 

The Storm Prediction Center (SPC) is part 

of the National Centers for Environmental 

Prediction (NCEP), which operates under 

NWS. The SPC is tasked with forecasting the risk of severe thunderstorms and 

tornadoes in the contiguous United States.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 1-3

Figure 1-1: NOAA SPC Storm Reports for April 25-28, 2011 tornado outbreakSOURCE: HTTP://WWW.SPC.NOAA.GOV
1-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

INTRODUCTION

Figure 1-2: 

NOAA SPC Storm Report for 

the May 22, 2011 tornado 

outbreak

SOURCE: HTTP://WWW.SPC.

NOAA.GOV

show NOAA’s Storm Prediction Center (SPC) storm reports for each day of the two outbreaks. The 

reports shown on these maps come from NWS Weather Forecast Offices. 

The mission of the MAT was to assess the performance of structures affected by the tornadoes, 

review safe room and shelter performance in the affected area (in particular the performance of safe 

rooms and storm shelters that received FEMA mitigation funding for construction), and describe the 

lessons learned to help future efforts more successfully mitigate damage from tornado events.

1.1.2 Team Composition

The MAT included FEMA Headquarters and Regional Office engineers and experts, technical 

consultants, and construction industry experts. Team members included structural engineers, 

architects, planners, wind engineers, civil engineers, meteorologists, electrical engineers and 

communications specialists. The MAT members are listed on the front pages of this document.

The MAT received invaluable support from home and business owners and guides in Alabama, 

Georgia, Missouri, Mississippi, and Tennessee who assisted the MAT during its deployment. These 

individuals accompanied the MAT through many of the affected areas, providing valuable insights 

regarding local communities and their experiences before, during, and after the tornadoes.

1.1.3 Methodology

FEMA deployed a MAT to Alabama, Mississippi, Georgia, and Tennessee on May 6, 2011 and to Joplin, 

MO, on June 1, 2011. The FEMA Region IV Regional Response Coordination Center, joint field 

offices (JFOs), and State and local government agencies informed the MAT of the tornado paths and 

preliminary damage data. This information guided the site selection for the field assessments. The 

members of the MAT visited several sites as a complete team to calibrate findings, after which they 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 1-5

INTRODUCTION

TENNESSEE

split into three teams to traverse the widespread affected areas across Alabama, Mississippi, Georgia, 

and Tennessee. This MAT report expands upon the content in previous MAT reports, and focuses on 

three additional areas: 1) how engineering and construction practices can be changed to reduce the 

loss of life in tornado events, 2) how damage affected the operation of critical facilities, particularly 

those involved in first response, and 3) how storm shelters and safe rooms performed in the events. 

Field Assessments: Field assessments for the April 25–28 tornado events began on May 6 and were 

conducted through May 13. In Alabama, assessments were made in the communities of Athens, 

Birmingham, Cordova, Cullman, Hackleburg, Harvest, Huntsville, Phil Campbell, Pleasant Grove, 

and Tuscaloosa. In Mississippi, assessments were made in the communities of Philadelphia, Raleigh 

and Smithville. In Tennessee, assessments were made in the communities of Chattanooga, Cleveland, 

and Dunlap. In Georgia, assessments were made in the community of Ringgold. Field assessments 

for the May 22 tornado event in Missouri began on June 1 and were conducted through June 4. 

Assessments were made in the cities of Joplin and Seneca. Figure 1-3 shows all of the communities 

visited by the MAT.

Figure 1-3: 

Communities in Alabama, Georgia, Mississippi, Tennessee, and Missouri visited by the MAT in 2011
1-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

INTRODUCTION

The MAT spent over 12 days in the field conducting site assessments and inspecting damage. All 

findings were documented through geotagged photographs and field notes, which were then 

condensed and organized to make the data easier to reference in the final analysis and report. The 

MAT took thousands of photographs, and compiled extensive field notes of observations made at 

numerous sites.

Wind Speed Ratings: One of the MAT’s goals was to determine if building damage observed was 

preventable, particularly for buildings subjected to the lower wind speeds located at the periphery 

of the tornado. To accomplish this goal, the MAT related observed building damage to the wind 

conditions experienced at that site using the Enhanced Fujita (EF) scale. The EF scale is used to 

classify the intensity of a tornado based on damage observed along its entire track; the scale ranges 

from EF0 (weakest) to EF5 (most violent). The EF scale is used both to classify the entire tornado 

track as well as to assess wind speeds experienced by an individual structure based on observed 

damage to the structure (refer to Sections 2.2, 2.3, and Appendix E for additional information). The 

MAT assigned structure-specific ratings in order to exercise engineering judgment about whether 

damage could have been avoided. 

EF scale ratings of tornado tracks are developed and published by the NWS. The NWS developed EF 

contours for the Joplin, MO, tornado and for some of the April 25–28, 2011 tornado outbreak tracks. 

For the other tracks, the NWS provided a rating for the center of tornado circulation along the track. 

The MAT report includes figures showing NWS EF contour ratings (when available) superimposed 

on a NOAA aerial photograph or a pre-tornado photograph. For locations where the NWS did not 

develop EF contours, the building discussion includes the NWS rating of the track at the center 

of its circulation in the vicinity of the building. The building discussion also includes the MATdetermined EF rating for the individual sites visited. Besides the MAT, other agencies and groups 

performed their own determinations on buildings throughout the affected area. 

Aerial Photographs: Soon after the April 25–28, 2011 tornado outbreak, NOAA shot aerial 

photographs of portions of many of the tornado tracks. NOAA also shot aerial photographs of the 

area damaged by the May 22, 2011 Joplin, MO, tornado. Relevant NOAA aerial photographs are 

included in this report to show the location of buildings visited by the MAT relative to the tornado 

track and to show other damage in its vicinity. For buildings in locations where NOAA did not obtain 

aerial photographs, pre-tornado aerial photographs of the building are included for reference. 

1.1.4 Types of Buildings and Structures Assessed by the MAT

The MAT assessed the overall structural performance and the performance of building envelope 

elements during its field investigations. If possible, building or facility owners were interviewed to gain 

insight into how the building occupants reacted during the tornado. The MAT spent considerable 

time assessing damaged buildings and only minimal time assessing buildings that were totally 

destroyed. Studying partially destroyed buildings provided the MAT the opportunity to determine 

why some buildings survived the tornadoes and why some failed. In many cases, the inspection of the 

damaged buildings revealed weaknesses in building design or construction. As part of their building 

investigations, the MAT assessed the effects of wind-borne debris (missile) impact on structural 

performance, as missile impact plays a key role in the success or failure of a building under tornadic 

wind loads. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 1-7

INTRODUCTION

The MAT did not look specifically for examples of construction techniques that, though not required 

by current building codes for this area of the country, are proven to minimize damage in other windprone areas (e.g., hurricane areas). These types of practices are often referred to as code-enhanced 

or best practices. The MAT did, however, take note of such practices if observed in the field. 

As described below, the structures selected by the MAT for damage assessment included the 

following five categories: residential building, commercial and industrial building, critical facilities, 

infrastructure, and personal protection and sheltering structures. 

Residential Buildings: Although residential construction was not its focus, the MAT visited many 

residential homes with a variety of construction types. The majority of one- and two-family residential 

buildings visited were older construction (pre-1970), but some newer homes less than 10 years old 

were also visited. Many of the single- and multi-family residences visited were unreinforced masonry 

or wood frame stick-built non-engineered construction on slab-on-grade foundations. The MAT 

attempted to observe residential buildings of all ages, particularly in areas where buildings would 

have been built under the International Residential Code (IRC), first published in 2000. 

Commercial and Industrial Buildings: The MAT assessed commercial and industrial buildings of 

engineered construction, including shopping plazas and large footprint stores, throughout the area 

damaged by tornadoes. The types of commercial and industrial buildings the MAT visited are 

normally designed by a design professional and included the following:

+ Tilt-up pre-cast concrete walls with steel joists 

+ Load-bearing masonry with steel joist 

+ Light steel frame 

+ Reinforced concrete frame with concrete masonry unit (CMU) infill walls

Critical Facilities: The MAT assessed critical facilities including schools, hospitals and healthcare 

facilities, and facilities used by first responders (police and fire departments and Emergency 

Operations Centers [EOCs] / Emergency Management Agencies [EMAs]). The MAT report presents 

the results categorized by use: schools are described in Chapter 6, while other critical facilities are 

described in Chapter 7. In addition to building performance, the MAT recorded whether the facility 

was equipped with a safe room or place of refuge and the functional loss resulting from the tornado 

damage. 

Infrastructure: The MAT assessed various infrastructure systems in Alabama, Mississippi, and 

Missouri. The infrastructure systems are categorized in this report by their use: water treatment 

and distribution facilities, waste water treatment facilities, and towers (both communications and 

antennae). Both free-standing towers and guyed towers were assessed.

Personal Protection and Sheltering Structures: The MAT examined personal protection and 

sheltering in areas directly in the path of the strong and violent (EF ranking of 2 or greater) tornado 

vortices and in areas on the periphery of tornadoes. The MAT visited three types of spaces: tornado 

refuge areas (residential and non-residential), hardened areas, and safe rooms and storm shelters. 
1-8 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

INTRODUCTION

Both small individual and larger community safe rooms were observed. Refer to Section 1.2 for 

definitions of personal protection and sheltering structures.

The residential and non-residential safe rooms and storm shelters observed by the MAT were installed 

or constructed as above-ground in-residence shelters, above-ground exterior shelters, below-ground 

in-residence shelters, and below-ground exterior shelters. The MAT visited safe rooms that had been 

constructed using FEMA Hazard Mitigation Grant Program (HMGP) funds, including underground 

in-residence safe rooms, above-ground residential safe rooms (such as the safe room shown in 

Figure 1-4), and community safe rooms. In addition to safe rooms constructed using HMGP funds, 

the MAT observed more than 16 other tornado refuge areas, hardened structures, storm shelters, 

and safe rooms of various levels of construction, including underground in-residence shelters, aboveground in-residence shelters, and community shelters.

Figure 1-4: 

HMGP-funded residential 

safe room in Smithville, MS, 

that was occupied during 

the storm, but was not in 

the tornado path
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 1-9

INTRODUCTION

1.1.5 Involvement of State and Local Agencies

FEMA encouraged the participation of State, county and local government officials, and locally 

based experts in the assessment process. Their involvement was critical and resulted in:

+ Improving the MAT’s understanding of local construction practices 

+ Encouraging the MAT to develop recommendations that were both economically and 

technically feasible for the communities involved

+ Facilitating communication among Federal, State, and local governments and the private sector

The MAT met with local emergency management and government officials in many of the cities 

and towns they visited. The officials were able to give an overview of the damage in their area and 

identify key sites to visit. The MAT also coordinated with the FEMA JFOs that had been set up in the 

area shortly after the tornadoes, and these offices provided invaluable information and resources 

for the MAT’s field activities. The MAT also met with several other groups that had been deployed 

immediately after the tornadoes and had gathered preliminary data on the damage, including:

1) A team assessing the Tuscaloosa damage. The team was funded by the National Science 

Foundation (NSF) and included representatives from the University of Florida (UF), University 

of Alabama (UA), Texas Tech University (TTU), Iowa State University, Oregon State University 

(OSU), South Dakota State University (SDSU), Simpson Strong Tie, and the Applied 

Technology Council (ATC).

2) A team assessing the Joplin damage. The team was funded by the American Society of Civil 

Engineers (ASCE) and included representatives from UF, UA, OSU, SDSU, and ATC. 

Meeting with these teams provided the MAT with valuable information, allowing it to establish 

a more efficient and effective plan to assess the impacted area. Appendix A lists these and other 

individuals who assisted the MAT in its field operations and report development.

1.1.6 Past Tornado MAT Deployments

Prior to the 2011 MAT deployment, FEMA had deployed two other tornado MATs: one after the April 

23–24, 2010 tornado outbreak in Mississippi and one after the May 1999 tornado outbreak in Kansas 

and Oklahoma. In addition, FEMA deployed a building sciences field team after each of two tornado 

outbreaks in 2007, one of which occurred in the Southeast and the other in Kansas. Although no 

MAT report was published after the 2007 tornadoes, Recovery Advisories were published shortly 

after each event to assist communities in rebuilding efforts. 

Mississippi Tornado Outbreak, April 23–24, 2010: Beginning the afternoon of Friday, April 23, 

and continuing through the evening of April 24, 2010 the Arkansas, Louisiana, and Mississippi 

region experienced severe weather, including multiple tornadoes, from a strong storm system. The 

most devastating tornado from this event developed in northern Louisiana and caused damage 

from Tallulah, LA, through eight counties in Mississippi. In response to this tornado outbreak, 

FEMA deployed a Pre-Mitigation Assessment Team (PMAT) to survey the general building damage 
1-10 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

INTRODUCTION

and the performance of the residential and community safe rooms located along the path of the 

tornado. The PMAT performed site visits and assessments to gather information on the tornado 

classification, building damage, building performance, and safe rooms. The PMAT’s observations, 

lessons learned, and recommendations regarding the performance of FEMA-funded residential and 

community safe rooms are presented in their report, Pre-Mitigation Assessment Team Report – Mississippi 

Tornado Outbreak, April 23rd – 24th: Damage and Safe Room Performance Observations, Recommendations, 

and Conclusions (FEMA 2010b).

Kansas and Oklahoma Tornado Outbreak, May 3, 1999: On the evening of May 3, 1999, an outbreak 

of tornadoes tore through parts of Oklahoma and Kansas, in areas that are considered part of 

“Tornado Alley,” leveling entire neighborhoods and killing 49 people. The storms that spawned the 

tornadoes moved slowly, contributing to the development and redevelopment of individual tornadoes 

over an extended period of time. On May 10, FEMA deployed a MAT to Oklahoma and Kansas to 

assess damage caused by the tornadoes. The MAT report written following the field assessments, 

titled FEMA 342, Building Performance Assessment Report – Oklahoma and Kansas, Midwest Tornadoes of 

May 3, 1999: Observations, Recommendations and Technical Guidance (1999a), presents observations, 

conclusions, and recommendations intended to help communities, businesses, and individuals 

reduce future injuries and the loss of life and property resulting from tornadoes and other highwind events. This 1999 MAT investigation led to the development of the First Edition of FEMA 361, 

Design and Construction Guidance for Community Safe Rooms (2000).

Tornado Outbreaks of 2007: In the early morning hours of February 2, 2007, a small but devastating 

outbreak of three tornadoes struck central Florida, impacting the area between Lady Lake and New 

Smyrna Beach. Two of the tornadoes were rated by the NWS as EF3 and the other was rated EF1. Less 

than 1 month later, on March 1, 2007, tornadoes hit Alabama and Georgia, causing damage and loss 

of life. Enterprise, AL, experienced one of the top 10 deadliest tornadoes to impact a school when, 

in the early afternoon hours, a tornado ripped through a high school, killing eight students. Later 

that day, a tornado severely damaged a hospital in Americus, GA. 

A few months later, on the evening of May 4, 2007, supercell thunderstorms formed across portions of 

the Midwestern United States, spawning tornadoes in several States. An intense supercell developed 

southwest of Greensburg, KS, that evening, resulting in the formation of 12 tornadoes. One of these 

tornadoes formed in northwest Comanche County and within an hour had reached Greensburg, KS, 

a small community of approximately 1,400 people, and traveled from the town’s southern edge to its 

northwest border. The tornado was rated an EF5 and destroyed or severely damaged the majority of 

the buildings in Greensburg.

FEMA deployed a building sciences team to the field following each of these tornado outbreaks to 

assess the damage. In order to provide the most immediate direct feedback to those in the affected 

areas during the early stages of reconstruction, FEMA published eight tornado Recovery Advisories 

to provide technical guidance. These can be found on the FEMA Library Web site, under 2007 

Tornadoes in Florida Recovery Advisories and 2007 Tornadoes in Kansas Recovery Advisories.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 1-11

INTRODUCTION

1.2 Terminology and Background for 

Tornado Protection Alternatives

As evidenced by this and previous MAT assessments, it is critical to take precautions and seek the 

best possible protection available to minimize the risk for injury or death in the event of a tornado. 

A basic understanding of the tornado hazard, as well as an understanding of relevant building codes 

and construction techniques, is helpful for individuals and communities to better mitigate against 

tornadoes. This section presents a background of tornado protection terminology and a history of 

FEMA’s role in developing technical guidance. 

FEMA has developed specific terminology to differentiate types of tornado refuge areas from other 

types of “shelters.” An understanding of these specific terms and the historic guidance is important 

since the terms FEMA uses to describe sheltering options are often similar, such as “safe room” and 

“storm shelter,” but have slightly different meanings (see text box on next page). Furthermore, the 

term “shelter” is used in different ways by different agencies and entities. For instance, the American 

Red Cross uses the term “shelter” to refer to temporary recovery areas. Similarly, homeless housing 

is often called “shelters.”

Most homes and buildings are typically designed only to the design wind speed prescribed in the 

codes, and are not designed to withstand tornado-force winds and impact from wind-borne debris. 

Even homes and buildings constructed in hurricane-prone regions would not survive a direct hit from 

a violent tornado because they are not designed to resist extreme wind speeds of 200–250 miles per 

hour (mph), but are only typically designed to resist speeds up to 150 mph. Furthermore, aside from 

wind-borne debris regions within hurricane-prone regions, design codes do not address impacts 

from wind-borne debris. Wind-borne debris can cause failure 

of a critical structural system in a building, which may then 

cause global failure and endanger its occupants. 

FEMA has provided technical guidance on tornado protection 

since 1980 when it released FEMA TR-83A, Interim Guidelines 

for Building Occupant Protection from Tornadoes and Extreme Winds 

(1980). Ten years later, FEMA issued additional guidance 

in FEMA TR-83B, Tornado Protection: Selecting and Designing 

Safe Areas in Buildings (1990). Then, in 1998, FEMA refined 

their approach to tornado protection and provided technical 

guidance on how to design and construct a “safe room” that 

provides near-absolute protection from the wind and windborne debris associated with tornadoes. This guidance is 

presented in the First Edition of FEMA 320, Taking Shelter from 

the Storm: Building a Safe Room Inside Your House (1998).3

Most recently updated in 2008, FEMA 320 (Figure 1-5) 

prescribes safe room designs that homeowners, builders, and 

3 The Third Edition of FEMA 320 (released in 2008) is titled Taking Shelter from the Storm: Building a Safe Room for Your Home or 

Small Business. However, readers should be aware that the First and Second Editions of FEMA 320 (released in 1998 and 1999, 

respectively) were titled Taking Shelter from the Storm: Building a Safe Room Inside Your House.

Figure 1-5: Cover of FEMA 320 (FEMA 

2008, Third Edition)
1-12 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

INTRODUCTION

TERMINOLOGY

Tornado refuge area is a general term used to describe any location where people go to seek cover during a tornado. Tornado refuge areas may have been constructed to comply with basic building 

code requirements (that do not consider tornado hazards). These areas may also have continuous 

load paths, bracing, or other features that increase resistance to wind loads. It is important for people 

to know that such an area may not be a safe place to be when a tornado strikes and they still may be 

injured or killed during a tornado event.

Best available refuge areas are areas in an existing building that have been deemed by a qualified 

architect or engineer to likely offer the greatest safety for building occupants during a tornado. It is important to note that, because these areas were not specifically designed as tornado safe rooms, their 

occupants may be injured or killed during a tornado. However, people in best available refuge areas 

are less likely to be injured or killed than people in other areas of a building (FEMA P-431, Tornado 

Protection: Selecting Refuge Areas in Buildings [October 2009]).

Hardened areas are designed and constructed to provide some level of protection, but do not necessarily meet International Code Council (ICC) / National Storm Shelter Association (NSSA) Standard 

for the Design and Construction of Storm Shelters (ICC 500) criteria or FEMA guidelines. These areas 

are commonly referred to by builders and homeowners as shelters.

Storm shelters provide life-safety protection; they are designed and constructed to meet ICC 500 

criteria. 

Safe rooms provide near-absolute protection; they are designed and constructed to meet the guidelines provided in FEMA 361, Design and Construction Guidance for Community Safe Rooms (2008a) 

or FEMA 320, Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business

(2008c).

Tornado 

Refuge 

Area

Best 

Available 

Refuge Area

Hardened 

Area or 

Room

Storm 

Shelter

 Safe 

Room

Designed to minimum building code 

requirements ✔ ✔ ✔ ✔ ✔

Evaluated by a design professional and 

identified as least vulnerable area/room 

in building

✔ ✔ ✔

Designed to consider wind speeds or 

wind-borne debris impacts at some 

level between code and ICC 500/FEMA 

criteria

✔

Designed specifically to provide lifesafety protection per ICC 500 or FEMA 

Criteria

✔ ✔

Designed specifically to provide nearabsolute protection per FEMA criteria 

(including operational and emergency 

planning criteria)

✔
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 1-13

INTRODUCTION

contractors can use to construct safe rooms in homes or small businesses. Design options include 

safe rooms located in basements or garages, or in an interior room of a new home or small business. 

Other guidance includes how to modify an existing home or small business to add a safe room in one 

of these areas. These safe rooms are designed to provide near-absolute protection for their occupants 

from the extreme winds expected during tornadoes and hurricanes and from flying debris, such as 

wood studs, that tornadoes and hurricanes usually generate.

In 2000, FEMA released the First Edition of FEMA 361 

(Figure 1-6). Updated in 2008,4 this publication contains 

guidance for architects, engineers, building officials, local 

officials and emergency managers, and prospective safe room 

owners and operators about the design, construction, and 

operation of safe rooms and storm shelters for extreme-wind 

events. It presents important information about designing 

and constructing community safe rooms, including design 

criteria for wind, wind-borne debris, and flood hazards. The 

2008 update to FEMA 361 also includes the technical design 

criteria used for the prescriptive safe room designs presented 

in FEMA 320. It includes guidance on shelter management 

and operations and has checklists to help designers, owners, 

and emergency management officials ensure safe rooms 

are correctly designed and constructed. FEMA 361 also has 

checklists that can be used to evaluate existing buildings 

that may be used as refuge areas if a FEMA 361-compliant 

safe room is not available in a community or jurisdiction. 

The refuge area checklists can help identify how vulnerable 

different areas of a building are to the effects of wind and 

wind-borne debris associated with tornadoes or hurricanes.

It is important to remember that the building codes 

and standards used in the United States prior to 

2008 did not address life-safety protection from 

tornadoes or hurricanes. Although the guidance 

from FEMA and others has existed since the late 

1990s, it was not until the release of ICC 500 in 2008 

that such criteria were introduced into building 

standards. Following the release of the ICC 500, 

the 2009 International Building Code (IBC) and IRC incorporated the standard by reference. This 

means that if a building is constructed to the 2009 IBC and IRC and there is a portion of the building 

designated to be a shelter, it must be designed to the criteria of the ICC 500, which has specific 

provisions on how to provide protection from extreme wind events and wind-borne debris associated 

with those events (Figure 1-7).

4 The Second Edition of FEMA 361 (2008) is titled Design and Construction Guidance for Community Safe Rooms.

Figure 1-6: Cover of FEMA 361 (FEMA 

2008, Second Edition)

Building codes aim to reduce the level of 

damage to structures during design wind 

events but do not address life-safety protection for building occupants in design or 

extreme wind events.
1-14 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

INTRODUCTION

However, at this time, neither the ICC 500 nor the International 

Codes (I-Codes) require shelters to be designed or constructed 

within buildings. ASCE 7, Minimum Design Loads for Buildings 

and Other Structures, also does not address tornadoes as part of 

the wind design considerations and requirements for buildings 

or other structures. Therefore, it is imperative that the design 

community, emergency management officials, and the general 

public develop a better understanding of the vulnerabilities of 

existing buildings to tornadoes and other high-wind events.

1.3 2011 Tornado Recovery Advisories

Through investigation and observation of the performance 

of both residential and non-residential buildings, the MAT 

developed eight new recovery advisories to provide guidance 

for post-tornado reconstruction; these recovery advisories 

were published soon after the events and are available online 

through the FEMA Library Web site5 and in Appendix F. The 

set of recovery advisories includes:

+ Recovery Advisory 1: Tornado Risks and Hazards in the Southeastern United States

+ Recovery Advisory 2: Safe Rooms: Selecting Design Criteria

+ Recovery Advisory 3: Residential Sheltering: In-Residence and Stand-Alone Safe Rooms

+ Recovery Advisory 4: Safe Rooms and Refuge Areas in the Home

+ Recovery Advisory 5: Critical Facilities Located in Tornado-Prone Regions: Recommendations for Facility 

Owners

+ Recovery Advisory 6: Critical Facilities Located in Tornado-Prone Regions: Recommendations for 

Architects and Engineers

+ Recovery Advisory 7: Rebuilding and Repairing Your Home After a Tornado

+ Recovery Advisory 8: Reconstructing Non-Residential Buildings After a Tornado

These guidance documents are directed not only toward architects, engineers, and contractors, but 

also to building owners, homeowners, and State and local government officials. This MAT report 

supplements the information provided in the recovery advisories and provides more detailed analysis 

and recommendations. 

5 FEMA Library, Tornado Recovery Advisories, www.fema.gov/library/viewRecord.do?id=4723

Figure 1-7: 

Cover of ICC 500 (ICC/NSSA 2008)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 1-15

INTRODUCTION

1.4 Organization of Report

This report is organized in the following manner:

Chapter 1: Provides an overview of the purpose and methodology behind the MAT’s activities.

Chapter 2: Provides a general background on tornadoes and a detailed discussion of the 

meteorological events that led up to the April 25–28, 2011 tornado outbreak in the mid-south area 

of the United States and the May 22, 2011 Joplin, MO, tornado.

Chapter 3: Presents a discussion of the general causes of observed failures, the regulations that 

govern construction, and recommended construction practices resulting from the MAT’s field 

investigations.

Chapter 4: Presents the MAT’s observations on the performance of residential buildings. The MAT 

assessed one- and two-family residences and multi-family residences.

Chapter 5: Presents the MAT’s observations on the performance of commercial buildings.

Chapter 6: Presents the MAT’s observations on the performance of schools. 

Chapter 7: Presents the MAT’s observations on the performance of healthcare and first responder 

facilities and EOCs.

Chapter 8: Presents the MAT’s observations on the performance of two infrastructure categories: 

water treatment and distribution facilities and towers (communications and antennae).

Chapter 9: Presents general information and the MAT’s observations related to refuge areas, 

shelters, and safe rooms/storm shelters.

Chapter 10: Provides conclusions based on the MAT’s observations; this information is intended to 

assist States, communities, businesses, and individuals who are recovering and rebuilding from the 

tornadoes. 

Chapter 11: Provides recommendations intended to assist individual, communities, and businesses 

through the reconstruction process and to help reduce future damage and impacts from similar 

tornadic wind events.

Appendix A: Lists contributors to the MAT including those who supported preparatory efforts, 

supported the MAT in the field, and contributed to writing and reviewing the MAT report. 

Appendix B: Provides the references cited in the report.

Appendix C: Provides a list of acronyms and their definitions.

Appendix D: Provides a glossary of terms.
1-16 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

INTRODUCTION

Appendix E: Provides a background on the development and use of the EF scale, as well as a summary 

of the EF scale ratings determined by the MAT for structures it accessed.

Appendix F: Includes the Recovery Advisories created for the April 25–28, 2011 tornado outbreak 

in the mid-south area of the United States and the May 22, 2011 Joplin tornado.

Appendix G: Provides prescriptive guidance to enhance wood-frame residential building 

performance when impacted by tornadoes rated EF2 or less or inflow winds associated with tornadoes 

rated EF3 or greater.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-1

2Meteorological Background 

and Tornado Events of 2011

The most violent tornadoes, with wind speeds of more than 200 

mph near ground level, are capable of tremendous destruction. 

From 1950 through 2006, tornadoes caused 5,506 

deaths and 93,287 injuries, as well as devastating 

personal and property losses.1 According to 

tornado occurrence data obtained from the 

NOAA SPC more than 1,275 tornadoes have been 

reported nationwide each year since 1997. The 

number of reported tornadoes has increased over 

the period 1950–2007 (Simmons and Sutter 2011), 

attributed in part to better reporting of tornadoes 

and better technology. 

1 The majority of the information contained in this section was obtained from the NOAA NWS SPC, http://www.spc.noaa.gov. The SPC, part of 

NWS, is responsible for forecasting the risk of severe thunderstorms and tornadoes in the contiguous United States.

According to the Glossary of Meteorology

(American Meteorological Society 2000), 

a tornado is “a violently rotating column 

of air, pendant from a cumuliform cloud or 

underneath a cumuliform cloud, and often 

(but not always) visible as a funnel cloud.” 
2-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

Despite the increase in tornado reports, high intensity tornadoes are still rare. The 2011 tornado 

season was remarkable for the number of strong and violent tornadoes that impacted populated 

areas, but it was not the most active tornado year in history (SPC).2 Super outbreaks similar to the 

April 27, 2011 and severe and isolated events like the Joplin, MO, tornado have occurred in the past 

(e.g., April 3–4, 1974). Strong and violent tornadoes such as those in 2011 can be expected to occur 

with 20–50 year periodicities in tornado-prone regions.3

This chapter presents a background on tornadoes and a detailed discussion of the events that led 

up to the April 25–28, 2011 tornado outbreak in the mid-south region of the United States and the 

May 22, 2011 Joplin, MO, tornado. This chapter introduces the events on which the observations, 

conclusions, and recommendations in the following chapters of this report are based. Included are 

a discussion on tornado prediction; a description of the Enhanced Fujita (EF) scale, the method 

used to rate tornado intensity based on observed damage; a general description of tornadoes and 

their associated wind and damage patterns; a discussion of NOAA’s NWS tornado warning systems 

and its method for applying EF ratings to tornadoes; and a narrative of the history, severity, and 

meteorological events of the spring 2011 tornadoes in Alabama, Georgia, Mississippi, Tennessee, 

and Missouri.

2.1 Tornado Prediction

Meteorologists use several parameters to predict the likelihood and type of severe weather that will 

occur. Two of the most important parameters for predicting long-track violent tornadoes (LTVTs) 

are Convective Available Potential Energy (CAPE) and Storm-Relative Helicity (SRH). Since the 

potential for tornadic storms can be predicted reasonably well using these two parameters, a third 

parameter, the Energy-Helicity Index (EHI) combines CAPE and SRH. High CAPE values represent 

an unstable atmosphere and are associated with warm weather and sunny skies. High SRH values 

reflect the potential for rotating updrafts and are associated with wind shear (changing wind speed 

and/or wind direction with height in the atmosphere). Generally, when the resulting EHI is greater 

than 4, there is a good possibility of severe tornadoes (EF2 and greater; refer to Section 2.2 for 

additional information related to EF scale ratings). Typically, the EHI is in the 5 to 6 range during 

most large tornadic outbreaks. A summary of these and other severe weather parameters can be 

found at NOAA’s NWS Weather Forecast Office Web site.4

Tornado Season in the Mid-South Region: Locations in the mid-south, including those areas 

subjected to the 2011 tornado events, experience their highest CAPE values during the summer 

months. However, SRH values are typically higher in the cooler months of late fall, winter, and 

spring, when active frontal systems and undulations in the flow pattern of the upper atmosphere are 

common. Most severe weather events in the mid-south are therefore characterized by one parameter 

being much higher relative to the other, and days when high CAPE values coexist with high SRH 

values are rare. During transitional months in the mid-south region, however, both SRH values 

and CAPE values can be high. Thus, the mid-south region has two main severe weather/tornado 

seasons, though tornadoes can occur throughout the year. A peak season occurs from late February 

2 The most active year on record is 1974 (http://www.ncdc.noaa.gov/oa/climate/severeweather/tornadoes.html#history) 

3 NOAA National Climatic Data Center, Weather/Climate Events, http://www.ncdc.noaa.gov/oa/climateresearch.html. See U.S. Storm Events 

Database.

4 NOAA NWS Weather Forecast Office, Louisville, KY, http://www.crh.noaa.gov/lmk/soo/docu/indices.php
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-3

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

through mid-April, and a secondary season sometimes occurs in November. The April 25–28, 2011 

outbreak was a little past the mean peak of the spring tornado season in the mid-south region.

Tornado Season in the Joplin, MO, Region: The tornado season in Joplin, MO, resembles more of 

a classic Great Plains regime where peak activity occurs in the spring. May is the peak month for 

the tornado season in Oklahoma, Kansas, and 

Missouri, with increased activity commonly 

occurring from April through June. The 

probability of tornadoes outside of these 3 

months is much lower than it is in the midsouth region.

2.2 Enhanced Fujita Scale

An important step in classifying tornado intensity was the development of the Fujita scale and the 

updated EF scale. These tornado intensity rating scales remain an important factor considered 

by architects and engineers in their evaluation of damage following a tornado. The Fujita scale, 

originally developed by Dr. Tetsuya T. Fujita in 1971, provided a method to rate tornado intensity 

by examining the affected area, allowing people to distinguish between weak and strong tornadoes. 

Since there was no reliable way to accurately determine wind speed of a tornado via instrumentation, 

the Fujita scale provided a method to rate the intensity of tornadoes based on the damage caused. 

While the Fujita scale was used for 33 years, it had its limitations. The Fujita scale did not include 

damage indicators (DIs) and did not provide a method to correlate construction quality with the 

observed variability in damage resulting from similar wind speeds. 

The EF scale, a new tornado strength rating model, was published in 2004 in A Recommendation 

for an Enhanced Fujita Scale (TTU 2004) and updated in 2006 (TTU 2006).5 The 2006 revision to 

this document updated the steps in assigning an EF scale rating to a tornado event. More detailed 

information can be found at the TTU Wind Science and Engineering Research Center Web site.6

In comparison with the Fujita scale, use of the EF scale has led to a more realistic understanding of 

tornadic wind speeds. It has made it easier to distinguish the areas outside of the central tornado 

track, which have lesser wind speeds, and areas where wind-resistant design practices may reduce 

damage. 

The EF scale follows the same basic format as the original Fujita scale and also includes six 

categories, from 0 to 5, representing increasing degrees of wind damage; however, the EF scale 

was developed using improved examinations of tornado damage to better classify the correlation of 

tornado damage with associated wind speeds. Table 2-1 lists the 3-second gust speeds based on the 

original Fujita and EF scale ratings. 

5 Available online from TTU at http://www.depts.ttu.edu/weweb/Pubs/fscale/EFScale.pdf

6 TTU Wind Science and Engineering Research Center Website, www.wind.ttu.edu

Tornadoes may travel in any direction, but most 

move from southwest to northeast or west to 

east. Unless noted otherwise, the tornadoes 

that caused the damage observed by the MAT 

moved from southwest to northeast.
2-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

Table 2‐1: Fujita Scale Converted to EF Scale

Fujita Scale Fujita Scale: 3-Second Gust (mph) EF Scale EF Scale: 3-Second Gust (mph)

F0 45–78 EF0 65–85

F1 79–117 EF1 86–110

F2 118–161 EF2 111–135

F3 162–209 EF3 136–165

F4 210–261 EF4 166–200

F5 262–317 EF5 Over 200

mph = miles per hour; EF = Enhanced Fujita

The EF scale uses 28 DIs to categorize building use and type of construction. Each DI includes 

damage description categories; each is assigned a number termed the degree of damage (DOD), and 

each has a damage description associated with an expected estimated wind speed. An example of 

the DOD and damage descriptions for a single-family residence as well as descriptions of the 28 DIs 

can be found in Appendix E. The DOD includes the expected wind speed as well as a lower- and 

upper-bound wind speed that would most likely produce 

the in observed damage. Photographs are included 

in the supporting documentation for the EF scale in A 

Recommendation for an Enhanced Fujita Scale (TTU 2006) 

to assist investigators. Appendix E provides additional 

information on the EF scale, including a list of the DIs 

and examples of damage description categories.

2.3 Tornado Winds and Damage Patterns 

The visible funnel cloud associated with and typically labeled the vortex of a tornado is not always the 

edge of the strongest winds. The radius of highest wind speeds in a tornado can be larger than the 

visible funnel cloud’s radius. The visible funnel cloud boundary is determined by the temperature 

and moisture content of the tornado’s inflowing air. It is important to remember that a tornado’s 

wind speeds cannot be determined just by looking at the 

tornado. In a tornado, the diameter of the vortex can 

change with time, so it is impossible to say precisely where 

a less intense region of the tornado’s wind flow ends and 

a more intense region begins. 

Figure 2-1 shows the types of damage that can be caused 

by the tornadic winds of a violent tornado. In general, 

as shown in the figure, the severity of the damage varies 

with distance from the vortex and wind speeds within the 

vortex. Note, however, that the rotation of a tornado can 

cause winds flowing into the vortex on one side to be greater than those on other sides. As a result, 

it is not uncommon for the area of damage on one side of the tornado to be more extensive. The 

colors in Figure 2-1 illustrate the expected tornado damage near the vortex of the tornado (darkest 

red) to the periphery of the tornado swath (lightest yellow). The damage expected at each of these 

wind speeds is explained below: 

Inflow is rapidly moving air near 

the surface that is being pulled radially into the vortex. Inflow speeds 

range from approximately 45–135 

mph depending on distance from 

the vortex and the intensity of the 

tornado.

For information on how the NWS 

uses the EF scale to derive its tornado ratings, refer to Section 2.4.2.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-5

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

+ EF5 wind speeds (dark red): Strong frame houses and engineered buildings are lifted from their 

foundations or are significantly damaged or destroyed. Automobile-sized debris is moved 

significant distances. Trees are uprooted and splintered 

+ EF4 wind speeds (dark orange): Well-constructed homes, as well as manufactured homes, are 

destroyed, and some structures are lifted off their foundations. Automobile-sized debris is 

displaced and often tumbles. Trees are often uprooted and blown over. 

Figure 2‐1: Potential tornado damage pattern 

SOURCE: ADAPTED FROM FIGURE 2-2 OF FEMA 342 (1999A)
2-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

+ EF3 wind speeds (light orange): Roofs and some walls, especially unreinforced masonry, are 

torn from structures. Small ancillary buildings are often destroyed. Manufactured homes on 

nonpermanent foundations can be overturned. Some trees are uprooted. 

+ EF2 wind speeds (yellow): Roofs are damaged, including the loss of shingles and some sheathing. 

Manufactured homes, on nonpermanent foundations can be shifted off their foundations. 

Trees and landscaping either snap or are blown over. Medium-sized debris becomes airborne, 

damaging other structures. 

+ EF1wind speeds (light yellow): Minor damage to roofs and broken windows occurs. Larger and 

heavier objects are displaced. Minor damage to landscaping and trees can be observed.

+ EF0 wind speeds (light blue): Some damage can be seen to poorly maintained roofs. Unsecured 

light-weight objects, such as trash cans, are displaced.

It is important to note the varying levels of damage to structures between the perimeter and the 

vortex of the tornado. Many of the mitigation recommendations presented throughout this report 

and in the Recovery Advisories (Appendix F) would be most effective along the periphery of a violent 

tornado (in the light blue to light orange range of Figure 2-1 or in the wind speed range of an EF0 

to EF2 tornado). Structures located in the dark orange range, between the periphery and the edge 

of the vortex (in the wind speed range of an EF3 tornado), would benefit from both the mitigation 

recommendations and adherence to model building codes. For structures directly in the path of a 

tornado (dark red area of Figure 2-1, or in the wind speed range of an EF4 to EF5 tornado), only 

engineered shelters would provide near absolute protection to occupants.

2.4 National Weather Service Tornado 

Warning Strategies and Ratings

The NWS was successful in forecasting the events in April and May, 2011 in large part due to 

improved forecasting ability, particularly after NWS modernization in the mid-1990s. Technological 

advances in the last 15 years, such as the introduction of Doppler radar, have allowed meteorologists 

to pinpoint small areas of rotation at the street and block level. Furthermore, improvements in shortand long-term weather forecasting models allow meteorologists a greater lead time for predicting 

weather conditions that may spawn tornadoes.

2.4.1 Tornado Watches and Warnings 

When the possibility of a tornado puts people at risk, it is important that they are informed so that 

they can take precautionary measures to shelter and protect themselves in the event that their home 

or business is impacted. Currently, the NWS SPC issues watches for large geographic areas where 

conditions for tornadoes are favorable. The local NWS office then issues warnings when a tornado 

has been observed by a spotter or when radar indicates strong rotation suggesting the presence of a 

tornado. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-7

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

The NWS warning comes in the form of a list of cities and towns that are predicted to be in the path 

of the storm and the times when the storm will reach a given location. These tornado warnings are 

disseminated through multiple media sources in different formats in order to convey the information 

to the public. Residents of communities are alerted about a tornado warning via television, radio, 

social media, internet, and sirens. Television coverage often includes a tornado polygon of the 

projected path that is based on the NWS warnings, giving viewers an easily understood graphic 

representation of the warnings.

False Alarm Ratios

There are times when a tornado warning is issued, but no tornado touches down. This occurs 

because radar-indicated rotation within a thunderstorm often does not indicate the actual presence 

of a tornado. For this reason, the majority of severe weather events and tornado warnings are for 

weak storms, producing winds with speeds in the EF0 or EF1 range. Often, circulation cannot be 

confirmed without a spotter in the field, so for these events it is difficult to tell whether or not 

they are actually tornadoes. The volume of such low intensity events may diminish the value of a 

warning when one is issued for a more serious storm, similar to those that occurred in the spring 

of 2011. Statistics documented by the NWS for tornado false alarm ratios in 2008 indicate a rate of 

75 percent. The NWS is trying to reduce this number to 70 percent (Brotzge et al. 2011). The false 

alarm ratio statistics can be misleading because forecasters are not given credit for close calls. 

New Experimental Tornado Warnings 

An experimental tornado warning method will be introduced at select NWS field offices beginning 

April 2, 2012. The traditional tornado warning will be retained in a modified form and two new 

categories will be added. The experimental warnings will be as follows:

+ Tornado warning: A tornado indicated by 

radar, but not confirmed by field spotters. 

+ Particularly dangerous situation (PDS) 

tornado warning: A tornado confirmed on the 

ground by field spotters or residents. 

+ Tornado emergency: The highest level of 

tornado warning; this warning will be issued if 

a large and potentially violent tornado is about 

to impact a densely populated area. 

2.4.2 NWS EF Rating Assignments 

NWS assigns tornado ratings using the EF scale rating system. For events with damage that is 

potentially greater than EF3 level, the NWS forms a Quick Response Team (QRT) consisting of 

meteorologists and one or two structural engineers. The QRT conducts a thorough evaluation 

of damage to structures along the tornado’s path and note any unusual observations. Unusual 

observations include tree debarking, pavement scouring, and other difficult to quantify phenomena 

associated with very high winds. 

The SPC has issued probabilistic forecasts of atmospheric hazards for many 

years. It issues a three-tiered and color coded probabilistic forecast on its 

Web site that shows risk categories of 

slight (light green), moderate (light red), 

and high (magenta) for areas forecasted to be impacted by severe weather

(http://www.spc.noaa.gov).
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METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

The QRT rates EF scale intensities for individual and surrounding structures while using multiple 

DIs and DODs (refer to Appendix E for additional information DIs and DODs). The data and 

ratings gathered by the QRT are used by NWS to construct wind speed contours that show wind 

speed decay from the vortex to the periphery of the damage swath.

For lower intensity tornadoes, the NWS forms a smaller assessment team to conduct a damage survey 

with specific objectives. The team locates the beginning, end, and widest section of the damage 

swath, and then rates the maximum intensity of the tornado using multiple DIs and DODs (refer to 

Section 2.2 for more information on DIs and DODs). The NWS assessment of weaker tornadoes is 

not as detailed as that performed by a QRT. All assessment personnel, whether QRT or not, undergo 

training on how to use the EF scale rating system. 

The NWS considers several DIs when assigning 

an EF scale rating to a tornado event. For this 

reason, structures along the path of a tornado 

may be assigned several different EF ratings 

ranging from EF0 to EF5, while the overall 

tornado intensity may be labeled EF4. For 

archival purposes, a tornado is officially labeled 

by the NWS according to its highest intensity 

along its path.

2.5 Tornado Events of Spring 2011

This section summarizes the events in the mid-south region of the United States from April 25 

to 28 and the events in Joplin, MO, on May 22. The information is summarized from post-storm 

assessments from NWS offices in Jackson, MS; Memphis, TN; Birmingham, AL; Huntsville, AL; and 

Springfield, MO, unless otherwise noted. Links to specific post-storm assessments are found in the 

references. EF ratings in this chapter are from NWS post-storm assessments.

2.5.1 April 25–28, 2011 Tornadoes in the Mid-South Area of the United States

The following subsections present the events of the April 25–28, 2011 tornadoes in the mid-south 

area of the United States. The events are presented chronologically, rather than geographically, in 

order to trace the outbreak from beginning to end using the perspective of those who witnessed the 

events. The tornado tracks for the April 25–28, 2011 outbreak in Alabama are shown in Figure 2-2 

and in Mississippi in Figure 2-3. The tornado tracks from the neighboring States of Tennessee and 

Georgia are not shown since the tornadoes that impacted those States originated in Alabama and 

Mississippi, where they caused much greater damage. The names referenced for the tornadoes are 

those that were widely used by NWS and the media in the aftermath of the tornadoes.

2.5.1.1 April 18–24, 2011

During the week of April 18–22, 2011, the meteorological community began to discuss a potentially 

significant severe weather scenario developing in forecasted model runs for the following week. As 

early as Tuesday, April 19, broadcast meteorologists and NWS personnel in Alabama were discussing 

the possibility of a major severe weather event within 8 days or so. Discussions among forecasters in 

NWS EF scale training and rating practices 

can be viewed on the following Web sites:

http://www.spc.noaa.gov/efscale/

http://www.wdtb.noaa.gov/courses/

EF-scale/index.html
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-9

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

Figure 2‐2: Map of tornado tracks associated with the April 27, 2011 outbreak in Alabama

SOURCE: HTTP://WWW.SRH.NOAA.GOV/BMX/?N=EVENT_04272011 APRIL 27, 2011, 12:00 P.M. TO 6:00 P.M

the Southeast escalated throughout the weekend after every model update. Forecasters thought that 

conditions suggested a very strong potential for supercells with LTVTs.

By Sunday, April 24, forecast soundings and severe weather parameters showed a high combination 

of CAPE and SRH values for the afternoon of Wednesday, April 27. The corresponding EHI values 

were forecasted in some areas to have an extremely high value of EHI greater than 9. Generally, 

when the EHI is over 4, there is a good possibility of strong (EF2 to EF3) and violent (EF4 to EF5) 

tornadoes. Typically, EHI is in the 5 to 6 range during large outbreaks. On Monday, April 27, when 
2-10 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

new model updates showed better agreement in 

timing and evolution of the event, meteorologists had 

greater confidence in the development of supercells 

with LTVT. This began a 48-hour period of warning.

2.5.1.2 April 25, 2011

The situation began to materialize in the early 

morning hours of April 25, when a very strong 

trough in the upper atmosphere strengthened and 

moved southward along the leeward side of the 

Rockies into the Great Plains, bringing cold polar air 

NWS and forecasters successfully 

predicted the severe tornado event.

Broadcast meteorologists and NWS 

personnel began predicting the possibility of severe weather a week before 

the event (http://weather.gov). By 48 

hours before the severe tornado events 

of April 25–28, they were actively warning the public about a historic severe 

weather day. 

Figure 2‐3: Map of tornado tracks associated with the April 26–27, 2011 outbreak in Mississippi

SOURCE: HTTP://WWW.SRH.NOAA.GOV/JAN/?N=2011_04_25_27_SVR
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-11

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

from Canada. Unseasonably warm, moist, 

and unstable air from the Gulf of Mexico 

was in place throughout much of the 

southern United States. A 1,000-millibar 

(mb) surface low was centered just west of 

Lubbock, TX, at 7:00 p.m. Central Daylight 

Time (CDT)7 on April 25 in an area of active cyclogenesis. Severe storms began to develop in the 

diffluent zone to the east of the developing system on the afternoon of April 25 across northeast 

Texas, southwest Arkansas, and northwest Louisiana. These storms formed into bow echoes that 

produced high winds and several tornadoes across Arkansas. The atmosphere briefly settled in the 

early morning hours of April 26 before quickly recharging.

2.5.1.3 April 26, 2011

At 7:00 a.m. on April 26, a 992 mb low was located near Davenport, IA, with a trailing cold front 

stretching south-southwest into Texas. A secondary surface low developed and deepened over Texas 

while a jet streak (faster-moving section of the jet stream) promoted uplift in the late afternoon 

hours. These conditions prompted the SPC to issue a high risk, severe weather outlook for southern 

Arkansas. High risk warnings are rare and indicate a significantly higher than normal chance for 

tornadic storms. According to the SPC archives, there were only seven high risk warnings between 

January 2007 and August 2011.

Numerous tornadoes evolved in Arkansas on the afternoon and evening of April 26 as the storms 

initially developed as supercells and transitioned into a quasi-linear convective system (QLCS). 

The QLCS raced eastward into Mississippi and Alabama overnight, evolving into a squall line and 

knocking out power for thousands. There were hundreds of reports of severe straight-line winds and 

21 tornadoes.

2.5.1.4 April 27, 2011, 2:00 a.m. to 12:00 p.m.

Linear squall line events normally produce isolated, weaker tornadoes in the EF0 and EF1 range, 

but some of the early morning (2:00 a.m. – 3:00 a.m.) tornadoes in Alabama on April 27 were 

rated EF2 and EF3. Squall line events are common in Alabama, and the early morning events may 

have left many residents assuming that the worst of the severe weather had simply arrived half a day 

early. Furthermore, the morning weather caused numerous power outages, depriving many people 

of access to local TV meteorologists during the critical afternoon hours. 

In the wake of the QLCS/squall line, skies slowly began to clear across northern Mississippi and 

Alabama, giving way to mostly sunny and very humid conditions with sustained southerly winds 

of 15 to 25 mph. Despite the clear skies, the forecasted conditions from the model runs of the 

preceding days were materializing into the perfect combination of instability and wind shear capable 

of creating the super outbreak of tornadoes on the afternoon of that day.

The SPC issued a PDS (particularly dangerous situation) tornado watch for Mississippi, Alabama, and 

portions of Tennessee shortly after noon. A 996 mb surface low had formed overnight in Arkansas 

7 All times given as CDT unless otherwise noted.

A bow echo is a bow-shaped line of convective 

storm cells often associated with swaths of damaging straight-line winds and small tornadoes.
2-12 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

and was tracking toward Memphis 

while strengthening. At the same 

time, a potent shortwave in the 

upper atmosphere was arriving 

and promoting further uplift over 

Mississippi and Alabama during 

the peak hours of afternoon 

heating. In the early afternoon, 

small supercell thunderstorms 

started to form and take on 

classic supercell characteristics.

2.5.1.5 April 27, 2011, 2:30 p.m. to 3:00 p.m.: Philadelphia, MS, 

Tornado #24, and Cullman, AL, Tornado #38

The first major tornado of the day formed near Philadelphia, MS, at approximately 2:30 p.m. and 

tracked northeast for 29 miles while briefly attaining EF5 status (shown as Tornado #24 on Figure 

2-3). Though over rural areas, this tornado produced three fatalities when it tossed a manufactured 

home several hundred yards.8

A short time later at 2:43 p.m., the 43-mile-long EF4 Cullman, AL, tornado (shown as Tornado #38 

on Figure 2-2) formed over Smith Lake and tracked northeast through the heart of Cullman, a city 

of 15,000. It was characterized by multiple vortices during the first 15 miles of its path. The base 

reflectivity image for the Cullman, AL, tornado is shown in Figure 2-4. The hook echo is circled in 

white on the image (Figure 2-4). The tornado continued northeasterly and reached peak intensity 

over rural areas as it passed north of Fairview, AL. This tornado was the first tornado of the day to 

be filmed via skycam and broadcast live to residents of north-central Alabama.

8 NOAA NWS, Weather Forecast Office, Jackson, MS, Tornado Outbreak April 25–27, 2011, 

http://www.srh.noaa.gov/jan/?n=2011_04_25_27_svr

Figure 2‐4: 

Base reflectivity and hook 

echo (white circle) for 

Cullman, AL

Cullman, AL

A PDS tornado watch provides the same recommended 

actions to the public, school officials, and emergency managers as other tornado watches. This terminology is often 

used by meteorologists and even occasionally used when 

broadcasting storm situations on the air. 

A shortwave trough (or shortwave) is a disturbance in the 

mid or upper part of the atmosphere which induces upward 

motion ahead of it. If other conditions are favorable, this upward motion can contribute to thunderstorm development 

ahead of a shortwave trough. 

(SOURCE: NWS GLOSSARY, HTTP://NWS.NOAA.GOV/GLOSSARY)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-13

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

2.5.1.6 April 27, 2011, 3:00 p.m.: Hackleburg to Huntsville, AL, Tornado #40

Just before 3:00 p.m., a discrete supercell rapidly evolved to the west as it crossed the Mississippi/

Alabama State line and began to acquire tornadic characteristics on radar. The Hackleburgto-Huntsville tornado that developed from this supercell tracked an amazing 107 miles before 

dissipating north of Huntsville, AL. It was rated at EF5 intensity in Hackleburg and Phil Campbell, 

and possibly reached peak intensity after Phil Campbell near Oak Grove, AL. The NWS justification 

for the EF5 status was based on numerous pieces of evidence, described below and in the body of 

this report. According to the SPC database updated in January 2012 (NOAA 2012), the Hackleburgto-Huntsville tornado caused 72 fatalities, which ranks it as the sixth deadliest single tornado 

since 1950.

A tornado warning was issued by the 

NWS Birmingham office at 2:59 p.m. for 

the Hackleburg/Phil Campbell area, and 

at 3:24 p.m., a tornado struck the town 

of Hackleburg, AL (shown as Tornado 

#40 on Figure 2-2). The base reflectivity 

radar image showing the hook echo in 

Hackleburg, AL, is shown in Figure 2-5. 

In Hackleburg, there was evidence of 

debris rowing (the piling of debris into 

rows aligned with wind direction), which 

occurs in a small percentage of the most 

violent tornadoes.

The tornado then continued northeast 

and struck the neighboring town of Phil 

Campbell 10 minutes later. The base reflectivity and relative velocity radar images for the tornado 

in Phil Campbell are shown in Figure 2-6. In Phil Campbell, which is located 10 miles northeast of 

Hackleburg, the damage was similar but more extensive. 

In Oak Grove, 20 miles northeast of Phil Campbell, the tornado caused widespread damage, 

including complete tree debarking in Oak Grove, the most noticeable compared to any other point 

along its track. Tree debarking is an indication of very intense winds; however, exact wind thresholds 

for tree debarking depend on tree species and tree health among other factors.

Base reflectivity is measured by Doppler radar 

and is related to the power, or intensity, of the reflected radiation sensed by the radar antenna. Base 

reflectivity is related to rainfall intensity (e.g., drop 

size and rainfall rate) and hail size (for large values 

of reflectivity). 

Hook echo is a radar reflectivity pattern characterized by a hook-shaped extension of a thunderstorm 

echo, usually in the right-rear part of the storm (relative to its direction of motion). A hook often is 

associated with a mesocyclone, and indicates favorable conditions for tornado development.

(SOURCE: NWS GLOSSARY, HTTP://NWS.NOAA.GOV/GLOSSARY/)

Figure 2‐5: 

Base reflectivity and hook 

echo (white circle) for 

Hackleburg, AL

Hackleburg, AL
2-14 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

Based on NWS damage assessments, the intensity of the tornado fluctuated from EF3 to EF4 as it 

continued northeast toward Huntsville. The community of Tanner, 28 miles northeast of Oak Grove 

and approximately 30 miles from the tornado’s end in Huntsville, appears to have experienced 

increased damage, at least in the upper-end EF4 range. With this tornado, Tanner has been 

struck by three tornadoes at or above EF4 intensity, twice in a 1974 outbreak and again in the 2011 

outbreak. Phil Campbell was also struck in the 1974 outbreak.9 This represents the most at-or-above 

EF4 intensity tornado occurrences for a single community.

2.5.1.7 April 27, 2011, 3:30 p.m.: Smithville, MS, Tornado #43

Only 25 minutes after the formation of the Hackleburg-to-Huntsville tornado, another storm was 

developing 20 miles to the southwest over Mississippi, with a track paralleling the Hackleburg storm 

(shown as Tornado #43 on Figure 2-2). The tornado first appeared north of Amory, MS, and at 

3:42 p.m. the EF5 tornado struck Smithville, MS. The base reflectivity and the relative velocity 

images for the tornado in Smithville, MS, are 

shown in Figure 2-7. This tornado was on the 

ground simultaneously with the EF5 to its 

east that was over Oak Grove, AL. The total 

length of the Smithville tornado track was 49 

miles and it caused 16 fatalities in Mississippi 

and 7 in Alabama.10

The Smithville, MS, tornado crossed into Alabama and struck the community of Shottsville, AL, 

where it was rated at EF3. The tornado dissipated 6 miles west of Hackleburg, close to the track of 

the Hackleburg-to-Huntsville tornado.

9 Historical storm event information is available through the NOAA National Climatic Data Center, http://www.ncdc.noaa.gov/oa/climate/

severeweather/extremes.html

10 NOAA NWS SPC, Annual U.S. Killer Tornado Statistics, http://www.spc.noaa.gov/climo/torn/fataltorn.html

The SPC successfully predicted the high risk 

areas. The area of northeast Mississippi and 

northwest Alabama was at the center of the 

SPC’s high risk zone.

Figure 2‐6: Base reflectivity and hook echo (white circle, left) and storm relative velocity (right) for Phil Campbell, AL

Phil Campbell, AL

Phil Campbell, AL
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-15

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

2.5.1.8 April 27, 2011, 3:38 p.m.: Cordova, AL, Tornado #41/#49

At approximately the same time the Smithville, MS, tornado formed, another tornadic supercell 

began its 123-mile-long path at 3:38 p.m., eventually striking Cordova, AL, 45 miles to the southsoutheast in Walker County (this tornado is shown as two tornadoes, #41 and #49, on Figure 2-2). 

This tornado was ranked EF1 to EF2 for most of its duration, but it briefly escalated into the EF3 

to EF4 range after crossing the future I-22 corridor and passing over Cordova, AL, resulting in 13 

fatalities.11 The base reflectivity and the relative velocity images for the tornado in Cordova, AL, are 

shown in Figure 2-8.

The downtown buildings of Cordova had already been directly impacted by a smaller, but still 

significant tornado during the early morning hours of April 27, when the squall line (described 

in Section 2.5.1.3) passed through. Power was still off from that event, leaving the warning siren 

inoperable during the afternoon. The afternoon Cordova tornado was ranked as an EF3 based on 

the damage in downtown Cordova. The afternoon track crossed the morning track just 50 yards 

south of the historic downtown. 

11 Ibid.

Figure 2‐7: Base reflectivity and hook echo (white circle, left) and storm relative velocity on right for Smithville, MS

Smithville, MS

Smithville, MS

Figure 2‐8: Base reflectivity and hook echo (white circle, left) and storm relative velocity on right for Cordova, AL

Cordova, AL Cordova, AL
2-16 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

The tornado achieved its maximum intensity of EF4 as it moved northeast of Cordova. It then 

continued northeast over hilly and rural terrain and, based on reported damage, possibly intensified 

after dropping off a bluff.

2.5.1.9 April 27, 2011: Macon County Supercell Thunderstorm, Tornado #46

The last major tornado of the day causing damage assessed by the MAT was spawned from the 

Macon County, MS, supercell thunderstorm. A small, discrete supercell developed over Newton 

County, MS, and looked ordinary for the first 20 minutes of its lifespan. However, there were no 

storms to the south of this cell to rob it of its inflow, suggesting potential strengthening. Though 

almost 100 minutes after forming, it was evident that this supercell had a high probability of directly 

impacting the city center of Tuscaloosa, a city of 83,000 and metropolitan area of almost 150,000 

people. TV meteorologists broadcasted a long-range polygon to show what would likely happen over 

the next hour, and the Birmingham Forecast Office of the NWS provided a 65-minute warning lead 

time for Tuscaloosa.12 Incredibly, this supercell thunderstorm would not dissipate until reaching 

Macon County, NC, almost 7 hours and 30 minutes later, after dropping several tornadoes along 

its path. Along its 80-mile path through Tuscaloosa and the Birmingham suburbs, it produced 64 

fatalities and injured over 1,000 people.13

At 4:43 p.m. the supercell thunderstorm became tornadic just to the southwest of Tuscaloosa, AL 

(shown as Tornado #46 on Figure 2-2). The base reflectivity and the relative velocity images for 

the tornado in Tuscaloosa, AL, are shown in Figure 2-9. The storm crossed I-20 near exit 68 at Joe 

Mallisham Parkway. It entered an industrial area where it damaged and destroyed many buildings, 

including the large building that housed Tuscaloosa County EMA. The tornado then crossed I-359 

and entered the residential areas of Tuscaloosa. A hardened room in a neighborhood was the 

only structure remaining after debris was cleared (structure is discussed in more detail in Section 

9.1.1). The tornado then passed over the busy commercial intersection of 15th Street and McFarland 

Boulevard. At this point, its intensity was rated at EF4 status and it continued to intensify and grow 

larger as it tracked into the Alberta section of Tuscaloosa.

12 NWS storm-based warnings and storm reports issued by a Weather Forecast Office can be viewed online at the Iowa Environmental Mesonet, 

Iowa State University Department of Agronomy, Web site, http://mesonet.agron.iastate.edu/cow/

13 NOAA NWS Weather Forecast Office, Birmingham, AL, Tuscaloosa-Birmingham EF-4 Tornado, April 27, 2011, http://www.srh.noaa.gov/

bmx/?n=event_04272011tuscbirm

Figure 2‐9: Base reflectivity and hook echo (white circle, left) and storm relative velocity on right for Tuscaloosa, AL

Tuscaloosa, AL Tuscaloosa, AL
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-17

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

Alberta Elementary School was severely damaged (see Chapter 6). Most of the older homes in 

Alberta, as many as 200 or more, were destroyed except for a few interior rooms. Tree debarking was 

more common here than in other areas struck by this tornado. The tornado then continued into 

the community of Holt. Most of the older homes in Holt, as many as 200, were completely destroyed 

while others were left with small interior walls intact. Damage observed in Holt further validated the 

EF4 rating for the tornado.

The tornado then exited the Tuscaloosa metropolitan area and tracked east-northeast across rural 

areas before heavily damaging the town of Concord in Jefferson County. After Concord, the tornado 

passed over the outer sections of Pleasant Grove. The base reflectivity and the relative velocity images 

for the tornado in Pleasant Grove, AL, are shown in Figure 2-10. 

The tornado next passed over the industrial area of Pratt City on the northern side of Birmingham, 

AL. The tornado weakened here, though it still produced extensive damage in Pratt City. The 

tornado continued to lose intensity, although briefly getting much wider, as it crossed I-65 near exit 

266 north of Birmingham. It finally dissipated in Fultondale, AL, where it briefly displayed multiple 

vortices before lifting.

Although the Tuscaloosa metropolitan area is frequently impacted by tornadoes, the city center had 

not been directly in the path of a major tornado since 1932. An F4 tornado affected the southern 

part of the city of Tuscaloosa on December 16, 2000. The April 8, 1998 F5 Oak Grove tornado track 

was less than 5 miles away from the April 27, 2011 track that devastated Pleasant Grove.14

2.5.2 May 22, 2011 Storms in Missouri

The May 22 Joplin, MO, tornado resulted in the highest number of fatalities for a single tornado 

since modern record keeping began in 1950. The official fatality count is 161 including both direct 

and indirect fatalities (City of Joplin 2011). 

14 Historical storm event information is available through the NOAA National Climatic Data Center, http://www.ncdc.noaa.gov/oa/climate/

severeweather/extremes.html

Figure 2‐10: Base reflectivity and hook echo (white circle, left) and storm relative velocity on right for 

Pleasant Grove, AL

Pleasant Grove, AL Pleasant Grove, AL
2-18 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

Unlike the April 25–28 tornado events in the mid-south, the May 22 Joplin, MO, tornado was an 

isolated occurrence on a day forecasted by the SPC as having only a moderate risk for tornado 

activity. Although the threat for severe weather and tornadoes existed, the forecasted conditions 

were not ideal to produce LTVT. Although there were 51 confirmed tornadoes across an eightState area that included Missouri, no other tornadoes developed on that day above EF3 intensity. 

The atmospheric conditions and thunderstorm cell dynamics rapidly evolved during the afternoon 

hours to produce a complex interaction of circumstances leading to the Joplin, MO, tornado.15

2.5.2.1 Summary of Synoptic Setting and Mesoscale Environment

In the days before May 22, 2011, meteorologists at the SPC identified conditions favorable for 

severe weather across a large area of the Great Plains and upper Midwest. A trough in the upper 

atmosphere was accompanied by a strong 996 mb surface low in eastern South Dakota. A cold front 

stretched from South Dakota to the Texas Panhandle with advection of warm, moist and unstable 

air ahead of the front. Several weaker tornadoes touched down in Minnesota and Wisconsin as 

forecasters had anticipated. An area of diffluence occupied much of the southern Plains in the 

vicinity of southwest Missouri. By the afternoon of May 22, high CAPE values were in place, and 

SRH values were increasing ahead of a dry line in Oklahoma.

A mesoscale discussion was issued at 3:48 p.m. from the SPC indicating the evolving tornado 

potential over southwestern Missouri with parameters more than sufficient to produce tornadic 

supercells. A broken line of severe thunderstorms initiated over Kansas and travelled generally 

southeast toward the Missouri border. Despite the evolving tornadic potential, as indicated by 

rapidly increasing EHI values immediately before the Joplin tornado, none of the Kansas storms 

materialized into tornadic cells. The supercell that would ultimately produce the Joplin tornado 

lacked classic structure as it approached the Missouri border.

Around 4:45 p.m., meteorologists observed a smaller storm coming out of Oklahoma and moving 

toward the northeast. This storm was on a collision course with the unstructured supercell in 

southeastern Kansas. At 5:05 p.m., the two storms collided and merged, as has happened before in 

numerous severe weather events. When cells merge, often the newly created supercell weakens or 

dissipates due to disruption of the circulation. However, in other instances in the region, such as the 

Pierce City, MO, 2003 tornado and the Picher, OK, 2000 tornado, merging cells produce a stronger 

supercell.

In the May 22, 2011 case, the rapidly rotating smaller cell was ingested by the dying larger cell. The 

newly created supercell began a transformation and started to acquire a more menacing classic 

shape. Based on the storm’s right-moving tendency and the presence of warm, moist, and unstable 

air, staff at NWS in Springfield, MO, issued a tornado warning 12 minutes later at 5:17 p.m., 

despite the storm’s marginal appearance. A short time later at 5:24 p.m., another small cell moving 

northeast was ingested, and at this point the Joplin supercell began to rapidly intensify and acquire 

tornadic characteristics.

15 A brief description of the synoptic setting and mesoscale environment for the Joplin tornado, as well as a summary of the NWS damage 

survey assessment, is located at: NOAA NWS Weather Forecast Office, Springfield, MO, Joplin Tornado Event Summary, May 22, 2011, 

http://www.crh.noaa.gov/sgf/?n=event_2011may22_summary
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 2-19

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

At 5:29 p.m., the supercell displayed a hook echo with a velocity couplet (tightly clustered incoming 

and outgoing winds on radar). The initial touchdown of the multiple-vortex tornado took place at 

5:34 p.m. on the southwestern side of Joplin. A storm relative velocity image was captured at 5:38 

p.m. and a base reflectivity image at 5:43 p.m. (Figure 2-11).

2.5.2.2 Damage and Path of the Joplin Tornado

Along its 22-mile path, and especially a 6-mile stretch in Joplin, the 0.75-mile-wide EF5 tornado 

destroyed and damaged thousands of homes. Numerous commercial buildings, schools, churches, 

and critical facilities were also destroyed or severely damaged. Joplin had the unfortunate 

circumstance of being located downwind of the merger collisions that perturbed the ordinary 

supercell and transformed it into a violent tornadic storm. An NWS assessment team observed 

damage consistent with previous EF5 tornadoes, including those from the April 27, 2011 outbreak. A 

full report on their findings can be found at the NOAA NWS, Weather Forecast Office, Springfield, 

MO, Web site.16

The tornado intensified rapidly after touching down near JJ Highway. By the time it entered a new 

residential area near Sunset Drive, the tornado was evolving from a multiple-vortex structure into a 

wedge. The sporadic damage on Sunset Drive suggests the possibility of multiple-vortex interaction. 

The tornado rapidly intensified as it crossed Schifferdecker Avenue and moved east-northeast 

toward St. John’s Regional Medical Center.

Based on damage observed at the St. John’s Medical Center, the MAT determined that the center 

of the tornado most likely passed over the northern parking lot of the hospital, producing a slightly 

weaker but still significant impact on the hospital. The damage in the parking lot and to buildings 

just west of the parking lot was extensive. Wind speeds in the parking lot and over adjacent buildings 

16 NOAA NWS, Weather Forecast Office, Springfield, MO, Joplin Tornado Event Summary, May 22, 2011, http://www.crh.noaa.gov/

sgf/?n=event_2011may22_summary

Figure 2‐11: Joplin, MO, base reflectivity with hook echo (white circle, left) at 5:43 p.m. and storm relative velocity 

at 5:38 p.m. (right)

Joplin, MO Joplin, MO
2-20 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

METEOROLOGICAL BACKGROUND AND TORNADO EVENTS OF SPRING 2011

to the west of the parking lot are estimated to have been higher than those that directly impacted 

the hospital (for additional information on the St. John’s Medical Center, refer to Section 7.1.4).

St. Mary’s Elementary School and Joplin High School were next in the path. Only the large steel 

cross and a portion of the façade were left of the St. Mary’s Elementary School building. Damage at 

Joplin High School suggested it took a direct hit as indicated by steel fence posts on the softball field 

facing opposite directions (refer also to Section 6.1.5). NWS rated the damage along this section of 

the tornado path to be EF4 mixed with some EF5. 

The tornado then veered almost due east and crossed the busy commercial intersection of 20th Street 

and Range Line Road. The commercial buildings of Home Depot, Walmart, and Academy Sports 

were heavily damaged here (refer to Chapter 5 for additional information). Slightly east of this 

intersection, the tornado veered southeast and began to weaken rapidly before crossing I-44. The 

storm immediately weakened once it resumed the same east-southeast vector it displayed in Kansas.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-1

3Design and Construction 

Considerations 

During field investigations, the MAT focused on identifying 

building components and construction practices that performed 

either poorly or notably well during the tornadoes.

Most buildings are not designed to withstand the extreme forces caused by the high wind speeds 

of severe or violent tornadoes (greater than 110 mph), and the vast majority fail when subjected to 

such conditions. However, the majority of tornadoes recorded in the United States are considered 

weak (EF1 or below), with maximum wind speeds of 110 mph. Wind speeds associated with EF0 and 

some EF1 tornadoes are less than or equal to the design wind speeds used in the majority of the 

United States,1 and properly designed and constructed structures should perform well under these 

conditions. In addition to high wind, tornadoes produce large quantities of fast moving wind-borne 

debris, which contributes to and sometimes causes building failures by penetrating the building 

envelope and allowing wind inside the structure.

1 Design wind speeds are higher in hurricane-prone regions of the United States, along the eastern and southeastern coast, than in 

other areas.
3-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

This chapter discusses the effects of wind loading on structures; the types and patterns of windborne debris observed in tornadoes; and the Federal, State, and local regulations that govern the 

areas affected by the tornadoes and the regulatory role in disaster mitigation efforts. 

3.1 Effects of Wind Loading on Structures

Effects of wind on a building include internal pressurization, increased lateral forces, uplift, and 

external pressures. Internal pressurization occurs when wind enters a building and lateral forces 

act either inward, created by the wind blowing directly on the face of a building, or outward, due to 

suction forces created when low pressure conditions occur inside the building. Most buildings are 

designed as enclosed structures with no large or dominant openings in the envelope that allow wind 

to enter. However, a breach in this normally enclosed building envelope due to broken windows, 

failed entry doors, or a failed garage door causes a significant increase in the net effective wind 

loads acting on the building under strong wind conditions. In such cases, the increased wind load 

may initiate a partial failure or cause a total failure of the primary structural system. A schematic 

diagram illustrating the increased loads due to a breach in the building envelope is shown in 

Figure 3-1.

Internal pressurization due to a breach of the building envelope (i.e., broken windows, failed 

garage door, missile impact in roof structure, etc.) may contribute to significant structural failures. 

Maintaining the integrity of the building envelope by limiting the size and number of openings 

created by the wind event in the building significantly improves the performance of elements in the 

structural system.

Primary structural systems are those that support the building against lateral and vertical loads. 

Many buildings observed by the MAT had structural systems that provided continuous load paths for 

high winds, but that were not sufficient for the extreme lateral and vertical uplift forces generated 

by tornadic winds. The MAT gathered information to determine whether the observed damage 

could have been prevented in buildings located in the peripheral areas of the wind field, those not 

in the direct path of the vortex of the violent tornadoes. Figure 3-2 shows a continuous load path in 

a CMU wall.

Winds moving around a structure create vertical and lateral forces that act on the building and 

cause several different failure modes (Figure 3-3). Uplift is a force caused by the wind accelerating 

around and over buildings and is affected by the geometric changes in the building shape 

(Figure 3-4).

Model building codes incorporate provisions that take into account the effects of internal 

pressurization on partially enclosed buildings, which are buildings with large permanent openings, 

by requiring higher design wind loads. Residential structures, considered enclosed structures, are 

typically not designed to withstand instantaneous wind load increases such as those that occur after 

an envelope breach. 

Some of the damage to buildings noted by the MAT was considered non-structural since only 

architectural and decorative finishes on the exterior were damaged (Figure 3-5). Engineering 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-3

DESIGN AND CONSTRUCTION CONSIDERATIONS

Figure 3‐1: Effects of a breach in a building envelope when the breach is on the windward (a) or leeward (b) side of a 

building, shown in plan and section views

SOU RCE: HTTP:// .WBDG.ORG/RESOURCES/ENV_WIND.PHP

standards such as ASCE 7-05, Minimum Design Loads for Buildings and Other Structures (2005), identify 

these elements as components and cladding and provide guidance for determining wind loads 

acting on them. ASCE 7-05 is the reference standard for the 2009 I-Codes.
3-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

Figure 3‐2:

Load path continuity in 

CMU wall

SOURCE: FEMA 577, FIGURE 4-26
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-5

DESIGN AND CONSTRUCTION CONSIDERATIONS

Figure 3‐3: Building failure modes in high-wind event

SOURCE: FEMA 342, FIGURE 3-3

Figure 3‐4:

Uplift pressures acting on a 

building
3-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

Figure 3‐5: Brick veneer blew off this high school cafeteria during the tornado in Phil Campbell, AL. Note that brick ties 

do not appear to be at the correct spacing, which may have contributed to the failure (shown in red circle in inset).

3.2 Wind-Borne Debris

Wind-borne debris, often referred to as missiles, can be generated in a wind storm, but is most 

common in tornadoes and can cause significant damage. Tornadoes generate some of the largest 

missiles and propel them with forces unequaled by any other wind storm. Wind-borne debris 

in tornadoes is a danger to life safety, buildings, and property. It can breach the envelope of a 

building, resulting in internal pressurization and structural failure, and it can kill or severely injury 

individuals who are unable to find shelter.

The funnel cloud of a tornado is composed of water vapor and debris carried by both the inflow winds 

and vortex winds of the storm (see Section 2.3). Smaller missiles (e.g., rocks, pieces of tree limbs, 

and pieces of shredded wood framing members such as those shown in Figure 3-6) can easily break 

common window glazing. This causes a rapid change in internal air pressure in a building, putting 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-7

DESIGN AND CONSTRUCTION CONSIDERATIONS

stress on the roof-to-wall connections and wall-to-wall or wall-to-floor connections. Medium-sized 

missiles (e.g., appliances; furniture; heating, ventilation and air-conditioning [HVAC] units; long 

wooden framing members; and larger tree limbs, also shown in Figure 3-6) can become airborne 

and cause considerable damage. Large missiles (e.g., propane tanks, trees, and roof trusses such as 

those shown in Figure 3-7) are often observed as rolling debris, but may also become airborne and 

can cause major damage to the structural systems of buildings they strike. Section 3.2.1 describes 

the types, sizes, and quantity of missiles observed by the MAT.

Figure 3‐6: 

Example of small- and 

medium-sized missiles 

commonly observed by the 

MAT (photograph taken 

near an apartment complex 

in Tuscaloosa, AL)

Figure 3‐7: 

Example of medium- to 

large-sized wind-borne 

missiles (photograph shows 

roof trusses displaced 

from a nearby building in 

Tuscaloosa, AL)
3-8 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

3.2.1 Missile Types and Sizes

The missile types observed by the MAT varied greatly across the geographic area impacted by 

the tornados because of the varying intensities of the tornadoes and the differences in the built 

environment in affected areas. In residential areas where buildings were primarily wood-frame 

construction with asphalt shingle roofs, most of the missiles observed were wood framing members, 

household contents, and brick veneer pieces. Adjacent to wooded areas and in areas with a high 

tree density, the missiles also included small- to medium-sized pieces of wood from the trees. The 

missiles in residential areas caused significant damage to the glazing, roofing systems, and exterior 

cladding of buildings. In non-residential areas, the missiles and wind-borne debris were primarily 

pieces of wood from trees and building appendages (including awnings, etc.). Table 3-1 lists typical 

debris observed during the field investigation, its classification, and the typical associated damage.

Table 3‐1: Wind-Borne Debris and Rolling Debris Classifications

Missile Size Typical Composition of Missile Associated Damage Observed

Small Rocks, dirt clods, pieces of trees, fragments of buildings 

(e.g., pieces of wood framing members, bricks)

Broken glazing, broken doors, some 

damage to light roof coverings

Medium

Appliances, HVAC units, long wood framing members, 

steel decks, trash containers, furniture, road signs, large 

tree limbs, fencing

Considerable damage to building 

envelope and roof structures

Large

Structural columns, beams, joists, roof trusses, large 

tanks, trees, parts of buildings and appendages (e.g., 

awnings, decks)

Damage to structural systems

The intensity of the winds in the vortex of a tornado are capable of creating missiles out of nearly 

any object, from building sections to bits of timber, and projecting these objects with such force as 

to cause significant damage to buildings and threaten life. The following illustrates the range of 

missile sizes and resulting missile damage the MAT observed.

Figure 3-8 shows a 2x4 piece of wood that pierced the roof of Alberta Elementary School in 

Tuscaloosa, AL. The source of this missile was most likely a dislodged piece of the roof framing 

system from elsewhere at the school (see also Section 6.1.1).

Figure 3‐8: 

Medium-sized missile that 

struck the roof of a school 

building (Tuscaloosa, AL)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-9

DESIGN AND CONSTRUCTION CONSIDERATIONS

Figure 3‐9: 

Large roof beam penetrated 

the roof of this home 

(Athens, AL)

Figure 3‐10: 

OSB damaged the first floor 

locker in Joplin High School 

(Joplin, MO)

Figure 3-9 shows a roof truss penetrating a home in Athens, AL, a town just north of Huntsville, AL. 

The truss most likely originated from the detached garage approximately 100 feet behind this home. 

Figures 3-10 and 3-11 show two instances of oriented strand board (OSB) as debris, one striking a 

school locker (Figure 3-10) and one impacting the roof of a home in a residential neighborhood 

(Figure 3-11). Poorly fastened trusses, rafters, and OSB have more potential to generate debris than 

material that is properly fastened.
3-10 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

Figure 3‐11: 

Small pieces of OSB debris 

penetrated the roof of a 

home (Harvest, AL)

Figure 3-12 shows metal sheathing blown from the roof of the 

Fultondale Fire Station in Fultondale, AL, and carried nearly 200 

feet. Figure 3-13 shows a car in Joplin, MO, with its roof penetrated 

by a 2x6 framing member. The MAT also observed cars that had 

become rolling debris during the tornado events, similar to other 

large debris types.

Figure 3‐12: 

Metal sheathing travelled 

200 feet as wind-borne 

debris and landed next to 

a building outside of the 

tornado swath 

(Fultondale, AL)

Seeking refuge in a 

car during a tornado 

should only be a last 

resort. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-11

DESIGN AND CONSTRUCTION CONSIDERATIONS

Figure 3‐13: 

A 2x6 missile penetrated 

the roof and seat of a car in 

a residential neighborhood 

just outside the damage 

track of the violent tornado 

in Joplin, MO

3.2.2 Wind-Borne Missile Quantity

The missile quantity the MAT observed varied depending on the location of the site and the level 

of damage in the adjacent areas. Where buildings were totally destroyed, debris and missiles often 

covered the ground (Figures 3-14 and 3-15). In wooded areas and residential areas that were heavily 

wooded, passage along the streets was often impossible due to the volume of tree debris present. 

Many buildings were covered with small puncture marks where the façade was pelted with windborne debris. Figures 3-14 through 3-17 show examples of the volume of missiles generated by the 

tornadoes.

Figure 3‐14: 

Wind-borne debris 

consisting of wood framing 

members and plywood 

sheathing near the Alberta 

Elementary School, 

Tuscaloosa, AL
3-12 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

Figure 3‐15: 

Large quantity of windborne debris covering the 

lawn of a nursing home in 

Joplin, MO

Figure 3‐16: 

Numerous missiles struck 

the outer wall of this 

non-residential building, 

including several that 

remained embedded 

(indicated by red circles) 

(Tuscaloosa, AL)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-13

DESIGN AND CONSTRUCTION CONSIDERATIONS

Figure 3‐17: 

Large pile of small- and 

medium-sized wind-borne 

debris outside of Joplin 

High School (Joplin, MO)

3.3 Federal, State, and Local Regulations

This section provides background on the Federal, State, and local regulations that govern building 

construction in the affected areas. Building codes are the technical requirements for design and 

construction of buildings and structures and are adopted to protect public health, safety, and 

general welfare. Since the early 1900s and until 2000, model building codes in the United States were 

developed by three regional model code organizations: Building Officials and Code Administrators 

International (BOCA), International Conference of Building Officials (ICBO), and the Southern 

Building Code Congress International (SBCCI). Prior to 2000, there were four primary model 

building codes adopted throughout the country. These included:

+ National Building Code promulgated by BOCA

+ Uniform Building Code promulgated by the ICBO

+ Standard Building Code (SBC) promulgated by the SBCCI

+ Council of American Building Officials One and Two Family Dwelling Code, promulgated by 

BOCA, ICBO, and SBCCI

In the early 1990s, the three model code groups formed the ICC, with the intent of creating a 

single, common set of building, fire, and life-safety codes for the entire United States. The ICC 

publishes what are known as the International Codes (I-Codes), which include the IRC, IBC, and 

International Fire Code, to name a few. The IBC and IRC specifically address designing buildings 

for high-wind events such as hurricanes through prescriptive criteria, or they reference ASCE 7, 

but neither addresses designing for the wind speeds that occur in tornadoes. The IBC and IRC are 

described more fully in Section 3.3.1.
3-14 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

The adopted building codes and regulations for both residential and non-residential/industrial 

buildings differ considerably throughout the country. Often, they vary significantly even within 

a State; one such example is Alabama (described in Section 3.3.3.1 below). The adopted code in 

each of the affected States at the time of the 2011 tornado outbreak is described in Sections 3.3.3.1 

through 3.3.3.5.

3.3.1 International Building Code and International Residential Code

The primary codes that address residential, non-residential, and critical facility construction are the 

IBC and IRC. To better address structural and architectural issues related to moderately high wind 

events, some State and local governments have adopted the I-codes (IBC and IRC). In addition, 

ICC 600, Standard for Residential Construction in High-Wind Regions (2008), provides guidance for 

residential construction. This standard specifies prescriptive methods for developing wind-resistant 

designs and construction details for residential buildings of masonry, concrete, wood-frame, or coldformed steel-frame construction sited in high-wind regions. 

The IBC is primarily a performance code, with some prescriptive provisions, that requires buildings 

and structures to be designed to meet the applicable requirements of the code and various 

referenced standards. The IRC addresses environmental loads such as high winds using a mostly 

prescriptive approach, so that many one- and two-family houses can be built without individual 

designs being prepared by architects and engineers. However, buildings and sites that fall outside 

the scope of the prescriptive limits, which include a maximum height and basic wind speed among 

other parameters, must be designed for the applicable loads. 

Although the IBC and IRC editions published before 2009 do not address the threat of tornadoes, 

they address wind loading by referencing ASCE 7 (1998 edition or earlier). The current edition of 

ASCE 7-10, Minimum Design Loads for Buildings and Other Structures (2010), has been incorporated 

into the 2012 I-codes.

3.3.2 International Codes and Storm Shelters

It is important to remember that the building codes and standards used in the United States before 

2008 did not address life-safety protection from tornadoes or hurricanes. Although guidance 

from FEMA and others has existed since the late 1990s, it was not until the release of ICC 500 in 

2008 that such criteria were introduced into building standards. The ICC 500 standard codifies 

much, but not all, of the extreme-wind shelter recommendations of FEMA 320 (1998, 1999, and 

2008) and FEMA 361 (2000 and 2008). Following the release of the ICC 500, the 2009 IBC and 

IRC incorporated the standard by reference. 

This means that if a building is constructed to 

the 2009 IBC and IRC, and there is a portion 

of the building designated to be a shelter, it 

must be designed to the criteria of the ICC 

500, which has specific provisions on how 

to provide protection from extreme wind 

events and wind-borne debris associated with 

those events.

At this time, neither the ICC 500 nor the I-Codes 

require that shelters be designed or constructed within buildings.

In addition, ASCE 7 does not address tornadoes 

as part of the wind design considerations and 

requirements for buildings or other structures. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-15

DESIGN AND CONSTRUCTION CONSIDERATIONS

FEMA 361, which was updated at the same time ICC 500 was released in 2008, uses the same wind 

speed maps and design process, and references ICC 500 for general building criteria, inspection 

criteria, and testing standards for debris impact resistance. While the tornado hazard design 

criteria are the same or can be applied in the same manner for both FEMA 361 and ICC 500 (if 

an alternative design is not used), certain criteria in the design and construction of a safe room, 

such as those related to the hurricane hazard (both wind design and wind-borne debris impact 

criteria), the flood hazard siting criteria, and emergency management considerations are different. 

Safe rooms constructed in accordance with FEMA 320 (2008a) and FEMA 361 (2008c), meet all 

criteria of the ICC 500 for storm shelters. Since the two sets of criteria are similar, but not the same 

in all applications, FEMA uses the term safe room to differentiate construction consistent with its 

criteria from that of ICC 500, which uses the term storm shelter. Refer to the text box in Section 1.2 

and Chapter 9 for more information regarding safe rooms, storm shelters, and hardened areas.

3.3.3 State and Local Codes and Regulations in Areas Visited by the MAT 

An understanding of the codes in effect in the areas visited by the MAT is important to the damage 

assessment. If no codes were in place at the time of the tornado, the performance of structures was 

interpreted differently than in those locations where codes were in place. For locations where codes 

were in place before the event, the MAT was able to assess the performance related to specific design 

requirements in the code, and therefore the success of the code. This section of the report presents 

a brief history of code adoption in the communities visited by the MAT as well as a discussion of 

statewide code adoption in the five States visited by the MAT.

Building codes and the materials referenced in the codes change over time. As the building codes 

evolve, jurisdictions may choose to adopt the newest code, which then takes precedent over the 

historical code. Buildings that were built, and typically permitted, prior to the adoption of a new 

code do not need to meet the requirements of the newly adopted code. Therefore, in a single 

jurisdiction, some buildings may be built to an older code, while other buildings may be built to a 

newer code. 

Tables 3-2 and 3-3 list the building codes in place during the past 5 years for commercial and 

residential buildings, respectively, in the communities affected by the tornadoes assessed in this 

report.
3-16 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

Table 3‐2: Historical Codes for Commercial Buildings

State Community

Commercial

December 

2007

December 

2008

December 

2009

December 

2010

December 

2011

AL

Arab NA NA NA NA IBC 2006

Birmingham IBC 2003 IBC 2003 IBC 2003 IBC 2009 IBC 2009

Fultondale 

(Jefferson 

County)

IBC 2003 IBC 2003 IBC 2003 IBC 2003 IBC 2009

Hunstville NA IBC 2003 IBC 2003 IBC 2003 IBC 2003

Tuscaloosa NA NA NA NA IBC 2009

GA Ringgold NA NA NA NA IBC 2006

MS Smithville NA NA NA NA IBC 2006

MO Joplin IBC 2000 IBC 2006 IBC 2006 IBC 2006 IBC 2006

TN

Cleveland NA NA NA NA IBC 2006

Hamilton County IBC 2003 IBC 2003 IBC 2003 IBC 2003 IBC 2003

SOURCES: ARAB BUILDING DEPARTMENT 2012; CITY OF BIRMINGHAM, AL; CITY OF CLEVELAND, TN; CITY OF HUNTSVILLE, AL; CITY OF 

JOPLIN, MO; CITY OF TUSCALOOSA, AL; HAMILTON COUNTY, TN; ICC; JEFFERSON COUNTY, AL, 2011; RINGGOLD, GA; SMITHVILLE, MS

NA = data not available

Table 3‐3: Historical Codes for Residential Buildings

State Community

Residential

December 

2007

December 

2008

December 

2009

December 

2010

December 

2011

AL

Arab NA NA NA NA IRC 2006

Birmingham IRC 2003 IRC 2003 IRC 2003 IRC 2009 IRC 2009

Fultondale 

(Jefferson 

County)

IRC 2003 IRC 2003 IRC 2003 IRC 2003 IBC 2009

Hunstville NA IRC 2003 IRC 2003 IRC 2003 IRC 2003

Tuscaloosa NA NA NA NA IRC 2006

GA Ringgold NA NA NA NA IRC 2006

MS Smithville NA NA NA NA IRC 2006

MO Joplin IRC 2000 IRC 2006 IRC 2006 IRC 2006 IRC 2006

TN

Cleveland NA NA NA NA IRC 2006

Hamilton County IRC 2003 IRC 2003 IRC 2003 IRC 2003 IRC 2003

SOURCES: ARAB BUILDING DEPARTMENT 2012; CITY OF BIRMINGHAM, AL; CITY OF CLEVELAND, TN; CITY OF HUNTSVILLE, AL; CITY OF 

JOPLIN, MO; CITY OF TUSCALOOSA, AL; HAMILTON COUNTY, TN; ICC; JEFFERSON COUNTY, AL 2011; RINGGOLD, GA; SMITHVILLE, MS

NA = data not available
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-17

DESIGN AND CONSTRUCTION CONSIDERATIONS

3.3.3.1 Alabama

The Alabama State Building Commission, which 

has jurisdiction over State-owned buildings, 

schools (public and private), hotels/motels, and 

theaters, adopted the 2009 IBC on September 

1, 2010. The State made no amendments to the 

original 2009 IBC. Local amendments, however, 

are permitted.

The following codes were in effect for new construction for the sites visited at the time of the MAT 

investigation: 

+ Arab, AL: 2000 SBC 

+ Birmingham, AL: 2009 IBC, 2009 IRC

+ Fultondale, AL: 2009 IBC, 2009 IRC

+ Huntsville, AL: 2003 IBC, 2003 IRC

+ Tuscaloosa, AL: 2009 IBC, 2006 IRC

Act 2010-746: Education Appropriations: On April 30, 2010, Governor Riley signed House Bill 459, 

Education Policy, into law, thereby enacting Act 2010-746, which required any new contract awarded 

on or after July 1, 2010 for the construction of a new public school (grades kindergarten to twelfth) 

to include a Building Commission of Alabama-approved safe space or hallway. Pursuant to Act 2010-

746, the Building Commission of Alabama adopted ICC 500 (2008) as the minimum building code 

for safe spaces. Safe spaces are required to comply with the building code requirements for tornado 

shelters. Compliance with the building code requirements for hurricane shelters is recommended, 

but not mandatory. Any renovations or additions to existing schools, or the addition of auxiliary 

buildings to an existing school, are not considered “a new public school” and are exempt.

Act 2010-185: Alabama Energy and Residential Codes Board: In 2010, Alabama adopted Act 

2010-185, Residential Energy Board, which established the Alabama Energy and Residential Codes 

Board. The Board has the authority to establish an energy code for non-residential and residential 

construction; it also has the authority to establish a residential code for one- and two-family 

dwellings. Because of this authority to adopt such a residential code, the board can potentially affect 

high-wind load resistance for buildings in Alabama. For the residential building code, the Board has 

adopted the 2009 IRC with several amendments. This State code only applies to jurisdictions that 

newly adopt a code and those that have an existing code and intend to update it after the effective 

date of the State code. Additionally, there is no time limit for jurisdictions that currently implement 

codes to update to the new State code. However, when a jurisdiction does decide to update its code, 

it must, at a minimum, comply with the State code. Jurisdictions may amend the State code once 

they have adopted it to incorporate more stringent requirements. 

Alabama has not 

adopted a statewide 

building code for all 

residential and nonresidential buildings.
3-18 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

3.3.3.2 Georgia

The State of Georgia has a statewide code for 

all residential and non-residential buildings. 

The Official Code of Georgia Annotated §8-

2-20(9) (B) identifies 10 State minimum 

standard codes, which the Board of Community 

Affairs has adopted. The State codes consist of 

a base code and a set of amendments specific 

to Georgia. Eight of the 10 State minimum 

standard codes are mandatory throughout Georgia. For residential construction, the base code 

currently in effect is the 2006 IRC with 2007, 2008, 2009, 2010, and 2011 State amendments. 

For non-residential construction, the base code is the 2006 IBC with 2007, 2009, and 2010 State 

amendments. The adopted IRC and IBC with the State amendments are 2 of the 10 “minimum 

standard codes.” For the areas the MAT visited, specifically Ringgold, GA, these codes are adopted 

for new construction.

3.3.3.3 Mississippi

Mississippi has not adopted a statewide 

building code, although it requires State 

buildings to meet the requirements set forth 

in the 1997 SBC, which is mandatory for all 

jurisdictions. Building code adoption and 

enforcement is primarily the responsibility of 

local jurisdictions. 

In 2006, Bill 31-11-33 created the Mississippi Building Code Council. The Mississippi Building 

Code Council requires that five coastal counties—Jackson, Harrison, Hancock, Stone, and Pearl 

River—enforce, on an emergency basis after a disaster event, all of the wind and flood mitigation 

requirements prescribed by the 2003 IBC and 2003 IRC. None of these counties were affected by the 

storms described in this report.

After the April 25–28 tornado events, the Town of Smithville, MS, adopted the 2006 IBC and 2006 

IRC at their May 24, 2011 meeting. To enforce the codes, the town contracted professional services 

to conduct building inspections. The 2006 IRC applies to residences that either are being totally 

rebuilt or have minor repairs being made following the storm damage. Non-residential structures 

have to comply with the 2006 IBC.

3.3.3.4 Tennessee

Of the affected areas the MAT visited in 

Tennessee, only the City of Cleveland in 

Bradley County and Hamilton County 

(including the City of Chattanooga as an 

incorporated city within this county) have 

local building codes per the State’s definition. 

Cleveland has adopted the 2006 IBC and 

Mississippi has not 

adopted a statewide 

building code for all 

residential and nonresidential buildings.

Tennessee has 

adopted a statewide 

building code for all 

residential and nonresidential buildings.

Georgia has 

adopted a statewide 

building code for all 

residential and nonresidential buildings.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 3-19

DESIGN AND CONSTRUCTION CONSIDERATIONS

2006 IRC, each with local amendments. Hamilton County (including the City of Chattanooga) has 

adopted the 2003 IBC and 2003 IRC. The rest of the affected areas did not have a locally adopted 

building code and would fall under the 2009 IRC statewide requirement for new residential 

construction and residential construction undergoing a change of use. 

Tennessee adopted the 2006 IBC as a statewide code in 2008, but excluded Chapter 11 (Accessibility 

and Electrical Components) and Chapter 27 (Equipment and Systems). On October 1, 2010, the 

State adopted the 2009 IRC with several amendments. The 2009 IRC applies to new construction 

and residential buildings for which the use is going to change. Cities and counties are allowed to opt 

out of the residential building code requirements via passage of a resolution to exempt the city or 

county by a two-thirds vote. Additionally, if a region of the State already has a residential building 

code enforcement program in place that is current within 7 years of the latest edition, they can file 

to become an exempt jurisdiction and are permitted to continue to operate under their current 

building codes. Currently, most highly populated areas in Tennessee fall under this category and 

are therefore exempt from enforcing the 2009 IRC. Local jurisdictions reserve the right to amend 

the code, if adopted.

The metropolitan area of the City of Nashville and Davidson County adopted both the 2006 IBC 

and the 2006 IRC with local amendments. Since they have a residential building code in place with 

their enforcement of the 2006 IRC and local amendments, they did not fall under the requirement 

to enforce the 2009 IRC as of October 1, 2010.

Tennessee has not adopted a standard regarding safe rooms.

3.3.3.5 Missouri

Like Mississippi, building codes in Missouri are 

adopted and enforced at the local level, though 

the 2000 IBC and 2000 IRC are effective 

statewide for State buildings. The State of 

Missouri Division of Facilities Management, 

Design and Construction have published a 

Designer Information Packet (2007)2 for State 

buildings. 

As a note, the City of St. Joseph, MO, passed an ordinance prior to the tornadoes requiring 

manufactured home communities to provide storm shelters for their residents. All storm shelters in 

the city are required to meet Americans with Disabilities Act requirements and the design criteria 

set forth by the current version of FEMA 361 (2008a). 

The City of Joplin has actively adopted building codes since 1961. Joplin adopted the 2006 IBC 

and IRC in 2008. After the May 22, 2011 tornado event, the Public Works Department passed an 

ordinance requiring measures beyond code requirements to ensure safety in high-wind events. The 

new ordinance changes the required spacing of foundation anchor bolts from 6 feet on-center to 

4 feet on-center; the bolts must also line up with the rebar required in concrete block cells. The 

2 Available online at the Missouri Office of Administration Web site, http://oa.mo.gov/fmdc/dc/fmdc_dip/index.htm

Missouri has not 

adopted a statewide 

building code for all 

residential and nonresidential buildings.
3-20 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

DESIGN AND CONSTRUCTION CONSIDERATIONS

new ordinance also requires additional hurricane fasteners on every rafter end and on trusses; 

where fastening had been required by previous code on every other truss every 4 feet, the code was 

amended to include fastening on every truss member.
4

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-1

Observations on Residential 

Building Performance 

The MAT observed residential building performance across the 

area impacted by the April 25–28, 2011 tornado outbreak and the 

May 22, 2011 Joplin, MO, tornado.

According to data assembled by NOAA’s NWS SPC, of all reported tornadoes in the United States 

between 1950 and 2006, nearly 95 percent have been rated as the equivalent of EF2 or less (up to 135 

mph for 3-second gust) (FEMA 2008a). While the April 25–28, 2011 tornado outbreak and May 22, 

2011 Joplin tornado were extraordinary in scale and number of lives lost, the majority of residential 

damages observed, described, and documented by the MAT was determined to have resulted from 

wind speeds estimated to be 135 mph or less based on the EF scale damage ranking indicators. Winds 

of this magnitude generate substantial forces that can result in significant damage, but could be 

mitigated through enhanced wind-resistant construction procedures.

While past MATs have focused primarily on building performance, this MAT was also tasked with 

gathering damage information needed to determine tornado ratings using the EF scale when 

possible (refer to Appendix E for more detail). Not all observed one- and two-family residences 
4-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

The EF scale assigns each damage indicator 

(DI) with specific damage description categories called degrees of damage (DOD) to estimate 

tornado wind speeds. Refer to Section 2.2 and 

Appendix E for additional information.

were rated by the MAT. In some cases, ratings 

were not assessed due to limited accessibility 

that prevented thorough observations. The 

NSF-funded Damage Study and Future Direction 

for Structural Design Following the Tuscaloosa 

Tornado of 2011 includes EF scale contour 

maps developed from extensive post-event 

DOD data collection and subsequent EF 

ratings (Prevatt et al. 2011b). 

Photographs in this chapter that were taken from sites that were rated include the assigned DOD and 

EF rating. It is important to note, however, that engineering judgment was exercised when assigning 

the wind speeds that range between a specified lower and upper bound. In some cases, the observed 

DODs were considered to be inflated by poor construction practices or failure to adhere to the model 

building codes. Accordingly, wind speeds selected in such cases fall into the lower bound prescribed 

by the EF scale and may result in a lower EF rating by the MAT. Furthermore, images of a particular 

DOD may not always be the highest DOD observed at a particular site. In some cases, a photograph 

of a lower DOD is included in this report to better illustrate a specific failure mode. Figure captions 

will indicate when an EF rating provided for an image is inconsistent with the illustrated DOD. 

This chapter is divided into two parts. The first describes observed damage to one- and two-family 

residences organized by the type of damage defined in eight DOD categories (2 through 9). The 

second describes damage to two multi-family residential complexes presented as detailed case studies. 

4.1 One- and Two-Family Residences

The main purpose of presenting one- and two-family residential damage observations in the order of 

EF scale and DODs is to illustrate the order of progressive failures and the need to maintain continuous 

load path connections to mitigate high-wind damage. More specifically, DOD observations advance 

our understanding of the relationship between wind speeds and damages, and how certain damages 

may be greatly reduced or avoided altogether through enhanced design practices. The following 

section briefly describes the EF scale-prescribed damage for residential buildings and progressive 

damage observed by the MAT, and is followed by detailed descriptions of observed damage of 

residential buildings grouped by the following eight DODs. 

+ Loss of roof covering and siding (DOD 2)

+ Glazing damage (DOD 3)

+ Uplift of roof decks (DOD 4)

+ Gable end walls: vulnerability related to uplift of roof deck (DOD 4)

+ Garage doors collapse inward (DOD 4)

+ House shifts off foundations (DOD 5)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-3

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

+ Roof structure removed (DOD 6)

+ Collapse of framed walls (DOD 7–9)

Trigger mechanisms or vulnerable features that appeared to initiate the observed failure mode 

are described when applicable. Likewise, observed damage that is not explicitly listed as a DOD is 

included with the category most closely related to that failure mode.

4.1.1 EF Rating Evaluation of Residential Buildings

The MAT’s investigation of residential buildings and subsequent wind-speed determinations use 

the prescribed EF scale for “One- and Two-Family Residences between 1,000 and 5,000 square feet 

with typical wood framed construction” as outlined in A Recommendation for an Enhanced Fujita Scale

(TTU 2006). One- and two-family residential structures are designated as DI 2 in the EF scale system 

and are accompanied by a specific list of DODs with which wind speeds can be estimated through 

observed damage. Based on a progression of damage from minimal visible damage to complete 

destruction, observed DODs specific to one- and two-family residences are shown in Table 4-1. A 

second DOD table for DI 5, which illustrates the progression of multi-family residential damages, is 

provided in Section 4.2.1.

Table 4-1: Degrees of Damage for One- and Two-Family Residences

DOD Damage Description

Lower- and UpperBound Wind Speed 

Range (3-second 

gust in mph)

Expected 

Wind Speed 

(3-second 

gust in mph)

1 Threshold of visible damage 53–80 65

2 Loss of roof covering material (<20%), gutters, and/or 

awning; loss of vinyl or metal siding 63–97 79

3 Broken glass in doors and windows 79–114 96

4 

Uplift of roof deck and loss of significant roof covering 

material (>20%); collapse of chimney; garage doors 

collapse inward; failure of porch or carport 

81–116 97

5 Entire house shifts off foundation 103–141 121

6 Large sections of roof structure removed; most walls 

remain standing 104–142 122

7 Exterior walls collapsed 113–153 132

8 Most walls collapsed except small interior rooms 127–178 152

9 All walls collapsed 142–198 170

10 Destruction of engineered and/or well-constructed 

residence; slab swept clean 165–220 200

SOURCE: TTU 2006

Definitions:

DOD = degree of damage mph = miles per hour
4-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

4.1.2 Description of Progressive Damage for One- and Two-Family 

Residential Buildings 

The first group of damages addressed—loss of roof covering and exterior siding, or DOD 2—typically 

precedes other phases. While nonstructural, damage to these elements can allow water intrusion 

which may weaken other systems and damage building contents. Damaged roof and wall covering 

elements may also become wind-borne debris that can cause building damage (Figure 4-1), injuries, 

and death. 

Figure 4-1:

Wind-borne asphalt shingle 

penetrated the gypsum 

board on both sides of this 

interior wall at Chastain 

Manor Apartment Complex 

(Tuscaloosa, AL)

The second group of damages addressed—glazing damage and garage doors collapse inward, or 

DODs 3 and 4—often accelerate the disintegration of the structure through wind pressurization of 

the interior. Whether the result of wind-borne debris shattering glazing or wind pressure causing 

garage doors to collapse, a breach in the building envelope subjects it to increased pressurization and 

allows the intrusion of wind-driven rain. Other common building envelope vulnerabilities include, 

but are not limited to, soffits, doors, and gable end walls.

The third group of damages addressed—uplift to roof decks, included with DOD 4—begins with 

the uplift of roof decking and may coincide with, but frequently follows, breaching of the attic level 

building envelope. The loss of roof decking weakens the roof structure’s ability to resist in-plane 

shear forces, and often results in the failure of the roof structure (DOD 6). Further contributing to 

the loss of the roof structure are failed roof-to-wall connections. When the roof structure is removed, 

lateral support (bracing) for the walls is lost. Collapse of exterior and interior walls constitute the 

later stages of overall structural failure (DOD 7–9), which typically progresses from the top down 

due to the loss of lateral support after the roof structure fails. This near-final phase of destruction 

is facilitated by the breakdown of connections between floors and walls, or by under-braced exterior 

walls that cannot resist in-plane shear forces. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-5

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-3:

Example of DOD 2 (loss of 

siding) (Tuscaloosa, AL; 

photograph courtesy of 

Tuscaloosa County EMA)

[MAT EF Rating = 0]

4.1.3 Loss of Roof Covering and Exterior Siding (DOD 2)

The MAT observed widespread loss of roof covering and siding; this was evident on both lightly 

damaged residential buildings and those with more advanced stages of wind-induced damage. Nearly 

all observed roof coverings were asphalt shingles (Figure 4-2). Figures 4-3 and 4-4 illustrate exterior 

walls with sections of vinyl siding peeled off by high winds. 

Figure 4-2:

Example of DOD 2 (loss 

of asphalt shingles) 

(Tuscaloosa, AL; photograph 

courtesy of Tuscaloosa 

County EMA)

[MAT EF Rating = 0]
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OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-5: 

Effect of wind on an 

enclosed building and 

a partially enclosed 

building 

SOURCE: FEMA P-55, 2011

4.1.4 Glazing Damage (DOD 3)

The MAT frequently observed damage to window and door glazing in residential buildings. Most 

glazing types are extremely vulnerable to the wind-borne debris prevalent in tornadoes. Once the 

glazing is compromised, the building envelope is breached. This leads to increased pressurization of 

the interior, which increases stresses in structural components and connections between components 

that can, in some cases, initiate a chain reaction of structural failures in the building. Figure 4-5 

illustrates the increased forces from pressurization on a partially enclosed building with a breached 

building envelope as compared to the enclosed building. 

Figure 4-4:

Example of DOD 2 (loss of 

siding) through DOD 6 (large 

sections of roof structure 

removed) (Joplin, MO)

[MAT EF Rating = 2]
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-7

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-6:

Double-glazed window 

with outer pane sacrificed 

(remaining fragments are 

circled in red), leaving the 

inner glazing intact (Mercy 

Village, Joplin, MO); refer 

also to Section 4.2.3 for a 

case study of Mercy Village

The MAT observed some buildings that benefitted from the installation of insulated glazing units 

(i.e., double-paned windows), where the outer pane was sacrificed but the inner pane remained 

intact, as illustrated in Figure 4-6. Energy code changes that require increased efficiency are leading 

to more double- and triple-paned glazing units in new residential construction. However, most 

windows of this type were not designed to provide extra protection from wind-borne debris and were 

breached on impact, as shown in Figure 4-7.
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OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-7:

Example of DOD 3 showing 

window with shattered 

double-glazing (Harvest, AL)

[MAT EF Rating = 2]1

1 More extensive building damage not apparent in this image resulted in a higher site DOD and EF scale rating.

4.1.5 Garage Doors Collapse Inward (DOD 4)

The MAT observed many failed overhead garage doors. Garage doors, particularly older double 

garage doors, are especially vulnerable to the effects of wind pressure. Older garage doors were not 

manufactured and rated to resist high winds. Wind pressure rated garage doors are now available, 

and may be code compliant while not meeting the wind pressure demands of some tornadoes. 

Positive wind pressure against the doors can lead to inward deflection as shown in Figure 4-8. Garage 

doors can also fail under negative wind loads. In Figure 4-8 the wider double door (16 feet or 18 feet 

wide) incurs a greater resultant force under the same wind pressure than the adjacent single door 

(8 feet or 9 feet wide) because of its larger area. Therefore, the threshold for failure of the larger, 

similarly constructed double garage door is lower than that of the smaller single door. In addition 

to the actual garage door failing, the lifting and track hardware is vulnerable to failure under wind 

pressures too.

Residential buildings whose garage doors collapse often exhibit progressive collapse in and above 

the garage that exceeds the damage elsewhere because of increased pressurization when the garage 

door fails. Figures 4-9 and 4-10 illustrate this effect; note the extensive damage above the garage in 

both homes—the ceiling and roof assembly are completely blown off—compared to the opposite 

side of the buildings, where some of the ceiling and roof remain intact. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-9

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

2 More extensive building damage not apparent in this image resulted in a higher site DOD and EF scale rating.

Figure 4-8:

Example of DOD 4 showing a 

wide garage door collapsed 

inward, while narrow garage 

door to left is intact. Note 

also the wind-borne missile 

in roof above (Joplin, MO). 

[MAT EF Rating = 2]2

Figure 4-9:

Example of damage including 

loss of large sections of roof 

(DOD 6) apparently initiated 

from garage door failure 

(DOD 4) (Joplin, MO) 

[MAT EF Rating = 2] 

Figure 4-10:

Example of how garage door 

failure (DOD 4) initiated 

progressive failure, including 

loss of the garage roof 

(DOD 6) (Joplin, MO) 

[MAT EF Rating = 2] 
4-10 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-11:

Example of DOD 4 showing 

roof decking blown off along 

eaves and hip (Zone 2 in 

Figure 4-12), where uplift 

pressures are greater than in 

the field of the roof (Joplin, 

MO) [MAT EF Rating = 2]3

3 More extensive building damage not apparent in this image resulted in a higher site DOD and EF scale rating.

4.1.6 Uplift of Roof Decks (DOD 4)

Many roof decks were observed to have separated from rafters or roof trusses. Most often, roof 

decking was in the form of 4-foot x 8-foot x 1⁄2-inch (nominal) OSB sheathing panels. In some older 

construction, nominal 1-inch x 8-inch planks were observed to comprise the roof deck. 

When isolated areas of the roof were observed to be missing decks, as shown in Figure 4-11, the 

missing portions were often at corners, along roof overhangs, and along hips and/or ridges (Zones 

2 and 3 as shown in Figure 4-12), where uplift pressures are greatest. Figure 4-13 shows a home 

where the roof decking separated above the eaves in an area where vinyl soffit material has been 

blown away, leading to increased pressures on adjacent roof decking. Nails between the decking 

and rafter or truss failed to resist uplift forces and allowed the decking to be pulled away from the 

structural framing. Roof decking above wide overhangs is particularly vulnerable to wind damage, 

as illustrated in Figure 4-14. 
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OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-12: Component and cladding wind pressures 

SOURCE: FIGURE 8-20 OF FEMA P-55 (2011A)
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OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

4 More extensive building damage not apparent in this image resulted in a higher site DOD and EF scale rating.

Figure 4-14:

Example of DOD 4 showing 

roof decking removed at 

wide eaves on hip roof (Phil 

Campbell, AL) 

[MAT EF Rating = 1] 

Poor construction methods can also decrease resistance to wind uplift. Figure 4-15 shows a residence 

where at least one of the roof deck nails along the panel edges failed to penetrate the rafter below. 

The expected performance is subsequently rendered weaker than intended by the building code or 

design professional. Improper spacing of fasteners and the use of improperly sized fasteners result 

in the same effect.

Figure 4-13: 

Example of DOD 4 showing 

where roof decking lifted 

and blew off above damaged 

soffit in roof Zone 2 (see 

Figure 4-12) (Birmingham, 

AL) [MAT EF Rating = 2]4 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-13

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

4.1.7 Gable End Walls: Vulnerability Related to Uplift of Roof Deck (DOD 4)

The MAT observed gable end wall failure on many residential buildings with roof deck loss. While 

not specifically included in the DODs for One- and Two-Family Residences (Table 4-1), this failure 

mode compromises the building envelope. Once the attic level envelope is breached, increased 

pressurization can initiate or accelerate roof deck separation. Gable end walls that lack adequate 

bracing are susceptible to failure from wind pressures. In Figure 4-16, the roof area adjacent to the 

failed gable end wall lost more roof decking than the rest of the roof. 

Figure 4-15:

Red circled roof deck nail not 

connected to rafter (edge 

shown with red dashed line) 

(Harvest, AL) 
4-14 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-16:

Example of DOD 4 showing 

damage to gable end of 

simple gable roof 

(Harvest, AL) 

[MAT EF Rating = 1] 

Figure 4-17:

Example of DOD 5 showing 

residential building shifted 

off masonry piers 

(Cullman, AL) 

[MAT EF Rating = 2] 

4.1.8 Entire House Shifts Off Foundation (DOD 5) 

The MAT observed few instances of entire houses shifting off of their foundations. Framing-tofoundation connection failure was most often observed to follow wall collapse (DOD 7 through 

9) and accordingly, those observations are included in Section 4.1.11. The older house depicted 

in Figure 4-17 was observed to have shifted off the raised pier and beam foundation. This house 

had no continuous exterior foundation walls, which provide more area for bottom plate anchorage 

than isolated piers. Further contributing to the observed failure of the bottom plate-to-foundation 

anchorage was the lack of bracing or connectivity between the top of the exterior piers. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-15

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-18:

Example of DOD 6 showing 

failed roof-to-wall 

connections that resulted 

in loss of roof structure 

(Harvest, AL) 

[MAT EF Rating = 2] 

4.1.9 Roof Structure Removed (DOD 6)

When roof decking resists uplift pressure and transfers those forces through fasteners to rafters or 

trusses, that load must be transferred from the rafter or truss to the framed wall below and from 

there to the foundation in a continuous load path. Failure to transfer uplift through roof-to-wall 

connectors results in the loss of the roof structure, as shown in Figure 4-18. 

The “birds-mouth” notched rafters spanning from hip to wall in Figure 4-19 separated from the 

plate and outlookers, and shifted toward the building corner. They were framed onto a single plate 

across the top of the joists below, a configuration that, while common, is not prescribed in the 2009 

IRC, and requires special attention in the application of roof-to-wall connectors and roof-to-ceiling 

tie-backs. The rafter shown in Figure 4-20 was found nearby and observed to have two small toe nails 

withdrawn from the plate. Even with proper nailing, the rafter shown in Figure 4-20 would likely 

have become the next weak link at this location by failing under stress because of improper or noncode-compliant notching. Cutting and notching limitations for sawn lumber rafters are found in 

Section R802.1.7 of the 2009 and 2012 IRC.

Figure 4-19:

Example of roof-towall connection failure 

facilitated by non-codecompliant construction: 

notched rafters, known as 

“bird’s mouth,” (red circle) 

displaced when roof-to-wall 

connections failed; red arrow 

indicates rafter bearing 

plate, yellow arrow indicates 

outlooker (Harvest, AL)

[MAT EF Rating = 1] 
4-16 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Metal connectors designed to transfer uplift forces from the rafter or truss to the wall below greatly 

enhance connectivity and were observed to outperform toe nail-only connections. In order to transfer 

uplift and lateral loads consistent with their maximum design capacities, metal connectors must be 

installed per the manufacturer’s instructions. 

Applications of metal connectors not in accordance with manufacturers’ installation instructions, 

including insufficient nailing and using the wrong nail size, can lead to the connection not performing 

to design capacity. For example, a 6d box nail as shown in Figure 4-21 has a withdrawal capacity of 

96 pounds when face-nailed into a Southern Yellow Pine #2 double 2x4 top plate, as compared with 

217 pounds for a 10d common nail.

Spacing of roof-to-wall connectors is also critical to the performance of roof-to-wall connections. 

The house shown in Figure 4-22 had a roof-to-wall connector on the indicated roof truss, but not on 

the adjacent one. While it used to be typical for designers to specify rafter-to-wall connectors at every 

other or every third rafter to meet the design requirements of basic design wind speeds, the greater 

loads exerted during tornadoes can render this minimal design-level connector schedule ineffective, 

even with correctly installed hardware. 

Figure 4-20:

Over-notched rafter found 

on ground with two toe nails 

withdrawn from plate (red 

circle) (Harvest, AL)

[MAT EF Rating = 1] 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-17

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-22:

Example of DOD 6 showing 

insufficient connection of 

single roof-to-wall connector 

on remaining chord of roof 

truss at left (red circle) 

and none on truss at right 

(Tuscaloosa, AL)

[MAT EF Rating = 2] 

Figure 4-21: 

Example of DOD 6 showing trusses were connected to walls with small 

hurricane ties. Red circle indicates area of inset photograph. Inset 

shows gauge indicating undersized 6d box nail remaining in roof-towall connector; the yellow circle indicates the appropriate nail size 

of 8d. (Phil Campbell, AL). [MAT EF Rating = 2]
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OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-23:

Example of DOD 6 showing 

failure of roof framing that 

resulted in loss of lateral 

support for the top of 

this wall (red arrow) (Phil 

Campbell, AL)

[MAT EF Rating = 2] 

Continuous load paths can be improved by 

extending the continuous wood panel wall 

sheathing across the floor system and bottom plate and/or by using metal straps to 

connect the wall to floor and floor to sill. At 

the second floor band, extend wall sheathing from upper and lower walls to meet at the 

band midpoint. Proprietary wall hold-down 

hardware (described in Appendix G, Section 

G3.3) is another effective attachment option.

4.1.10 Collapse of Framed Walls (DOD 6–9) 

When roof and ceiling or roof truss-to-wall connections fail and leave the top of the framed wall 

unsupported, walls become especially vulnerable to collapse. Therefore, the roof/ceiling or floor 

connection to the top and bottom of the framed wall is critical to maintain stability and prevent wall 

collapse. Figure 4-23 shows a home where the roof system was blown off, removing the lateral support 

for the top of the wall and allowing it to be blown in. 

The floor system above the garage shown in Figure 4-24 separated from the framed exterior walls, 

allowing both the floor and walls to collapse. As shown in the inset to Figure 4-24, the double top 

plate of the garage entry wall was pulled away either with the fallen floor system or collapsed portion 

of the garage entry wall. The deeper floor system above the garage, which was installed to span the 

garage without intermediate support, appeared to be framed onto a lower top plate that interrupted 

the continuity of the top plate and weakened the connection to the adjacent walls.

Walls with inadequate bracing were observed 

to be especially vulnerable to collapse under 

in-plane shear forces. Garage entry walls, like 

that shown in Figure 4-25, often have a small 

percentage of full-height sheathed lengths with 

respect to the overall wall length and often 

collapse before other exterior walls collapse. Any 

exterior wall that lacks code-compliant (2009 

and 2012 IBC R602.10) lengths of full height 

solid sheathed (or alternatively braced) sections 

is susceptible to failure from in-plane shear. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-19

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-24: Example of DOD 6 showing pressurization of this garage from failure of the garage door/wall removed the 

support for the second story floor system (red circle). Inset shows where top plate of garage entry wall separated with 

floor or wall (red circles). Note former location of entry wall top plate—separated and missing from top of studs—is 

lower than the interior wall top plate due to deeper floor system (Harvest, AL). [MAT EF Rating = 2] 

Figure 4-25:

Example of DOD 6 where 

most walls remained 

standing, but under-braced 

garage entry wall failed 

(Joplin, MO) 

[MAT EF Rating = 2] 
4-20 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Under-braced framed wall collapse was not exclusive to walls with overhead garage doors, however. 

The MAT also observed openings in framed walls that had large windows or entry doors. Figure 4-26 

shows what appears to have been a sunroom. In this instance, wall collapse may have been further 

enabled by a weak connection between the wall, raised floor system, and bottom plate. Often the 

bottom plate of the wall is merely nailed to the raised floor system. 

Figure 4-26:

Example of DOD 6 showing 

under-braced framed 

sunroom wall failure. Note 

long window bottom on 

right (red arrow) and the 

failure of nailed wall-tofloor connection on left wall 

(yellow arrow) (Harvest, AL). 

[MAT EF Rating = 2] 

4.1.11 Wall Framing-to-Foundation Connection Failure: 

Damage Related to Collapse of Framed Walls (DOD 7–9) 

As noted in Section 4.1.8, the MAT observed that failures of framing-to-foundation connections 

often followed wall collapse. Examples of failed connections included bottom plates of framed walls 

attached directly to stem walls and slabs. Failure of foundation anchorage was observed along the 

exterior stem walls of garage slabs in newer houses where walls were framed atop CMU, as shown in 

Figures 4-27 and 4-28. The homes shown in Figures 4-27 and 4-28 are located in the same community. 

Figure 4-27 shows the top of the garage stem wall with the wall bottom plate missing. In Figure 4-28, 

the bottom plate of the wall remained connected to the top row of CMUs, but the top row of CMU 

separated from the foundation wall below because there was no reinforcement or other tension 

connection within the CMU wall. Furthermore, the MAT observed the absence of grout in the cells 

of the damaged CMU walls in both of these homes, including locations where anchor bolts should 

have been installed. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-21

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-27:

Example of wall framingto-foundation connection 

failure. Wall and bottom 

plate separated from 

foundation where anchorage 

of collapsed framed wall 

failed because anchors 

lacked embedment in grout. 

Note CMU wall with no 

reinforcement or solid grout 

(Harvest, AL).

[MAT EF Rating = 2] 

Figure 4-28: 

Example of wall framingto-foundation connection 

failure. Bottom plate remains 

connected to top row of 

CMU, but CMU wall failed 

due to lack of reinforcement 

for continuous load path 

(Harvest, AL). 

[MAT EF Rating = 2]
4-22 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-29:

Wall-to-foundation 

connection failure where 

concrete nails remained in 

stained concrete slab and 

bottom plate (missing) pulled 

over the heads of the nails 

(red circles) (Hackleburg, AL)

[MAT EF Rating = 3] 

Other bottom plate-to-slab foundation connection failures 

were observed where bottom plates were attached to the 

concrete slab foundation using only concrete nails (often 

called cut nails), as shown in Figures 4-29 and 4-30. The 

illustrated wall-to-slab failure is typical in that either the 

plate was separated from the slab by lifting around the 

nails (nails remained embedded), like in Figure 4-29, or 

the nails pulled out of the concrete with the plate leaving 

behind small cones of missing concrete, as shown in Figure 

4-30. This damage was rated EF3 due to missing walls, 

but the damage may have occurred in part due to poor 

connections rather than solely to high winds.

Although the residence in Figures 4-29 and 4-30 appears to be older construction, the MAT observed 

recently constructed dwellings were also observed to have driven nails used to attach bottom plates 

to masonry or poured concrete foundations instead of IRC-required anchor bolts. Figure 4-31 shows 

a newly constructed residential building in Tuscaloosa, AL (completed December 2010) where the 

bottom plates in some areas had been secured with only concrete cut nails. Concrete nails provide 

significantly less resistance to uplift and lateral forces than similarly spaced 1⁄2-inch-diameter anchor 

bolts with 7 inches of minimum embedment.

Proper installation of foundation 

anchorage is critical for a foundation to perform as intended 

under design conditions.

Non-code-compliant foundation 

attachments were observed to 

fail prematurely when exposed to 

high winds. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-23

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-30: 

Wall-to-foundation failure 

where bottom plate and 

concrete nails were 

pulled out by high winds. 

Shallowly embedded 

concrete nails pulled small 

cones of concrete up with 

bottom plate (red circles) 

(Hackleburg, AL).

[MAT EF Rating = 3]

Figure 4-31: 

Wall-to-foundation 

connection failure. Note 

slab failure along right 

edge where the bottom 

plate separated and the nail 

was removed (red arrow). 

A remaining cut nail is 

indicated by the red circle. 

(Tuscaloosa, AL). 

[MAT EF Rating = 4]
4-24 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

4.2 Multi-Family Residences

The MAT visited only a few multi-family residences in the post-event investigations. The MAT 

observations at Chastain Manor in Tuscaloosa, AL, and at Mercy Village Apartments in Joplin, MO, 

are presented below as case studies in building performance of multi-family residential buildings. 

Some of the buildings at Chastain Manor were in the direct path of a powerful tornado—rated by 

the NWS as an EF4 in this vicinity—and suffered significant damage. While a direct hit from an 

EF4 tornado is rare, the observations from Chastain Manor illustrate the value of on-site safe rooms 

and storm shelters and comprehensive emergency operations planning, particularly for residential 

dwellings in tornado-prone regions. Conversely, Mercy Village did not take a direct hit and incurred 

fewer damages by comparison. Furthermore, the MAT observed that damage at Mercy Village seemed 

to be less severe than surrounding buildings and consequently reviewed the construction drawings 

after the site visit. The following sections discuss the MAT’s findings. 

4.2.1 EF Rating Evaluation of Multi-Family Residential Buildings

Table 4-2 shows the DODs for multi-family residences (DI 5) and their respective wind speeds. 

Table 4-2: Degrees of Damage for Multi-Family Residences

DOD Damage Description

Lower- and Upper-Bound 

Wind Speed Range 

(3-second gust in mph)

Expected Wind Speed 

(3-second gust in mph)

1 Threshold of visible damage 63–95 76

2 Loss of roof covering (<20%) 82–121 99

3 Loss of roof decking; significant loss of 

roof covering (>20%) 107–146 124

4 Uplift or collapse of roof structure leaving 

most walls standing 120–158 138

5 Most top story walls collapsed 138–184 158

6 Almost total destruction of top two stories 155–205 180

SOURCE: TTU 2006 

Definitions:

DOD = degree of damage mph = miles per hour

4.2.2 Chastain Manor Apartments (Tuscaloosa, AL)

Location of Facility in Tornado Path: The MAT observed Chastain Manor, a senior living community 

in northeastern Tuscaloosa, AL. Figure 4-32 shows an aerial view of Chastain Manor after the tornado. 

The NWS rated the center of the tornado circulation in the vicinity of the Chastain Manor buildings 

as an EF4. According to the property developer,5 approximately 22 of the 25 leased units were 

occupied when the tornado struck; there were two reported fatalities. The apartment community 

had only opened in December 2010, and fewer than half of the available units were leased at the time 

of the tornado strike. 

5 TBG Residential, 3825 Paces Walk, SE, Suite 100, Atlanta, GA 30339
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OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-32: Aerial view of Chastain Manor Apartments in relationship to the approximate centerline of the tornado 

damage swath (red line).6 The green circle indicates the two-story apartment buildings, the yellow circle shows the 

location of the leasing office, and the blue circle shows the location of a one-story apartment building (Tuscaloosa, AL).

SOURCE: ALL AERIAL PHOTOGRAPHS ARE FROM NOAA IMAGERY (HTTP://NGS.WOC.NOAA.GOV/STORMS ) UNLESS OTHERWISE NOTED

Facility Description: Chastain Manor is a 56-unit senior apartment home community that opened 

in December 2010. Unlike Mercy Village, the MAT did not have access to construction drawings for 

Chastain Manor. The complex is divided into two sets of dwellings, including a set of one-story units 

and a set of two-story units. A small one-story leasing office foundation was situated between the two 

sets of dwellings. 

The single row of connected one-story units was on the property’s higher ground, with shared, open 

entranceways between units. Basic construction consisted of pre-engineered wood roof trusses that 

spanned from front to back. Main roof trusses were supported by girder trusses at each end in some 

areas and by exterior bearing walls in others. All roof trusses were attached with hurricane framing 

connectors where supported by framed walls. Single-story walls—mostly non-load-bearing because 

6 The red line in this and all similar figures represents the center of the damage swath. The track location is approximated by the MAT 

based on post-event aerial photographs. The actual centerline of the vortex is offset from the centerline of the damage.
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of the girder trusses described above—were framed with 2x4 studs at 16 inches on center atop slabon-grade foundations. Exterior walls were sheathed with 7/16-inch wood structural panels. The units 

had porch columns that the MAT observed lacked any positive connection to the slab below.

The two rows of two-story apartment buildings on the lower-lying terrain had shared, open 

entranceways and stairs between the units. Basic construction was similar to the one-story units with 

respect to roof framing and framed walls, but the foundations differed somewhat. Although the 

two-story building foundations were slab-on-grade (similar to the one-story building), some units 

were separated by masonry retaining walls necessitated by grade changes, so that slabs separated 

by the retaining wall were at different elevations. Exterior porches of the two-story units were 

constructed with suspended concrete slab floors in the upper units supported by steels beams on 41⁄4-

inch (outside) diameter standard steel pipe columns. Each observed column (upper and lower) was 

originally attached to the concrete slab with four 1⁄2-inch-diameter expansion bolts through 1⁄2-inchthick steel base plates. The embedment depth, while modest at approximately 2 inches, was more 

substantial than the one-story unit’s porch columns. 

General Wind Damage: The wind damage observed by the MAT varied significantly across Chastain 

Manor despite the similarity in the layout of the units (within each set of buildings), materials used, 

and construction method. 

In the one-story units, observed damage ranged from uplift of roof decking (DOD 3) for a few 

connected units at one end of the building to uplift or collapse of roof structure with most walls 

standing (DOD 4) for the remainder of the building (Figure 4-33). Where they remained intact, the 

unanchored porch columns in the one-story units were rotated and/or out of plumb (Figure 4-34).

As indicated by the green circle in Figure 4-32, the units at the northeast end of the two-story 

apartment buildings were bisected by the center of the tornado and sustained the greatest damage. 

For the selected DI 5, observed damage to the two-story apartment buildings varied from uplift of 

roof decking (DOD 3) as shown on several units in Figure 4-35 to complete destruction (DOD 6) 

as shown by the slab swept clean (Figure 4-36). Despite the enhanced column connection in the 

two-story units (shown in Figure 4-35), some of the porches were destroyed by the tornado, and two 

columns were found embedded in the adjacent hillside (Figure 4-37).

Figure 4-33: 

One-story Chastain Manor 

Apartments suffered damage 

varying from roof decking 

uplift to collapse of roof 

structure 
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OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-35: 

Example of DODs 3 and 4 

showing two-story Chastain 

Manor Apartments with 

varying roof damage. Note 

upper and lower steel pipe 

porch columns (red circles).

Figure 4-34: 

One-story Chastain Manor 

Apartment unanchored porch 

column that rotated at top 

and bottom of column (red 

circles)
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OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-36: 

Example of DOD 6 showing 

two-story Chastain Manor 

Apartments completely 

destroyed by the tornado 

with slabs swept clean

Figure 4-37: 

Two-story Chastain Manor 

Apartment steel porch 

column (shown in-place 

in Figure 4-34) was blown 

away and embedded in 

neighboring hillside

Bottom plates in the leasing office (Figure 4-38) and two-story apartment buildings (Figure 4-36) 

were removed from the thickened slab foundation in multiple locations. In some areas, the bottom 

plates were stripped away from the foundation, leaving the anchor bolts embedded in the foundation 

with washers still attached (Figure 4-39). The washers used between the anchor nut and plate were 1 

inch in diameter. While the washer size for the bottom plate anchor is not specified in Section 2308.6 

of the 2012 IBC, high-wind areas along the coast are required to use 3-inch-square washers, which 

significantly increase resistance to plate uplift.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-29

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-38: 

Most of the bottom plates 

were blown off the Chastain 

Manor leasing office 

Figure 4-39: 

Two-story Chastain Manor 

Apartment slab with bottom 

plate pulled over remaining 

anchor bolt and 1-inch 

diameter washer; red circles 

indicate where bolt and plate 

were connected prior to 

damage

MAT EF Rating: Using DI 5 (Apartments, Townhouses, and Condos), the MAT selected DOD 6 

for the two-story units at Chastain Manor, which were the most damaged at the site. Applying the 

expected wind speed range for DOD 6 (155–205 mph), the MAT derived the tornado intensity as EF4 

(166–199 mph) based on the observed building damage for the two-story units. Hence, the estimated 

wind speed experienced by the building greatly exceeded the basic design wind speed of 90 mph.
4-30 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

4.2.3 Mercy Village Apartments (Joplin, MO)

Location of Facility in Tornado Path: The MAT visited the Mercy Village Apartments located in 

Joplin, MO. Figure 4-40 shows an aerial view of the apartments prior to the tornado, and Figure 4-41 

shows an aerial view of the apartments after the tornado. The Mercy Village Apartment building was 

approximately 1,100 feet from the center of the tornado damage swath, rated by the NWS as EF5 in 

this location. According to Mercy Housing, Inc. management,7 approximately 60 out of the total 70 

apartment residents were at home when the tornado passed by. There were no reported fatalities.

Facility Description: Mercy Village Apartments, a 66-unit retirement community on the campus of St. 

John’s Regional Medical Center, is a three-story, wood-frame apartment building. The construction 

drawings were produced in 2003, so the apartment building is approximately 7 or 8 years old. The 

drawings indicate the building was engineered to the requirements of the 2000 IBC.

Figure 4-40: 

Aerial photograph showing 

Mercy Village (red circle) 

prior to tornado

SOURCE: © GOOGLE EARTH

7 Jennifer Erixon, Mercy Housing Inc., 1999 Broadway, Suite 1000, Denver, CO 80202.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-31

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-41: 

Aerial photograph of Mercy 

Village (red circle) after the 

tornado; red line indicates 

the approximate centerline 

of the tornado damage swath 

(Joplin, MO) 

The layout of the building is “L” shaped with a central core on the northwest corner and wings 

extending in perpendicular directions. One wing is oriented north-south and the other east-west. 

The exterior of the building is a combination of brick veneer and fiber cement board siding. Basic 

construction consists of pre-engineered wood roof trusses at 24 inches on center that are attached 

to framed walls at each end with metal hurricane framing (roof-to-wall) connectors. The bottom 

chords of gable end trusses were observed to be braced at 48 inches on center. Braces extend 9 feet 

back from end walls and are attached to blocking between the trusses. As configured, the described 

bracing was designed to resist potential inward or outward deflection of the gable end truss bottom 

chords and served to protect the integrity of the roof envelope. 

Elevated floors between units are framed with 18-inch-deep pre-engineered wood floor trusses 

spaced at 16 inches on center and spanning from exterior walls to the center corridors. Floor framing 

between corridors is 2x10 floor joists at 16 inches on center. Exterior walls were observed to be 

framed with 2x4 studs at 16 inches on center and sheathed with 7/16-inch wood structural panels. 

Interior walls are similarly framed, but sheathed with 5/8-inch thick gypsum board. Designated 

interior shear walls are reinforced and attached to adjoining structural elements with proprietary 

hold-down hardware and metal straps. One side of the transverse shear walls has a resilient channel 

against the stud for sound attenuation, which negated approximately half of the design-intended 

shear wall capacity. Exterior walls were observed to be attached to the foundation with anchor bolts. 
4-32 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

East

Stair

Tower

North Wing

Figure 4-45

West Wing

South Stair Tower

Figure 4-44

Elevator Tower

Figure 4-43

Figure 4-42: 

Aerial photograph of Mercy 

Village after tornado showing 

building areas identified in 

“General Wind Damage” 

(Joplin, MO) 

General Wind Damage: The MAT observed wind damage to Mercy Village Apartments that included 

damage to siding and brick veneer, structural damage to stair towers and dormers, glazing damage, 

roof covering damage, and roof decking damage. Since most of the exterior envelope remained 

functional, the damage to the interior spaces was limited to areas where the exterior envelope was 

compromised. Units where glazing was destroyed suffered damage. The damage to the corridors was 

primarily from water infiltration. Figure 4-42 shows the locations of the damaged areas at the Mercy 

Village Apartments.

Sections of brick veneer fell off the elevator tower and caused damage to the single-story roof sections 

around the main entrance, maintenance room, and bathrooms, as shown in Figure 4-43. Aside from 

the elevator tower, damage to the brick veneer was minimal. The observed brick veneer damage 

was likely caused by debris impact and did not appear to indicate building movement relative to the 

foundation (or any significant movement of the building below the third floor). The brick veneer was 

attached with adjustable wall ties at 16 inches on center vertically and 32 inches on center horizontally 

as specified. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-33

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-43: 

West wall and elevator tower 

where brick fell off and 

damaged one-story roof (red 

circle)

Figure 4-44: 

Damage to the gable end 

wall at south stair tower 

end. Note third floor wall is 

missing and second floor 

wall is bowed outward (red 

arrow).

A section of wall between the third floor and roof was blown away at both stair towers (located at the 

each end of the building). Additionally, the gable end walls at both tower ends were either missing or 

suffered extensive damage, as shown in the south stair tower in Figure 4-44. A short section of wall 

that extended from the end of the stair tower back to the building was still present at each end, but 

was unsecured and no longer vertically plumb. The stair stringers and landings separated slightly 

from the perimeter wall above the second floor, and the end wall bowed outward at both stair towers. 

Similarly, the gable face of the easternmost dormer on the south wall of the east wing was missing. 

Much of the dormer roof decking was also blown off. 
4-34 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

The gable end wall of the east stair tower (not shown in Figure 4-44) was damaged, but remained 

intact, due in part to the truss bracing described in the previous section (Facilities Description). 

The truss braces on the east stair tower appeared to have held the building together long enough to 

prevent more extensive roof damage in that area.

Nearly all of the glazing on the north wing was damaged by wind-borne debris or wind pressure, as 

shown in Figure 4-45, and about half the windows on the west wing had damaged glazing. In many 

of the rooms where glazing was damaged on the third floor, especially on the north wing, the roof 

appeared to have lifted slightly off the walls and been set back down. The MAT did not observe any 

horizontal displacement. The MAT inferred the lifting movement from cracks observed between the 

interior walls and the ceiling. 

Sections of roof decking were missing in various locations at the building, but the vast majority of 

the building’s roof decking remained intact. There were some locations where 2x4 nail plates (a.k.a. 

“sleepers”) were installed between the top chord of the trusses and the sheathing to address truss 

misalignment that occurred during construction. In these locations the nail plates had pulled away 

from the top chord of the trusses, as shown in Figure 4-46 and the inset, because of decreased nail 

penetration in the truss chord. Although the roof decking remained tight against the nail plates, 

there was inadequate nail capacity between the nail plates and truss top chords to resist the required 

tributary area uplift. Where the decking was directly attached to the trusses, it remained tight and 

secure.

MAT EF Rating: Using DI 5 (Apartments, Townhouses, and Condos), the MAT selected DOD 3 for 

this facility. Using the expected wind speed range for DOD 3 (107–146 mph), the MAT derived the 

tornado rating as EF2 (110–137 mph) based on damage to the building. Hence, the estimated wind 

speed experienced by the building was above the basic wind speed of 90 mph that the building was 

Figure 4-45: 

Damaged glazing on the 

interior courtyard of north 

wing building; majority of 

glazing was damaged
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-35

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Figure 4-46: Nails through roof sheathing and nail plates have separated from roof trusses (red circles) because of 

wind pressures. Inset shows close-up of 2-inch nail withdrawal where nail plates separated from the roof truss. 

designed to withstand. The NWS rated the core of the track in the vicinity of Mercy Village as an 

EF5, which is above the MAT EF2 rating for this building. Mercy Village was approximately 1,100 

feet away from the centerline of the tornado; accordingly, wind speed decay would result in a lower 

speed at the facility. 

4.3 Summary of Conclusions and Recommendations

Table 4–3 provides a summary of the conclusions and recommendations for Chapter 4, 

Observations on Residential Building Performance, and provides section references for supporting 

observations. Additional commentary on the conclusions and recommendations is presented in 

Chapters 10 and 11. 
4-36 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Table 4-3: Summary of Conclusions and Recommendations for Residential Building Performance

Observation

Conclusion

(numbered according 

to Chapter 11)

Recommendation

(numbered according 

to Chapter 12)

Examples of recent non-compliant (IRC) 

construction:

•	 Over-notched rafters lacking connection 

to floor diaphragm: Figures 4-19, 4-20 

(Section 4.1.9)

•	 Discontinuous top plate: Figure 4.24 

(Section 4.1.10)

•	 Ungrouted CMU below missing bottom 

plate anchors: Figure 4-27 (Section 4.1.11)

•	 Bottom plate attachment with cut nails: 

Figure 4.31 (Section 4.1.11)

Conclusion #1

Failure to adopt a current 

version of code or having 

no uniform code leaves 

residential buildings 

vulnerable to wind damage.

At the time of publication of 

this report, current codes are 

the 2012 or 2009 IRC.

Recommendation #1

Adopt and enforce current 

model building codes.

At the time of publication of 

this report, current codes are 

the 2012 or 2009 IRC.

Examples of non-compliant (IRC) bottom 

plate attachment:

•	 Figure 4-31 shows a newly constructed 

residential building in Tuscaloosa, AL 

(completed December 2010) where the 

bottom plates in some areas had been 

secured with only concrete cut nails. 

(Section 4.1.11)

•	 Additional examples of IRC exceptions to 

bottom plate attachment in Figures 10-1 

and 10-2

Conclusion #2

Failure to adhere to the 

structural provisions of 

the model building code as 

written can result in buildings 

that are vulnerable to 

structural damage.

Recommendation #2

Increase emphasis on code 

compliance. 

Recommendation #3

Maintain and rigorously 

enforce the adopted 

model building code 

since amendments or lax 

enforcement practices may 

weaken the continuous load 

path of the building.

Examples subcategorized by specific failure 

modes in following rows 

Conclusion #9

Voluntary implementation 

of better design and 

construction practices could 

mitigate damage. 

Improved design and 

construction and 

implementation of details and 

techniques that are already 

required in coastal high-wind 

regions will significantly reduce 

property damage caused 

by tornadoes rated EF2 or 

less (i.e., estimated wind 

speeds of 135 mph or less) 

and to buildings located at 

the periphery of more severe 

events. 

Recommendation #15

Implement voluntary best 

practices to mitigate damage 

to one- and two-family 

residential buildings. 

Prescriptive guidance is 

provided in Appendix G to 

enhance performance of 

components, cladding, and 

critical load path connections 

observed to have failed during 

the spring 2011 tornado events. 

The prescriptive guidance is 

intended to improve building 

performance as described in 

the following rows.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 4-37

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Observation

Conclusion

(numbered according 

to Chapter 11)

Recommendation

(numbered according 

to Chapter 12)

Examples of roof or wall covering that 

became wind-borne debris endangering 

surrounding buildings and their occupants as 

shown in Figure 4-1(Section 4.1.2)

Examples of damage that wall or roof 

covering that likely led to water intrusion in 

Figures 4.2 and 4.3 (Section 4.1.3)

•	 Loss of Roof and Wall 

Covering: Roof and wall 

covering blown away 

by high winds and uplift 

forces became wind-borne 

debris that endangered 

surrounding buildings 

and their occupants. 

Buildings that suffered roof 

covering loss were often 

further damaged by water 

intrusion.

•	 Improve roof and wall 

coverings per Section 

G.3.1. 

Examples of unprotected glazing and wide 

garage doors (16 or 18 feet wide):

Figure 4-6, 4-7, 4-8 (Section 4.1.4 and 4.1.5)

Examples of increased damages resulting 

from breaching of the building envelope:

Figures 4-9 and 4-10 (Section 4.1.5)

•	 Component Damage: 

Component damage, 

whether shattered glazing 

or collapsed garage doors, 

often led to other structural 

and non-structural damage 

because of increased 

pressurization and water 

intrusion that followed 

breaching of the building 

envelope. Unprotected 

glazing and wide garage 

doors (16 or 18 feet wide) 

were particularly vulnerable 

as was expected 

from previous MAT 

assessments.

•	 Increase awareness of 

glazing damage and 

strengthen garage doors 

per Section G.3.1. 

Examples of damages that appeared to 

be triggered by increased pressurization 

resulting from damaged soffits and gable 

end walls:

Figures 4-13 and 4-16 (Section 4.1.6)

Example of poorly fastened roof deck to roof 

structure that appeared to play a role in the 

loss of roof decking:

Figure 4-15 (Section 4.1.6)

•	 Uplift of Roof Decking:

Loss of roof decking often 

appeared to be triggered 

by increased pressurization 

resulting from damaged 

soffits, window failures, 

and gable end walls. Poor 

fastening of roof decking 

to the roof structure also 

appeared to play a role in 

the loss of roof decking.

•	 Strengthen roof decking 

(sheathing) attachment 

per Section G.3.2. 

Examples of failed roof to wall connections 

are shown in 

Figures 4-18 through 4-22 (Section 4.1.9)

•	 Loss of Roof Structure:

The weak link most often 

identified as responsible for 

loss of roof structure was 

the roof-to-wall connection.

•	 Strengthen roof-towall connections per 

Section.G.3.2. 

Table 4-3: Summary of Conclusions and Recommendations for Residential Building Performance (continued)
4-38 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON RESIDENTIAL BUILDING PERFORMANCE

Observation

Conclusion

(numbered according 

to Chapter 11)

Recommendation

(numbered according 

to Chapter 12)

Examples of wall collapse observed to result 

from failed attachment of floor and ceiling 

systems to walls:

Figures 4-23 and 4-24 (Section 4.1.10)

Examples of wall collapse observed to result 

from inadequate bracing of framed walls: 

Figures 4-25 and 4-26 (Section 4.1.10)

•	 Wall Collapse: Wall 

collapse was observed 

to result from failed 

attachment of floor and 

ceiling systems to walls 

and inadequate bracing of 

framed walls.

•	 Failure of Wall Bottom 

Plate Attachment:

Foundations typically 

performed adequately, 

but in some instances the 

connection of walls to the 

foundations system failed 

because of inadequate 

connection of the bottom 

plate.

•	 Improve wall 

performance through 

sheathing attachment, 

hold-down installation 

and better top plate 

splicing per Section 

G.3.3. 

•	 Improve wall-to-floor 

connections and bottom 

plate attachment per 

Examples of failure of wall connection to Section G.3.3. 

foundation:

Figures 4-27 through 4-31 (Section 4.1.11)

Example of the exceptional case where DOD 

5 preceded DOD 6:

Figure 4-17 shows example of house 

shifting off of foundation prior to loss of roof 

structure and wall collapse (Section 4.1.9). 

Conclusion #43

Order of DOD choices for 

DI 2 (One- and Two-Family 

Residences) in the EF 

rating scale does not follow 

observed damage patterns.

As noted in Chapter 4, most 

residences rated by the MAT 

followed the order of DODs 

prescribed by the EF scale 

closely, with the exception of 

DOD 5 (Entire House Shifts 

off Foundation). It was very 

unusual for DOD 5 to precede 

DOD 6. In the one documented 

case (Figure 4-17), the 

observed residence was older 

construction. 

Recommendation #45

Modify EF scale DI 2 (Oneand Two-Family Residences).

Based on the MAT’s 

observations for DI 2 (Oneand Two-Family Residences), 

DOD 5 (“entire house shifts 

off foundation”) was rarely 

witnessed, unlike DODs 4 and 

6, and should be eliminated 

from the list of DODs.

Table 4-3: Summary of Conclusions and Recommendations for Residential Building Performance (concluded)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-1

5Observations on Commercial 

and Industrial Building 

Performance

The MAT visited numerous tornado-damaged commercial and 

industrial buildings to assess building performance and reasons 

for failures.

This chapter describes the results of the MAT’s observation of commercial and industrial buildings 

damaged during the April 25–28, 2011 tornadoes in the mid-south of the United States and the 

May 22, 2011 tornado that struck Joplin, MO. It provides a general description of the damage observed 

across the impacted area and provides seven case studies with detailed damage descriptions. This 

chapter evaluates commercial and industrial building structural designs and the effects of various 

design decisions and construction techniques on a building’s resistance to tornado damage. The 

MAT’s observations focused on the Main Wind Force Resisting System (MWFRS) of the observed 

building, with special attention on continuous load paths and structural connections. Although 

failures may have propagated from secondary building elements or the building envelope, it was 
5-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

the failure of the MWFRS or portions of the critical load paths that resulted in loss of significant 

sections of building or partial to full building collapses, in several instances causing loss of life. 

Summary of Primary Failure Modes Observed by the MAT

The major structural failures observed by the MAT were caused directly by extreme wind loads that 

exceeded the design strength of the building structural systems. Many of the failures observed by 

the MAT were likely a combination of the MWFRS being overloaded by secondary building elements 

or by insufficient load path connections of the MWFRS. The term failure is used in this chapter 

to mean a structural material or building structural system that was loaded beyond its resistance 

capacity. In this context, failure does not imply a design failure occurred; it means that the building 

or component was challenged by a force larger than it was capable of resisting. 

The larger commercial buildings observed by the MAT were designed to function as enclosed 

buildings. Portions of the building shells were designed to act as both the envelope and the MWFRS 

that transfers loads into the foundation in lieu of internal bracing. Therefore, when damage to the 

roof and walls occurred, damage to the MWFRS also occurred. When the building envelope of this 

type of building is breached, the resulting pressurization effectively changes the enclosed building 

into a partially enclosed building (refer to Section 3.1 for additional information). Once the building 

is effectively a partially enclosed building, the key structural components experience significantly 

higher wind loading than they were designed to resist. The MAT observed buildings that were 

damaged at wind speeds lower than the design wind speed because of increased pressurization. 

Role of Existing Building Code

It is important to note that current building code wind speeds do not represent the influence 

from tornados. ASCE 7-10 does not provide requirements for minimum design loads specific to all 

tornadic events, but does address tornadoes in the Commentary. Section C26.5.4 Limitation (p. 513) 

as follows: 

“It is recognized that tornadic wind speeds have a significantly lower probability of 

occurrence than the basic wind speeds. In addition, it is found that in approximately 

one-half of the recorded tornadoes, gust speeds are less than the gust speeds 

associated with basic wind speeds.” 

Thus while the forces from tornadoes of lesser intensities, such as those rated EF0 and EF1, fall 

within the design parameters of wind speeds represented in the current ASCE 7 standard, the 

forces from very strong tornadoes (EF3, EF4, and EF5) are well above the forces currently required 

for building design (refer to Section 2.2 and Appendix E for more information on the EF rating 

scale). Many of the damaged commercial and industrial buildings observed by the MAT were large 

structures. The buildings appeared to have been designed in accordance with the governing codes 

in effect at the time they were built. Therefore, it is most likely that the dramatic building failures 

observed by the MAT were not the result of poor design or construction, but rather the result of 

forces being applied to these buildings that were above the expected design parameters. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-3

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Organization of Chapter

The observed failures of commercial and industrial buildings (summarized in Sections 5.1, 5.2, 5.3, 

and 5.4) were more closely associated with the construction type of the building rather than the 

use of the building. Therefore, this chapter is organized by building construction type rather than 

by building use. The location of each building described in this MAT report is shown in Figures 

5-1 through 5-3 with each building location shown in relationship to the centerline of the tornado 

damage swath.

This chapter summarizes five building types and the typical failures observed by the MAT specific 

to each building type. Where significant time was spent evaluating a particular site or issue, 

additional information is provided for that location as a case study. The types of structural failure 

conditions observed by the MAT were common across various locations due to common commercial 

construction methods and the consistency of materials manufacturing. 

Figure 5-1: Location of Joplin, MO, buildings described in Chapter 5

SOURCE FOR TORNADO TRACK: HTTP://WWW.CRH.NOAA.GOV/SGF/?N=EVENT_2011MAY22_SUMMARY
5-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-3: Location of Jefferson Metro Care medical office in Birmingham, AL, described in Section 5.2.4

SOURCE FOR TORNADO TRACK: HTTP://WWW.SRH.NOAA.GOV/BMX/?N=EVENT_04272011TUSCBIRM

Figure 5-2: Location of Tuscaloosa, AL, buildings described in Chapter 5

SOURCE FOR TORNADO TRACK: HTTP://WWW.SRH.NOAA.GOV/SRH/SSD/MAPPING/
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-5

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

5.1 Tilt-Up Precast Concrete Walls with Steel Joist Roof System

The MAT observed several damaged 

buildings constructed using tilt-up precast 

walls with a steel joist roof system. This type 

of building construction is described in 

Section 5.1.1 and its typical failure modes in 

Section 5.1.2. One of these, a Home Depot, 

was assessed in detail and is presented as a 

case study in Section 5.1.3. 

5.1.1 Description of Construction 

Method and Load Path

The construction erection procedures of 

precast concrete and tilt-up concrete panel construction are similar in process. These construction 

practices were developed to eliminate the use of difficult, expensive, and time-consuming vertical 

forming of wall elements. In these casting methods, concrete wall panels are made by placing 

concrete in forms that are laid flat on a casting bed. The panel is then either brought to the project 

site or picked up from its onsite casting bed and “tilted” into place. During construction, the panels 

are braced until the connections and load transferring systems are in place.

The tilt-up method reduces the scaffolding work associated with masonry work or poured concrete 

lifts associated with cast-in-place methods. This construction is typically used for long span roof 

systems and high ceilings, and is therefore commonly used in large commercial super-centers 

(supermarkets, household goods, and building material supply stores), as well as warehouses, 

industrial buildings, agricultural facilities and other high-ceiling single-story applications. 

Tilt-up concrete panels are typically relatively thin, usually 7 to 12 inches thick. The individual 

panels may be multi-story, and some designs have reached heights of 50 feet and higher. Wall panels 

are typically supported on concrete foundations and may be connected to the floor slab with a castin-place perimeter strip between the wall and the slab. Although in many applications panels do not 

need anchorage due to their heavy weight, the code requires a minimum of two ties per panel and 

connections that rely solely on friction from gravity may not be used. Interior column and frame 

systems are commonly used for intermediate support of multiple stories or roof systems. Roof systems 

in these types of structures may rest on a corbel formed into the wall panel or, more commonly, may 

be attached with embedded weld plates and brackets at the top of the tilt-up concrete panels.

The load paths of these buildings are straightforward because of the small number of elements 

involved, which makes the relatively few connections and components in the building very important. 

The elements of these types of diaphragm structures are connected in a system that allows the 

various loads to be transferred from element to element down to the foundations: 

+ Uniform vertical loads are carried by the roof deck to the joists. Vertical point loads are taken 

directly to the joists. Horizontal loads are distributed to the roof deck and gathered at shear 

walls. 

Following the tornado in Joplin, MO, the Tilt-Up 

Concrete Association formed a task force to investigate claims made by an article that criticized 

the failure and failure modes of tilt-up concrete 

wall construction during the tornado. Their report, Analysis of Damage from Historic Tornado 

in Joplin, Missouri, U.S.A. on May 22, 2011, a 

Report to the Technical Committee of the TiltUp Concrete Association by the Natural Disaster 

Task Force, was published in January 2012.
5-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

+ The joists then transfer the loads through the joist seats to the joist girders at panel points. In 

some cases, the joists transfer the loads through their seats to beams or walls. 

+ The joist girders then transfer loads to either columns or walls. The walls sit on foundations and 

convey the accumulated forces directly via contact and anchorage. 

The connections between these building elements are therefore critical due to the loads flowing 

through them. Horizontal and vertical uplift loads on the roof deck are typically transferred via 

puddle welds to the joists that support the deck, or to collector elements at the walls. Welds are also 

used to transfer forces from joists to joist girders, joists to walls, joist girders to columns, joist girders 

to walls, and to connect columns to base plates. 

5.1.2 Typical Failure Modes Observed by the MAT

Structural failure and catastrophic collapse of this building type was observed in several locations. 

One example of tilt-up construction, a Home Depot, was assessed in detail and is presented as a 

case study (Section 5.1.3). Although some failures may have been the result of overload on the 

long span roof systems, the more common condition observed was the failure of the roof deck-tojoist connections and the roof-to-wall panel connections. These connection failures in the MWFRS 

diaphragm and at the top of the wall allowed the large sections of wall panels to collapse. 

Due to the open nature of most buildings using this 

construction method, the collapse of the very heavy fullheight floor-to-roof wall panels did not produce interior 

pockets of space where occupants could take cover and 

survive during catastrophic structural failures. Significant 

damage to building interiors and resulting injury to 

occupants occurred when these buildings’ non-redundant main structural support systems were 

overloaded. When one panel failed, the loads shared by the adjacent wall panels increased markedly, 

resulting in the propagation of failure to more of the wall panels, sometimes leading to complete 

collapse of the exterior walls and roof. 

5.1.3 Home Depot (Joplin, MO)

The 108,000-square-foot Home Depot, located in Joplin, MO, is a typical example of a tilt-up concrete 

building destroyed by a very intense tornado. According to a local Home Depot representative, there 

were seven fatalities. Twenty-eight people in the store survived. 

Location of Facility in Tornado Path: The MAT inspected the Home Depot in Joplin, MO (location 

shown in Figure 5-1), which was destroyed during the tornado. Figure 5-4 shows the building after 

the tornado and its location in relationship to the centerline of the tornado damage swath. The 

NWS rated the center of the tornado circulation in the vicinity of the building as an EF4 to EF5. 

A typical 9-inch-thick x 25-footwide x 30-foot-high panel weighs 

about 84,000 pounds.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-7

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Facility Description: The Home Depot had a footprint of 240 feet by 450 feet. The structural system 

for this large building used the following structural and roof covering elements:

+ Membrane roofing

+ Insulation board

+ Metal roof deck 

+ Open web steel joists

+ Open web steel joist girders

+ Square tube columns supporting joist girders

+ Precast concrete exterior walls

+ Shallow foundations

Figure 5-4: Aerial view of Home Depot (yellow circle) in Joplin, MO, in relationship to the approximate centerline of the 

May 22, 2011 tornado damage swath (red line)1 (Joplin, MO)

SOURCE: ALL AERIAL PHOTOGRAPHS ARE FROM NOAA IMAGERY (HTTP://NGS.WOC.NOAA.GOV/STORMS) UNLESS OTHERWISE NOTED

1 The red line in this and all similar figures represents the center of the damage swath. The track location is approximated by the MAT 

based on post-event aerial photographs. The actual centerline of the vortex is offset from the centerline of the damage.
5-8 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-5: 

Field east of Home Depot 

with roof debris (Joplin, MO)

General Wind Damage: After the tornado, some of the precast concrete walls were still standing 

in the northeast corner of the building and partially along the southwest side. The remainder of 

the wall panels had collapsed. Some of the wall panels had collapsed inwards, while others had 

collapsed outwards.

Roof System

The connection failures and loss of lateral support of the structural elements led to the total collapse 

of the roof structure, which in turn led to the collapse of the walls. Large portions of the roof 

membrane, insulation board, and metal deck diaphragm were lifted from the building and moved 

outside of the building footprint to the open field east of the Home Depot (Figure 5-5). The roof on 

the front (east) bay remained attached to the joists inside the collapsed foot print. 

As previously noted, the roof deck is typically connected to the joists by puddle welds. An example 

of a failed puddle weld used to connect the metal deck to the top chord of the steel joists is shown in 

Figure 5-6. The MAT noted this type of connection on each of the metal deck structures observed 

at the Home Depot. The roof metal deck acted as a lateral diaphragm and was the primary loadcarrying system for lateral loads in the building. Once the roof deck connections failed the steel 

open web bar-joists and joist girders lost their lateral support and became unstable. 

One of the advantages of the steel joist system is that it is a more cost effective system than a 

traditional steel system of wide flange beams and girders. The joists are lightweight and they can 

be widely spaced and be used on long spans. The system is primarily designed to carry downward 

vertical loads and can carry horizontal loads that are parallel to the length of the joist. 

A disadvantage of the system is that the combination of the elements used in constructing the 

joists and joist girder and its length create members that have little horizontal capacity when 

loaded laterally in an un-braced condition, as was the case described above when the roof deck 

connection failed. This weakness is also evident in the joist girders, which became un-braced when 

the connection between the joists and joist girders failed. Figures 5-7 and 5-8 demonstrate the lack 

of rigidity in an un-braced joist system.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-9

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-7: 

Joist girder and column 

failure. The column-to-joist 

girder is shown by the red 

arrow (Joplin, MO).

Figure 5-6: 

Failed puddle welds that 

connected the metal roof 

deck to the top chord of the 

joist (red arrows) (Joplin, 

MO)

Another common practice in the industry is not welding the bottom chord to the stabilizer plate 

on joist girders at the column support. The bottom chord was not connected at the Home Depot 

and the MAT noted several instances of separation at this location (Figure 5-8). In some buildings, 

the bottom chord is welded if the system is designed as a moment frame system, but if analysis 

determines that the structure is adequate for the design loads without welding the bottom chord, 
5-10 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

it is appropriate and encouraged to not 

make this connection rigid. Alternatively, 

welding the bottom chord at this location 

can help keep the bottom chord from 

buckling provided the connection is 

capable of resisting the tension induced at 

this point by the uplift of the joist. However, 

complications can occur if the construction 

sequence gets out of order and if snow 

loads are expected. The bottom plate must 

be welded after all the dead loads are in 

place to prevent damage to the lower chord 

as it deflects and rotates to carry the dead 

load. If the bottom chord is to be welded to 

the stabilizer plate, this must be indicated 

on the plans and considered in the girder 

design as a special loading condition. Yet 

another option is to use a loose fit bolt in a 

slotted hole in lieu of a welded connection 

at the stabilizer plate.

When single-story, large footprint and multi-story 

commercial buildings fail during tornadoes, large 

amounts of debris may be generated at the building sites (see Figures 5-7, 5-12, 5-16, 5-21, and 

5-34). To address the structural concerns related 

to this, FEMA 361 and the ICC 500 provide design 

criteria to account for debris on the roofs of safe 

rooms and storm shelters and also state that falling and collapse hazards need to be considered 

with designing, siting, and constructing these protective areas. FEMA 361 and this publication also 

provide guidance on operational considerations 

that state equipment and communication systems 

should be maintained within safe rooms and tornado refuge areas to assist with the rescue and 

extraction of individuals from such areas when a 

building collapse occurs.

Figure 5-8: 

Separation at bottom chord 

to stabilizer plate (red arrow) 

(Joplin, MO)

Interior Columns

The interior columns at the Home Depot were hollow structural steel (HSS) tube sections located on 

a grid approximately 40 feet x 50 feet, a common industry practice for lightweight steel frames. The 

columns were attached to the foundations with a 4-bolt base plate that was welded to the column 

and a 4-bolt connection at the top to the joist girders. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-11

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-9: 

Buckled column (Joplin, MO)

The column elements performed well while the column tops were pulled to the east by the roof 

translation. Once the roof deck and steel joist connections broke, the lateral and uplift loads on the 

columns were reduced and the translation stopped. 

The MAT observed a column that buckled against the racking system (Figure 5-9). Some columns 

failed when the hooked anchor bolts for the column pulled out of the concrete. Other columns 

experienced failure at the base plate due to shear and tension (Figure 5-10). As the column rotated, 

the force on the compression side of the base plate sheared the bolts and the tension side pulled the 

hooked anchor bolts free. The code allows the use of hooked anchor bolts when columns are subject 

to compression only. When anchor bolts are subject to tension a more positive anchorage is created 

by using headed anchor bolts in lieu of hooked anchor bolts.
5-12 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Exterior Walls

The exterior walls of the Home Depot building were precast tilt-up concrete panels. In this type of 

construction, the connection at the base of the wall is a steel plate or angle welded to an embedded 

steel plate in the footing and the wall. The roof connections consist of an embedded steel plate in 

the wall connected to the roof members. Where the steel joists are perpendicular to the wall, there 

are pockets or a ledger angle where the wall panels support the joists. Figure 5-11 shows an example 

of a failed joist support pocket at the Home Depot building. 

Figure 5-11: 

Joist support pocket at top 

of a precast wall. The red 

arrow points to weld marks 

from the connection to the 

framing member seat on the 

embedded plate. The yellow 

arrow points to the light blue 

insulation layer between the 

concrete shells (Joplin, MO).

Figure 5-10: 

Bolt failure at interior column 

resulting from shear and 

tension. The hooked anchor 

bolts pulled out of the slab 

(red arrow) (Joplin, MO).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-13

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-11 also shows that the panels of the Home Depot building were insulated, which means 

there were two layers of concrete with a layer of insulation in the center. The two layers of concrete 

are usually connected by ties and concrete ribs at the perimeter and sometimes in the center of the 

panel. This detail was not exposed, however, and the MAT was unable to observe the connection. 

The design dictates whether there are other connections along the vertical joints between individual 

wall panels. The MAT did not observe any panel-to-panel connections in the Home Depot building. 

For wall panels parallel to the steel joists, the connection to the roof diaphragm is provided by a deck 

support angle attached to the wall panel with bolts or weld plates. The roof deck is then attached 

to this angle. There are more substantial connections from the joist girders to the wall panels than 

from joists to wall panels. There is also an additional connection where the joist bridging attaches 

to the wall. The bridging is provided by the steel joist supplier. This connection is often very small 

and lightly designed as the required bridging member sizes are also small. This bridging is one of 

the methods used to keep the bottom chords from buckling as it reduces the un-braced length of 

the chord. 

When the connections between the panels and the roof system fail or the roof system becomes 

unstable due to loss of the diaphragm, the panels became tall cantilevered walls. Exterior tilt-up 

walls are not typically designed to withstand this condition, and certainly not when subjected to 

large lateral forces created by high winds. With high wind pressures, they can become unstable 

and collapse. It is worth noting that they do not fail in bending, which is typically the worst design 

loading condition and occurs during the initial construction lifting operation. Instead, they collapse 

by failing to resist rotation about the bottom of the panel when subjected to lateral loading.

The MAT observed several types of failures of the roof-to-wall connections at the Home Depot 

building including failures of the joist girder-to-wall connections, failure of the joist-to-joist girder 

connection (Figure 5-12), failure at joist seats (Figure 5-13), and failures of the weld plates (Figures 

5-14 to 5-16). These kinds of failures were part of a chain of failures that led to the collapse of most 

of the walls. 

In the area shown in Figure 5-12 the product racking system maintained some integrity as 

the building structural elements failed; this area could possibly have been used as a location to 

take refuge as an option of last resort. However, the level of protection would have been poor, as 

protection from both wind-borne debris and store contents would have been minimal.
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OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-13: 

The joist seats came free of 

their bearing locations when 

both the seat-to-joist weld 

(yellow arrow) and the seatto-embed plate weld (red 

arrow) broke (Joplin, MO)

Figure 5-12: 

Failure of joist-to-joist girder 

connection shown by broken 

welds (yellow arrow); red 

arrow shows location where 

bridging angle is touching 

insulation bundles 

(Joplin, MO)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-15

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-14: 

Example of weld plate and 

joist failure. The joist seat 

was torn from the joist (red 

arrow) and the anchor studs 

from embed plate were torn 

out of the concrete (yellow 

arrow) (Joplin, MO).

Figure 5-15: 

The panel at the weld 

plate failed (red arrow) 

(Joplin, MO)
5-16 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Foundations

The foundations for the Home Depot were not damaged by the tornado event. The MAT did not 

note any movement of the interior foundations. The anchor bolt failures (described in Exterior Walls

above) occurred before there was any movement of the foundation.

MAT EF Rating: Using DI 12 (Large Isolated Retail Building), the MAT selected DOD 7 (“complete 

destruction of all or a large section of the building”) for this building. Using the expected wind 

speed for DOD 7, the MAT derived the tornado ranking as EF4 (165–170 mph winds). Therefore, 

the estimated wind speed experienced by the building was well in excess of the 90 mph code design 

requirements for this location. The MAT EF4 rating for the Home Depot is the same as the NWS 

rating of EF4 for the center of the tornado circulation at this location. 

Functional Loss: The Home Depot in Joplin, MO, is a complete loss. 

5.2 Load Bearing Masonry with Steel Joist Roof System

The MAT observed numerous buildings constructed using load bearing masonry walls with steel 

joists as the roof system. This type of building construction is described in Section 5.2.1 and its 

typical failures modes in Section 5.2.2. Detailed case studies for the buildings are presented in 

Section 5.2.3 through Section 5.2.5.

Figure 5-16: 

Example of a weld plate 

failure. Note the attached 

joist (red arrow) and the joist 

pocket at the top of the wall 

panel (yellow arrow) 

(Joplin, MO)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-17

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

5.2.1 Description of Construction Methods and Load Path

Older masonry construction: Masonry construction varies depending on the type and size of 

the concrete blocks and whether the masonry system is reinforced. Older construction is often 

unreinforced or inadequately reinforced and is more likely to collapse in what are current design 

wind speeds. Owners and operators of older buildings constructed prior to the implementation 

of current building codes can either retrofit the masonry with reinforcement to allow for better 

performance or should be aware that occupants in these buildings will need to seek more substantial 

buildings during high-wind events. Refer to Chapter 9 for information on refuge areas and safe 

rooms/storm shelters.

Bond beams in multiple story construction: Reinforced and unreinforced masonry walls can be 

used in multiple-story construction. Intermediate stories and roof systems can be attached to a 

grouted bond beam or corbel constructed into the masonry wall. Steel joists or trusses may span 

between these walls to create floors. Roof trusses are attached at the top of the wall using either a 

top plate or they may rest on top of a bond beam. The bond beam is intended to serve two purposes: 

lateral load transfer along the length of the wall or vertical load transfer from the roof system. 

Wall-to-footing/wall-to-roof connections: In order to provide load path continuity at the connection 

between the masonry wall and footings, some physical connection must be made between the 

reinforcing steel in the footing and in the wall. Reinforcing steel is used for this connection since 

the tensile strength of masonry and grout materials is extremely low and it can only be relied on for 

compression. Reinforcing steel used to make the wall-to-footing connection must be of a sufficient 

size and length (development length) to transfer the loads. Similarly the wall-to-roof connection 

needs to be able to provide a complete load path into the wall reinforcement from the roof elements. 

5.2.2 Typical Failure Modes Observed by the MAT

Older masonry construction: Inevitably, many of the older buildings the MAT observed collapsed 

during the tornado outbreak. These failures were observed not only in the direct path of the 

tornado, but also on the tornado periphery where wind speeds were lower and somewhat closer to 

design level wind speeds. 

Bond beams in multiple story construction: The MAT checked the top sections of toppled walls 

for the presence of bond beams. Failures of the bond beams were noted by the MAT in buildings 

located along periphery areas of the tornado damage swath, suggesting either wall or roof loads 

larger than the wall system was designed to transfer or a concrete strength that was insufficient. 

Wall-to-footing/wall-to-roof connections: Failures observed by the MAT occurred in two primary 

locations: the roof-to-wall connection or at the footing-to-wall connection. The MAT found 

reinforcing steel in walls and footings to be spaced too infrequently or it was absent altogether in 

some cases. Where present, development lengths of failed sections of wall were measured and found 

to be inadequate.
5-18 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

5.2.3 Strip Mall – Dry Cleaner, Two Large Retail Stores, 

and Other Stores (Tuscaloosa, AL)

Location of Facility in Tornado Path: The MAT observed a small strip mall in Tuscaloosa, AL 

(location shown in Figures 5-2 and 5-17), which was destroyed during the April 27, 2011 tornado. 

This strip mall contained a dry cleaner, two large retail stores, a fitness center and other businesses. 

The dry cleaner was located on the far west end of the strip mall, retail store “A” was located at the 

northeast end of the mall, and retail store “B” was adjacent to and south of the first store. The fitness 

center is described in detail in Section 5.3.3. 

The dry cleaner was very near the centerline of the tornado damage swath; the NWS rated the 

center of the tornado circulation in this location as an EF4. The MAT made detailed observations of 

the dry cleaner, described below.

Facility Description: The dry cleaner building had a footprint of roughly 150 feet by 160 feet. The 

structural and roof covering systems for this building used the following elements:

+ Membrane roofing

+ Insulation board

Figure 5-17: Aerial view showing the locations of the dry cleaner building (red box), fitness center (yellow box), retail 

store “A” (blue box) and retail store “B” (green box) in relationship to the approximate centerline of the April 27, 2011 

tornado damage swath (red line) and (Tuscaloosa, AL) 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-19

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

+ Metal roof deck 

+ Open web steel joists

+ Unreinforced CMU exterior walls

+ Shallow Foundation

General Wind Damage: After the tornado, only one exterior wall and two interior walls of the dry 

cleaner were left standing. Most of the CMU walls collapsed inward on the building and the roof 

was either torn away or collapsed in on the building.

Exterior Unreinforced CMU Walls

The exterior walls on the dry cleaner building were constructed of unreinforced CMU. The walls 

had some horizontal joint wire reinforcing but no vertical reinforcing or grouted cells. The walls on 

the front and rear of the building failed, collapsing inward on the building. The connections at the 

roof failed causing the walls to behave as a tall cantilever wall, which caused the bending stresses to 

exceed the material stress capacity. Figure 5-18 shows collapsed unreinforced masonry walls. The 

wall shared with the adjoining building was left standing, as were a few of the smaller interior walls. 

These walls were supported by roofing from two sides. Since the roof was left mostly intact on the 

other side of the wall, the wall had some lateral support and remained standing.

The connection at the base of the wall typically consists of reinforcing steel that is embedded into 

the foundation and then extended up into the CMU cells. The cells are then grouted, locking the 

reinforcing in place and allowing it to transfer both lateral and uplift load. The walls of the dry 

cleaning building did not have any visible steel connection between the base of the CMU wall and 

the foundation. The CMU walls relied on the block mortar joints and self-weight to support the wall. 

Figure 5-19 shows the lack of reinforcing in the entire wall and also at the connection between the 

base of the CMU wall to the foundation. The failure sequence is captured in Figures 5-20 and 5-21.

Figure 5-18: 

Steel joist (red arrow) 

in midst of collapsed 

unreinforced masonry wall 

at the dry cleaner store 

(Tuscaloosa, AL)
5-20 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-19: 

Solid steel hot rolled sections 

(red arrow) left in beam 

pockets of CMU building 

section. These supported 

the steel joists shown in 

Figure 5-18. Also note lack 

of reinforcement in the 

wall and wall-to-foundation 

connection (Tuscaloosa, AL).

Figure 5-20: 

Sequence of failure for 

CMU wall at the dry cleaner 

building: wall buckling and 

initial separation (red arrow) 

was followed by complete 

separation of wall from 

bond beam (yellow arrow) 

and then by collapse of wall 

(green arrow) 

(Tuscaloosa, AL)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-21

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Exterior Unreinforced CMU Walls: Roof System

The roof connection consisted of an embedded steel plate attached to the bond beam connected to 

the roof members. Where the steel joists were perpendicular to the wall there were typically pockets 

or a ledger angle where the joists were supported (Figure 5-22). This connection tied into a bond 

beam running along the front and back walls of the dry cleaner building. When the wall failed and 

collapsed (Figure 5-23), the bond beam also failed and collapsed, bringing the bar joist roof system 

down with it.

MAT EF Rating: Using DI 10 (Strip Mall), the MAT selected DOD 8 (“collapse of exterior walls; 

closely spaced interior walls remain standing”) for this building. Using the expected wind speed 

for DOD 8, the MAT derived the tornado ranking as EF3 (140–150 mph winds). Therefore, the 

estimated wind speed experienced at the building was well in excess of the 90 mph building code 

design requirements for this location. The MAT EF3 rating for the dry cleaner is lower than the 

NWS rating of EF4 for the center of the tornado circulation near this location; however, the building 

was not located directly in the core of the track.

Functional Loss: The dry cleaner building is a complete loss as the exterior walls and roof were 

destroyed. The two large retail stores are also complete losses. 

Figure 5-21: 

Global wall instability 

failure. The CMU blocks are 

lying loosely on the ground 

and many have rotated 

(yellow arrow) due to the 

complete separation of all 

the blocks. Note lack of 

reinforcement in the wall and 

especially between wall and 

footing (red arrow). Inset 

shows a close-up view of 

the separation of the blocks 

(Tuscaloosa, AL).
5-22 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

5.2.4 Jefferson Metro Care (Birmingham, AL)

Location of Facility in Tornado Path: The MAT visited the Jefferson Metro Care facility in 

Birmingham, AL (location shown in Figure 5-24), which was destroyed during the April 27, 2011 

tornado. The Jefferson Metro Care facility was located just north of the centerline of the tornado 

damage swath. The NWS rated the center of the tornado circulation in the vicinity of this facility 

as EF2.

Figure 5-23: 

Steel joists with joist seat 

and bond beam on top of 

collapsed wall (red arrow). 

Wall fragmentation shows 

lack of reinforcement in the 

wall (Tuscaloosa, AL).

Figure 5-22: 

View of steel joist pockets in 

CMU wall where joists pulled 

out (red arrows); the exterior 

CMU wall fell inwards, 

shown in the foreground 

(Tuscaloosa, AL)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-23

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Facility Description: The Jefferson Metro Care building had a footprint of roughly 130 feet by 75 

feet. The structural and roof covering system for this building used the following elements:

+ Built-up roofing

+ Insulation board

+ Metal roof deck 

+ Open web steel joists

+ Steel beam girders

+ CMU with brick veneer exterior walls

+ Shallow foundation

General Wind Damage: Most of the exterior walls of the facility withstood the tornado, but a large 

portion of the northwest roof was damaged when the building envelope was breached at the front 

windows. Inflow winds resulted in high uplift forces on the roof. The windows along the front 

exterior walls were blown in by windward pressure.

Figure 5-24: Aerial view showing the Jefferson Metro Care Facility (red box) in relationship to the approximate 

centerline of the April 27, 2011 tornado damage swath (red line) (Birmingham, AL)
5-24 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Exterior CMU Walls with Brick Veneer

The exterior walls of the Jefferson Metro Care building were constructed of CMU with a brick veneer. 

The MAT was unable to inspect the reinforcement in the majority of the walls that did not fail. 

The roof connection to the exterior walls consisted of an embedded steel plate attached to bond 

beams. The roof joists were then welded to the steel embed plates. This connection tied into a bond 

beam running along the front and back walls of the building. The bond beam was supported by, 

but not connected to, a steel beam over the front windows. The bond beam along the front of the 

building broke away from the steel beam when the roof system was torn away, as shown in Figure 

5-25. The interior joist seats tore away from their support on interior steel beams when they folded 

over the roof toward the rear of the building.

Figure 5-25: 

Failed bond beam-tostructural steel connection 

over front windows (red 

arrow) (Birmingham, AL)

Roof System

The roof consisted of an open web steel bar joist system with a metal roof deck and membrane 

roofing. Most of the roof failures were a result of failure of the welds for the metal deck diaphragm, 

bar joists, and main structural beams. Figures 5-26 and 5-27 show the failed roof deck connections. 

Once struck by high winds, the roof decking was pulled off the bar joists as it was pulled over toward 

the rear of the building. 

Another failure identified was the lack of continuity between the roof structure and the walls. 

Figure 5-28 shows where a bond beam cell has been stuffed with paper to limit the flow of the grout 

indicating a serious quality control issue during construction. Figure 5-29 shows a similar condition 

where the CMU cell is still attached to the steel joist but detached from the wall. Figure 5-30 shows a 

CMU bond cell that was torn from both the wall and the steel joist.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-25

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-28: 

This CMU cell was found 

on the ground adjacent 

to the structure (shown 

upside down). The bond 

beam cell is sealed with 

paper to keep grout from 

flowing into lower cells 

(red arrow) and thus 

there was no connection 

to lower elements. The 

embed plate can be seen 

attached (yellow arrow) 

(Birmingham, AL).

Figure 5-27: 

Failed roof deck with no 

connections between the 

roof deck and the joists 

(red arrows) (Birmingham, 

AL)

Figure 5-26: 

Roof joist lifted off front 

(red arrow) and folded over 

rear half of building (yellow 

arrow) (Birmingham, AL)
5-26 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-29: 

Bar joist with embed 

plate and bond beam cell 

still attached (red arrow) 

(Birmingham, AL)

Figure 5-30: 

Embed plate with bond beam 

cell (red arrow) on roof 

(Birmingham, AL)

MAT EF Rating: Using DI 9 (Small Professional Building), the MAT selected DOD 7 (“uplift or 

collapse of entire roof structure”) for this building. Using the expected wind speed for DOD 7, the 

MAT derived the tornado rating as a high EF1 (100–105 mph winds). Therefore, the estimated wind 

speed experienced by the building was in excess of the 90 mph building code design requirements 

for this location. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-27

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

The nearest damage survey point assessed by NWS had a rating of EF2. The Jefferson Metro Care 

building falls within the swath projected from NWS for an EF1 rating, which matches the EF rating 

derived by the MAT.

Functional Loss: The main floor experienced moderate damage from wind-borne debris and 

water damage after the roof system was torn away from the front part of the building. This damage 

rendered the building uninhabitable. The tenant, Jefferson Metro Care, relocated to another nearby 

facility to resume their practice. The building will need significant repairs to the roof and interior 

before it can be fully functional.

5.2.5 Walmart (Joplin, MO)

Location of Facility in Tornado Path: The MAT inspected the Walmart in Joplin, MO, which was 

severely damaged during the May, 2011 tornado. Figure 5-1 shows the location of the Walmart with 

respect to the tornado damage swath in Joplin. Figure 5-31 shows the building after the tornado 

and the tornado damage swath in the vicinity of the building. The Walmart was located just north of 

the centerline of the tornado damage swath. The NWS rated the center of the tornado circulation 

in the vicinity of the Walmart as EF5. According to a local Walmart representative, there were three 

deaths among the 200 occupants who were inside the facility during the tornado. 

Figure 5-31: Aerial view of a Walmart in Joplin, MO (red box) in relationship to the approximate centerline of the 

May 22, 2011 tornado damage swath (red line) (Joplin, MO)
5-28 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Facility Description: The Walmart building footprint was approximately 180,000 square feet, 300 

feet x 600 feet. The structural and roof covering system consisted of the following elements:

+ Membrane roofing

+ Insulation board

+ Metal deck roof 

+ Open web steel joists

+ Open web steel joist girders

+ Square tube columns supporting joist girders

+ Exterior reinforced CMU walls 

+ Shallow foundations

General Wind Damage: The north portion of the Walmart building remained standing (Figure 

5-32) with the majority of its roof structure in place. The south portion of the building lost its roof 

structure and some of the exterior walls collapsed. At the time the MAT visited, site cleanup of 

the interior space had been in progress for several days and most of the store contents had been 

removed. 

Figure 5-32: 

The relatively undamaged 

west elevation of Walmart 

after the May 22, 2011 

tornado (Joplin, MO)

Roof System

There are two damage levels that occurred within this structure. 

North half of building: Within the west side of the north half of the building, the structure remained 

relatively undamaged, though water infiltration occurred in two places. The roof membrane was 

compromised, which allowed water infiltration. The exterior envelope of the structure was also 

compromised, at the north entry on the west side, which allowed water into the interior space via 

the doors.

The east side of the building within the north half was compromised. The east wall and roof were 

destroyed beginning at approximately the loading docks on the east side (Figures 5-33 and 5-34). 

The failures resulted in significant water infiltration. Figure 5-35 is looking north inside the space; 

note the water level inside the Walmart bag in the lower right corner of the photograph.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-29

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-33: 

Interior of the north half of 

the Walmart, looking east. 

Fallen roof structure shown 

in right side of the picture 

(red arrow) (Joplin, MO).

Figure 5-34: 

Destroyed east side of north 

half of Walmart (note loading 

dock facing south) (Joplin, 

MO)
5-30 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

South half of building: The south half of the building was hardest hit as it was closest to the tornado 

track. The roof system, including structural members, failed and compromised the integrity of the 

load carrying systems.

Puddle welds were used to connect the steel roof deck to the top chords of the steel joists. The MAT 

observed many instances where this connection failed. Figure 5-36 shows the deck supporting the 

steel joist since the joist girder is no longer there. Figure 5-37 is taken from the outside of the roof 

portion of the building looking north; the insulation board is still in place on much of the roof, but 

the roof membrane is missing.

The typical connection of steel joists to joist girders is provided by welds from the joist seat to the 

girder top chord. Figure 5-38 shows the failure of these welds in this roof assembly. Another industry 

practice is not welding the bottom chord to the stabilizer plate on joist girders at the column 

support. This allows for slight flexural movement and rotation at the supports of the girders as they 

get loaded and unloaded. If the system is designed as a moment frame system this is often welded. 

At the Walmart, the bottom chord was not welded. Without the bottom chord being welded all of 

the torsional resistance of the joist must occur at the top chord angle seat connection. The MAT 

observed several instances of separation such as shown in Figure 5-39.

Figure 5-35: 

Interior of the north half 

of building showing water 

infiltration collected in bags 

(red arrow) (Joplin, MO)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-31

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-36: 

Interior view from the 

south half of the building 

looking toward the east. 

This shows the boundary of 

roof damage to the south 

portion of the building. Note 

deck supported by steel 

joist (Joplin, MO).

Figure 5-37: 

View of the south half of 

the building looking north 

showing roof damage. Note 

the missing roof membrane 

(Joplin, MO).

Interior Columns

The interior columns were steel HSS (tube) sections. The MAT observed several instances where the 

columns were leaning at a severe angle, but were still attached to the foundation, indicating good 

anchorages that survived large deformations. Figure 5-40 shows a column that is bent completely 

over, but is still attached to the foundation. Figure 5-41 shows the roof structure that remained 

standing in the south portion of the building.
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OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-39: Joist girder rotated at the column; the 

bottom chord was not attached to the stabilizer 

plate (shown by red arrow). The joists were attached 

with welds to the joist girder top chord. This weld 

connection failed in the location shown (yellow arrow) 

(Joplin, MO).

Figure 5-38: Typical connection of two steel joists to joist 

girder. While the joist seat from one joist remains (red 

arrow), the weld failed at the other joist seat connection 

(blue arrow) (Joplin, MO).

Figure 5-40: 

Collapsed column with hooked anchor 

bolts remains attached to the foundation 

at the base (Joplin, MO)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-33

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-42: 

Reinforcing steel in Walmart 

foundation (Joplin, MO)

Figure 5-41: 

Roof structure remaining in 

south half of Walmart. The 

red arrow shows the location 

of a column embedded in the 

wall (Joplin, MO).

Exterior Walls

The exterior walls of the Walmart were reinforced CMU. In the northwest portion of the building 

the walls performed adequately (Figure 5-41, upper right side). The walls on the south half of the 

building and northeast half of the building collapsed. The connections at the roof failed and caused 

the walls to behave as a tall cantilever wall which caused the bending stresses in the wall and the 

shear and moment stresses at the base of the wall to exceed the material stress capacity.

The connection at the base of the wall typically consists of reinforcing steel embedded into the 

foundation and then extended into the CMU cells. The cells are then grouted, locking the 

reinforcing in place and allowing it to transfer both uplift and lateral loads. Figure 5-42 shows 

reinforcing cast into the foundations.
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OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

The roof-to-wall connection for a CMU wall system is similar to the connections for a precast tilt-up 

wall system. The connections consist of an embedded steel plate connected to the roof members. 

Where the steel joists are perpendicular to the wall there are pockets or a ledger angle where the 

joists are connected. The walls that are parallel to the joists are connected to the roof diaphragm 

with a deck support angle attached to the panel with bolts or weld plates and the deck is attached 

to the angle. There are more substantial connections at the joist girders. An additional connection 

also occurs where the joist bridging attaches to the wall, which is provided by the steel joist supplier. 

This connection is often neglected as the typical bridging member sizes are small or are poorly 

connected to the joists and girders reducing the effectiveness of the roof in resisting load reversals 

and uplift. 

The roof connections at Walmart were of this typical design. The joists were connected to the walls 

by welding to embedded steel plates grouted into the CMU. The joist girders were supported on 

columns embedded in the walls (Figure 5-41 red arrow). The Walmart roof joists were connected to 

the joist girders with welds at the joist seat to top chord connections (Figure 5-39). 

In some areas of the store, the roof and walls stayed intact enough that refuge could be found. The 

MAT observed a relatively undamaged space located in the southern end of the Walmart (Figures 

5-43 through 5-45). Although the performance may have been circumstantial, this smaller space 

could have been a candidate for an area of refuge and designed/constructed accordingly.

Figure 5-43: 

Partial collapsed wall in 

southern half of store (note 

deck support angle at top of 

wall); area of limited damage 

shown by red arrow 

(Joplin, MO)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-35

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-45: 

Another view of the area 

shown in Figure 5-44. 

Photograph was taken 

looking east (Joplin, MO). 

Figure 5-44: 

Area of relatively limited 

damage. Photograph was 

taken looking north (Joplin, 

MO). 

MAT EF Rating: Using DI 12 (Large Isolated Retail Building), the MAT selected DOD 6 (“inward or 

outward collapse of exterior walls”) for this building. Using the expected wind speed for DOD 6, the 

MAT derived the tornado rating as EF4 (165–175 mph winds). Therefore, the estimated wind speed 

experienced by the building was well in excess of the 90 mph building code design requirements 

for this location. The MAT EF4 rating for the Walmart is lower than the NWS rating of EF5 for the 

center of the tornado circulation near the building. 

Functional Loss: The Walmart in Joplin is a complete loss. 
5-36 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

5.3 Light Steel Frame Buildings 

The MAT observed damaged buildings that were constructed using light steel frames. This type of 

building construction is described in Section 5.3.1 and its typical failure modes in Section 5.3.2. 

Two buildings of this construction type were assessed by the MAT and are described in detail in 

Sections 5.3.3 and 5.3.4. A lack of wind resistance was observed in the roof purlins and the frame-tofoundation connection in this light steel frame construction.

5.3.1 Description of Construction Method and Load Path

Light steel frame construction is common for commercial buildings. These buildings are typically 

only one or two stories. They range from steel stud framing systems, which are constructed in a 

manner similar to wood framed buildings, to pre-engineered steel rigid frame truss buildings (i.e., 

pre-engineered metal building [PEMB]) that are fabricated offsite and erected on foundation slabs 

and covered with light gauge steel panels. 

Steel stud framing systems: Steel stud framing systems are commonly used for either light steel 

framed buildings or infill walls for other building systems. These walls are typically braced by using 

steel straps or angles attached to the outside of wall systems. The interior of the walls are usually 

gypsum wallboard and the exterior is covered with brick veneer, an exterior insulation and finishing 

systems (EIFS), or textured paneling systems. Steel framing also allows for large openings for glazing 

or doors, making it common for commercial store fronts. Roof systems are either wood or steel truss 

systems and depend on larger steel sections to carry loads down the framing system and into the 

foundation.

Pre-engineered metal buildings: PEMBs consist of a series of pre-engineered trusses, which are 

a set of columns and roof beams fabricated into a continuous steel frame section or “bent”. These 

sections are bolted to a foundation or slab by anchor bolts. The walls and roof are framed with a 

system of channels or z-shaped purlins (for roofs) and girts (for walls) before being covered with 

light gauge steel panels. Due to the extent of prefabrication available, these buildings can be quickly 

constructed for a relatively low cost. The frames resist lateral loading along the column and beam 

lines, but as these loads are applied, significant loads are transferred to the foundations of the 

building. 

5.3.2 Typical Failure Modes Observed by the MAT

Light steel frame buildings have been developed to make this construction type economical to build. 

These structures often experience significant structural damage in high-wind events because there 

is no redundancy in their design and they are best suited where only normal downward vertical 

loads are the primary design loads. Failures observed by the MAT typically occurred either in the 

base plate/anchor bolt system or the anchor bolt pulling out of the foundation

High winds often damage the exterior finish or glazing of light steel frame buildings. Most of the 

exterior finish or glazing failures observed by the MAT in light steel frame buildings were the result 

of unprotected glazing or insufficient attachment of exterior cladding or veneers to the structural 

frame. Once the glazing is breached, the building interior is exposed to wind pressures, which 

subject the lightly built roof system to increased uplift loads. 
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OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

5.3.3 Fitness Center (Tuscaloosa, AL)

Location of Facility in Tornado Path: The MAT inspected a fitness center in Tuscaloosa, AL, which 

was destroyed during the tornado. The location of this building is shown in Figure 5-2. Figure 5-46 

shows the building after the tornado and the tornado damage swath in the vicinity of the building. 

This building was just east of the buildings discussed in Section 5.2.3. The fitness center was located 

on the southern periphery of the centerline of the tornado damage swath. The NWS rated the 

center of the tornado circulation in the vicinity of this building as an EF4.

Facility Description: The footprint of the building that sustained the most damage was roughly 90 

feet by 130 feet. The structural and roof covering system consisted of the following elements:

+ Metal roofing and siding

+ Metal roof purlins

+ Insulation 

+ Secondary metal framing

+ Steel clear-span moment frame system

+ Shallow foundations

Figure 5-46: 

Aerial view of the 

fitness center (red box) 

in relationship to the 

approximate centerline of 

the April 27, 2011 tornado 

damage swath (red line) 

(Tuscaloosa, AL)
5-38 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

General Wind Damage: The southern part of the building was completely destroyed, while some of 

the northern part of the building was left standing (Figure 5-47). The failures observed were due to 

a breach of the building envelope from inflow winds that then resulted in excessive wind pressures 

being exerted on the MWFRS.

Figure 5-47: 

Front (north side) of fitness 

center building 

(Tuscaloosa, AL)

The MWFRS of the north end of this building performed well relative to the buildings in the 

immediate surroundings and exhibited ductility through much of the failure, providing cavities 

in which people could survive. The main column frame anchorages to the foundation performed 

well in the context of extreme overload (Figure 5-48). The column tore free from the base plate 

at the weld leaving the base plate and anchor rods in place. The steel anchor rods and base plates 

were stressed to the point of full yield—characterized by exaggerated deformation—which led to a 

failure of the welds to the columns (Figure 5-49).

MAT EF Rating: Using DI 21 (Metal Building Systems), the MAT selected DOD 7 (“progressive 

collapse of rigid frames”) for this building. Using the expected wind speed for DOD 7, the MAT 

determined the tornado rating as EF3 (140–145 mph winds). Therefore, the estimated wind speed 

experienced by the building was well in excess of the 90 mph building code design requirements for 

this location. 

The MAT EF3 rating for the fitness center is somewhat lower than the NWS rating of EF4 for the 

portion of the tornado track near the building. The nearest NWS survey point was a small retail 

building approximately 1,000 feet west of the fitness center. The fitness center was not in the center 

of the tornado track and accordingly, wind speeds away from the center would result in a lower 

speed at the building.

Functional Loss: Most of the fitness center building in Tuscaloosa was destroyed. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-39

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-48: 

The anchor bolts of this base 

plate connection performed 

well while the weld along 

the base of the steel 

column failed (red arrow) 

(Tuscaloosa, AL)

Figure 5-49: 

Ductile end column at 

southwest corner of building 

(red arrow). The anchor 

bolts remained attached to 

both the foundation and the 

column (Tuscaloosa, AL).

5.3.4 St. Paul’s United Methodist Church (Joplin, MO)

Location of Facility in Tornado Path: The MAT inspected St. Paul’s United Methodist Church 

in Joplin, MO, which was heavily damaged during the tornado. The church was located on the 

periphery of the tornado track; the NWS rated the center of the tornado circulation in the vicinity 

of the church as EF2. Figure 5-1 shows the location of the building relative to the tornado damage 

swath. Figure 5-50 shows a close-up aerial view of the building and its proximity to the tornado 

damage swath.
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OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Facility Description: The footprint of the building that sustained the most damage was roughly 

11,700 square feet with dimensions of 90 feet by 130 feet. The structural and roof covering system 

consisted of the following elements:

+ Metal roof decking

+ Metal roof purlins

+ Insulation 

+ Secondary metal framing

+ Steel clear-span moment frame system

+ Shallow foundations

General Wind Damage: The southern wing of the St. Paul’s United Methodist Church complex was 

heavily damaged to the point of being substantially destroyed. The MWFRS used for the building 

exhibited good performance and was left standing as well as several interior walls (Figure 5-51). 

However, the roof, siding, and end walls were completely removed. The damage to these building 

envelope elements was due to the breaching of the building envelope from tornado winds, which 

Figure 5-50: Aerial view of St. Paul’s United Methodist Church (red box) (Joplin, MO) in relationship to the approximate 

centerline of the May 22, 2011 tornado damage swath (red line) (Joplin, MO)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-41

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

resulted in a failure of these secondary elements relieving the internal wind pressure from the 

MWFRS (Figure 5-52). The primary main column frames and their anchorage to the foundation 

performed very well (Figure 5-53).

Figure 5-51: 

Intact PEMB main frames 

(red arrow) (Joplin, MO)

Figure 5-52: 

Roof system purlins intact 

with metal roof clip released 

(red arrows) (Joplin, MO)
5-42 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

MAT EF Rating: Using DI 21 (Metal Building Systems), the MAT selected DOD 3 (“metal roof or 

wall panels pulled from the building”) for this building. Using the expected wind speed for DOD 3, 

the MAT derived the tornado ranking as EF1 (100–105 mph winds). Therefore, the estimated wind 

speed experienced by the building was in excess of the 90 mph building code design requirements 

for this location. The MAT EF1 rating for the church is lower than the NWS rating of EF2 for the 

center of the tornado circulation near the building.

Functional Loss: The southern wing of the St. Paul’s United Methodist Church complex will need 

to be completely rebuilt. Although large portions of the MWFRS remained intact, the secondary 

elements suffered severe damage. This exposed the interior to major wind damage that will require 

full reconstruction.

5.4 Reinforced Concrete Frame with CMU Infill Walls

The MAT inspected one building constructed using a concrete frame with CMU infill walls. This 

type of building construction is described in Section 5.4.1 and its typical failure modes in Section 

5.4.2. The MAT findings for the building are described in Section 5.4.3. The building was located 

outside of the periphery of the tornado damage swath; the NWS rated the center of the tornado 

circulation in the vicinity of this building as EF4 to EF5. The damage may have been due to the 

building being taller than any of the surroundings and therefore more exposed to the high winds. 

Figure 5-53: 

Secondary framing (light 

gage infill walls) failed 

(yellow arrow) while the 

main frames survived (red 

arrow) (Joplin, MO)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-43

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

5.4.1 Description of Construction Method and Load Path

Reinforced concrete frame buildings are commonly used in multi-story commercial and industrial 

buildings. The building’s primary structural elements are cast-in-place concrete, which creates 

a large heavy structural frame. The structural elements are the floor system, the beams or joists 

for the floors, the columns, and the foundations. This construction typically results in substantial 

redundancy in the structural systems. 

5.4.2 Typical Failure Modes Observed by the MAT

The failures observed by the MAT in reinforced concrete frame buildings were limited to the 

secondary elements and the building envelope. The MWFRS of the buildings remained undamaged 

by the tornado winds. 

5.4.3 Ozark Center for Autism (Joplin, MO)

Location of Facility in Tornado Path: The MAT inspected the Ozark Center for Autism in Joplin, 

MO, which was damaged during the tornado. The building is located just outside the periphery of 

the tornado damage swath; the NWS rated the center of the tornado circulation in the vicinity of 

this facility as EF4 to EF5 (Figure 5-1). Figure 5-54 shows a close-up aerial view of the building after 

the tornado and its relationship to the tornado damage swath.

Facility Description: The building footprint of the Ozark Center for Autism is approximately 450 

feet x 250 feet. The structural and roof covering systems include:

+ Standing seam metal roof 

+ Ballasted roof covering (original system)

+ Poured-in-place concrete roof and floor slabs

+ CMU elevator and stair shafts

+ Poured-in-place concrete columns

+ CMU infill walls

+ Exterior furring and metal wall panels over the CMU

+ Steel roof trusses (east extension)

General Wind Damage: The structural core of the Ozark Center for Autism was not significantly 

damaged; the structural systems on this building performed very well. The building envelope, 

however, was heavily damaged. The primary damage occurred to the roofing materials and glazing 

(Figure 5-55). The metal architectural panel siding on the building failed, as would be expected in 

this type of event.

After the tornado, the damage to the building consisted of:

+ Loss of exterior skin

+ Loss of roof 
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OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

+ Loss of exterior glazing

+ Water damage to the building interior 

+ Loss of exterior building walls at the two-story extension

Building Construction

The Ozark Center is a three-story main building that has a two-story extension on the east side 

(Figure 5-56). Figure 5-57 shows the typical interior layout of the main building with a perimeter 

beam and column system. There are two rows of center columns in the two-story extension. The slab 

is thickened between the rows of center of columns at each level. The remainder of the building is 

cast-in-place concrete. 

Figure 5-54: Aerial view of the Ozark Center for Autism (red circle) in relationship to the approximate centerline of the 

May 22, 2011 tornado damage swath (red line) (Joplin, MO)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-45

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-55: 

East elevation of the Ozark 

Center for Autism showing 

damage to glazing and siding 

(Joplin, MO).

Figure 5-56: East elevation from northeast corner of building. The structural core of the taller building performed well, 

as did the CMU infill. The wing in the nearside of the figure is a two-story extension. Wood wall-framing debris can be 

seen in the foreground (Joplin, MO).
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OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Figure 5-57: 

Two-story extension on east 

side of building shown in 

Figure 5-56; view shows 

typical interior layout 

(Joplin, MO)

Roof System

The roof system on the main building consists of a poured-in-place concrete roof deck that was 

subsequently covered over by adding steel purlins attached to the roof deck at approximately 5 feet 

on center. The original concrete roof deck was undamaged. The MAT observed clips in place that 

would accept new roof material, most likely a metal roof deck system. The connection of the roof 

material to the purlins had failed and the roof material was not observed at the site (Figure 5-58). 

Figure 5-58: 

Roof of the third-story main 

building. The roof overbuild 

purlins are shown with green 

arrows while the roof clips 

that unlatched are shown by 

red arrow (Joplin, MO).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-47

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

The roof framing system at the two-story extension is constructed with engineered steel girders and 

steel joists that span between them. A metal roof deck is connected to the joists (Figure 5-59) and a 

ballasted roof system is placed over that. The same layered roof construction was used on the threestory main building.

A portion of the deck in the northeast corner of the two-story extension failed when the puddle 

weld connections failed, but the core structure remained in place (Figure 5-60).

Figure 5-59: 

Roof section at two-story 

extension showing how the 

metal roof deck diaphragm 

is connected to the joists 

(Joplin, MO)

Figure 5-60: 

View of roof of the two-story 

extension observed from the 

third floor. Note the failed 

decking at the corner (red 

arrow) (Joplin, MO)
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OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Floor System

The floor system is a reinforced poured-in-place concrete slab that spans between the perimeter 

beams and interior columns. It is approximately 61⁄2 inches thick with a dropped section between 

the center columns. The MAT did not observe any damage to the floor system. 

Exterior Walls 

The exterior walls of the main building consisted of a 4-foot-high CMU wall that was framed between 

the concrete columns. The CMU walls did not show signs of distress. The glazing that spanned from 

the top of the CMU walls to the underside of the concrete beam above was destroyed. 

The exterior walls of the two-story extension were wood-framed walls with studs spaced at 

approximately 16 inches on center; these walls were destroyed. Portions of the wood can be seen in 

the foreground of Figure 5-56.

Building Beams and Columns

The building layout is on column lines that are 21 feet x 17 feet. The two center columns are 

approximately 6 to 8 feet apart. The MAT did not observe any damage to the concrete beam-andcolumn structural frame system. 

MAT EF Rating: Using DI 17 (Low-Rise Building), the MAT selected DOD 5 (“uplift of lightweight 

roof structure”) for this Ozark Center. Using the expected wind speed for DOD 5, the MAT derived 

the tornado ranking as EF3 (150-mph winds). Therefore, the estimated wind speed experienced by 

the building was well in excess of the 90 mph building code design requirements for this location. 

The MAT EF3 rating for this building is substantially higher than the NWS rating of EF0 for this 

area. The NWS rated the center of the tornado circulation for this tornado as an EF5, but the Ozark 

center was outside the swath derived by the NWS. It is clear, however, the building incurred damage 

from tornado wind speeds. It is possible that the height of the building contributed to the damage, 

as it is considerably higher than the surrounding structures.

Functional Loss: The Ozark Center will need repairs to non-structural elements, as the main 

structure performed well and remained intact. 

5.5 Summary of Conclusions and Recommendations

Table 5-1 summarizes the conclusions and recommendations for Chapter 5, Observations on Commercial 

and Industrial Building Performance, and provides references for supporting observations. Additional 

commentary on the conclusions and recommendations is presented in Chapters 10 and 11.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-49

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Table 5-1: Summary of Conclusions and Recommendations for Commercial and Industrial Building Performance

Observations

Conclusions

(numbered according 

to Chapter 10) 

Recommendations

(numbered according 

to Chapter 11)

Specific failure states and building survivability 

that could be addressed in the codes are seen 

in:

•	 Home Depot (Section 5.1.3)

•	 Fitness Center (Section 5.3.3)

Conclusion #3

Wind provisions of 

the current codes and 

standards are insufficient 

to manage building 

performance in overload 

events.

Recommendation #4

Include failure states and 

survivability in building 

codes and standards.

Large-footprint commercial structures with 

long-span roofs that would have possibly 

benefited from being Risk Category III under 

ASCE 7-10:

•	 Home Depot (Section 5.1.3)

•	 Walmart (Section 5.2.5)

Conclusion #3

Wind provisions of 

the current codes and 

standards are insufficient 

to manage building 

performance in overload 

events.

Recommendation #5

Change risk category for 

large-footprint commercial 

structures with long-span 

roofs to Risk Category III 

under ASCE 7-10.2

Tornado hazard was not adequately addressed 

in the codes and standards used for 

construction:

•	 Home Depot (Section 5.1.3)

•	 Strip Mall (Section 5.2.3)

•	 Jefferson Metro Care (Section 5.2.4)

•	 Walmart (Section 5.2.5)

•	 Fitness Center (Section 5.3.3)

Conclusion #3

Wind provisions of 

the current codes and 

standards are insufficient 

to manage building 

performance in overload 

events.

Recommendation #6

Improve design approach in 

ASCE 7 and IBC to address 

risk consistently across 

hazards.

Buildings that experienced wind loads that 

exceeded design wind loads:

•	 Home Depot (Section 5.1.3)

•	 Walmart (Section 5.2.5)

•	 Fitness Center (Section 5.3.3)

Conclusion #3

Wind provisions of 

the current codes and 

standards are insufficient 

to manage building 

performance in overload 

events.

Recommendation #7

ASCE 7 should improve 

the commentary on code 

limitations.

Building codes and standards do not have 

clear risk tolerances defined, leading to 

misinformed decisions when seeking shelter 

from a tornado: 

•	 Home Depot (Section 5.1.3)

•	 Walmart (Section 5.2.5)

Conclusion #3

Wind provisions of 

the current codes and 

standards are insufficient 

to manage building 

performance in overload 

events.

Recommendation #8

Clarify risk tolerance in 

ASCE 7 and IBC.

2 A Risk Category is assigned to buildings based on the risk to human life, health, and welfare associated with potential damage or 

failure of the building (per ASCE 7-10). The assigned Risk Category, I through IV, dictates the mean return interval for a design event 

that should be used when calculating the building’s resistance to the events. In ASCE 7-05, Risk Categories were called “Occupancy 

Categories.”
5-50 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Observations

Conclusions

(numbered according 

to Chapter 10) 

Recommendations

(numbered according 

to Chapter 11)

Buildings that could have potentially benefited 

from redundancy of the MWFRS, ductility of 

connections, resilience, alternate load paths, 

design for load reversal, robust perimeter 

element design, continuity of boundary 

elements, good connectivity, and inclusion of 

discrete MWFRS components: 

•	 Home Depot (Section 5.1.3)

•	 Strip Mall (Section 5.2.3)

•	 Jefferson Metro Care (Section 5.2.4)

•	 Walmart (Section 5.2.5)

•	 Fitness Center (Section 5.3.3)

•	 St. Paul’s United Methodist Church 

(Section 5.3.4)

•	 Ozark Center for Autism (Section 5.4.3)

Conclusion #3

Wind provisions of 

the current codes and 

standards are insufficient 

to manage building 

performance in overload 

events.

Recommendation #9

Include best practices for 

wind design in IBC.

Buildings that did not have a best available 

refuge area identified, a FEMA 361 or ICC 

500-compliant safe room or storm shelter:

•	 Home Depot (Section 5.1.3)

•	 Strip Mall (Section 5.2.3)

•	 Jefferson Metro Care (Section 5.2.4)

•	 Walmart (Section 5.2.5)

•	 Fitness Center (Section 5.3.3)

Conclusion #3

Wind provisions of 

the current codes and 

standards are insufficient 

to manage building 

performance in overload 

events.

Recommendation #16

Install a storm shelter or 

safe room or identify best 

available refuge areas in 

large-footprint buildings.

Lack of adequate signage provided to building 

users and occupants regarding building’s 

design capacity:

•	 Home Depot (Section 5.1.3)

•	 Walmart (Section 5.2.5)

Conclusion #10

There was inadequate 

signage in commercial 

buildings. 

There is a lack of adequate 

signage in large commercial 

buildings to give building 

users and occupants a better 

understanding of a building’s 

design capacity.

Recommendation #17

For all public buildings, 

install signage in a 

conspicuous place at 

building entrances. 

According to management personnel 

interviewed by the MAT at a Lowes in 

Tuscaloosa, AL, flip charts helped the 

response of the store operators during the high 

stress and confusion of the tornados event by 

providing emergency protocols. Flip charts 

could have been potentially helpful for:

•	 Home Depot (Section 5.1.3)

•	 Strip Mall (Section 5.2.3)

•	 Jefferson Metro Care (Section 5.2.4)

•	 Walmart (Section 5.2.5)

•	 Fitness Center (Section 5.3.3)

Conclusion #11

Emergency operations flip 

charts can aid in decision 

making.

Recommendation #18

Place decision-making 

check lists or flip charts in 

prominent locations.

Table 5-1: Summary of Conclusions and Recommendations for Commercial and Industrial Building Performance 

(continued)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 5-51

OBSERVATIONS ON COMMERCIAL AND INDUSTRIAL BUILDING PERFORMANCE

Observations

Conclusions

(numbered according 

to Chapter 10) 

Recommendations

(numbered according 

to Chapter 11)

Buildings which used unreinforced masonry as 

primary support:

•	 Strip Mall (Section 5.2.3)

Conclusion #12

URM performed poorly as 

primary support.

Recommendation #19

Do not use URM in primary 

or critical support areas of 

a building.

The MAT noted that the connections between 

primary structural members on many buildings 

were the initial point of failure of the structural 

systems:

•	 Home Depot (Section 5.1.3)

•	 Walmart (Section 5.2.5)

•	 Ozark Center for Autism (Section 5.4.3)

•	 Jefferson Metro Care (Section 5.2.4)

Conclusion #13

Connections between 

primary structural members 

were often the initial point 

of failure.

Recommendation #20

Use screws in deck-to-joist 

connections instead of 

puddle welds.

Buildings that could have potentially benefited 

from enhancements to building connections 

beyond code requirements:

•	 Home Depot (Section 5.1.3)

•	 Walmart (Section 5.2.5)

•	 Ozark Center for Autism (Section 5.4.3)

•	 Jefferson Metro Care (Section 5.2.4)

Conclusion #13

Connections between 

primary structural members 

were often the initial point 

of failure.

Recommendation #21

Include enhancements 

to building connections 

beyond the code 

requirements.

Large-footprint commercial structures with 

long span roofs which progressively collapsed:

•	 Home Depot (Section 5.1.3)

•	 Walmart (Section 5.2.5)

Conclusion #14

Lack of redundant stability 

systems or non-discrete 

structural systems 

contributed to progressive 

collapse.

This type of failure occurred 

in large-footprint commercial 

structures with long-span 

roofs occurred when small 

local failures progressed to 

larger areas of failure.

Recommendations #22, 

#23, and #24

(#22) Incorporate 

redundancy in the MWFRS. 

(#23) Incorporate more 

redundancy in the design of 

large-footprint buildings.

(#24) Use discrete 

structural systems in large, 

long-span buildings.

Table 5-1: Summary of Conclusions and Recommendations for Commercial and Industrial Building Performance 

(concluded)

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-1

6Observations on Critical 

Facility Performance: Schools

The MAT observed a total of 41 critical facilities in the path of 

tornado tracks or track periphery areas across five States. 

Critical facilities include schools, healthcare facilities, police and fire stations, and emergency 

operations centers (EOCs). Critical facilities are vitally important to communities that have been 

struck by tornadoes. Functional schools are needed to provide educational continuity and they 

are often used to provide space for recovery operations. Functional hospitals and other healthcare 

facilities are needed to treat injuries and provide routine on-going care to the community. Functional 

police and fire stations and EOCs are needed to manage their normal mission, along with response 

and recovery operations after an event. 

The tornadoes in April and May of 2011 significantly affected many critical facilities, totally 

destroying some of them and severely interrupting the operations of several others. Some of the 

observed facilities were damaged by winds that were below current design wind speeds. Most of 

the critical facilities observed did not perform any better than commercial buildings and several 

performed poorly. The damage to these buildings resulted in occupant deaths and injuries, and 

put many other occupants at risk of injury. Building damage also placed additional burdens on 
6-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

response and recovery personnel as they endeavored to provide assistance to their communities 

after the event.

Chapters 6 and 7 describe the performance of some of these critical facilities. The facilities that are 

discussed in Chapters 6 and 7 were selected to document lessons learned, both good and bad. Some 

these facilities are representative of various issues, such as common tornado vulnerabilities of older 

buildings. Other facilities are discussed because of their unique attributes. 

In addition to describing facility performance, Chapters 6 and 7 also report on operational issues 

associated with tornado watches and warnings issued by the NWS. Because of different strategies 

that may be implemented for schools versus healthcare, police and fire stations, and EOCs, schools 

are addressed in this chapter and the other facilities are addressed in Chapter 7. See Section 6.2 for 

discussion of operational issues in the respective chapters. 

General Discussion on Critical Facilities

Critical facilities are Category III and IV buildings as defined in the 2009 IBC (Section 1604, General 

Design Requirements, Table 1604.5) and ASCE 7-05 (Section 1.5, Classification of Buildings and Other 

Structures, Table 1-1). Category III and IV buildings include, but are not limited to, hospitals and 

other medical facilities, fire and police stations, primary communications facilities, EOCs, schools, 

shelters, and power stations and other facilities required in an emergency. FEMA considers critical 

facilities as those buildings that are essential for the delivery of vital services or protection of a 

community (FEMA 2007a). 

The 2009 edition of the IBC has only two special wind-related provisions pertaining to Category III 

and IV buildings: 

+ Importance Factor: The Importance Factor for these buildings is 1.15, rather than the 1.0 factor 

that is used for most other types of buildings. Using the 1.15 Importance Factor effectively 

increases the wind design loads by 15 percent.

+ Wind-borne debris loads: For buildings located within wind-borne debris regions (as defined in 

ASCE 7-05) of hurricane-prone regions, exterior glazing is required to be impact resistant. For 

Category III and IV buildings located where the basic wind speed is 130 mph or greater, the 

glazing is required to resist a larger momentum missile load than the glazing on other types of 

buildings. 

This provision is not applicable to the facilities observed by the MAT, because none of the facilities 

were located in a hurricane-prone region.

Critical Facilities Observed by the MAT 

All of the 41 observed critical facilities were located where the basic (design) wind speed prescribed 

in IBC 2009 is 90 mph. Table 6-1 lists the type and total number of critical facilities observed by the 

MAT. The locations of the Tuscaloosa and Joplin critical facilities described in this report are shown 

on Figure 6-1 (April 25–28 tornado event) and Figure 6-2 (May 22, Joplin, MO, tornado event); the 

schools described in this chapter are highlighted. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-3

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Table 6‐1: Number of Critical Facilities Observed by the MAT

Facility Type Alabama Georgia Mississippi Tennessee

Joplin,

Missouri

Total Number 

of Facilities 

Observed by MAT

Total Number of 

Facilities Described 

in MAT Report

Schools 

(Section 6.1) 9 2 1 2 6 20 6

Hospitals/

healthcare 

(Section 7.1 )

3 0 0 0 2 5 4

Police, Fire 

(Section 7.2 ) 10 0 2 0 3 15 4

EOCs 

(Section 7.3 ) 2* 0 0 0 0 2 2

Total 23 2 3 2 11 42 16

* The Cullman County EOC, AL, was visited but was not in the tornado track (see Section 7.3.2).

Figure 6‐1: Location of Tuscaloosa, AL, critical facilities described in Chapters 6 and 7. The EOC (southwestern end of 

tornado track shown, red line) is approximately 4.7 miles from the LaRocca Nursing Home (northeastern end of tornado 

track shown).

SOURCE FOR TORNADO TRACK: HTTP://WWW.SRH.NOAA.GOV/SRH/SSD/MAPPING
6-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

In addition to the 41 critical facilities that were in tornado tracks or track periphery, the MAT visited 

some additional facilities that were outside of the tracks or track periphery. Some of these additional 

critical facilities were not struck by high winds, and thus were not damaged. However, some of these 

additional critical facilities were damaged by thunderstorm winds. None of the observed schools 

located outside of tracks or track periphery are discussed in this report.

6.1 Building Performance

In addition to their traditional role as educational facilities, schools can play an important role in 

providing space for recovery after a tornado. Thus, their loss of use can affect a community’s ability 

to rapidly respond to the needs of disaster victims, as well as hamper resumption of school activities. 

6.1.1 Alberta Elementary School (Tuscaloosa, AL)

Location of Facility in Tornado Path: The location of the Alberta Elementary School is shown in 

Figure 6-1. Figure 6-3 shows an aerial view of the tornado track in the vicinity of the school. The 

NWS rated the center of the tornado circulation in the vicinity of the school as an EF4. According to 

Figure 6‐2: Location of Joplin, MO, critical facilities described in Chapters 6 and 7. It is approximately 4.5 miles 

from the St. John’s Medical Center (western end of tornado track) to the East Joplin Middle School (eastern end of 

tornado track).

SOURCE FOR TORNADO TRACK: HTTP://WWW.CRH.NOAA.GOV/SGF/?N=EVENT_2011MAY22_SUMMARY

Map source: Bing Maps
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-5

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

a representative of the school district, the school was not occupied when the tornado struck because 

the NWS warnings were issued well in advanced of the tornado.

Facility Description: The Alberta Elementary School opened in 2002. The one-story school had 

three classroom wings and a central core area. The central core area included the cafeteria, kitchen, 

media center, multipurpose room, music room, and offices. The wings and core area had 4:12 sloped 

roofs composed of asphalt shingles over plywood decking over wood roof trusses. The exterior walls 

were load bearing. At the wings and portions of the core, the exterior walls were brick veneer over 

steel studs. Other portions of the exterior core walls were brick veneer over reinforced CMU. 

According to the contract drawings, the building was designed in accordance with the 1994 SBC. 

However, the wind loads were based on the 1995 edition of ASCE 7 using a basic wind speed of 90 

mph, Importance Factor of 1.15, and Exposure B.2

The school had severe weather tornado refuge areas identified on floor plans that were posted in 

corridors. The refuge areas for the two surviving wings were located in the central core area (shown 

by the red arrow in Figure 6-4).3

Figure 6‐3: Aerial view of tornado track in vicinity of Alberta Elementary School (yellow circle). The center of the 

damage swath is approximated by the red line1 (Tuscaloosa, AL).

SOURCE: ALL AERIAL PHOTOGRAPHS ARE FROM NOAA IMAGERY (HTTP://NGS.WOC.NOAA.GOV/STORMS ) UNLESS OTHERWISE NOTED

1 The red line in this and all similar figures is intended to represent the center of the damage swath. The track location is approximated 

by the MAT based on post-event aerial photographs. The actual centerline of circulation is offset from the centerline of the damage.

2 The basic wind speed, Importance Factor, and Exposure for this facility are the same in both the 1995 and 2005 editions of ASCE 7.

3 Presumably the tornado refuge area in the wing of the school that was destroyed was also located in the central core area where all 

the buildings converged, but the MAT was unable to confirm this. 
6-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

General Wind Damage: One classroom wing and most of the central core collapsed (Figures 6-4 

to 6-6, 6-9, and 6-10). The tornado refuge areas for the two surviving wings were destroyed (Figure 

6-5). Figure 6-5 shows a portion of the collapsed central core area and the two wings that survived. 

The MAT judged the limited damage at the surviving wings to be due to shielding provided by the 

third wing and core area, rather than increased strength of these two wings.

Figure 6‐5: 

View of the central core area. 

Tornado refuge areas for the 

two surviving wings were 

in the collapsed area (red 

circle). The yellow arrows 

indicate the two surviving 

wings (Tuscaloosa, AL).

Figure 6‐4: 

Area shown in yellow circle 

of Figure 6-3. The classroom 

wings are indicated by “W” 

and the core area by “C.” 

The general location of the 

tornado refuge areas for the 

two surviving wings is shown 

by the red arrow. Yellow 

arrows indicate remnants 

of corridors between the 

core and wings. The blue 

arrows indicate restroom 

remnants. The yellow box 

indicates kitchen remnants 

(Tuscaloosa, AL).

W

W

W

C
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-7

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Several of the interior walls in the core area were reinforced CMU. Most of these walls collapsed. 

At the wall shown in Figure 6-6, the rebar was spaced at 4 feet on center. The rebar that was in the 

collapsed portion had only about 2 inches of embedment into the grouted CMU that is still in place 

and does not significantly strengthen the joint between the base of the wall and the floor or provide 

resistance to toppling. Similar splice laps were noted at exterior walls.

Figure 6-6:

Interior reinforced CMU 

wall in the central core area 

where rebar had deficient 

splice lap. Inset shows a 

close-up of the deficient 

splice lap (Tuscaloosa, AL).

Figure 6-7 shows one of the surviving classroom wings. All of the exterior windows and the glass 

vision panels in the exit doors were broken (there were eight windows along each of the long walls). 

This wing also lost a substantial amount of underlayment and asphalt shingles. The wing to the left 

of the area shown in the photograph lost a significant amount of deck sheathing at the far (south) 

end and several trusses were missing. Figure 6-8 shows the corridor in the surviving wing shown in 

Figure 6-7. A portion of the corridor wall partially collapsed.
6-8 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6-9 shows the view looking down the corridor of the classroom wing that collapsed. The 

remnant shown by the red arrow is a restroom in the core area. The remnant shown by the blue 

arrow is the corridor between the collapsed wing and core. Figure 6-10 shows the reinforced CMU 

restroom remnant in the collapsed wing. The entire restroom area was open to the sky and there was 

a substantial amount of debris within the rooms. Although corridors and restrooms are sometimes 

the best available refuge areas, injury or death may occur in corridors and restrooms that are not 

specifically designed as safe rooms or storm shelters as shown in Figures 6-8 through 6-10 and as 

discussed in Chapter 9.

Figure 6‐7: 

Center classroom wing 

remains standing while the 

wing to the right (red arrow) 

collapsed (Tuscaloosa, AL)

Figure 6‐8: 

Partially collapsed 

corridor wall (red arrow) 

(Tuscaloosa, AL)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-9

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐9: 

Looking down the corridor 

of the collapsed classroom 

wing; red arrow indicates 

a bathroom in the core 

remnant and yellow 

arrow indicates a corridor 

that remained standing 

(Tuscaloosa, AL)

Figure 6‐10: The reinforced CMU walls around the restroom were left standing, but the rooms were littered with debris 

(as shown in the inset). The wall with the brick veneer (red arrow) was an exterior wall (Tuscaloosa, AL).

MAT EF Rating: Using DI 15 (Elementary School), the MAT selected DOD 10 (“total destruction 

of a large section of building or entire building”) for the school. Using the expected wind speed 

for DOD 10, the MAT derived the tornado rating as EF4 (166–200 mph) based on damage to this 

building. Hence, the estimated wind speed experienced by the building was substantially above the 

basic wind speed of 90 mph the building was designed for. As shown in Figure 6-3, this building is 

near the center of the damage swath. The MAT EF4 rating for this building correlates with the NWS 

rating of EF4 for the center of the tornado circulation. 
6-10 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

The MAT judged the wind damage at this school to be due to its subjection to wind speeds 

substantially above the design wind speed. 

Functional Loss: The building will need to be reconstructed before school can resume at this 

location. According to the school district’s Web site, the students were temporarily housed at 

another school for the 2011–2012 school year. The goal is to have the new Alberta facility ready for 

occupancy in the fall of 2012. 

6.1.2 University Place Elementary School (Tuscaloosa, AL)

Location of Facility in Tornado Path: The location of the University Place Elementary School is 

shown in Figure 6-1. Figure 6-11 shows a view of the school after the tornado. Figure 6-12 shows 

an aerial view of the tornado track in the vicinity of the school. The NWS rated the center of the 

tornado circulation in the vicinity of the school as an EF4. According to a representative of the 

school district, the school was not occupied when the tornado struck because the NWS warnings 

were issued well in advanced of the tornado.

Figure 6‐11: 

University Place Elementary 

School after the tornado. 

The red arrow shows the 

collapsed second story of 

one of the classroom wings. 

Several broken windows 

were boarded up at the time 

of the MAT visit (blue arrow) 

(Tuscaloosa, AL).

Facility Description: The University Place Elementary School opened in 1997. A gymnasium was 

added in 2008. The original building had two two-story classroom wings, a two-story media center 

and office area, cafeteria, kitchen, and multipurpose room, as shown in Figure 6-13. All areas 

had 3:12 sloped metal roof panels attached to steel roof deck supported by steel roof joists. The 

exterior walls are brick veneer over CMU bearing walls. The bearing walls of the classroom wings 

are unreinforced. The bearing walls of the media center and multipurpose wing are reinforced. 

The joists were welded to a plate that had two headed studs embedded into a single bond beam with 

two #4 horizontal steel reinforcing bars. The second floor assembly was precast, pre-stressed hollowcore slabs with a concrete topping. The slabs rest on the CMU; there is no tie between the slabs and 

CMU. According to the contract drawings, the building was designed in accordance with the 1991 

SBC, using a basic wind speed of 70 mph (fastest-mile).4 For this building, the wind loads derived 

from the 1991 SBC for the roof structure are similar to those derived from the 2005 edition of 

ASCE 7. 

4 A 70 mph fastest-mile equates to about a 90 mph 3-second peak gust.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-11

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐12: Aerial view of the tornado track in the vicinity of the University Place Elementary School (yellow circle). 

The center of the damage swath is approximated by the red line (Tuscaloosa, AL).

Figure 6‐13: 

Close-up of Figure 6-12 

showing classroom wings 

A and B and multipurpose 

wing (cafeteria, kitchen, 

and multipurpose room)5 

(Tuscaloosa, AL)

5 The multipurpose room 

debris was removed before 

the MAT visited this site.

Gym 2008

Media 

center

Classroom

Wing A

Classroom

Wing B

Kitchen Cafeteria

 Multipurpose room
6-12 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

The gymnasium is a pre-engineered metal building. Some of the walls are brick veneer over CMU, 

while other walls are metal panels. According to the contract drawings, the building was designed in 

accordance with the 2003 IBC, using a basic wind speed of 90 mph, Importance Factor of 1.15, and 

Exposure C.

The school did not have a tornado safe room or storm shelter. The first floor corridors in the two 

classroom wings were the designated refuge areas. The corridors ran down the center of each wing. 

Each wing had a pair of standard exit doors with glass vision panels at the end of the corridor.

General Wind Damage: Several exterior windows were broken (Figure 6-11). Most of the exterior 

and interior walls of the second floor of classroom wing A collapsed (Figures 6-11, 6-13, and 6-14). 

About 75 percent of the roof decking of classroom wing B blew off (Figures 6-13 and 6-14) and 

about 25 percent of the roof joists also blew off of this wing. Some of the second floor exterior wall 

of classroom wing B also collapsed (Figure 6-15 and 6-16).

The multipurpose wing was also heavily damaged. At the cafeteria, all of the roof decking and 

several of the roof joists were blown off (Figure 6-17). At the kitchen, much of the roof decking and 

some roof joists were blown off (Figure 6-18). Some brick veneer and exterior CMU also collapsed. 

The multipurpose room was destroyed (Figure 6-18). There were two girders at the multipurpose 

Figure 6‐14: View looking south showing damage of the classroom wings (red arrows) and multipurpose wing (blue 

oval). The yellow arrow indicates damaged walkway canopy (Tuscaloosa, AL).

PHOTOGRAPH COURTESY OF TUSCALOOSA COUNTY SHERIFF’S OFFICE

Gym

Classroom

Wing A

Multipurpose wing

Classroom

Wing B
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-13

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐15: View looking north showing wall and roof structure damage to classroom wing B (red arrow) and damage 

to the multipurpose wing (blue oval) (Tuscaloosa, AL)

PHOTOGRAPH COURTESY OF TUSCALOOSA COUNTY SHERIFF’S OFFICE

Figure 6‐16: 

View of the second floor damage to classroom wing B (red 

arrow in Figure 6-15). The inset shows a joist welded to a 

plate that was anchored to a bond beam where one of the 

headed studs broke off (red arrow). Hollow core slabs are 

shown, indicated by the yellow arrow (Tuscaloosa, AL).

Classroom

Wing B

Multipurpose wing

Hollow 

core 

slabs
6-14 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐17:

View inside the cafeteria 

(Tuscaloosa, AL)

Figure 6‐18: 

View toward the cafeteria 

(yellow arrow) and kitchen 

(red arrow) from within the 

multipurpose room. The 

inset shows a multipurpose 

room girder supported by a 

concrete column that is still 

in place (Tuscaloosa, AL).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-15

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐19: 

Multipurpose room girder. Lack of alignment of the bolt 

holes in the top and bottom plates (see insets) prevented 

installation of the anchor bolts (Tuscaloosa, AL).

room. The girders were supported by concrete columns (Figure 6-18 inset). One remained in place 

(Figure 6-18) and one blew away or collapsed (Figure 6-19). 

The contract drawings indicate that the two multipurpose room girders were to be attached to the 

concrete columns with two 3⁄4-inch diameter anchor bolts. At the failed girder shown in Figure 6-19, 

the girder bearing plate consisted of two plates that were welded together. There were two holes that 

were large enough to accommodate 3⁄4-inch bolts in the bottom plate (Figure 6-19 top left inset). 

However, there was only one slotted hole in the top plate (Figure 6-19 bottom inset). Because of 

inadequate hole alignment, it was not possible for the girder plates to be anchored by 3⁄4-inch bolts. 

Both ends of the girder were similar. Apparently the girder simply rested on top of the concrete 

column. The contract drawings also show a C-shaped plate that was to be anchored to the concrete 

column with headed studs. The bottom chord of the girder was to slip between the top and bottom 

of the C. The girder was not to be attached to the C. The C-shaped plate was not installed at the 

girder chord shown in the Figure 6-18 inset.
6-16 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Several joist connections were observed. Figure 6-20 shows where a joist was welded to the girder 

shown by the yellow ovals on the left photograph of Figure 6-20. The right photograph of Figure 

6-20 shows where a joist was welded to a bearing plate that was anchored to a bond beam. All of the 

observed welds were of poor quality.

Figure 6‐20: The yellow ovals on the left photograph show weld remnants where a joist was attached to the girder. The 

red ovals on the right photograph show weld remnants where a joist was attached to a bearing plate at a bond beam 

(Tuscaloosa, AL).

Several deck welds were observed. Weld quality was variable, even within a few feet along a given 

joist. The weld in the left photograph of Figure 6-21 was quite strong—the decking tore. In the 

right photograph of Figure 6-21, however, the weld burnt through the joist flange and therefore this 

weld provided little attachment. Weld quality variability was also observed by MATs after the 1999 

tornado outbreak (FEMA 342) and several hurricanes.6

Figure 6-22 shows what remains of the exterior end wall of the multipurpose room. A reinforced 

CMU bearing wall was present where the rebar extends through the slab. In this area, the rebar 

extends 51⁄2 to 7 inches out of the slab; hence, it had deficient splice overlap with the rebar in the 

CMU. The contract drawings specified a 1-foot 10-inch-overlap for vertical splices.

The gymnasium (Figure 6-14) experienced only slight damage. There was some gutter damage, and 

most of the canopy walkway roof blew away (Figure 6-14). The MAT judged the damage to be due 

to the location of the gymnasium with respect to the tornado track, rather than building strength.

6 FEMA P-424, Design Guide for Improving School Safety in Earthquakes, Floods, and High Winds, recommends a screw 

attachment be specified, rather than puddle welds, because screws are more reliable and much less susceptible to workmanship 

problems (2010a).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-17

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐21: Red arrow shows a strong weld attaching a piece of decking to the joist (the dark area shown by the 

yellow arrow is a shadow). The photo on the right shows a weak deck attachment where the weld burnt through 

the joist (Tuscaloosa, AL).

Figure 6‐22: 

Rebar extending out of the 

slab at the multipurpose 

room end wall 

(Tuscaloosa, AL)
6-18 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

MAT EF Rating: Using DI 16 (Junior or Senior High School),7 the MAT selected DOD 10 (“most 

interior walls of top floor collapsed”) for the school. Considering the observed workmanship issues, 

the MAT assessed the wind speed as between the expected and lower-bound wind speeds for DOD 

10. Hence, the MAT derived the tornado rating as EF3 (136–165 mph) based on damage to this 

building. Therefore, the estimated wind speed experienced by the building was substantially above 

the basic wind speed of 90 mph the building was designed for. 

As shown in Figure 6-12, this building is near the center of the damage swath. The NWS rated the 

center of the tornado circulation in the vicinity of the school as an EF4, which is above the MAT EF3 

rating of the school. Because the school is on the left side of the center of the circulation, the wind 

speed at the school should be less than the wind speed at the center of circulation.8

The MAT judged the wind damage at this school to be due to its subjection to wind speeds 

substantially above the design wind speed. Poor workmanship issues also contributed to the building 

damage.

Functional Loss: The school will need to be reconstructed before school can resume at this 

location. According to the school district’s Web site, the students are temporarily housed at a former 

elementary school for the 2011–2012 school year.

6.1.3 Ringgold High School and Ringgold Middle School (Ringgold, GA)

Location of Facilities in Tornado Path: The Ringgold Middle and High Schools are near one 

another (Figure 6-23). Both schools were damaged during the April 2011 tornado outbreak. The 

NWS EF contour ratings (see Section 1.1.3 for additional information) in the vicinity of the schools 

are shown on Figure 6-23. The area was under 

tornado watches for most of the day the 

tornado struck. According to a representative 

of the school district, students and staff were 

dismissed early due to the weather forecast. 

The schools were not occupied when the 

tornado struck. 

6.1.3.1 Ringgold High School

Facility Description: The high school was constructed in 1973. Eleven classrooms were added in 

1977 and nine were added in 1985. A second (auxiliary) gymnasium, administrative offices, and an 

art center were added in 2008. Figure 6-24 is a view of the high school prior to the tornado.

The NWS developed EF rating contours for the 

Ringgold and Joplin tornadoes. EF contours 

were not developed by NWS for the Tuscaloosa 

tornado.

7 Because this school has two stories, the Junior or Senior High School DI was judged to be more appropriate than the elementary 

school DI.

8 The wind speed is higher on the right side of the center of circulation than it is on the left side.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-19

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐23:9 View of the Ringgold High School (yellow box) and Ringgold Middle School (red box) prior to the April 2011 

tornado. The art center and cheerleading/wrestling facility are shown by the green and blue arrows. NWS EF contour 

ratings are also shown (Ringgold, GA).

SOURCE: © GOOGLE EARTH

9 NOAA did not take post-tornado aerial photographs of this location, so a pre-storm image is used here for reference.

EF2

EF1

EF0

EF0

EF1
6-20 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

One of the classroom wings has two stories and another has one story. Most of the roof assemblies 

were fully adhered single-ply roof membrane systems over steel roof decks supported by steel roof 

trusses; there were also some aggregate ballasted single-ply membranes. The exterior walls of the 

school are primarily brick veneer over CMU, but some portions are exterior insulation and finishing 

systems (EIFS) over metal studs over CMU. There were four portable classrooms on the campus. 

Two classrooms on the west side of the high school were not damaged (Figure 6-25). Although they 

were not damaged, the MAT observed them to gather data on their condition and potential for 

becoming sources of wind-borne debris, and to assist in determining the EF rating. The portable 

classrooms were supported by stacked CMU and anchored down using an embedded anchor and 

galvanized metal strapping typical of manufactured homes. The MAT noted some of these anchors 

were in poor condition, some were loose, and one was completely corroded through (Figure 6-25 

inset). Due to the condition of the foundation and anchorage straps, it is assumed that wind speeds 

around the portable classrooms were minimal since no shifting on the foundations appeared to 

have occurred.

The other two portable classrooms were double-wide units. They were also located on the west side 

of the high school. One classroom moved off its foundation and had extensive roof and wind-borne 

debris damage. The other classroom also had extensive roof and wind-borne debris damage. Both 

of these classrooms were demolished prior to the MAT site visit.

Figure 6‐24: 

Close-up view of Figure 6-23 

showing the Ringgold High 

School prior to the April 2011 

tornado (Ringgold, GA)

SOURCE: © GOOGLE EARTH

Auxilary 

gym 

(2008)

Aggregate 

ballasted 

single-ply

roof 

membrane

Administrative 

offices (2008)

Portable 

classroom 

(see also 

Figure 6-25)

Original 

gym
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-21

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

The school did not have a tornado safe room or storm shelter. However, as part of the emergency 

preparedness plan, tornado refuge areas throughout the building were pre-determined in 

coordination with the fire department, sheriff’s office, the local emergency manager, and school 

system personnel. According to a rehabilitation contractor project manager, the following areas were 

to be used as tornado refuge areas during severe weather events: lower-level corridors, restrooms, 

and the band and chorus rooms. The band and chorus rooms did not have exterior windows. Doors 

along the corridor had glass vision panels. A pair of standard exit doors with glass vision panels and 

tempered glass lites above led from the corridor to the exterior. The MAT was unable to determine 

the amount of reinforcement in the CMU walls. It was also unclear what ceiling/floor system 

separated the refuge areas from the gymnasium above. After the tornado, the refuge areas were 

found to be free from damage and debris. 

General Wind Damage: The tornado struck the south end of the high school (Figure 6-26). The 

most significant damage was to the gymnasium roofs (Figures 6-27 and 6-28), which resulted in 

water infiltration that caused damage to the wood floor. The wood gymnasium floor was then 

demolished (Figure 6-29). 

Figure 6‐25: 

View of one of the portable 

classrooms. The red arrows 

indicate anchor straps. The 

strap shown in the inset had 

corroded through (yellow 

arrow) (Ringgold, GA).
6-22 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐26: 

View of the 2008 

auxiliary gymnasium 

(red arrow) and 

original gymnasium 

(yellow arrow on 

right). The yellow arrow on 

left indicates the location 

of a ballasted roof system. 

Most of the windows within 

the red oval were broken. 

The black band (included in 

the red box) is where EIFS 

blew off. The insets show 

the classroom wings that 

are beyond the gymnasium 

(left inset) and first floor 

glazing damage (right inset) 

(Ringgold, GA).

Figure 6‐27: 

View of the two 

gymnasium roofs. The red 

arrow shows the 2008 

auxiliary gymnasium (see 

also Figures 6-26 and 

6-28). The EPDM (black) 

membrane is over the 

original gymnasium. Note 

the displaced rooftop 

equipment. The red box 

shows a portion of the 

middle school beyond. The 

inset shows wind-borne 

debris damage to the 

EPDM roof (Ringgold, GA).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-23

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

The roof of the original gymnasium shown in Figure 6-27 had a fully adhered ethylene propylene 

diene monomer (EPDM) membrane over wood fiberboard over an aggregate surface built-up roof. 

The primary failure mode was EPDM lifting and peeling. However, as shown by the inset at Figure 

6-27, areas of the membrane were punctured by wind-borne debris. The old built-up roof acted as 

a secondary membrane and likely prevented little if any water from leaking into the gymnasium. 

However, rain entered the gymnasium where the rooftop equipment shown in Figure 6-27 was 

blown off the curb. Gas lines were broken at the displaced rooftop equipment shown in Figure 6-27. 

Damage to the EIFS was noted (Figure 6-26); in some areas the metal studs blew away, while in 

other areas the EIFS’s gypsum board substrate blew away. There were also several broken windows.

The roof of the 2008 auxiliary gymnasium had a fully adhered single-ply membrane over 

polyisocyanurate insulation over an acoustical steel deck (Figure 6-28). The primary failure mode 

was membrane lifting and peeling. As shown in the inset at Figure 6-28, some of the decking lifted.

A lower roof adjacent to the 2008 auxiliary gymnasium (see Figures 6-24 and 6-26 for location) 

had an aggregate ballasted EPDM roof system (Figure 6-30). The winds were such that most of 

the aggregate on this roof was not scoured. However, the windows shown in the Figure 6-30 inset 

were likely broken by the roof aggregate. An adjacent roof had a fully adhered single-ply membrane 

over polyisocyanurate insulation over steel deck. This roof membrane blew away (oval area at 

Figure 6-30).

In addition to the above damage, the 2008 art center (shown in Figures 6-23 and 6-31) and the 

cheerleading/wrestling facility (shown in Figures 6-24 and 6-32) were damaged.

Figure 6‐28: 

View of the roof of the 

2008 auxiliary gymnasium 

(see also red arrow in 

Figure 6-27); inset shows 

lifted decking (red circle) 

(Ringgold, GA)
6-24 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐30: 

View of the aggregate 

ballasted roof. The fully 

adhered roof membrane 

blew away; inset below (red 

box)shows broken windows 

(Ringgold, GA).

Figure 6‐29: 

The loss of the roof covering 

shown in Figure 6-28 led 

to water intrusion that 

damaged the floor below. 

The damaged floor needed 

to be removed and replaced 

(Ringgold, GA).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-25

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

MAT EF Rating: Using DI 16 (Junior or Senior High School), the MAT selected DOD 6 (“damage 

to or loss of wall cladding”) for the school. Using the expected wind speed for DOD 6, the MAT 

derived the tornado rating as EF1 (86–110 mph) based on damage to this building. Hence, the 

estimated wind speed experienced by the building was not substantially above the current basic 

wind speed of 90 mph. 

As shown in Figure 6-23, the NWS derived the rating as EF1 at the southern end of the high school, 

which correlates with the MAT EF1 rating for this building.

Some of the wind damage at this school was due to damage from wind-borne debris. The MAT 

judged other building damage to be due to inadequate wind resistance.

Functional Loss: According to a representative of the school district, the high school was repaired 

in time for the start of the 2011–2012 school year. A replacement cheerleading/wrestling field 

house was constructed and ready for occupancy in November. A replacement art center will be 

incorporated into a pending theater project that was in the planning stage prior to the tornado.

Figure 6‐31: 

The roof covering was blown 

off of the 2008 art center. 

The metal wall covering and 

insulation was also blown off 

the CMU. The art center was 

subsequently demolished 

(Ringgold, GA).

Figure 6‐32: 

At the wrestling facility, 

most of the metal roof 

panels were blown off, much 

of the steel framing was 

damaged, and a portion of 

the unreinforced CMU wall 

collapsed. This facility was 

subsequently demolished 

(Ringgold, GA).
6-26 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

6.1.3.2 Ringgold Middle School

Facility Description: The middle school was constructed in 1955. Nine classrooms were added in 

1978 and four were added in 1985. A second (auxiliary) gymnasium was added in 2008. Figure 6-33 

is a view of the middle school prior to the tornado.

Figure 6‐33: 

View of the Ringgold Middle 

School prior to the April 2011 

tornado (Ringgold, GA)

SOURCE: © GOOGLE EARTH

Original 

gym

Auxilary 

gym 

(2008)

One of the classroom wings has two stories, but most of the school is one story. Some of the roof 

decks are poured gypsum, others are cementitious wood-fiber, and the 2008 auxiliary gymnasium 

has a metal deck. The facility has a structural steel frame. Most of the exterior walls are brick veneer 

over CMU. Some walls are EIFS over metal studs. 

There were six portable classrooms on the campus (one of which was a double-wide unit). The 

double-wide unit and two of the single-wide units were destroyed. The other three units had 

extensive roof and wind-borne debris damage. These three classrooms were demolished prior to the 

MAT’s site visit.

The school did not have a tornado safe room or storm shelter. However, as part of the emergency 

preparedness plan, tornado refuge areas throughout the building were pre-determined in 

coordination with the fire department, sheriff’s office, the local emergency manager, and school 

system personnel. After the tornado, the refuge areas were found to be free from damage and 

debris. 

General Wind Damage: The damage experienced by the middle school illustrates the common 

wind vulnerabilities in schools of this era. The roof membrane blew off much of the building. Most 

of the gypsum roof deck blew off the portion of the classroom wing shown by the blue oval in Figure 

6-34. Other damage is shown in Figures 6-35 to 6-38.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-27

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐34: View of the Ringgold Middle School (the inset shows the left portion of the school). The 2008 auxiliary 

gymnasium (yellow arrow) and original gymnasium (red arrow) are shown. Most of the roof deck was lost in the area 

shown by the blue oval. The yellow box indicates an area where walls and glazing were damaged (Ringgold, GA).

Figure 6‐35: 

This wing lost most of its 

roof decking, and a portion 

of the brick veneer and 

unreinforced CMU collapsed 

(Ringgold, GA)

The cementitious wood-fiber deck panels blew off the original gymnasium along one perimeter, 

resulting in standing water on the gymnasium floor (Figure 6-37). Cementitious wood-fiber panels 

also blew off over some of the classrooms and overhang shown in Figure 6-38. Figure 6-38 also 

shows a wall that blew in (the damaged wall is shown in the blue oval of Figure 6-34). The wall was 

EIFS over metal studs. The stud track was attached to a concrete sill with powder-driven fasteners 

spaced at 231⁄2 inches and 261⁄2 inches. The fasteners only had about inch of embedment. The two 

windows adjacent to the wall opening and the window at the right of Figure 6-38 were broken, as 

were several other windows at this wing.

MAT EF Rating: Using DI 16 (Junior or Senior High School), the MAT selected DOD 6 (“damage 

to or loss of wall cladding”) for the school. Considering the building age and observed damage, the 

MAT assessed the wind speed as between the expected and lower-bound wind speeds for DOD 6. 

Hence, the MAT derived the tornado rating as EF1 (86–110 mph) based on damage to this building. 

Therefore, the estimated wind speed experienced by the building was not substantially above the 

current basic wind speed of 90 mph. 

As shown in Figure 6-23, the NWS derived the rating as EF2 at the middle school, which is different 

from the MAT EF1 rating for this school.
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐36: 

View from within a 

classroom. The yellow 

arrow shows the area of the 

collapsed wall that is shown 

in Figure 6-35. In this area, 

the deck bulb-tees also blew 

off. The inset shows an area 

of this wing where some 

form-board (yellow arrow), 

a bulb-tee (blue arrow), and 

the gypsum deck (red arrow) 

were still in place 

(Ringgold, GA).

Figure 6‐37: Deck panels blew off the original gymnasium. The 

inset shows the resulting standing water on the wood floor 

(Ringgold, GA).

INSET PHOTOGRAPH COURTESY OF CATOOSA COUNTY PUBLIC SCHOOLS
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-29

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Some of the wind damage at this school was due to damage from wind-borne debris. The MAT 

judged other building damage to be due to inadequate wind resistance, which is reflective of the 

codes, standards, and design practices in the era when the majority of this school was constructed. 

Functional Loss: According to a representative of the school district, the sixth and seventh grade 

students were able to return to their classrooms at the start of the 2011–2012 school year. However, 

the eighth grade students temporarily attended the high school while repairs were made to their 

classrooms. Two single-wide and one double-wide portable classrooms were brought to the site for 

the chorus and band. 

6.1.4 Joplin East Middle School (Joplin, MO)

Location of Facility in Tornado Path: The location of the Joplin East Middle School is shown in 

Figure 6-2. Figure 6-39 shows an aerial view of the tornado track in the vicinity of the school as well 

as the NWS EF contour ratings in the vicinity of the school. The school was not occupied when the 

tornado struck (the tornado occurred on Sunday evening).

Facility Description: The Joplin East Middle School opened in 2009. The one-story school is 

over 130,000 square feet, with approximately 45 classrooms, an auditorium, four computer labs, 

a library, and a gymnasium (Figure 6-40). The auditorium and gymnasium had a single-ply roof 

membrane over polyisocyanurate insulation over steel roof deck supported by a steel roof structure. 

The auditorium and classroom wing (primarily one story) had brick veneer over reinforced CMU 

bearing walls. The gymnasium had brick veneer over insulation installed over precast concrete walls.

The middle school had a Tornado Evacuation Plan with six interior rooms designated as areas of 

“Tornado Safe Shelter” (Figure 6-41). Although these designated areas may have been the planned 

tornado refuge areas, they did not possess the wind pressure and wind-borne debris resistance 

specified in FEMA 361 (2008a) or ICC 500 (2008). Hence, they were not safe rooms or storm 

shelters (refer to Chapter 9 for additional discussion of safe rooms capable of providing life-safety 

protection for occupants).

Figure 6‐38: 

EIFS wall failure, glazing 

damage, and roof deck blowoff (Ringgold, GA)
6-30 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐40: 

Close-up of Figure 6-39. 

Major areas of blow-off of 

the roof membrane and roof 

deck are shown by the blue 

and yellow arrows 

(Joplin, MO).

Figure 6‐39: Aerial view of the tornado track in the vicinity of the Joplin East Middle School (yellow circle). The center 

of the damage swath is approximated by the red line. NWS EF contour ratings are also shown (Joplin, MO).

EF2

EF2

EF3

EF4

EF3

Auditorium

Gymnasium
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-31

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐41: Interior rooms designated as “shelters” in the middle school’s Tornado Evacuation Plan. The inset shows 

the “shelter” signage (Joplin, MO).
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

General Wind Damage: Figure 6-40 shows an aerial view of the damage at the middle school. 

The most severe damage occurred on the southern end of the school, where the auditorium and 

gymnasium were located, while the northern end suffered less damage. The auditorium roof and 

the two exterior walls collapsed (Figure 6-42). At the gymnasium, two roof trusses and an exterior 

wall collapsed inward upon loss of lateral bracing (Figures 6-43 to 6-46).

Figure 6‐42: 

View of the collapsed 

auditorium roof and both 

exterior walls (Joplin, MO)

Figure 6‐43: 

View of the gymnasium. 

The red box in the inset 

shows where the truss 

was attached to the wall. 

The yellow circle indicates 

the end of the collapsed 

truss shown in Figure 6-45 

(Joplin, MO).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-33

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐45: 

Roof truss and wall debris 

on the gymnasium floor 

(Joplin, MO)

Figure 6‐44: 

View of the end of the 

collapsed truss (yellow 

circle) shown in Figure 6-43 

(Joplin, MO)
6-34 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

The remainder of the middle school received damage from wind-borne debris, including glazing 

damage, as well as water damage due to damaged roof covering, decking, and rooftop equipment 

(Figures 6-40 and 6-47). The rain intrusion caused damage to the HVAC equipment, ceiling boards, 

floor coverings, and furnishings.

Figure 6‐46: 

Brick veneer/insulation/

precast concrete wall on the 

gymnasium floor (Joplin, MO)

Figure 6‐47: 

View of rain infiltration 

damage in a school corridor 

(Joplin, MO)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-35

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

MAT EF Rating: Using DI 16 (Junior or Senior High School), the MAT selected DOD 7 (“collapse 

of tall masonry walls at gym, cafeteria, or auditorium”) for the middle school. Considering the 

building age and observed damage, the MAT assessed the wind speed as between the expected and 

upper-bound wind speeds for DOD 7. Hence, the MAT derived the tornado rating as EF2 (111–135 

mph) based on damage to this building.10 Therefore, the estimated wind speed experienced by the 

building was above the basic wind speed of 90 mph the building was designed for. 

As shown in Figure 6-39, the NWS derived the rating as EF3 at the middle school, which is different 

from the MAT EF2 rating for this school. 

The MAT judged the wind damage at this school to be due to its subjection to wind speeds 

substantially above the design wind speed and to wind-borne debris.

Functional Loss: According to the repair contractor that was on-site during the MAT’s visit, power 

was restored within 10 days to most of the northern/classroom portion of the building and crews 

began repairs in an effort to have the facility functional by the start of the 2011–2012 school year. 

However, repairs were not completed in time due to the extensive damage. According to the school 

district’s Web site, an industrial park warehouse was converted into a temporary school for the start 

of the 2011–2012 school year. 

6.1.5 Joplin High School (Joplin, MO)

Location of Facility in Tornado Path: The location of the Joplin High School is shown in Figure 6-2. 

Figure 6-48 shows an aerial view of the tornado track in the vicinity of the school, as well as the NWS 

EF contour ratings in the vicinity of the school. The school was not occupied when the tornado 

struck since the tornado occurred on Sunday evening.

Facility Description: Joplin High School opened in 1968 and extensively renovated in 2003, including 

the addition of the library/media center. The school had one- and two-story classroom wings, two 

gymnasiums, a performance auditorium, cafeteria, library/media center, and a 1,300-square-foot 

television station (Figure 6-49). The north classroom wing contained a basement classroom section 

whose corridor was relatively undamaged during the tornado.

The high school had several construction systems:

+ The north classroom wing had a built-up membrane roof system over lightweight insulating 

concrete over metal decking. The exterior wall consisted of brick veneer over unreinforced 

masonry infill walls. The exterior masonry extended approximately 4 feet above the floor. There 

was EIFS over metal studs between the masonry and floor or roof above. 

+ An addition to the north classroom wing had a membrane roof system over steel roof deck 

supported by steel joists. Exterior walls were brick veneer over reinforced CMU.

10 A team deployed by ASCE observed both the Joplin Middle School and High School (Prevatt et al. 2011a). This team performed a 

failure analysis by calculating estimated loads and resistance to determine EF ratings. The MAT’s approach used the DI/DOD EF 

rating system. It should be understood that both methodologies involve some uncertainties, and therefore ratings of wind speed 

can vary.
6-36 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐48: Aerial view of the track in the vicinity of the Joplin High School (yellow circle). The center of the damage 

swath is approximated by the red line. NWS EF contour ratings are also shown (Joplin, MO).

+ The library/media center had a membrane roof system over steel deck supported by preengineered bowstring trusses supported by steel columns. End walls were CMU bearing walls. 

+ The one-story classroom wing along the west side of the courtyard had a membrane roof system 

over steel deck supported by steel joists. The exterior walls were brick veneer over reinforced 

CMU bearing walls. The primary gymnasium had a built-up roof system over steel deck over 

steel joists supported by girders spanning east to west. The girders were supported on steel 

columns that were supported on concrete pilasters. The roof at the west wall was supported 

by steel columns at approximately 15 feet on center. There was brick veneer over unreinforced 

CMU between the columns. 

+ The second gymnasium had a membrane roof system over steel deck over steel joists that 

spanned between joist girders. The exterior load-bearing walls were brick veneer over reinforced 

CMU. 

+ The auditorium had a membrane roof system over steel deck over steel joists supported by a 

structural steel frame system. Infill walls were brick veneer over unreinforced CMU. 

The high school did not have a tornado safe room or storm shelter. The lower level corridors on the 

northwest wing were the designated tornado refuge areas (Figure 6-50). The tornado blew some 

debris such as insulation and other building materials into the corridor, but the overall condition of 

this area of the building was relatively undamaged.

EF4

EF5

EF2

EF3

EF3

EF2

EF4
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-37

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐49: 

Close-up of Joplin High 

School shown on Figure 6-48 

(Joplin, MO)

Library/

media 

center

Primary

gymasium

Second

gymasium

Auditorium

Classroom 

wing west of 

courtyard

North 

classroom 

wing

Courtyard
6-38 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

General Wind Damage. As shown in Figure 6-49, the primary gymnasium collapsed and portions 

of the auditorium collapsed. The long roof spans and unreinforced masonry infill walls contributed 

to the collapses at these areas. In other parts of the building, the exterior wall collapsed, the roof 

covering was damaged, and some glazing was damaged as described below. 

North classroom wing: Extensive exterior wall damage occurred at this wing (Figure 6-51). In 

most locations the connection of the stud tracks to the CMU and floor or roof slab failed. In some 

instances the unreinforced masonry wall also failed. The roof system was damaged but most of the 

roof deck remained in place.

The exterior reinforced masonry wall and roof structure at the second floor corridor at the north 

end of this wing collapsed (Figure 6-52). The wall and roof assembly debris fell into the corridor 

(Figure 11-2). This portion of the building appeared to be an addition. 

Library/media center: A portion of the roof covering was destroyed, which resulted in interior water 

damage. Some exterior glazing was also broken. 

Classroom wing along the west side of courtyard: The east masonry wall collapsed into the courtyard 

(Figure 6-53). The CMU was connected with rebar dowels into the footing; at the top of the wall the 

CMU was connected to a ledger angle that was welded to the roof deck. There was an approximately 

2-foot-tall parapet above the ledger angle. The majority of the angle stayed connected to the CMU, 

with the welded connections between the deck and angle failing. The angle was installed with 

expansion bolts into ungrouted cells. There was no connection between the exterior walls and the 

interior classroom transverse walls. This discontinuity in the load path contributed to the collapse 

of the exterior wall. 

Figure 6‐50: 

View of a corridor designated 

as tornado refuge area. The 

debris was blown into the 

corridor during the tornado 

(Joplin, MO).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-39

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐51: 

North classroom wing. The 

inset shows a close-up of 

the opposite side of the wing 

(Joplin, MO).

Figure 6‐52: 

Collapse of the exterior brick 

veneer/reinforced CMU wall 

and roof assembly into the 

corridor at the north end of 

the north classroom wing 

(Joplin, MO)
6-40 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Primary gymnasium: The gymnasium shown in Figure 6-54 collapsed. The west wall was 

approximately 37 feet tall—it fell into the gymnasium. The connection between the pilasters and 

columns that supported the roof girders failed. The columns were connected with two 11⁄2-inch 

diameter bolts, each 3 feet long, as shown in the inset at Figure 6-54. Most of the steel roof deck blew 

off. Only a small portion of it remained within the gymnasium space. Collapse of the brick veneer/

unreinforced CMU end wall and blow-off of the roof decking caused the failure. Once the integrity 

of the load path was disrupted, there was a progressive failure.

The second gymnasium, to the south of the primary gymnasium, had most of its metal roof panels 

blown off (Figure 6-55). The gymnasium had a wood floor. 

Auditorium: The steel roof deck and several of the steel joists blew off (Figure 6-56). Portions of the 

25-foot-tall brick veneer/unreinforced CMU wall collapsed (Figures 6-56 and 6-57).

Figure 6‐53: 

Collapsed brick veneer/

reinforced CMU. The red 

arrow indicates where 

the ledger angle is still 

connected to the CMU. 

The yellow arrow indicates 

where the angle’s expansion 

bolts pulled out of the CMU 

(Joplin, MO).
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Figure 6‐54: 

View of the collapsed 

gymnasium. The inset shows 

the base plate (red arrow) 

and an anchor bolt (yellow 

arrow) that connected the 

girder support column to the 

pilaster (Joplin, MO).

Figure 6‐55: 

Interior view of the second 

gymnasium (Joplin, MO)
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Figure 6‐57: 

South wall of the 

auditorium, showing 

collapse of the masonry 

infill wall (Joplin, MO)

Figure 6‐56: 

North wall of the auditorium 

(Joplin, MO)
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

MAT EF Rating: Using DI 16 (Junior or Senior High School), the MAT selected DOD 11 (“complete 

destruction of all or a large section of building) for the high school. Considering the building age 

and the observed damage, the MAT assessed the wind speed to be the lower-bound wind speed for 

DOD 11.11 Hence, the MAT derived the tornado rating as EF3 (136–165 mph) based on damage to 

this building.12 Therefore, the estimated wind speed experienced by the high school was substantially 

above the basic wind speed of 90 mph.

As shown in Figure 6-48, NWS derived the rating as EF4 at the southern end of the high school, 

which is different from the MAT EF3 rating for this school. 

The MAT judged the wind damage at this school to be due to its subjection to wind speeds 

substantially above the design wind speed and to wind-borne debris.

Functional Loss: According to a representative of the school district, school resumed in August 

2011 in a temporary facility. The existing high school will be demolished and replaced with a new 

building. 

6.2 Operational Issues

On March 1, 2007 at 1:12 p.m., a tornado struck a school in Enterprise, AL, resulting in the deaths 

of eight students (FEMA 2008a). During the tornado, students had sought refuge in hallways, away 

from windows, an area that is commonly used as a tornado refuge area in schools. In this case, the 

refuge area sought out by students and teachers in the Enterprise, AL, school was vulnerable to 

collapse. Following this tornado event and the school tragedy, the NWS published the results of 

their post-tornado investigation, in which it was determined that school officials in Enterprise had 

made appropriate safety decisions based on the information available. The report notes that due to 

multiple severe weather warnings throughout that day, there was no safe period of time in which 

they could have enacted an early dismissal. In their recommendations, the NWS stated that the 

benefits of using hardened safe rooms should be promoted, especially in non-residential buildings 

where many people gather, such as schools (NOAA 2007b). 

In the violent tornadoes of April and May 2011, several schools were directly impacted. Fortunately, 

none of the schools were occupied at the time the tornadoes struck. The 2007 incident in Enterprise, 

AL, and the several near misses in the spring of 2011 brought to the forefront the importance of 

identifying a decision-making process for school administrators in the event of a tornado warning. 

To better understand current school decision-making processes in tornado-prone regions, members 

of the MAT held interviews with 10 school districts (Table 6-2) that were impacted in spring of 2011.

11 DOD 11 is for complete destruction of all or a large section of building. As shown on Figure 6-49, much of the southern end of the 

school collapsed. The collapsed areas were the primary gymnasium and auditorium. DOD 7 is “collapse of tall masonry walls at 

gym, cafeteria, or auditorium.” However, in the judgment of the MAT, DOD 11 was appropriate based on proximity of and damage to 

these two areas.

12 A team deployed by ASCE observed both the Joplin Middle School and High School (Prevatt et al. 2011a). This team performed a 

failure analysis by calculating estimated loads and resistance to determine EF ratings. The MAT used the DI/DOD EF rating system. 

It should be understood that both methodologies involve some uncertainties, and therefore ratings of wind speed can vary.
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Table 6-2: List of School Districts Interviewed by the MAT

Location Number of Students

Alabama

Decatur City 8450 

Huntsville City 23,000

Walker County 8,000

Tuscaloosa County 18,000

Marion County 3,524

Cullman City 3,017

Limestone County 9,018

Georgia

Catoosa County 11,009

Mississippi

Monroe County 2,300 

Missouri

Joplin 7,911

The MAT asked representatives from each school district a series of questions related to school 

operational decisions during severe weather. These questions, grouped into three categories, were: 

+ Severe Weather Policy

+ What is the official severe weather policy in your school district?

+ Does the policy vary for different types of severe weather?

+ Who makes the final decision and how long is the process?

+ Is the decision based on hazardous weather probability and does it include input from local 

NWS or TV personnel or others?

+ Are there other factors that influence the decision?

+ Severe Weather Communication and Decision Making

+ Is it the preference of the district to dismiss students early or keep them at school?

+ Does that depend on the type of severe weather?

+ Approximately how many students are in after-school programs?

+ Are there areas of refuge designated in each school?

+ Where are these areas?

The interviews conducted by the MAT revealed that school district response plans for severe weather 

ranged from taking refuge within the school, early dismissal/delayed start, and closing the school. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-45

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Among the school districts interviewed, it was noted that regardless of the type of severe weather, 

the safe transportation of students was a common factor in decision making. Depending on the 

size of the district and the area covered, buses may require 45 minutes to 2 hours to complete their 

routes. Therefore, most of the districts interviewed stated that they prefer to dismiss school early if 

severe thunderstorm and tornado events are expected to occur near the end of the school day, and 

delay the start of school if such events are expected to occur in the morning. 

6.2.1 Severe Weather Policy 

The fundamental decision faced by school district personnel on days when tornadoes are forecasted 

is whether to dismiss students or have them take refuge at school. The following discussion presents 

some of the challenges that schools face and a summary of the findings for the 10 school districts 

interviewed by the MAT. 

The school districts indicated that taking shelter within the school is the preferred option for 

schools that have a FEMA 361-compliant safe room or an ICC 500-compliant storm shelter. Of the 

10 districts interviewed, only two stated they had safe rooms compliant or nearly compliant with 

FEMA 361(2008a) and a third district is in the process of applying for school safe rooms. During 

field assessments, the MAT found safe rooms at two of the 12 schools in one district and two of the 

18 schools in the other. 

The school districts stated that schools without a compliant safe room or storm shelter must follow the 

district’s severe weather policy regarding whether to keep students in the school or dismiss them. 

The following is a summary of the actions taken in the school districts interviewed: 

+ Early dismissal: Seven of the 10 districts interviewed by the MAT stated that their policy is to 

dismiss students early, if possible. Based on the interviews, early dismissal is scheduled to provide 

ample time for busses to transport students to their residences in advance of impending severe 

weather. This approach disperses students over a wide area and decreases liability for school 

districts. Although the probability of a point location such as a school being directly hit by a 

tornado is lower than the probability of numerous homes being struck in an area, there was 

a general perception on the part of the school districts that the chances of a large number 

of student fatalities is lower when students are in their own residences versus gathered in one 

location at school. 

+ Sheltering in schools: When dismissing students early is not possible due to rapidly changing 

weather conditions, students and staff must take cover in portions of buildings that were not 

designed to withstand tornadoes. 

The school districts indicated that 

parents are permitted to pick up their 

children at their discretion in these 

situations. Students remaining in the 

schools are directed to take refuge in 

an area identified by the school. 

The school districts that were interviewed stated that they are reviewing their severe weather policies 

to decide what is best for their given situation. For example, in the Catoosa County, GA, school 

district (Ringgold, GA), students who reside in manufactured homes or poorly constructed homes 

FEMA Recovery Advisory 6, Critical Facilities Located 

in Tornado-Prone Regions: Recommendations for 

Architects and Engineers (Appendix F) provides 

guidance on identifying best available refuge areas.
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

are encouraged to stay at school, while others are either picked up by their parents or dismissed early. 

Another consideration cited by school districts is whether there might be more student fatalities 

when students are sent home than kept at school, as children who are sent home early may have to 

make severe weather safety decisions on their own if their parents are not at home. 

6.2.2 Severe Weather Communication and Decision Making

Alabama School Districts: The communication process used by the Alabama school districts was 

very consistent among those the MAT interviewed (Figure 6-58). The NWS field offices in Huntsville 

and Birmingham coordinate webinars and webcasts that are broadcast to State and County EMA 

personnel. The County EMA personnel then communicate directly with school superintendents, 

school transportation and facilities managers, or school severe weather decision teams. In smaller 

districts, the superintendent often makes cancellation decisions directly, while in larger districts, 

severe weather teams or facility managers make the decision. Sometimes district officials attend 

webinar sessions with County EMA personnel, while in other cases, County EMA personnel report 

to district officials who do not attend the webinar. In both cases, the line of communication starts 

with the NWS, and the urgency of the situation as it pertains to school closing is then relayed by 

State and County EMA, though these agencies do not directly make decisions regarding school 

cancellations. No specific severe weather thresholds or criteria exist for school cancellation; however, 

the districts report considerable pressure to monitor the proceedings of neighboring districts.

Figure 6‐58: 

Flowchart depicting severe 

weather decision making 

process used by school 

districts in Alabama
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 6-47

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

Joplin School District: The Joplin, MO, district uses a severe weather team (SWT) of four individuals, 

each responsible for a school zone of several facilities (Figure 6-59). Each SWT member contacts five 

to six facilities to tell them to take refuge, with an estimated total phone time of 10 minutes. Refuge 

is sought if winds are forecasted to exceed 75 mph or if the facility is under a tornado warning. The 

individual schools monitor weather Web sites and a NOAA weather radio on severe weather days, 

and they work in conjunction with the district’s SWT. The principal of a school can decide to direct 

the students and faculty to designated areas within the school before getting a call from the SWT. 

After the storm has passed, SWT members call facilities to provide the all-clear.

Figure 6‐59: 

Flowchart depicting severe 

weather decision making 

process used by the Joplin, MO, 

School District

6.2.3 Changes for the Future

Out of the 10 districts interviewed, seven are satisfied with their tornado safety plans and do not 

intend to change them as a result of the events of spring 2011. Of these seven districts, one plans to 

increase communication with neighboring districts on days when tornadoes are forecasted. Another 

district is conducting more frequent drills, increasing focus on communication, and evaluating 

refuge areas. 
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: SCHOOLS

In one Alabama district, the 2011 tornadoes resulted in discussions with law enforcement and 

utilities about severe weather information dissemination during and after the event. In this Alabama 

district, power was knocked out by severe weather on the morning of the April 27th, which disrupted 

normal avenues of communication. After the tornado, law enforcement and utilities personnel 

communicated with the schools. Thus, although the district may deem their policy satisfactory for 

actions to take before a tornado, they may need to adopt contingency plans for operating after a 

tornado. 

The remaining three districts—Tuscaloosa County, AL; Monroe County, MS; and Joplin, MO— are 

planning to make changes in the future. According to a representative from Tuscaloosa County, the 

county is seeking hazard mitigation assistance for eight FEMA 361-compliant school safe rooms to 

be incorporated into existing and future building plans, which represents 25 percent of the schools 

in the district. In Smithville, MS (Monroe County School District), there are plans to construct 

a dual-purpose gymnasium and FEMA 361-compliant safe room that can be used by the entire 

district. In Joplin, MO, FEMA 361-compliant safe rooms were constructed at temporary locations 

for the schools that were destroyed by the tornado. At other schools in Joplin, schools have cleared 

basements to use as tornado refuge areas; however, not all students can fit into the basement areas. 

The schools plan to house students in interior rooms during tornado events as a last resort.

6.2.4 Summary

The MAT noted the following based on its interviews with school districts located in the impacted 

areas:

+ School officials give considerable thought to closure decisions and the safety of students. This 

high level of attention results from: 1) the school district’s responsibility for protecting students 

and staff, and 2) the school district’s interest in having a strategy that minimizes liability.

+ In the districts interviewed, there were no uniform severe weather thresholds or criteria for 

making school cancellation decisions. 

+ In the districts interviewed, there were no existing criteria in use for evaluating areas of the 

schools used for refuge during tornadoes. 

6.3 Summary of Conclusions and Recommendations

Table 7-1 provides a summary of the conclusions and recommendations for Chapters 6 and 7, and 

provides section references for supporting observations. Additional commentary on the conclusions 

and recommendations is presented in Chapters 10 and 11. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-1

7Observations on Critical 

Facility Performance: 

Healthcare, First Responder, and 

Emergency Operations Centers

The MAT observed a total of 41 critical facilities in the path of 

tornado tracks or track periphery areas across five States. 

A general discussion of critical facilities pertinent to both chapters is presented in the introduction 

to Chapter 6. This chapter presents information on healthcare facilities, first responder (police and 

fire) facilities, and EOCs. 

All of the 41 observed critical facilities were located where the basic (design) wind speed prescribed 

in IBC 2009 is 90 mph. Table 6-1 lists the type and total number of critical facilities observed by the 

MAT. The locations of the Tuscaloosa and Joplin critical facilities described in this report are shown 

on Figure 7-1 (April 25–28, 2011 tornado event) and Figure 7-2 (May 22, 2011 tornado event); the 

facilities described in this chapter are highlighted. 
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

In addition to the 41 

critical facilities that were 

in tornado tracks or track 

periphery areas, the MAT 

visited some additional 

facilities that were outside 

of the tracks or track 

periphery. Some of these 

additional critical facilities 

were not struck by high 

winds, and thus were not 

damaged. However, some 

of these additional critical 

facilities were damaged by 

thunderstorm winds. 

Sections 7.1.1 and 7.3.2 

describe two facilities 

that were not struck by 

The National Institutes of Standards and Technology (NIST) established a research team to study of the impacts of the disaster in 

Joplin, MO.

The objectives of the NIST technical study include:

•	Determine the characteristics of the wind hazard from the tornado

•	Determine the pattern, location and cause of injuries and fatalities, 

and how these numbers were affected by emergency communications and the public response to those communications

•	Determine the performance of residential, commercial and critical 

(police stations, firehouses, hospitals, etc.) buildings

•	Determine the performance of lifelines (natural gas, electrical distribution, water, communications, etc.) as they relate to maintaining 

building operation 

•	Make recommendations, if warranted, for improvements to building 

codes, standards and practices based on the findings of the study

Figure 7‐1: Location of Tuscaloosa, AL, critical facilities described in Chapters 6 and 7. The EOC (southwestern end of 

tornado damage swath shown, red line) is approximately 4.7 miles from the LaRocca Nursing Home (northeastern end 

of tornado damage swath shown).

SOURCE FOR TORNADO TRACK: HTTP://WWW.SRH.NOAA.GOV/SRH/SSD/MAPPING
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7‐2: Location of Joplin, MO, critical facilities described in Chapters 6 and 7. The St. John’s Medical Center 

(western end of tornado damage swath, red line) is approximately 4.5 miles from the East Joplin Middle School 

(eastern end of tornado damage swath). 

SOURCE FOR TORNADO TRACK: HTTP://WWW.CRH.NOAA.GOV/SGF/?N=EVENT_2011MAY22_SUMMARY

tornadoes. Section 7.1.1 describes a healthcare facility located just outside of a tornado periphery area; 

although not struck by the tornado, the facility response to the near miss provided an opportunity 

to learn some operational issues. Section 7.3.2 describes an EOC that was not in the tornado path. It 

is included because it has design enhancements intended to allow the facility to remain operational 

even if struck by a violent tornado. Except for the critical facilities discussed in Sections 7.1.1 and 

7.3.2, none of the observed critical facilities outside of the tornado tracks or track periphery areas 

are discussed in this report.

7.1 Hospitals and Health Care Facilities

Health care facilities are at the front line of community protection, especially during and after a natural 

disaster event. Their capacity to continue to provide services to existing patients, and to respond to 

the needs of victims following a disaster, depends not only on protecting the integrity of the structure and the building envelope, but on the facilities’ ability to carry out their intended functions with 

little or no interruption. Continued and uninterrupted operation of health care facilities, regardless 

of the nature of the disaster, is one of the most important elements of a community’s continuity of 

operations (COOP) and disaster recovery program. 

Map source: Bing Maps
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Evacuation 

location

Approximate

location of tornado 

debris shown in 

Figure 7-6

Approximate

location of 2x4 

framing tornado 

debriis 

7.1.1 Birmingham Nursing and Rehabilitation Center (Birmingham, AL)

Location of Facility near Tornado Path: The Birmingham Nursing and Rehabilitation Center was 

not damaged. Figure 7-3 shows a view of the nursing home after the tornado. Figure 7-4 shows 

an aerial view of the tornado track. This facility was a few hundred yards from the periphery of a 

tornado that NWS rated as an EF2 at the center of circulation. 

Lessons Learned: Although the facility was not damaged, this event provided useful lessons. The 

MAT was advised by facility personnel that the facility has periodic training for various hazards, and 

in certain events, the facility is required to evacuate all occupants. The staff can evacuate all the 

residents in less than 10 minutes. 

As the tornado approached the facility, the staff believed there was a natural gas leak in the building 

due to an intense gas smell in the air. The smell was thought to be coming from their facility. However, 

the gas smell was actually from lines in nearby neighborhoods that had been broken by the tornado. 

The gas was driven into surrounding areas ahead of the storm. Being unaware of the approaching 

tornado, and believing that they were in imminent danger due to a gas leak in the facility, the 

occupants were moved in a matter of minutes to an outdoor courtyard (Figure 7-3).

Figure 7-3: 

Aerial view of the 

nursing home. The 

red arrow shows 

the courtyard where 

residents were 

evacuated to. The 

blue arrows show 

impact locations of 

wind-borne debris 

(Birmingham, AL). 

SOURCE: © GOOGLE 

EARTH
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-4: Aerial view of the nursing home (yellow circle) in relation to the approximate centerline of the tornado 

damage swath, shown by the red line1 (Birmingham, AL) 

SOURCE: ALL AERIAL PHOTOGRAPHS ARE FROM NOAA IMAGERY (HTTP://NGS.WOC.NOAA.GOV/STORMS) UNLESS OTHERWISE NOTED

1 The red line in this and all similar figures is intended to represent the center of the damage swath. The track location is approximated 

by the MAT based on post-event aerial photographs. The actual centerline of circulation is offset from the centerline of the damage.

Soon after the facility was evacuated, the facility director realized that a tornado was nearby and on 

an apparent intercept path with the nursing home (Figure 7-4). The occupants were moved back into 

the facility corridors, which were designated as the tornado refuge areas for the facility (Figure 7-5).

Figure 7-5: 

View of interior corridors 

that serve as the residents’ 

tornado refuge area 

(Birmingham, AL)

EF contours were 

not developed 

by NWS for sites 

in Birmingham, 

Tuscaloosa, and 

Fultondale, AL, 

and Smithville, 

MS, described in 

Chapter 7.
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Although the facility did not experience tornado damage, wind-borne debris landed near the nursing 

home as shown in Figures 7-3 and 7-6.

Figure 7-6: 

This portion of a roof from 

a nearby house was found 

across the street from the 

nursing home. The roof 

portion is approximately 10 

feet x 20 feet. The damage 

potential for a missile 

of this size is very high 

(Birmingham, AL).

Figure 7-7: 

The emergency generator 

(red arrow) is located near 

many trees that could easily 

have damaged the generator 

and taken it out of service 

(Birmingham, AL)

The nursing home had an emergency generator that was located outdoors (Figure 7-7). Although it 

was not damaged during this event, the generator was susceptible to tree fall and wind-borne debris 

damage.
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

7.1.2 LaRocca Nursing Home (Tuscaloosa, AL) 

Location of Facility in Tornado Path: The location of LaRocca Nursing Home is shown in Figure 7-1. 

Figure 7-8 shows an aerial view of the tornado track in the vicinity of the nursing home. The NWS 

rated the center of the tornado circulation in the vicinity of the nursing home as an EF4. There were 

68 occupants (including residents and staff) in the facility when the tornado struck. No injuries 

occurred at this facility (DeMonia 2011).

Facility Description: This older skilled nursing facility had capacity for 75 residents. A portion of 

the northern wing had two floors. The remainder of the facility was one story. The steep-slope roofs 

had asphalt shingles over 1x6 plank decking supported by rafters. The exterior bearing walls were 

wood studs with 1x6 plank boards, wood fiberboard sheathing, and brick veneer. The facility did not 

have a storm shelter or safe room.

General Wind Damage: Portions of the roof structure were blown off of four areas (Figures 7-9 to 

7-12). Some brick veneer was blown off (Figure 7-10), several windows were broken (Figures 7-11 

and 7-13), tree-fall caused roof structure and wall damage (Figure 7-14), and some exterior walls 

collapsed (Figure 7-15).

The facility had two emergency generators, one on the north side of the facility and the other on the 

southwest. Both generators were outdoors. Had the wall collapsed outward rather than inward, the 

generator shown in Figure 7-15 may have been taken out of service.

Figure 7-8: Aerial view of the track in the vicinity of the nursing home (yellow circle). The center of the damage swath is 

approximated by the red line. Inflow damaged the nursing home and buildings within the blue box (Tuscaloosa, AL). 
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-9: 

Close-up of the nursing home 

shown in Figure 7-8. Red 

arrows indicate where the 

roof structure was blown off 

(Figures 7-10 to 7-12). The 

yellow arrow indicates a tree 

on the roof (Figure 7-14). 

The blue arrow indicates the 

generator shown in Figure 

7-15 (Tuscaloosa, AL).

Figure 7-10: 

Roof structure and brick 

veneer were blown off the 

nursing home 

(Tuscaloosa, AL)

Fig 7-14

Fig 7-10

Fig 7-11

Fig 7-12 Fig 7-15
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-12: 

Interior damage as a result 

of roof structure blow-off 

(Tuscaloosa, AL)

Figure 7-11: Roof structure blown off over resident rooms. The inset 

is a view from within one of the rooms. The window was broken. 

(Tuscaloosa, AL).
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-14: 

Tree-fall damage. Note 

the boarded-up broken 

windows. The inset shows 

a close-up of the tree-fall 

damage (Tuscaloosa, AL).

Figure 7-13: 

View of the two-story 

wing. Most of the 

windows along this 

façade were broken 

(Tuscaloosa, AL).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-11

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

MAT EF Rating: Using DI 5 (Apartments, Condominiums, and Townhouses; Three Stories or Less), 

the MAT selected DOD 4 (“uplift or collapse of roof structure leaving most walls standing”) for this 

facility.2 Considering the age of the facility and observed damage, the MAT assessed the wind speed 

as between the expected and lower-bound wind speeds for DOD 4. Hence, the MAT derived the 

tornado rating as EF2 (111–135 mph) based on damage to this building. Therefore, the estimated 

wind speed experienced by the building was above the current basic wind speed of 90 mph. 

The NWS rated the center of the tornado circulation in the vicinity of the nursing home as EF4, 

which is above the MAT EF2 rating of this building. As shown in Figure 7-8, the nursing home is 

away from the center of circulation. Accordingly, wind speed decay would result in a lower speed at 

the nursing home.

Some of the wind damage at this nursing home was due to wind-borne debris. The MAT judged 

other building damage to be due to wind speeds substantially above the design wind speed, as well 

as inadequate wind resistance, which is reflective of the codes, standards, and design practices in the 

era when this nursing home was constructed. 

Functional Loss: Prior to the late afternoon tornado strike, the residents were moved into corridors 

that were designated for use during tornadoes (DeMonia 2011). There were no injuries during the 

tornado. 

It was not possible to evacuate the residents immediately after the tornado had passed because both 

of the roads from the facility to the street were blocked by several fallen trees. Residents were moved 

to portions of the building that were not badly damaged. It was the following morning before one of 

the roads was cleared and the residents and staff evacuated. 

Figure 7-15: 

Generator at the southwest 

side of the facility (red 

arrow). Note the roof 

structure blow-off and wall 

collapse (Tuscaloosa, AL).

2 There is no DI for nursing homes. The type of construction listed for DI 5 is applicable to this nursing home. 
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7.1.3 Greenbriar Nursing Home (Joplin, MO) 

Location of Facility in Tornado Path: The location of the Greenbriar Nursing Home is shown in 

Figure 7-2). Figure 7-16 shows an aerial view of the track in the vicinity of the nursing home. Figure 

7-17 shows the nursing home before and after the tornado. The NWS EF contour ratings in the 

vicinity of the nursing home are shown on Figure 7-16. According to a representative of the nursing 

home, there were approximately 89 residents and 20 staff in the facility at the time the tornado 

struck.

Facility Description: This skilled nursing facility was built in 1965. It had a maximum occupancy of 

120 residents. The 30,311-square-foot building had one core area and four wings. Figure 7-17 shows 

the nursing home before and after the tornado. The building was constructed with unreinforced 

CMU with brick veneer walls supporting wood roof trusses. 

The facility did not have a storm shelter or safe room. Residents and staff used the central hallway as 

a tornado refuge area.

General Wind Damage: Almost the entire building was destroyed (Figures 7-17 to 7-19). According 

to witnesses, the tornado blew open the exterior doors and imploded the windows, leading to roof 

blow-off and wall collapse. 

Figure 7-16: Aerial view of the track in the vicinity of the nursing home (yellow circle). The center of the damage swath 

is approximated by the red line (Joplin, MO). 

EF1

EF2

EF4

EF5

EF4

EF3

EF3

EF2
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-17:

Close-up of Figure 7-16 showing the damaged nursing 

home. The inset shows the nursing home before the 

tornado struck (Joplin, MO).

INSET SOURCE: © GOOGLE EARTH

Figure 7-18: 

Aerial view of the nursing 

home (red oval) after the 

tornado (Joplin, MO)
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

MAT EF Rating: Using DI 9 (Small Professional Building),3 the MAT selected DOD 9 (“total 

destruction of entire building”) for this facility. Considering the building age and observed damage, 

the MAT assessed the wind speed as between the expected and lower-bound wind speeds for DOD 9. 

Hence, the MAT derived the tornado rating as EF3 (136–165 mph) based on damage to this building. 

Therefore, the estimated wind speed experienced by the building was substantially above the current 

basic wind speed of 90 mph. 

As shown in Figure 7-16, NWS derived the rating as EF5 at the nursing home, which is above the 

MAT EF3 rating of this building. The actual wind speed of the tornado at this site may have been 

higher than an EF3. However, since the expected wind speed for total destruction of a DI 9 facility 

is 157 mph, a determination of a higher wind speed could not be made with a facility of this type 

of construction. To assess whether higher winds may have occurred, a stronger facility (such as the 

hospital discussed in Section 7.1.4) would need to be evaluated. 

The MAT judged wind damage at this nursing home to be due to it being subjected to wind speeds 

that were substantially above the design wind speed.

Functional Loss: According to a representative, the nursing home had a maximum occupancy of 

120 residents; at the time the tornado struck, there were approximately 89 residents and 20 staff. 

There were 16 fatalities. Ten residents and one staff member died immediately, and five additional 

residents later died of their injuries. One quadriplegic victim died outside of the building when 

struck by wind-borne debris. Following the tornado, residents were evacuated to other facilities in 

the area. The nursing home will be completely rebuilt. 

Figure 7-19: 

Only one wall remained 

standing at the nursing home 

(Joplin, MO)

3 There is no DI for nursing homes. The type of construction listed for DI 9 is applicable to this nursing home. However, DI 9 is for 

buildings less than 5,000 square feet. Therefore, using DI 9 for this size of nursing home may underestimate the wind speed. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-15

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

7.1.4 St. John’s Medical Center (Joplin, MO)

Location of Facility in Tornado Path: The location of the St. John’s Medical Center is shown in 

Figure 7-2. Figure 7-20 shows an aerial view of the tornado track in the vicinity of the hospital. The 

NWS EF contour ratings in the vicinity of the hospital are shown on Figure 7-20. According to a 

representative of the hospital, it was occupied by staff and approximately 180 patients when the 

tornado struck. Five patients lost their lives and a number of patients and staff were injured. 

Facility Description: The St. John’s Medical Center was constructed in 1968, with a second East 

Tower added in 1985 (Figure 7-21). The hospital had 367 beds and its emergency care department was 

level II trauma certified. The original tower had a concrete frame with cast-in-place concrete floors 

and a built-up roof. The East Tower addition had a steel frame with cast-in-place concrete floors, a 

single-ply membrane roof system, an aggregate ballasted roof system on the three-story portion of 

the addition, and precast concrete wall panels. The towers were joined by a steel superstructure with 

elevator shafts. The emergency room was located along the northwest corner of the hospital in the 

original tower; most of the surgery rooms and the intensive care unit (ICU) were in the East Tower 

addition. The one-story building that housed an emergency generator and switchgear had a steel 

deck, steel roof joists, and EIFS over unreinforced CMU exterior walls.

The hospital had an electronic medical records system with the data stored in the medical office 

building/outpatient center, which was connected to the hospital via a tunnel. The data were routinely 

backed up to an offsite location outside of the area impacted by the tornado.

Figure 7-20: Aerial view of the track in the vicinity of the St. John’s Medical Center (yellow circle). The blue arrow 

indicates the medical office building/outpatient center (shown in Figure 7-28). The center of the damage swath is 

approximated by the red line. The location of Greenbriar Nursing Home (Section 7.1.3) is indicated by the green circle 

(Joplin, MO).

Medical office building/

outpatient center (Figure 7-28)
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

The hospital did not have a tornado safe room or storm shelter. The hospital’s tornado procedure 

entailed moving patients into corridors, except in the ICU, where patients and hospital personnel 

were to remain in the unit and seek protection to the extent possible. Evacuation sleds were available 

to help move patients down stairwells and corridors during an emergency in the event elevators were 

not working. 

General Wind Damage: Most of the exterior windows were broken, which resulted in injuries to 

patients and staff as well as extensive interior damage (Figure 7-22). See also Figure 5 in Tornado 

Recovery Advisory No. 5, Critical Facilities Located in Tornado-Prone Regions: Recommendations for Facility 

Owners (FEMA 2011c) in Appendix F. 

There was extensive blow-off of roof membranes on both towers and lower-level roofs, and some 

roof decking blow-off on the lower-level roofs (Figure 7-21), blow-off of roof aggregate (Figure 7-23), 

collapse of brick veneer walls at the original tower (Figure 7-24 inset), collapse of metal wall panels 

at the East Tower addition (Figure 7-24), and collapse of a precast concrete wall panel at the loading 

dock (Figure 7-25). A hospital representative told the MAT that engineers working on behalf of the 

hospital determined that the structural steel frame of the East Tower addition had been twisted by 

the tornado.

Figure 7-21: 

Close-up of Figure 7-20 

showing St. John’s Medical 

Center (Joplin, MO) 

Emergency 

generator and 

switchgear 

building

Original tower

East tower

(1985 addition)

Administration 

area
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-22: 

View of the glazing damage 

at patient rooms (Joplin, MO)

Figure 7-23: 

This parking lot was littered 

with 11⁄2-inch nominal 

diameter aggregate from the 

ballasted roof membrane. 

(Joplin, MO).
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-24: 

Collapse of a portion of the 

exterior metal composite 

foam wall panels at the East 

Tower addition (red arrows). 

The inset shows collapsed 

brick veneer at the Original 

Tower. Most of the glazing 

shown in this photograph was 

broken (Joplin, MO).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-19

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Several of the lower-level areas, including an equipment room and an administrative area, had metal 

roof decking blown off (Figures 7-26 and 7-27). Some exterior walls also collapsed (Figure 7-27).

Figure 7-25: 

View of a missing precast 

concrete wall panel (red box) 

at the loading dock 

(Joplin, MO)

Figure 7-26: 

Metal decking blow-off 

and glazing damage in the 

administrative area 

(Joplin, MO)
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

The water main and natural gas lines had been labeled at some point prior to the tornado and were 

closed soon after the event, thereby avoiding flooding, fire, and explosion. 

The hospital had two emergency generators, one within the original tower and the other within 

the building shown in Figure 7-21. The generator/switchgear building collapsed, which resulted in 

total loss of electrical power throughout the hospital. This building is shown in Figures 12 and 13 of 

Tornado Recovery Advisory No. 6, Critical Facilities Located in Tornado-Prone Regions: Recommendations 

for Architects and Engineers (FEMA 2011b) in Appendix F. The generator in the original tower did not 

function because the switchgear was severely damaged by the building collapse. 

The medical office building/outpatient center, which housed the medical records server, experienced 

significant glazing damage, EIFS puncture by wind-borne debris, EIFS blow-off, and roof membrane 

and roof decking blow-off (Figures 7-21 and 7-28). The on-site medical records server did not survive, 

but the data were remotely backed up.

MAT EF Rating: Using DI 20 (Institutional Building), the MAT selected DOD 10 (“collapse of some 

top story exterior walls”) for the hospital. Using the expected wind speed for DOD 10, the MAT 

derived the tornado rating as EF3 (136–165 mph) based on damage to this building. Hence, the 

estimated wind speed experienced by the building was substantially above the current basic wind 

speed of 90 mph.

Using DI 17 (Low-Rise Building, 1–4 Stories), the MAT selected DOD 6 (“significant damage to 

exterior walls and some interior walls”) for the medical office building/outpatient center. Considering 

the building age and observed damage, the MAT assessed the wind speed as between the expected 

and lower-bound speeds for DOD 6. Hence, the MAT derived the tornado rating as EF 3 (136–165 

Figure 7-27: 

Exterior wall collapse (EIFS 

over unreinforced CMU) at an 

equipment room (Joplin, MO) 
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

mph) based on damage to this building. Therefore the estimated wind speed experienced by this 

building was substantially above the current basic wind speed of 90 mph. 

As shown in Figure 7-20, the NWS derived the rating as EF3 at the medical office building/outpatient 

center, which correlates with the MAT EF3 rating for this building. The NWS derived the rating as 

EF5 at one portion of the hospital and EF4 at other portions, which are different from the MAT EF3 

rating for this building. 

The MAT judged wind damage at this hospital to be due to wind-borne debris and its subjection to 

wind speeds substantially above the design wind speed. 

Functional Loss: According to a representative, the hospital was occupied by staff and approximately 

180 patients when the tornado struck. Five patients lost their lives during evacuation efforts and a 

number of patients and staff were injured as well. 

Figure 7-28: 

Metal decking blow-off and 

glazing and EIFS damage 

(red arrows) at the medical 

office building/outpatient 

center. Inset shows a 

close-up of the damage 

(Joplin, MO).
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

With loss of all electrical power and other significant damage to the building, it was necessary to 

evacuate the hospital. The emergency lighting in the stairways and corridors was powered by the 

emergency generator. With loss of the generators, and in the absence of battery-powered exit lighting 

as a secondary back-up, patients were evacuated down dark stairways and through dark corridors. 

The hospital was evacuated in about 11⁄2 hours. Patients were either moved to an initial emergency 

triage area that was set up near the heliport or to another hospital in town. 

Within a week, a temporary 60-bed hospital was established across the parking lot from the existing 

hospital. On January 3, 2012, construction of a new 825,000-square-foot hospital began to replace 

the former St. John’s Medical Center at a new location in Joplin. The new hospital is scheduled to be 

completed by 2015, with an estimated construction cost of $345 million. Demolition of the existing 

hospital is expected to take 5 months, and hospital officials plan to donate the land to the City. 

Hospital personnel expressed the importance of having electronic patient records, which eased the 

process of evacuating patients to other hospitals and enabled the quick transition to the temporary 

60-bed hospital. 

7.2 First Responder Facilities (Police and Fire)

Police and fire rescue facilities are critical to disaster response because an interruption in their 

operation as a result of building or equipment failure may prevent rescue operations, evacuation, 

assistance delivery, or general maintenance of law and order, which can have serious consequences 

for the community.

7.2.1 Fultondale Municipal Complex (Fultondale, AL) 

Location of Facility in Tornado Path: Figure 7-29 shows an aerial view of the tornado track in the 

vicinity of the Fultondale Municipal Complex. The NWS rated the center of the tornado circulation 

in the vicinity of this complex as an EF2.

The Fultondale municipal complex has four major buildings (Figure 7-30): 1) Fire Department, 

2) Library/“Shelter,” 3) Building and Inspections Department, and 4) City Hall (which houses the 

police station, jail, and natural gas utility offices). According to a representative of the complex, 

citizens seeking refuge from the tornado were in the library when the tornado struck. The jail was 

also occupied during the event. The Municipal Complex was damaged in several locations. 

+ The Fire Department lost the entire roof structure over the apparatus bay.

+ The Library/“Shelter” had damage to the siding and mansard. The entrance to the “Shelter,” 

referred to hereafter as a tornado refuge area, is shown by the yellow arrow in Figure 7-30. 

+ The roof structure of the Buildings and Inspections Department was lifted off and came to rest 

upside down in the area indicated by the blue oval at Figure 7-30.

+ The City Hall and Police Station had roof damage to the porte-cochere (red box in Figure 7-30), 

and the emergency generator was taken out of service by a fallen tree (red arrow).
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-29: Aerial view of tornado track in the vicinity of Fultondale Municipal Complex in Alabama (yellow circle). The 

center of the damage swath is approximated by the red line (Fultondale, AL).

SOURCE: © GOOGLE EARTH

Figure 7-30: Tornado winds damaged an emergency generator (red arrow) and a roof (red box), and lifted a roof (final 

location shown by blue box). Yellow arrow shows the “shelter” entrance (Fultondale, AL).

SOURCE: © GOOGLE EARTH

Library/”Shelter”

Fire Department

Building and 

Inspections 

Department

City Hall and Police
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

7.2.1.1 Fire Department

Facility Description: The fire department is a PEMB that was built around 1995. The walls have 

brick veneer cladding over the frame. 

General Wind Damage: The apparatus bay doors collapsed, most of the metal roof covering blew 

off, and some of the metal fascia blew off (Figures 7-31 and 7-32).

MAT EF Rating: Using DI 21 (Metal Building Systems),4 the MAT selected DOD 3 (“metal roof or 

wall panels pulled from the building”) for this facility. Using the expected wind speed for DOD 3, 

the MAT derived the tornado rating as EF1 (86–109 mph) based on damage to this building. Hence, 

the estimated wind speed experienced by the building was not substantially above the current basic 

wind speed of 90 mph.

The MAT judged the wind damage at this fire station to be due to inadequate wind resistance.

Functional Loss: According to a representative of the complex, two pieces of apparatus that received 

minor damage were freed from the damaged building and were in service in less than 2 hours. 

Several more hours were required to free the balance of the equipment. Although damaged, the 

building remained useable after debris removal. The building will need substantial work to bring it 

back into full service. 

Figure 7-31: 

The apparatus bay doors of 

the fire department collapsed 

(Fultondale, AL)

4 There is no DI for fire stations. DI 21 was deemed appropriate for this facility. 
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-32: 

The metal roof panels blew off 

the apparatus bay of the fire 

department. The panels unlatched 

from the clips, shown at another 

angle in the inset (Fultondale, AL).

7.2.1.2 Library and “Shelter”

Facility Description: The library was built in the early to mid-1970s. The Fultondale Community 

“Shelter” is located in the daylight basement of the library. The tornado refuge area was well 

publicized and was used by up to 150 people during the day of the storms. The refuge area has glass 

doors and a window wall system (Figure 7-33) that do not possess the wind pressure and wind-borne 

debris resistance specified in FEMA 361(2008a) or ICC 500 (2008). Therefore, the glazing presents 

a potential hazard to the occupants. Because of the glazing vulnerability, this area is considered a 

tornado refuge area rather than a storm shelter or safe room (refer to Section 9.1 for additional 

information).

General Wind Damage: The library had minimal damage to the metal panel fascia at the entrance 

vestibule (Figure 7-33). There was also some brick veneer damage on the side of the building that 

faced the fire station. This damage was minor and easily repaired. 
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

MAT EF Rating: Using DI 17 (Low-Rise Building, 1–4 Stories), the MAT selected DOD 1 (“threshold 

of visible damage”) for this facility. Using the expected wind speed for DOD 1, the MAT derived the 

tornado rating as EF0 (65–85 mph) based on damage to this building. Hence, the estimated wind 

speed experienced by the building was below the current basic wind speed of 90 mph.

The MAT judged the wind damage at this building to be due to inadequate wind resistance, which is 

reflective of the codes, standards, and design practices in the era when this facility was built.

Functional Loss: The building did not experience a loss of function.

7.2.1.3 Building and Inspections Department

Facility Description: The Buildings and Inspections Department building was constructed in the 

late 1970s to house a medical response vehicle. The building has CMU bearing walls and a wood 

truss roof system. 

General Wind Damage: The roof structure lifted off the walls and flipped over in one complete 

piece into the side yard (Figures 7-30 and 7-34). The top course of the CMU wall was made from 

cap blocks and not a bond beam (Figure 7-35). The trusses were attached to a wooden plate that was 

nailed into the cap blocks. The cap blocks had no positive anchorage to the main wall. The wall also 

appeared to be unreinforced masonry and was damaged. 

Figure 7-33: 

The library is on top of the community tornado refuge 

area. The note in the window (red circle) directed 

people to the “shelter” below (Fultondale, AL).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-27

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

MAT EF Rating: Using DI 9 (Small Professional Building), the MAT selected DOD 7 (“uplift or 

collapse of entire roof structure”) for this facility. Considering the building age and observed 

damage, the MAT assessed the wind speed as the lower-bound wind speed for DOD 7. Hence, the 

MAT derived the tornado rating as EF1 (86–110 mph) based on damage to this building. Therefore, 

the estimated wind speed experienced by the building was not substantially above the current basic 

wind speed of 90 mph.

The MAT judged the wind damage at this building to be due to inadequate wind resistance, which is 

reflective of the codes, standards, and design practices in the era when this building was constructed. 

Figure 7-34: The roof structure of the Buildings and Inspections Department building blew off in one complete section 

(red arrow). The yellow oval area is shown in Figure 7-35 (Fultondale, AL).

Figure 7-35: 

Note the inadequate 

anchorage from the truss 

nailer (red arrow) that 

was nailed to the wall top 

cap block (blue arrow). 

The inset shows a closeup. Also note the lack of 

anchorage between the top 

cap block and the main wall 

(Fultondale, AL).
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Functional Loss: According to a representative of the complex, the building was determined to be 

a total loss. After the tornado, the department temporarily relocated to the basement of the library. 

7.2.1.4 City Hall

Facility Description: The City Hall was built in 1985. It is a single-story, light-framed building with 

a truss roof.

General Wind Damage: The City Hall 

lost its metal roof covering over the portecochere (Figure 7-36). The emergency 

generator was taken out of service by a 

fallen tree. The tree caused the generator 

to shift, which broke the natural gas fuel 

line (Figure 7-37).

MAT EF Rating: Using DI 17 (Low-Rise 

Building, 1–4 Stories), the MAT selected 

DOD 2 (“loss of roof covering (<20%)”) for 

this facility. Considering the building age and observed damage, the MAT assessed the wind speed 

to be between the expected and lower-bound wind speeds for DOD 2. Hence, the MAT derived the 

tornado rating as EF0 (65–85 mph) based on damage to this building. Therefore, the estimated 

wind speed experienced by the building was below the current basic wind speed of 90 mph.

The MAT judged the small amount of wind damage at this building to be due to inadequate wind 

resistance, which is reflective of the codes, standards, and design practices in the era when this 

facility was built. The damage to the generator was due to a tree that was too close to the generator.

Functional Loss: According to a representative of the complex, the loss of City power and damage 

to their emergency generator resulted in no lighting (other than flashlights) or ventilation in the jail 

area. Once the natural gas line to the generator was repaired, the building operated on emergency 

power. Municipal power was restored approximately 3 days after the tornado. The building damage 

was minor and easily repaired.

Figure 7-36: 

The front of the City Hall 

showing damage to the 

metal roof covering over the 

entrance (Fultondale, AL)

A properly protected generator should not be taken out of service by a fallen tree. FEMA Recovery 

Advisory No.6, Critical Facilities Located in 

Tornado-Prone Regions: Recommendations for 

Architects and Engineers (Appendix F), provides 

recommendations for architects and engineers 

including enhancements to generators to avoid interrupted operations.
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-37: 

Back of the City Hall. The red 

arrow points to the generator 

that was disabled by a fallen 

tree (Fultondale, AL).

7.2.1.5 Summary of the MAT EF Ratings for the Fultondale Municipal Complex 

For two of the Fultondale Municipal Complex buildings, the MAT derived an EF0 rating. An EF1 

rating was derived for the other two buildings. 

As can be seen in Figure 7-30, the four buildings are near one another; hence, they likely experienced 

similar wind speeds. The buildings may have experienced different wind loads due to differences in 

angle of attack, shielding, or exposure. However, the different EF ratings may be due to uncertainties 

in the accuracy of the wind speeds associated with the different DIs and DODs. The NWS rated the 

center of the tornado circulation in the vicinity of the complex as an EF2, which is above the MAT 

EF0 and EF1 ratings of the complex. As shown in Figure 7-29, the complex is on the left periphery of 

the center of circulation. Accordingly, the wind speed at the complex should be less than the wind 

speed at the center of circulation.5

7.2.2 Tuscaloosa Fire Station 4 (Tuscaloosa, AL)

Location of Facility in Tornado Path: The location of Tuscaloosa Fire Station 4 is shown in Figure 

7-1). Figure 7-38 shows an aerial view of the tornado track in the vicinity of the fire station. The NWS 

rated the center of the tornado circulation in the vicinity of the fire station as an EF4. According to 

a representative of the fire department, four fire station personnel were in the building when the 

tornado struck—none were injured.

Facility Description: This fire station, which opened in 1952, had a modified bitumen roof membrane 

system over a cast-in-place concrete deck. Some of the exterior walls were brick (which appeared to 

be bearing walls). Other exterior walls were stucco over wire lath over furring over what appeared to 

be cast-in-place concrete. The apparatus bay had two sectional doors at the front and back of the bay. 

The facility did not have a storm shelter or safe room.

5 The wind speed is higher on the right side of the center of circulation than it is on the left side.
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Figure 7-38: Aerial view of the track in the vicinity of the fire station (yellow circle). The center of the damage swath is 

approximated by the red line (Tuscaloosa, AL). 

General Wind Damage: The MAT also observed nearby apartment buildings when they visited 

this fire station because the fire station’s specific construction type is not covered in the EF rating 

system. Therefore, damage to two nearby apartment buildings was used to determine EF ratings (as 

discussed later). 

Apartment Buildings: The two nearby apartment houses were heavily damaged (Figure 7-39). The 

apartment house shown by the left yellow arrow lost its entire wood roof structure, and a portion of 

the unreinforced CMU wall collapsed. The wood-frame apartment house shown by the right yellow 

arrow lost the roof structure, and several of the exterior and interior walls on the second floor 

collapsed.

Fire Station: At the fire station, all four apparatus bay doors were blown away, all of the exterior 

windows were broken, the roof membrane was punctured in a few areas, some of the cap sheet was 

blown away, and some rooftop equipment was blown away. 

Figure 7-40 is a view of the fire station and the adjacent apartment building. The inset shows were 

a section of stucco and lath was broken away by wind-borne debris. The marks on the wall indicate 

the amount of debris that impacted this area. Figure 7-41 is a view of the fire station living quarters. 

All of the windows were broken. Fire station personnel took refuge in the rest room shown in Figure 

7-42. Figure 7-43 shows the wood-framed apartment building behind the fire station.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-31

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-39: The fire station is within the red circle. The apparatus bay is indicated by the blue arrow, and the living 

quarters are indicated by the green arrow. The yellow arrows indicate the nearby heavily damaged apartment buildings 

(Tuscaloosa, AL).

PHOTOGRAPH COURTESY OF TUSCALOOSA COUNTY SHERIFF’S OFFICE

Figure 7-40: 

View of the fire station. The blue arrow indicates the boarded 

up apparatus bay. The red arrow indicates boarded up 

windows. The yellow arrow indicates the adjacent apartment 

building with unreinforced CMU walls. The inset shows a 

section of stucco and lath broken away by wind-borne debris 

(red circle). (Tuscaloosa, AL).
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Figure 7-41: 

View of the living quarters of the 

fire station from outside; inset 

shows the interior. Note the 

amount and size of wind-borne 

debris adjacent to the walls 

(Tuscaloosa, AL).

Figure 7-42: 

View of a restroom toward 

the center of the fire station 

where occupants took 

refuge. Note the mattress 

that was taken into the room 

for additional protection 

(Tuscaloosa, AL).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-33

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-43: View of the wood-frame apartment building behind the fire station. The inset shows 

the far end of the building. The walls were brick veneer over wood fiberboard over wood studs 

(Tuscaloosa, AL).

MAT EF Rating: Because of this fire station’s unusual type of construction, none of the DIs were 

judged appropriate for it. Therefore, two nearby apartment buildings were used instead, and they 

were rated as follows: 

Masonry apartment building: Using DI 7 (Masonry Apartments or Motel), the MAT selected DOD 

5 (“collapse of top story walls”) for this facility. Considering the building age and observed damage, 

the MAT assessed the wind speed to be between the expected and lower-bound wind speeds for 

DOD 5. Therefore, the MAT derived the tornado rating as EF2 (111–135 mph) based on damage to 

this building. 

Wood-frame apartment building: Using DI 5 (Apartments, Condominiums, and Townhouses; Three 

Stories or Less), the MAT selected DOD 5 for this facility. Considering the building age and observed 

damage, the MAT assessed the wind speed to be between the expected and lower-bound wind speeds 

for DOD 5. Therefore, the MAT derived the tornado rating as EF3 (138–167 mph) based on damage 

to this building. 
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As can be seen in Figure 7-38, the wood-frame apartment building with the EF3 rating was closer to 

the center of the tornado circulation than the masonry apartment building with the EF2 rating, so 

the difference in the ratings may be due to wind speed decay. However, the difference may also be 

due to uncertainties in the accuracy of the wind speeds associated with the DODs. 

Based on the apartment building EF ratings, the fire station either experienced EF2 or EF3 winds. 

Hence, the estimated wind speed at the fire station was either above or substantially above the current 

basic wind speed of 90 mph. 

The NWS rated the center of the tornado circulation in the vicinity of the fire station as EF4, which 

is above the MAT EF2 or EF3 ratings of the fire station. As shown in Figure 7-38, the fire station is 

to the left of the center of circulation. Accordingly, the wind speed at the fire station should be less 

than the wind speed at the center of circulation.

The damaged glazing was due to wind-borne debris. The damage to the apparatus bay doors was 

due to either wind-borne debris, or more likely, wind pressures that were substantially above the 

pressures the doors were designed for. The MAT judged the good performance of the structural 

system to be due to the use of concrete. 

Functional Loss: According to a representative of the fire department, one fire engine and one 

personal vehicle were in the apparatus bay when the tornado struck. The engine was damaged to 

an extent that it was not usable for emergency response. Fire station personnel therefore provided 

assistance to the community on foot. The personal vehicle was totaled. 

For about the first week after the tornado, the damaged fire station was used to provide services. 

Then for about two weeks, personnel from this station operated out of Fire Station 6. After that time 

period, a temporary station was set up about two blocks from Fire Station 4. The temporary station 

consisted of a mobile office and a canvas apparatus bay.

A new facility will be built for Fire Station 4 at another location. Plans for the damaged fire station 

have yet to be determined at the time of this report.

7.2.3 Webster’s Chapel Volunteer Fire Department (Wellington, AL)

Location of Facility in Tornado Path: An aerial view of the Webster’s Chapel Volunteer Fire 

Department prior to the tornado is shown in Figure 7-44. The NWS EF contour ratings in the vicinity 

of the fire station are shown on Figure 7-44. According to a representative of the fire department, the 

fire station was occupied shortly before the tornado struck, but the occupants left the station before 

the tornado struck and sought refuge in a church across the street, which was outside of the tornado 

track and not damaged.

Facility Description: The Webster’s Chapel Volunteer Fire Department was originally designed as 

a school several decades ago. When the facility was converted to a fire station, there was only one 

apparatus bay. A new apparatus bay was added circa 2007 (Figure 7-45). The original building was 

wood-frame construction with brick veneer walls. The multipurpose room had an aggregate surface 

built-up roof system over a cementitious wood-fiber deck. The older apparatus bay had a wood roof 

structure and unreinforced CMU walls. The new apparatus bay is a PEMB with metal roof and wall 

panels.
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-44: View of the Webster’s Chapel Volunteer Fire Department (red arrow) in relation to the tornado.6 The red 

triangle indicates the location of two houses where NWS rated the tornado as EF4. The yellow triangles indicate the 

locations of houses where NWS rated the tornado as EF2 (Wellington, AL).

SOURCE: © GOOGLE EARTH

SOURCE OF TORNADO TRACK: NOAA (HTTP://NGS.WOC.NOAA.GOV/STORMS)

The facility did not have a storm shelter or safe room.

General Wind Damage: The tornado struck the corner of the building where the multipurpose 

room and old apparatus bay were located. At the old apparatus bay, the rolling doors blew in on the 

equipment, the roof structure blew off, and part of the back wall collapsed (Figure 7-46). The roof 

membrane was blown off the multipurpose room, a few windows were broken, and portions of the 

roof structure and exterior wall were blown away on the backside of the building (Figure 7-47). The 

new apparatus bay had some wind-borne debris damage (inset at Figure 7-45), but this portion of the 

building did not experience high winds.

6 NOAA did not take post-tornado aerial photographs of this tornado. Therefore, a pre-storm image was used for this figure.
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Figure 7-45: 

View of the Webster’s Chapel 

Volunteer Fire Department after 

the tornado. The new apparatus 

bay is indicated by the red 

arrow. The older apparatus 

bay is indicated by the yellow 

arrow. The inset shows windborne debris damage at the 

back side of the new apparatus 

bay. The green arrows indicate 

plywood debris that penetrated 

the metal wall panel sidelaps 

(Wellington, AL).

Figure 7-46: 

View of the old apparatus 

bay of the Webster’s Chapel 

Volunteer Fire Department. 

The multipurpose room is 

indicated by the red arrow 

(Wellington, AL).

Figure 7-47: 

View of the back of the 

building. The old apparatus 

bay is shown by the yellow 

arrow and the new bay by 

the red arrow. Roof structure 

and wall damage occurred 

within the red box. The 

debris in the foreground is 

from the multipurpose room 

roof and the old apparatus 

bay (Wellington, AL).
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

MAT EF Rating: Only the old apparatus bay portion of the facility was rated. Using DI 14 (Automobile 

Service Building),7 the MAT selected DOD 6 (“uplift or collapse of roof structure”) for this facility. 

Considering the facility age and observed damage, the MAT assessed the wind speed as near the 

lower-bound wind speed for DOD 6. Hence, the MAT derived the tornado rating as EF1 (86–110 

mph) based on damage to this building. Therefore, the estimated wind speed experienced by the 

building was not substantially above the current basic wind speed of 90 mph. 

As shown in Figure 7-44, the NWS derived the rating as EF1 in the vicinity of the fire station, which 

correlates to the MAT EFI rating.

The MAT judged the wind damage at this fire station to be due to inadequate wind resistance, 

which is reflective of the codes, standards, and design practices in the era when this building was 

constructed. 

Functional Loss: According to a representative of the fire department, all three pieces of equipment 

in the old apparatus bay were significantly damaged and were therefore not available for response 

and recovery operations. 

7.2.4 Smithville Police Department (Smithville, MS)

Location of Facility in Tornado Path: Figure 7-48 shows an aerial view of the tornado track in the 

vicinity of the Smithville Police Department. Figure 7-49 shows the building prior to the tornado. 

The NWS rated the center of the tornado circulation in the vicinity of the police department as an 

EF5. According to a representative of the police department, there were seven people in the building 

at the time the tornado struck, five of whom were injured by the tornado damage. None of the 

injuries was life threatening.

Facility Description: The Smithville Police Department was constructed in 1962. It was previously 

the town’s health department building. The building was constructed of unreinforced CMU with 

brick veneer. The building had brick veneer over 4-inch-wide CMU walls. Truss wire was noted with 

8 inches-on-center shear reinforcement. 

The facility did not have a storm shelter or safe room.

General Wind Damage: During the storm, the roof of the police department was blown off, and 

large portions of the walls on the north, east, and south sides of the building collapsed (Figure 

7-50). Figure 7-51 shows a photograph taken directly after the tornado. To the left side of the figure, 

a portion of the building’s walls can be observed. Figure 7-52 shows the damage to the police station 

looking south from the back (north) side of the building. The collapse of the east wall, which is also 

depicted in Figure 7-53, can be noted in Figure 7-49.

7 There is no DI for fire stations. The type of construction listed for DI 14 is applicable to this fire station. 
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Figure 7-48: Aerial view of the tornado track in the vicinity of the Smithville Police Department (yellow circle). The 

center of the damage swath is approximated by the red line (Smithville, MS). 

Figure 7-49: 

Smithville Police Department 

prior to the tornado 

(Smithville, MS) 

SOURCE: © GOOGLE EARTH
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-50: 

Smithville Police Department 

(close-up of Figure 7-48). 

The red arrow indicates the 

room where refuge was 

taken during the tornado 

(Smithville, MS).

Figure 7-51: 

Smithville Police 

Department. Note the 

collapsed communications 

tower (red arrow) (Smithville, 

MS).

PHOTOGRAPH COURTESY OF TIM 

BURKITT, FEMA
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East wall

Figure 7-53: 

View of the collapsed 

east wall (red arrow) and 

restroom (blue arrow) 

of the Smithville Police 

Department. Note that 

some of the restroom walls 

collapsed (Smithville, MS).

PHOTOGRAPH COURTESY OF 

DARWIN HATHCOCK, CHIEF OF 

POLICE

Figure 7-52: 

The red arrow indicates the 

office where two children 

and an adult took refuge 

under the desk 

(Smithville, MS)

PHOTOGRAPH COURTESY OF 

DARWIN HATHCOCK, CHIEF OF 

POLICE
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

MAT EF Rating: Using DI 9 (Small Professional Building),8 the MAT selected DOD 8 (“collapse 

of exterior walls; closely spaced interior walls remain standing”) for this facility. Considering the 

building age and observed damage, the MAT assessed the wind speed to be between the expected 

and lower-bound wind speeds for DOD 8. Hence, the MAT derived the tornado rating as EF2 (111–

135 mph) based on damage to this building.9 Therefore, the estimated wind speed experienced by 

the building was above the current basic wind speed of 90 mph. 

The NWS rated the center of the tornado circulation in the vicinity of the Smithville Police Department 

as an EF5, which is different from the MAT EF2 rating of this building. As shown in Figure 7-48, the 

police department was on the right side of the center of the damage swath, and hence the right side 

of the center of circulation, where the wind speed is the highest. It is likely that there was wind speed 

decay between the center of circulation and the police station. The MAT judged the wind damage at 

this police station to be due to wind speeds that were above the design wind speed and inadequate 

wind resistance, which is reflective of the codes, standards, and design practices in the era when this 

police station was constructed. 

Functional Loss: According to a representative of the police department, there were seven people in 

the building at the time the tornado struck—four employees and three civilians, including one adult 

and two children—who came to the police station to seek refuge. One occupant injured his arm and 

shoulder when winds tore a door from his grasp, while another sustained injuries from debris. 

Communications for emergency response after the tornado were hampered by the collapse of the 

communications tower at the police department. The department had a hand-held walkie-talkie, but 

communication with the Smithville Fire Department, Monroe County Sheriff’s Department, the 911 

call center, and the Amory Police Department was not possible because of tornado damage at these 

other sites. The patrol car radios did not work because they had gotten wet. The cell phone circuits 

were also jammed. The Smithville Police Department was unable to let other emergency personnel 

know how bad the damage was and what their immediate needs were.

The police officers had no working or accessible equipment. The patrol cars were destroyed. Without 

equipment, the officers used pieces of wood as pry bars to try to rescue people trapped in cars and 

rubble. Doors from houses were used as backboards to transport the injured. 

The facility did not have an emergency generator on site, but did have access to generators that could 

have been set up if needed. 

As a result of the tornado, the Smithville Police Department lost complete functionality at its original 

location and has been relocated to the town hall, where it shares the space with the mayor’s office. 

The town has plans to rebuild a facility that will house the police, fire, water, and town hall services 

in one building.

8 There is no DI for police stations. The type of construction listed for DI 9 is applicable to this facility.

9 It should be noted that the walls of the police station that were still standing immediately following the tornado were demolished 

several days later, before the MAT and other assessment teams arrived. The demolition caused another damage assessment team 

to derive an EF4 rating for this facility using DI 9, DOD 9 (“total destruction of entire building”), and the upper-bound wind speed. 

As evidenced by the damage photographs provided to the MAT, the selection of DOD 9 and an EF4 rating was not reflective of 

conditions immediately after the tornado. 
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7.3 Emergency Operations Centers 

EOCs function as the physical location at which the coordination of information and resources to 

support incident management (on-scene operations) activities normally takes place.10 The command 

and response personnel must remain on duty, in full readiness for action both during and in the 

aftermath of a disaster. In addition to personnel and resources, EOCs house the information and 

communications systems that provide feedback to the emergency managers to help them make 

decisions about efficient and effective deployment of resources. They also relay information to local 

residents, storm shelters, media, and other first responders, while providing continuity of government 

and COOP. The loss of an EOC can severely affect the overall response and recovery in the area. For 

these reasons, the performance of these facilities in tornadoes is of utmost importance.

7.3.1 Tuscaloosa EOC (Tuscaloosa, AL)

Location of Facility in Tornado Path: The Tuscaloosa EOC was housed in the Curry Building city 

complex. Figure 7-54 shows an aerial view of the tornado track in the vicinity of the Curry Building 

city complex. The NWS rated the center of the tornado circulation in the vicinity of the Curry 

Building as an EF4. According to a representative of the city, there were approximately 15 people in 

the EOC at the time the tornado struck, none of whom was injured.

The EOC was located on the ground floor of the southeast corner (red circle in Figures 7-54 and 

7-55). Figure 7-56 is a view of the EOC before and after the tornado.

Facility Description: The Tuscaloosa County EMA was housed in the Curry Building city complex, 

which was constructed in 1967 as a textile manufacturing plant and later used as an automotive parts 

manufacturing facility. The Curry Building city complex also housed the Environmental Services 

Department and general storage. 

Most of the southern end of the complex (which housed the EOC) was a two-story steel-framed 

building with a built-up roof over steel decking. The exterior walls were unreinforced CMU with brick 

veneer. The first floor had a daylight basement. Most of the second floor had a high bay (equivalent 

to two stories). 

Most of the remainder of the building (in the yellow rectangle in the Figure 7-54 inset), was a onestory steel-framed building with a built-up roof over steel decking. Some of the exterior walls were 

unreinforced CMU with brick veneer, while others were metal panels. There were several loading 

dock doors on the north and west sides of the building. 

The Curry Building did not have a tornado safe room or storm shelter. However, there was a tornado 

refuge area within the EOC and another tornado refuge area shown by the blue circle at the Figure 

7-54 inset and at Figure 7-55.

General Wind Damage: Most of the area shown in the yellow rectangle in the Figure 7-54 inset 

collapsed (Figures 7-57 and 7-58).

10 Definition for EOC from the National Response Framework (http://www.fema.gov/emergency/nrf/glossary.htm#E) 
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-54: Aerial view of the track in the vicinity of the Curry Building city complex (blue rectangle). The center of 

the damage swath is approximated by the red line. The yellow circle indicates the EOC’s collapsed communications 

tower. The red arrows indicate damaged buildings. In the inset, the red oval shows the EOC and the blue circle shows a 

tornado refuge area. Most of the area in the yellow rectangle collapsed (Tuscaloosa, AL). 
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Figure 7-55: Oblique view of Figure 7-54 showing the Curry Building. The green circle indicates the EOC’s emergency 

generator. The red circle shows the ground floor of the southeast corner, the location of the EOC. The blue circle shows 

the tornado refuge area. 

PHOTOGRAPH COURTESY OF TUSCALOOSA COUNTY SHERIFF’S OFFICE

Figure 7-56:

View of the southeastern 

end of the Curry Building 

before the tornado struck. 

The EOC is located on the 

ground floor of the red box. 

The floor above the EOC 

collapsed (green line). The 

building to the left of the EOC 

(blue X) collapsed. The inset 

shows post-storm conditions 

(Tuscaloosa, AL).

SOURCE: © GOOGLE EARTH
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-45

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-57: 

View of a portion of the 

collapsed one-story area 

(Tuscaloosa, AL)

Figure 7-58: 

View of a portion of a 

collapsed loading dock area 

(Tuscaloosa, AL)
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

There was a tornado refuge area in a portion of the first floor in the southwest corner of the building 

(red oval, Figure 7-59). This area was marked with a sign reading “emergency shelter” that had a 

tornado graphic. The exterior walls in this area were concrete and had adequate strength to resist 

tornado wind forces. However, the rolling door, personnel door with glass vision panel, and the wall 

louver lacked sufficient wind pressure and wind-borne debris impact resistance for the area to be 

considered a safe room or storm shelter. The floor above this refuge area collapsed, indicated by the 

blue oval, and the roof decking blew off adjacent to this area as indicated by the red arrow. Further 

along the building, a portion of the roof structure and exterior wall collapsed as indicated by the 

blue arrow.

Most of the steel decking and some joists were blown off of the southern portion of the building 

(Figure 7-60) and much of the brick veneer/CMU wall collapsed. The metal door shown at the inset 

was buckled inward by CMU debris. 

Figure 7-61 is a close-up of the Figure 7-56 inset, showing the EOC area.

MAT EF Rating: Using DI 23 (Warehouse Building), the MAT selected DOD 7 (“total destruction 

of a large section of building or entire building”) for the portion the facility that housed the EOC 

(i.e., the southern portion of the complex). Considering the building age, the MAT assessed the 

wind speed to be between the expected and lower-bound wind speeds for DOD 7. Hence, the MAT 

derived the tornado rating as EF3 (136–165 mph) based on damage to this portion of the building. 

Therefore, the estimated wind speed experienced by the building was substantially above the current 

basic wind speed of 90 mph.

The NWS rated the center of the tornado circulation in the vicinity of the Curry Building city 

complex an EF4, which is different from the MAT EF3 rating of the EOC portion of this building. As 

shown in Figure 7-54, the EOC was on the right side of the center of the damage swath and hence, 

the right side of the center of circulation, where the wind speed is the highest. It is likely that there 

was wind speed decay between the center of circulation and the EOC. 

The MAT judged the poor wind performance of the Curry Building city complex to be due to 

wind speeds that were substantially above the design wind speed and inadequate wind resistance, 

which is reflective of the codes, standards, and design practices in the era when this building was 

constructed. The good performance of the structural system at the EOC and refuge area was judged 

to be due to the use of concrete. 

Functional Loss: According to a representative of the city, there were approximately 15 people in 

the EOC at the time the tornado struck, including a worker and two family members who were in the 

Environmental Services Department prior to taking refuge in the EOC. Although the area housing 

the EOC did not comply with FEMA 361 (2008a) or ICC 500 (2008) criteria for safe rooms and 

storm shelters, the exterior concrete walls and concrete slab of the second floor provided a level of 

occupant protection during this event and none of the occupants were injured. 

The emergency generator did not come on when normal power was lost because the lines connecting 

it to the EOC were severed during the storm. The EOC was flooded because the fire sprinkler system 

was damaged during the tornado. The EOC also lost communications because a large nearby 

communications tower collapsed (Figure 7-54 and Section 8.3.1.1). 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-47

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-59: 

View of the refuge area 

(red oval). Note the rolling 

door, personnel door, and 

louver wall openings (yellow 

arrows). The floor above 

the refuge area (blue oval) 

collapsed and the roof 

decking in the adjacent 

area (red arrow) blew off. A 

portion of the roof structure 

and exterior wall collapsed 

(blue arrow) 

(Tuscaloosa, AL).

Figure 7-60: Part of the southern portion of the building. The inset shows a metal door that buckled inward 

(Tuscaloosa, AL).
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Figure 7-61: 

The door with the red arrow 

leads to the EOC area. The 

inset shows the area above 

the EOC that collapsed 

(Tuscaloosa, AL).

The EOC lost complete functionality as a result of the tornado. The EOC had no functionality for 

approximately an hour after the tornado, at which point they set up at the Tuscaloosa Police Department 

for several hours. Following this, the EMA was relocated to the UA EOC until approximately May 3, 

at which point it was moved to a temporary location at the Alabama Fire College. A new permanent 

location will be required. 

The Environmental Services Department is planning to build a new building and a recycling plan 

on the site of the collapsed Curry Building city complex. The Department temporarily moved into 

modular buildings across the street after the tornado. Destruction of the Department’s facility 

hampered pickup of recyclables and trash in the first days after the tornado. 
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

7.3.2 Cullman County EOC (Cullman, AL)

This facility was not struck by the Cullman tornado on April 27, 2011. Although the facility was not 

damaged, it is presented in this chapter because of special enhancements that were incorporated 

into its design in order to avoid facility disruption if struck by a tornado. 

In 2008, the Cullman County EMA moved into its new facility in the basement of the newly constructed 

Cullman County Water Department Building.11 The EMA portion of the facility was designed as a 

safe room in accordance with FEMA 361 (2000) to resist the wind pressures and wind-borne debris 

associated with EF5 tornadoes (Figure 7-62): wind speeds of 250 mph (3-second gust) and debris 

impact from a 15-pound 2x4 board missile traveling horizontally at 100 mph. 

The design criteria were selected by the County and the architect to ensure that EMA staff would be 

safe and that operations would be maintained if the facility were impacted by a tornado.

The EMA portion of the facility occupies approximately 6,250 square feet and includes a reception 

area, an operations room that is approximately 1,000 square feet (Figure 7-63), bath rooms, two 

conference rooms, six offices, storage facilities, a communications closet, and a large multi-purpose 

room. All these areas are located within the reinforced concrete basement of the building. Two 

stairwells and one elevator provide access to the below-grade portions of the facility. The stairwells 

are also constructed of reinforced concrete and spiral downward from the above-grade entrance 

to the operations room. The emergency generator, air handler, and heating system for the facility 

are located within a special room in the above-ground portion of the facility. The walls and roof 

of the room protecting the generator were constructed from reinforced concrete to also meet the 

FEMA 361 (2000) criteria.

Figure 7-62: 

An exterior view of the 

Cullman County government 

building housing the Water 

Department (above grade) 

and the County EMA facility 

(below grade) (Cullman, AL) 

11 The facility was designed by Harris & Associates Architects and Planners, Birmingham, AL.
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Figure 7-63: 

Interior view of the 

emergency operations room 

of the Cullman County EMA 

facility (Cullman, AL)

FEMA 361 (2000) design elements and criteria implemented by the owner and architect include:

+ A design wind speed of 250 mph and wind-borne debris impact protection for the EOC portion 

of the facility and also for the generator room.

+ Wind-borne debris protection of the openings in the generator and mechanical room area to 

resist a 15-pound 2x4 missile traveling horizontally at 100 mph. This was created with concrete 

baffle walls. Use of concrete wall baffles allowed the use of traditional louvers between the 

baffles.

+ Protection of fuel storage. This was achieved by placing the large tank for the generator below 

ground (including all piping connecting the tank to the generator).

+ Protection of building systems (for example, the heating and air handling systems) by locating 

the equipment within the same protected space as the generator. Note: the cooling systems 

for the facility were not in the protected space. Since the EOC is located below grade, it was 

determined that protecting the cooling system was not critical and that the facility could 

function for a short period of time if this system were not available. 

+ Location of all communications systems, switches, and computer servers for both the EMA and 

the Water Department within the lower level.

+ Provision of food and water storage within the lower level.

+ Provision of a large multipurpose conference room within the lower-level area that holds over 

100 operational personnel for use by the EMA or others responding to an event. 
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OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

+ High ceilings and multiple layers of lighting. These elements give the facility a light and open 

feel in spite of the fact that it is totally underground with no natural lighting. The underground 

facility maintains a more constant temperature with less difficulty and cost than an aboveground facility. 

+ Provision of space for additional staff when needed for emergency response. During times of full 

activation, such as was experienced on April 27, 2011, the two full-time Cullman County EMA 

staff members were joined by more than 20 people. Representatives from the local emergency 

response community rotated through on 12-hour shifts to assist the EMA personnel. This 

included both paid and volunteer response agencies. Staff can also be supplemented as needed 

by administrative personnel from other county departments such as the Revenue Commission, 

etc. The multipurpose space adjacent to the EOC on the lower level provides protected space for 

the county staff plus any additional emergency responders who may be at the facility during 

an event.

According to the architect, the portions of the facility designed to the FEMA 361 (2008a) criteria 

were constructed for approximately $200 per square foot for a total cost of roughly $1,250,000. By 

contrast the upper floor of the facility (used for other Cullman County offices) was constructed at a 

cost of approximately $120 per square foot. If constructed to the building code in effect at the time, 

the EMA portion of the facility would have cost approximately 50 percent less. Implementing the 

FEMA 361 criteria for the selected portions of the facility ended up accounting for approximately 65 

percent of the total building cost. By choosing to spend an additional 25 percent on the facility, the 

owner and architect were able to achieve both personal protection for the 25 County staff and also 

provide continuity of operations during events. Additionally, based on FEMA 361 criteria regarding 

the number of occupants, the multipurpose room can provide protection for the facility staff as well 

as up to 300 additional persons (if needed). 

The construction of this facility shows how a community, with no Federal funding assistance, was able 

to implement the best-available guidance on tornado-resistant construction to design and construct 

a building that provides life-safety protection for the EMA staff , and also provides for continuity of 

operations if struck by a tornado. 

7.4 Summary of Conclusions and Recommendations

Table 7–1 provides a summary of the conclusions and recommendations for Chapters 6 and 7, and 

provides section references for supporting observations. Additional commentary on the conclusions 

and recommendations is presented in Chapters 10 and 11. 
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Table 7‐1: Summary of Conclusions and Recommendations for Critical Facility Performance

Observation(s) Conclusion Recommendation

Schools which sustained damage and did not 

have a FEMA 361-compliant safe room or ICC 

500-compliant storm shelter:

•	 Alberta Elementary School (Section 6.1.1)

•	 University Place Elementary School (Section 

6.1.2)

•	 Ringgold High School and Ringgold Middle 

School (Section 6.1.3)

•	 Joplin East Middle School (Section 6.1.4)

•	 Joplin High School (Section 6.1.5)

911 call stations, EOCs, or fire, rescue, ambulance, 

and police stations that sustained damage and did 

not have a FEMA 361-compliant safe room or ICC 

500- compliant storm shelter:

•	 Fultondale Municipal Complex (Section 7.2.1)

•	 Tuscaloosa Fire Station 4 (Section 7.2.2)

•	 Webster’s Chapel Volunteer Fire Department 

(Section 7.2.3)

•	 Smithville Police Department (Section 7.2.4)

•	 Tuscaloosa EOC (Section 7.3.1)

Conclusion #4

IBC-compliant facilities 

can be susceptible to 

building damage.

Recommendation #10

Propose IBC code 

change. 

Submit IBC code change 

proposal to require a FEMA 

361-compliant safe room or 

ICC 500-compliant storm 

shelter in all areas where 

shelter design wind speeds 

are 250 mph or greater 

for all new kindergarten 

through 12th grade schools. 

Recommendation #11

Propose IBC code change 

Submit IBC code change 

proposal to require a FEMA 

361-compliant safe room or 

ICC 500-compliant storm 

shelter in all areas where 

shelter design wind speeds 

are 250 mph or greater 

for all 911 call stations, 

emergency operation 

centers, and fire, rescue, 

ambulance, and police 

stations.

Older facilities with significant wind-resistance 

vulnerabilities:

•	 Ringgold High School and Ringgold Middle 

School (Section 6.1.3)

•	 Joplin High School (Section 6.1.5)

•	 Webster’s Chapel Volunteer Fire Department 

(Section 7.2.3)

•	 Smithville Police Department (Section 7.3.4)

Conclusion #16

Older facilities were 

susceptible to damage 

from weak tornadoes. 

Older facilities were subject 

to considerable building 

damage and disruption of 

facility operations when 

struck by even weak 

tornadoes

Recommendation #25

Perform a vulnerability 

assessment.

Facilities lacking of adequate signage, for example:

•	 Joplin East Middle School (Section 6.1.4)

•	 Fultondale Municipal Complex’s Library 

(Section 7.2.1)

•	 Tuscaloosa EOC (Section 7.3.1)

Conclusion #17

There was a lack of 

adequate signage 

directing occupants to 

refuge areas. 

(See also Conclusions #8 

and #28)

Recommendation #26

Identify best available 

refuge areas.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 7-53

OBSERVATIONS ON CRITICAL FACILITY PERFORMANCE: HEALTHCARE, FIRST RESPONDER, AND EOCS

Observation(s) Conclusion Recommendation

Critical facilities in path of tornado track with 

lack of FEMA 361-compliant safe room or ICC 

500-compliant shelter:

•	 Alberta Elementary School (Section 6.1.1)

•	 University Place Elementary School (Section 

6.1.2)

•	 Ringgold High School and Ringgold Middle 

School (Section 6.1.3)

•	 Joplin East Middle School (Section 6.1.4)

•	 Joplin High School (Section 6.1.5)

•	 LaRocca Nursing Home (Section 7.1.2)

•	 Greenbriar Nursing Home (Section 7.1.3)

•	 St. John’s Medical Center (Section 7.1.4)

•	 Fultondale Municipal Complex (Section 7.2.1)

•	 Tuscaloosa Fire Station 4 (Section 7.2.2)

•	 Webster’s Chapel Volunteer Fire Department 

(Section 7.2.3)

•	 Smithville Police Department (Section 7.2.4)

•	 Tuscaloosa EOC (Section 7.3.1)

Conclusion #5 and #18

(#5) Many of the critical 

facilities observed lacked 

safe rooms and/or storm 

shelters.

(#18) There was a lack 

of safe rooms and 

storm shelters in critical 

facilities.

Recommendation #27

Include safe rooms in 

design of new facilities.

Critical facilities with glazing damage, for example:

•	 Alberta Elementary School (Section 6.1.1)

•	 Ringgold High School and Ringgold Middle 

School (Section 6.1.3)

•	 Joplin High School (Section 6.1.5)

•	 LaRocca Nursing Home (Section 7.1.2)

•	 St. John’s Medical Center (Section 7.1.4)

•	 Tuscaloosa Fire Station 4 (Section 7.2.2)

Conclusions #15 

Glazing is susceptible to 

damage.

Recommendation #28

Enhance building design 

to better withstand 

tornadoes.

Critical facilities that did not remain operational 

following a tornado:

•	 Alberta Elementary School (Section 6.1.1)

•	 University Place Elementary School (Section 

6.1.2)

•	 Ringgold High School and Ringgold Middle 

School (Section 6.1.3)

•	 Joplin East Middle School (Section 6.1.4)

•	 Joplin High School (Section 6.1.5)

•	 LaRocca Nursing Home (Section 7.1.2)

•	 Greenbriar Nursing Home (Section 7.1.3)

•	 St. John’s Medical Center (Section 7.1.4)

•	 Fultondale Municipal Complex (Section 7.2.1)

•	 Tuscaloosa Fire Station 4 (Section 7.2.2)

•	 Webster’s Chapel Volunteer Fire Department 

(Section 7.2.3)

•	 Smithville Police Department (Section 7.2.4)

•	 Tuscaloosa EOC (Section 7.3.1)

Conclusion #4

IBC-compliant facilities 

can be susceptible to 

building damage.

Recommendation #29

Strengthen facilities to 

remain operational. 

Table 7‐1: Summary of Conclusions and Recommendations for Critical Facility Performance (concluded)

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 8-1

8Observations on 

Infrastructure Performance

Natural hazards not only damage buildings but can also damage 

and disrupt a community’s infrastructure. Infrastructure damaged 

during disaster events can have a widespread effect on a 

community’s ability to recover and significantly delay its return to 

normal functioning.

While MATs have historically concentrated on the performance of buildings, this MAT also assessed 

the performance of some utilities that were affected by the tornadoes, including water treatment 

and distribution facilities and towers (communications and antennae). The MAT also visited a 

wastewater treatment facility that performed well during and after the event and determined that 

lessons applicable to similar facilities could be learned. 

The MAT assessed infrastructure in Tuscaloosa, AL, and Smithville, MS. The Tuscaloosa facilities 

the MAT visited are shown in Figure 8-1. The Smithville facilities are shown in Figure 8-2. 
8-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8‐1: Locations of infrastructure assessed by the MAT in Tuscaloosa, AL

SOURCE FOR TORNADO TRACK: HTTP://WWW.SRH.NOAA.GOV/SRH/SSD/MAPPING

The MAT visited several infrastructure facilities and assessed tornado damage and its effects on 

those facilities; however, the MAT did not provide EF ratings for the structures for two reasons. First, 

no EF scale DIs are established for some of the infrastructure types the MAT visited, and second, 

the effects of high winds on the infrastructure were not always the result of direct damage to the 

infrastructure, but rather to the utilities that served the infrastructure. Most notably, the high winds 

did not damage the water treatment and distribution systems the MAT observed, but did damage 

the electric lines that fed those systems; therefore, the most serious consequences of the tornadoes 

on those facilities were not from direct damage, but from the loss of electrical power. 

8.1 Water Treatment and Distribution Facilities

Water treatment and distribution facilities typically consist of a water source, a treatment facility, 

and a system of water distribution pipelines that deliver treated water to customers. Depending on 

the relative elevations between the water sources and the customers and the geographical location 

of those customers, water storage towers and water pumping stations may also be present. Water 

towers can be vulnerable to high-wind events, particularly when the amount of water stored in 

them is low, and water treatment facilities and water pumping stations can be vulnerable to service 

interruptions when electrical power is lost. Long-duration service interruptions can be devastating 

to a community trying to recover from a natural hazard event. Service interruptions can also lead to 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 8-3

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

contamination of the treated water and create significant health hazards. Following the devastating 

April 2011 tornadoes, the MAT visited two water treatment facilities, one in Tuscaloosa, AL, and one 

in Smithville, MS.

8.1.1 Tuscaloosa Water Works (Tuscaloosa, AL)

The Tuscaloosa Water Works is part of the Tuscaloosa Water Works and Sewer Department. 

According to their Web site, the Tuscaloosa Water Works delivers more than 10 billion gallons of 

water to their customers annually. They serve over 200,000 customers in the City of Tuscaloosa 

and surrounding communities of Carrols Creek, Coaling, Coker, Englewood-Hulls, Foster-Ralph, 

Mitchell, and Peterson. 

Location of Facility in Tornado Path: Figure 8-3 shows an aerial view of the tornado damage swath. 

NWS rated the center of the tornado circulation as EF4 in the vicinity of one of the Tuscaloosa 

Water Works storage towers and the DCH Regional Medical Center, a local hospital served by the 

Tuscaloosa Water Works that suffered reduced water pressure after the tornado. 

Facility Description: The Tuscaloosa Water Works system has 575 miles of water mains that are 4 

inches in diameter or larger and 3,684 public fire hydrants. The Tuscaloosa Water Works collects 

Figure 8‐2: Locations of infrastructure assessed by the MAT in Smithville, MS. The NWS track is not shown since it 

varied greatly from MAT observations.

SOURCE FOR TORNADO TRACK: MAT-DERIVED

Map source: Bing Maps
8-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8‐3:

Aerial view showing the approximate centerline of the damage 

swath (red line)1 in relationship to the Tuscaloosa Water Works 

storage tower (yellow circle, top inset) and the DCH Regional 

Medical Center (yellow circle, bottom inset)

SOURCE: ALL AERIAL PHOTOGRAPHS ARE FROM NOAA IMAGERY (HTTP://NGS.

WOC.NOAA.GOV/STORMS) UNLESS OTHERWISE NOTED

1 The red line in this and all similar figures represents the center of 

the damage swath. The track location is approximated by the MAT 

based on post-event aerial photographs. The actual centerline of 

the vortex is offset from the centerline of the damage.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 8-5

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

water from the Ed Love Lake and the smaller Jerry Platt Lake. The Ed Love plant can treat up to 

45.7 million gallons per day (MGD). The Jerry Platt plant can treat up to 14 MGD. Water is treated 

at two treatment plants, pumped into 13 storage towers, and fed to customers. The system can store 

25.4 million gallons of treated water, 20.6 million gallons of which are stored in tanks; the remaining 

quantity is stored in the distribution piping. 

Emergency power at the Ed Love plant consists of two 1,500-kilovolt-ampere diesel generators that 

allow the plant to fully function while normal power is lost. There are 23 booster pumps in 8 booster 

pump stations that fill the storage tanks and control system pressure. The pumps range in size from 

25 to 100 horsepower. The pumps are powered by overhead electrical lines from the local electrical 

utility; no emergency generators are in place to provide alternate power to the pumps.

General Wind Damage and Functional Loss: The Tuscaloosa Water Works storage towers were 

outside of the tornado’s swath and were not damaged. However, tornadic winds along the track 

destroyed hundreds of buildings and other structures in Tuscaloosa. The tornado winds also 

destroyed miles of overhead electrical transmission and distribution lines and damaged or destroyed 

electrical substations. Power to the area was interrupted, and several water service lines were broken 

when buildings were destroyed by the tornado. Figure 8-4 shows representative damage to overhead 

lines and substations. Shortly after the storm, line breaks contributed to large amounts of water loss, 

but the larger water line breaks were isolated within hours, so water losses through line breaks were 

quickly minimized. Smaller line breaks were isolated within 2 to 3 days.

Electrical power, however, was not restored for several days, and without power to drive the lift 

pumps that fill tanks and booster pumps for system pressure, the storage tanks drained and system 

pressures dropped. Water service was affected, including water service to critical facilities. For 

example, approximately 7 hours after the storm, the normal 90 pounds per square inch (psi) of 

water pressure normally provided to DCH Regional Medical Center (location shown in Figure 8-3) 

dropped to 25 psi. With the reduced water pressure, toilets on upper floors would not flush and the 

low water-pressure levels required the hospital to shut down a boiler supplying steam to their central 

sterilization equipment. Without sterilization equipment, surgical procedures were curtailed. 

Figure 8‐4: 

Representative damage to 

overhead electrical lines 

and substations along the 

tornado path 

(Tuscaloosa, AL)
8-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

8.1.2 Smithville Water Treatment and Distribution System (Smithville, MS)

Smithville, MS, is supplied by a 42 MGD water treatment and distribution system. Surrounding 

areas are supplied by a separate rural water treatment and distribution system. The urban and rural 

systems serve approximately 450 clients each. The rural system was not damaged by the tornadoes 

and was not inspected. Observations of the system in Smithville proper are described below.

Location of Facility in Tornado Path: A tornado touched down west to southwest of Smithville 

and travelled east to northeast. NWS rated the center of the this tornado circulation as EF5.

The approximate centerline of the tornado damage swath is shown in Figure 2-2 (tornado #43) and 

below in Figure 8-5. Figure 8-5 also shows the location of the Smithville Water Treatment Plant and 

storage tower, as well as the location of a 300-foot-tall guyed cellular tower that collapsed (discussed 

in Section 8.3.2.1).

Figure 8‐5: Aerial view showing the approximate centerline of the tornado damage swath in Smithville, MS (red 

line), the Smithville Water Treatment and Distribution System Plant (blue circle), and the 300-foot-tall cellular tower 

discussed in Section 8.3.2.1 (yellow circle)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 8-7

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Facility Description: The Smithville Water Treatment and Distribution System Plant is shown in 

Figure 8-6. The water for the urban system is drawn from two wells, treated, stored in an underground 

clear well, and then pumped into a large storage tank (Figure 8-7). From the storage tank, treated 

water is gravity-fed to customers. Treatment consists of aeration, sand filtration, chlorination, and 

pH control. Since the well water is high in dissolved iron, it is also treated for iron removal. The 

wells, treatment plant, lift pumps, and storage tower are all on Earl Frye Street in Smithville. 

Water is pumped from the treatment facility clear well to the storage tank with two 20-horsepower 

lift pumps. The pumps are operated lead/lag (i.e., only one pump operates at a time). The pumps 

are supplied by overhead electrical lines. The facility does not have any emergency or standby 

generators for alternate power.

Figure 8‐6: 

Smithville Water Treatment 

Plant and storage tower 

(red box) aerial photograph 

pre-dates the tornado 

(Smithville, MS)

SOURCE: © GOOGLE EARTH

General Wind Damage: At the Smithville Water Treatment and Distribution System Plant, the 

tornado destroyed a small building constructed of unreinforced CMU and damaged a small storage 

building constructed of metal frames and metal wall and roof panels (Figure 8-8). The buildings 

were used for secondary non-critical functions like maintenance and storage, and the damage did 

not significantly affect operations.
8-8 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8‐7: 

Water tower after the 

tornado (Smithville, MS)

Figure 8‐8: Destroyed unreinforced CMU building (left) and damaged metal-framed building (right) (Smithville, MS)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 8-9

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

The water treatment control equipment was in a building constructed of reinforced masonry 

(Figure 8-9). While close to the other buildings and exposed to similar winds, the stronger 

reinforced building was not extensively damaged.

Figure 8‐10: Debris impact damage to Smithville, MS, water tank: photograph on left shows where debris struck the 

water tank itself (red circle) and photograph on right shows the repaired compression strut that was damaged by windborne debris (red box)

Figure 8‐9: 

Reinforced CMU building housing control equipment (left) and 

undamaged water treatment control equipment (right) (Smithville, MS)

The storage tower was struck by large pieces of wind-borne debris (Figure 8-10). The debris impacted 

the tank itself and a compression strut that provides lateral bracing and support for the tower legs. 

At the time of the MAT visit, the impacted area of the tank was not repaired, but the damaged 

compression strut had been straightened and reinforced. System operators did not know whether 

the repairs were completed under the direction of a design professional.
8-10 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Water pumps and pump controllers were located outside (Figure 8-11). Even though wind-borne 

debris was widespread in the area, they were not damaged. However, high-pressure chlorine 

cylinders were stored outside and only lightly secured with small-gage chain (Figure 8-12). Some 

cylinders were dislodged and displaced nearly 100 yards by the tornadic winds.

Figure 8‐11: 

Lift pumps and controls of 

the Smithville, MS, water 

plant were exposed, but not 

damaged

Figure 8‐12: 

Lightly secured chlorine 

cylinders; some were 

displaced by high winds 

(Smithville, MS)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 8-11

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Functional Loss: While critical equipment 

was not damaged (even though much of it 

was exposed), the tornado destroyed overhead 

electrical lines and disrupted power to the 

Smithville, Water Treatment and Distribution 

System Plant. The tornado also broke fire 

hydrants and destroyed most of the buildings 

in town. The destruction of buildings damaged 

much of the water service piping laterals that 

supplied individual customers.

The damage to distribution piping and water 

service piping laterals resulted in rapid water loss. Since there were no emergency or alternate power 

supplies serving the lift pumps, the storage tank drained rapidly, and there was a loss of system 

pressure in the distribution system. The loss of system pressure can allow groundwater to enter 

distribution piping and contaminate the treated water in the system. Although operators stated 

that they did not know if water contamination occurred after the tornado, the water treatment and 

distribution system plant issued “Boil water before use” orders to its customers as a precautionary 

measure. During the MAT’s visit 11 days after the event, distribution and service line breaks had 

been repaired or isolated, and system pressure was restored. Operators of the system were awaiting 

water test results before lifting the “Boil water before use” orders. 

8.2 WasteWater Treatment Facilities

A functioning wastewater treatment facility is critical for recovery after a natural disaster. Long-term 

loss of a wastewater treatment facility can create significant health hazards. The MAT interviewed 

the director of the Tuscaloosa Waste Water Treatment Plant. The plant managed to continue 

running after the tornado even though the facility experienced wind damage and normal power 

supply to the plant was lost.

8.2.1 Tuscaloosa Waste Water Treatment Plant and Collection System (Tuscaloosa, AL)

The Tuscaloosa Waste Water Treatment Plant treats effluent from the entire city and surrounding 

service areas. The plant has a current capacity of 30 MGD, but plans to add an additional 15 MGD 

in 2013. 

Location of Facility in Tornado Path: The location of the Tuscaloosa Waste Water Treatment Plant 

is shown in Figure 8-1. Figure 8-13 shows an aerial view of the centerline of the tornado damage 

swath in the vicinity of the Tuscaloosa Waste Water Treatment Plant. 

Facility Description: The Tuscaloosa Waste Water Treatment Plant is a 30 MGD plant that serves 

Tuscaloosa and surrounding areas. Power for the water treatment facility is normally provided by 

the local electrical utility from overhead distribution lines. The treatment plant itself has on-site 

emergency diesel generators that allow the plant to operate during prolonged power outages. Also, 

approximately 50 of the 60 remote lift stations that pump untreated effluent to the treatment plant 

are equipped with emergency generators.

Chlorine is a hazardous material and 40 CFR 

355.30 triggers emergency planning requirements when more than 100 pounds of chlorine 

is stored. Containers of chlorine should be 

protected from exposure to weather, extreme 

temperatures changes, and physical damage, and they should be stored separately 

from flammable gases and vapors and combustible substances.
8-12 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

General Wind Damage and Functional Loss: The director of the Tuscaloosa Water Works and 

Sewer Department stated that the tornado disrupted the normal utility power to the plant and 

remote lift stations, and caused damage to roof systems, doors, and windows at the treatment plant. 

While normal power was lost, the system continued to operate on emergency power during and 

after the event with no overflow or discharge of untreated effluent. Some of the remote lift stations 

lacked emergency power, and effluent had to be pumped into trucks for transportation to the 

central treatment plant. The loss of doors, windows, and roof coverings allowed water to enter the 

treatment plant building, but the water entry did not disrupt operations.

8.3 Towers (Communications and Antennas)

Communications towers support antennae that serve cellular phones, emergency management 

systems (EMSs), fire, police, and other critical functions. Since the number and type of antennae 

mounted on any given tower varies greatly, the functional effects of losing a tower can only be 

determined on a case-by-case basis. 

Figure 8‐13: Aerial view of the Tuscaloosa Waste Water Treatment Plant (yellow rectangle) in relation to the approximate 

centerline of the April 27, 2011 tornado damage swath (red line)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 8-13

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Towers fall into two general categories: guyed towers and free-standing towers. Guyed towers use a 

system of steel cables that provide lateral support for a single vertical mast. One end of each cable is 

connected to the tower, and the other end is connected to earth anchors or concrete foundations. 

Guy wires are usually installed in sets of three, with each guy wire spaced 120 degrees from adjacent 

wires. Guy wires are tensioned so that the lateral loads on the mast are balanced, and the mast itself 

is exposed only to compression loads. The mast in a guyed tower is typically quite slender since the 

mast is primarily loaded in compression, and lateral wind loads are resisted by the guy wires. 

Free-standing towers can be either latticed structures or solid structures. Solid structures are not 

solid through their cross-sections but rather their interiors are hollow and their outer surfaces solid. 

Unlike guyed towers, free-standing towers do not rely on guy wires and anchors for lateral support. 

For a free-standing tower to function, it must be strong enough to resist all lateral loads imposed on 

it from a design event. It must also be able to transfer those loads to a suitable foundation and the 

foundation must be large enough and strong enough to transfer all applied loads to the supporting 

soils below. Without guys, free-standing towers must have a wide footprint and large foundations to 

prevent overturning and toppling. 

8.3.1 Free-Standing Towers

The MAT assessed two latticed towers: a 250-foot tower used by the Tuscaloosa EMS and a 300-

foot cellular tower. It also evaluated a solid cellular tower near a retail center in Tuscaloosa, AL 

(see Section 5.2.3); although the MAT did not visit this tower, it evaluated to tower’s performance 

by reviewing photographs taken from a helicopter during a flyover 3 days after the tornado struck 

the area. 

8.3.1.1 Latticed 250-Foot EMS Communications Tower (Tuscaloosa, AL)

The Tuscaloosa EOC (described in Section 7.3.1), which was destroyed by the tornado, was served 

by a free-standing, latticed, 250-foot-tall communications tower. The tower supported antennae for 

fire, police, and the EOC. The 250-foot EMS tower was located at N33.177933° and W87.563561°.

Location of Facility in Tornado Path: The location of the EMS communications tower is shown in 

Figure 8-1. Figure 8-14 shows an aerial view of the centerline of the tornado damage swath near the 

EMS communications tower. The EMS communications tower was within 1,000 feet of the center of 

the tornado damage swath.

Facility Description: The EMS communications tower was relatively new, having been constructed 

within the last 2 years. The tower was a triangular-based latticed steel structure on concrete 

foundations. The tower bases were spaced 20 feet apart and constructed with six 7/8-inch-diameter 

anchor bolts on poured concrete foundation caps. The size and depth of the foundation could not 

be determined visually. 

General Wind Damage and Functional Loss: The EMS communications tower collapsed during the 

storm and fell across the road that separates it from the EOC. By the time of the MAT’s visit, the tower 

had been removed, and only its concrete base remained. The tower was, however, photographed by 

EMS staff from the ground the day of the event (Figure 8-15) and from a helicopter 3 days after the 

tornado struck it on April 27 (Figure 8-16).
8-14 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8‐14: Aerial view of the approximate centerline of the tornado damage swath (red line) in the vicinity of the 

latticed 250-foot EMS communications tower (yellow circle) (Tuscaloosa, AL) 

Figure 8‐15: 

View of toppled EMS 

communications tower 

taken by EMS personnel 

after the tornado. Note the 

wind-displaced material 

(discussed in text) adhered 

to the tower 

(Tuscaloosa, AL). 

PHOTOGRAPH COURTESY 

OF TUSCALOOSA COUNTY 

SHERIFF’S OFFICE
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 8-15

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

The MAT noted fresh shear cracks in the concrete foundation bases (Figure 8-17). The cracks 

resulted from tensile loading in the tower/base connection and suggest that bending occurred in 

the concrete tower base.

Figure 8‐16: View of the collapsed EMS communications tower (yellow oval); the EOC across 35th Street is also shown 

(red oval) (Tuscaloosa, AL). The communications tower was cut, and the debris that was across the road was removed 

(yellow triangle).

PHOTOGRAPH COURTESY OF TUSCALOOSA COUNTY SHERIFF’S OFFICE

Figure 8‐17: 

Photograph shows the sixbolt tower base with cracks 

in concrete foundation cap 

(red oval) (Tuscaloosa, AL)
8-16 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Wind-displaced materials adhered to the 

latticed EMS communications tower (Figure 

8-16). The adhered materials consisted of 

chain link fence fabric and webbing interwoven 

into the fabric. The adhered materials created 

nearly solid surface areas that increased the 

amount of surface area exposed to wind 

pressures, thereby increasing the wind loads on 

the tower. 

The MAT could not determine if the winddisplaced materials adhered to the EMS 

communications tower before or after it 

collapsed. Since fencing is generally not an 

engineered structure, and communications 

towers are generally extensively engineered, it 

is highly likely that the fencing was displaced before the tower collapsed. If this was the case, any 

displaced fencing material that wrapped around the tower would have increased wind loads and 

could have contributed to the tower failure.

ASTM E1996, Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors, and Impact 

Protective Systems Impacted by Windborne Debris in Hurricanes (2009), which is referenced in the windborne debris requirements of the 2012 IBC, specifies missile types and sizes ranging from small steel 

balls that simulate roof surface aggregate to large 2x4 framing members that simulate debris from 

destroyed upwind structures. However, there is no specification for materials that do not puncture 

building envelopes, termed here as “wind-displaced materials” (see text box). Currently there is no 

consensus standard on wind-displaced materials and no guidance on how to treat their effects on 

wind loading of structures. 

8.3.1.2 Latticed 300-Foot Cellular Tower (Tuscaloosa, AL)

A 300-foot latticed cellular tower was located approximately 0.6 mile northeast of the EMS 

communications tower. Like the EMS communications tower, the cellular tower was a latticed style 

free-standing tower. Unlike the EMS tower, the cell tower was older and appeared to have been in 

service for years. The 300-foot cellular tower was located at N33.184515° and W87.557541°.

Location of Facility in Tornado Path: The location of the latticed 300-foot cellular tower is shown 

in Figure 8-1. Figure 8-18 shows an aerial view of the centerline of the tornado damage swath in the 

vicinity of the 300-foot latticed cellular tower; also shown is the location of the EMS communications 

tower 0.6 mile to the southwest (described in Section 8.3.1.1). The 300-foot cellular tower was 

approximately 500 feet north of the center of the tornado damage swath.

Facility Description: The bases of the 300-foot latticed cellular tower were spaced 30 feet apart and 

consisted of six 11⁄2-inch diameter anchor bolts set in cast-in-place concrete (Figure 8-19).

In this section, the MAT introduces a new 

term: wind-displaced materials. Historically 

these materials have been referred to as windborne debris. 

While both wind-displaced materials and 

wind-borne debris are created by high-wind 

events, their effects on downwind structures 

are very different. Wind-borne debris tends 

to puncture building envelopes, while winddisplaced materials tend to wrap around or 

adhere to downwind structures and can increase wind loads on those structures. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 8-17

OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8‐18: Aerial view of the approximate centerline of the tornado damage swath (red line) in the vicinity of the 300foot latticed cellular tower (yellow oval). Also shown is the 250-foot EMS tower described in Section 8.3.1.1 (blue oval) 

(Tuscaloosa, AL). 

Figure 8‐19: 

Base for 300-foot latticed 

cellular tower 

(Tuscaloosa, AL)
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OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

General Wind Damage and Functional Loss: The 300-foot latticed cellular tower was completely 

destroyed by the April 27, 2011 tornado. Figure 8-20 shows the collapsed cellular tower.

No wind-displaced building materials were seen physically adhered to the fallen latticed tower. 

However, a large metal building southeast of the tower had been destroyed (Figures 8-21 and 8-22), 

and large sections of metal panels were scattered throughout the area. The MAT also observed 

a trailer frame leaning against the fence surrounding the cell tower base (Figure 8-23). These 

observations suggest that the storm created large amounts of wind-borne debris and wind-displaced 

sheathing in the vicinity of the tower and wind-displaced material likely struck the tower.

Figure 8‐20: 

View of the 300-foot latticed 

cellular tower that collapsed 

during the tornado event 

(Tuscaloosa, AL)

Figure 8‐21: 

Photograph of the 300-foot 

cellular tower (yellow oval) 

and the metal building to the 

southeast (blue box) before 

the April 27, 2011 tornado 

(Tuscaloosa, AL) 

SOURCE: © GOOGLE EARTH
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OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8‐22: 

View of the collapsed 300foot cellular tower (yellow 

oval) and the destroyed 

metal building southeast 

of the tower (blue box) in 

relation to the approximate 

centerline of the tornado 

damage swath (red line) 

(Tuscaloosa, AL)

PHOTOGRAPH COURTESY 

OF TUSCALOOSA COUNTY 

SHERIFF’S OFFICE

Figure 8‐23: 

Remnants of a trailer that 

struck the fence surrounding 

the 300-foot cellular tower 

(Tuscaloosa, AL)

8.3.1.3 Solid Cellular Tower, 13th Street (Tuscaloosa, AL)

A solid cellular tower near 13th Street in Tuscaloosa, AL, was not visited during the MAT field 

reconnaissance, but was assessed by reviewing aerial photographs taken during a flyover 3 days after 

the April 27, 2011 tornado event. While this limited assessment did not provide detailed information 

on the performance of the tower, it allowed the MAT to make the observations described below. 

Web-based data from Google Earth Pro (liscensed) indicate that the tower is located at N33.201454° 

and W87.521943°. Although this tower was within the tornado damage swath, the cellular tower did 

not collapse during the event. 
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OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Location of Facility in Tornado Path: The location of the solid cellular tower is shown in Figure 

8-1. Figure 8-24 shows an aerial view of the centerline of the tornado damage swath in the vicinity of 

the solid cellular tower. The cellular tower is within 500 feet of the centerline of the tornado damage 

swath in an area where the storm caused extensive damage and destruction to nearby buildings. 

Facility Description: Oblique aerial photographs taken during a flyover 3 days after the event 

show that the tower is free-standing (i.e., not guyed) and of a solid style, tapered-steel construction 

(Figure 8-25). Although the aerial photographs do not allow precise measurements of tower height, 

the MAT estimates the tower to be approximately 300 feet tall based on its height relative to nearby 

buildings. 

General Wind Damage and Functional Loss: The aerial photographs show that the tower withstood 

the event without collapsing.

Figure 8‐24: Aerial view of the approximate centerline of the tornado damage swath (red line) in the vicinity of the solid 

cellular tower left standing after the tornado (yellow circle) (Tuscaloosa, AL)
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OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8‐25: 

Aerial view of solid cellular 

tower left standing after 

event. Insert shows aerial 

view of the tower amidst 

destroyed buildings 

(Tuscaloosa, AL).

PHOTOGRAPH COURTESY 

OF TUSCALOOSA COUNTY 

SHERIFF’S OFFICE

8.3.2 Guyed Towers

Like all towers, guyed towers can fail during high-wind events such as tornadoes. High winds can 

create forces that exceed a tower’s strength and can create wind-borne debris that damages portions 

of it. High winds can also create wind-displaced materials that can adhere to a tower’s mast or guys, 

increasing the wind loads the tower must resist to avoid failure. In addition, guyed towers are at risk 

because all guys and anchors must be functional for the tower to remain stable. The loss of even one 

guy can result in tower collapse. 

8.3.2.1 300-Foot Guyed Cellular Tower (Smithville, MS)

The MAT inspected a 300-foot guyed cellular tower in Smithville, MS. The 300-foot guyed tower 

is located approximately three-quarters of a mile west-southwest of the Smithville water tower 

(described in Section 8.1.2) and 1.25 miles west-southwest of the center of town. The guyed tower is 

situated in an open field approximately 450 feet northwest of Highway 25.

Location of Facility in Tornado Path: The 300-foot-tall guyed cellular tower is shown in Figure 8-2 

and 8-26. The centerline of the tornado damage swath is approximately 200 yards southeast of the 

tower. There were few buildings near the tower, but the MAT noted wind-borne debris and winddisplaced materials littering the cellular tower site. 
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Figure 8‐26: Aerial view of the 300-foot guyed cellular tower (yellow circle) in relationship to the approximate centerline 

of the tornado damage swath (red line) in Smithville, MS. The Smithville water tower shown in Figures 8-5 through 8-7 

is northwest of the guyed tower and circled in blue for reference.

Facility Description: The guyed tower was laterally supported by three sets of earth anchors. The 

guys and anchors were oriented approximately at 60 degrees (east-northeast), 180 degrees (south) 

and 300 degrees (west-northwest), as shown in Figure 8-27.

The mast was connected to each of the guy anchors with five galvanized guys (both 5/16- and 

7/16-inch-diameter guys were used) and turnbuckles (Figure 8-28). The ground anchor shafts were 

2 inches in diameter. The MAT could not determine if each of the three anchor shafts terminated 

in an earth anchor or in a buried concrete mass.

General Wind Damage and Functional Loss: The tower collapsed during the event (Figure 8-29), 

and by the time the MAT visited the site 11 days after the event, preliminary clean-up activity had 

occurred and a temporary tower had been erected on site. The upper portion of the collapsed tower 

had been moved to clear the access road to the site.
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OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8‐28: 

Guy attachment plate, 

turnbuckle, and anchor shaft 

(Smithville, MS)

Figure 8‐27: 

Aerial photograph showing 

the 300-foot-tall guyed 

cellular tower after the 

tornado; the yellow lines 

show the location of the 

original guys, and the red 

box shows the position 

of the tower remnants 

observed by the MAT 

(Smithville, MS)

SOURCE: © GOOGLE EARTH
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OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8-29: Collapsed 300-foot cellular tower (blue box). The triple guy in the foreground (red oval) is one of the three 

supports for the temporary tower on the site (Smithville, MS).

Wind-displaced building components struck and adhered to the south guy (Figure 8-30). The 

anchor that secured those guys failed and was dragged several feet though the ground (Figure 8-31). 

The remnants of the tower indicate that it fell to the west. The location of the fallen tower, the 

presence of the wind-displaced materials adhered to the southern guy, and the failure of the guy 

anchor suggest that wind-displaced materials overloaded the southern anchor, and the failure of the 

southern anchor caused the tower to collapse.

Figure 8‐30: 

Wind-displaced building 

materials wrapped around 

the 300-foot cellular tower 

guy (Smithville, MS)
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OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Figure 8‐31: 

The anchor securing one 

guy was dragged several 

feet through the ground 

(Smithville, MS)

8.4 Summary of Conclusions and Recommendations

Table 8-1 provides a summary of the conclusions and recommendations for Chapter 8, Observations 

on Infrastructure Performance, and provides section references for supporting observations. Additional 

commentary on the conclusions and recommendations is presented in Chapters 10 and 11. 

Table 8‐1: Summary of Conclusions and Recommendations for Infrastructure Performance

Observation(s) Conclusion Recommendation

Failed towers due at least in part to winddisplaced materials: 

•	 Latticed 250-Foot EMS Communications 

Tower (Section 8.3.1.1)

•	 Latticed 300-Foot Cellular Tower 

(Section 8.3.1.2)

•	 300-Foot Guyed Cellular Tower 

(Section 8.3.2.1) 

Conclusions #6 and #21

(#6) Wind-displaced 

materials affected 

communications towers.

(#21) Wind-displaced 

materials affected tower 

performance.

Recommendations #30 

and #31

(#30) Work collaboratively to 

better understand the risks of 

wind-displaced materials on 

communications towers. 

(#31) Work collaboratively to 

better understand the effects 

of wind-displaced materials 

on latticed structures.
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OBSERVATIONS ON INFRASTRUCTURE PERFORMANCE

Observation(s) Conclusion Recommendation

Reliance of systems on utility power to 

operate lift or booster pump resulted in loss 

of system pressure when portions of electrical 

distribution systems were destroyed:

•	 Tuscaloosa Water Works in Alabama 

(Section 8.1.1)

•	 Smithville, MS, water treatment and 

distribution system (Section 8.1.2) 

Conclusion #19

Lost utility power caused 

loss of system function.

Recommendation #32

Provide an alternate electrical 

source.

Failed communications and cellular towers:

•	 Latticed 250-Foot EMS Communications 

Tower (Section 8.3.1.1)

•	 300-Foot Guyed Cellular Tower 

(Section 8.3.2.1)

Conclusion #20

Guy anchors failed when 

struck by wind-displaced 

materials.

Recommendation #33

Work collaboratively to better 

understand communications 

tower performance.

Table 8‐1: Summary of Conclusions and Recommendations for Infrastructure Performance (concluded)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 9-1

9Observations on Tornado 

Refuge Areas, Hardened 

Areas, and Safe Rooms 

Although hurricanes in the Southeast have received most of the 

attention in recent years, the threat and risk from tornadoes in the 

central and eastern portions of the United States is real.

A total of 11,629 tornadoes were recorded by NOAA’s SPC for the 60-year study period from 1950 

through 2010 (NOAA 2011). Between 2000 and 2011, Alabama alone experienced 636 tornadoes 

with an associated 296 fatalities, and Missouri experienced 668 tornadoes with an associated 234 

fatalities. For occupants of buildings not hardened to meet FEMA or ICC criteria to provide lifesafety protection from tornadoes, it is critical to adequately plan how to minimize loss of operations 

and loss of life.

During severe weather, building occupants should be moved to a location in the building that is best 

protected from potential wind-borne debris and least susceptible to collapse. While these areas do 
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

not provide near-absolute protection (unless designed as safe rooms), they may reduce the number 

of occupants injured or killed. Appropriate tornado refuge areas should be identified by architects, 

engineers, or design professionals familiar with FEMA 361 and FEMA P-431, Tornado Protection: 

Selecting Refuge Areas in Buildings (2009b) (refer also to Section 1.2). These tornado refuge areas 

are usually interior locations with short-span roof systems, reinforced masonry or concrete walls, 

and no glazed (glass) openings. The tornado refuge areas that typically perform the best during 

tornadoes are corridors, small interior rooms, and restrooms. Although homeowners and building 

owners may have identified such areas for use during severe weather and implemented construction 

measures to improve their performance, these areas have not generally been designed specifically 

to provide occupant protection. In the absence of access to a safe room, tornado refuge areas are 

typically a “last choice” or “only option” for those seeking protection. It is important to note that 

tornado refuge areas do not guarantee safety and offer only limited protection from wind and windborne debris; however, if they are identified correctly, they offer the most protection for building 

occupants seeking refuge during tornadoes and are better than no protection at all. Additional 

information identifying refuge areas during tornadoes is provided in this chapter.

This chapter describes the differences between tornado refuge areas, hardened areas, storm shelters, 

and safe rooms (Section 9.1). It includes the MAT’s field observations made after the April 25–28, 

2011 tornado outbreak and the May 22, 2011 Joplin, MO tornado event regarding each of these types 

of protection areas (Sections 9.2 to 9.4). Section 9.5 presents observations related to travel time to 

places where individuals sought shelter during the tornadoes, and Section 9.6 presents observations 

related to compliance issues of both residential and community shelter areas not constructed to the 

stated criteria of the FEMA guidelines or ICC 500 standard.

9.1 Terminology and Examples

Buildings and portions of buildings that protect people during a tornado can be classified into four 

levels; in order of increasing level of protection, these levels of protection range from “minimal 

protection afforded” to “designed to provide near-absolute life-safety protection.” 

+ Tornado refuge areas are constructed to regular 

building code requirements, but may also have 

continuous load paths, bracing, or other features that 

increase resistance to wind loads. It is important for 

people to know that such an area may not be a safe 

place to be when a tornado strikes and they still may 

be injured or killed during a tornado event.

+ Best available refuge areas are areas in an existing 

building that have been deemed by a qualified 

architect or engineer to likely offer the greatest safety 

for building occupants during a tornado (defined in 

accordance with FEMA P-431). It is important to note 

that occupants of such areas may be injured or killed 

during a tornado since these areas are not specifically 

designed as tornado safe rooms. However, people in 

The MAT uses the terms “safe 

room” and “storm shelter” to 

describe only those hardened 

structures that meet the FEMA or 

ICC criteria for life-safety protection 

(see Section 1.2). Other structures, 

buildings, or portions thereof that 

have been described by their users 

as “shelters” but are not designed 

to accepted criteria for life-safety protection are identified here as 

hardened rooms, hardened structures, or tornado refuge areas.
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

the best available refuge areas are less likely to be injured or killed than people in other areas of 

a building.

+ Hardened areas or rooms are constructed for protection, but not specifically to set criteria. The 

difference between a hardened area and a best available refuge area is that specific portions of 

the area are designed to carry or resist higher loads from wind or wind-borne debris.

+ Storm shelters/safe rooms are constructed to meet criteria set forth in FEMA 320, FEMA 361, or 

ICC 5001

The MAT’s observations for the types of structures described above are presented in Sections 9.2 

to 9.5. However, it is important that the public and possible users of storm shelters and safe rooms 

understand that the levels of protection provided by structures designed according to ICC 500 

and FEMA guidance documents is notably more complete and safer than the level of protection 

provided by a building or structure in which part of the criteria set for the in those documents is 

implemented. Sections 9.1.1 and 9.1.2 provide observations from the field assessments to further 

define how these types of structures are different.

9.1.1 Hardened Areas: Areas Designed to Provide Some Protection

Some structures or portions of buildings observed by the MAT were designed and constructed to 

provide some level of protection, but did not meet the FEMA or ICC criteria; in some cases, this is 

because they were constructed prior to publication of the safe room guidance. These types of areas 

are often referred to as shelters by those who seek refuge in them. These hardened areas typically 

provide an improved level of protection for occupants from building or structural failure, but often 

do not follow FEMA or ICC design criteria. It is important to note that, beyond the basic ability to 

provide life-safety protection, hardened areas typically do not account for many of the other human 

factors addressed by ICC and FEMA criteria for storm shelters and safe rooms. Such factors include 

adequate space for occupants, ventilation, water, toilets, and other design elements to meet occupant 

needs.

Figure 9-1 shows a hardened room or “shelter” constructed in a residence in Tuscaloosa, AL, just 

weeks before the April 27, 2011 tornado. The home was directly in the path of the tornado as it 

moved through the Forrest Lake neighborhood of Tuscaloosa. This hardened room in the home did 

not collapse during the event, but the wooden door to its interior provided minimal protection from 

wind forces and wind-borne debris impacts. (The hardened room was not used during the tornado 

because the owners were not at home when the tornado struck Tuscaloosa.) Because the door did 

not meet the criteria from FEMA or ICC, the room should not be called a safe room or storm shelter 

because this component is not designed or tested to provide the same level of life-safety protection 

as the rest of the structure.

1 The 2008 versions of FEMA 320, FEMA 361, and ICC 500 are intended in this chapter unless another date is specified.
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9.1.2 Storm Shelters and Safe Rooms: Areas Designed for Life-Safety Protection

Storm shelters are structures, buildings, or portions of buildings that have been designed and 

constructed to meet ICC 500 criteria and offer protection from extreme weather events, such as 

tornadoes and hurricanes. Storm shelters provide life-safety protection for their occupants. By 

contrast, a safe room is a hardened structure or area of a building that has been designed and 

constructed to provide near-absolute protection against both wind forces and the impacts from 

wind-borne debris, as defined in the FEMA safe room publications. In addition to providing lifesafety protection from wind and wind-borne 

debris, structures built to the FEMA safe room 

criteria meet and exceed all of the design criteria 

in the ICC 500 and also consider other emergency 

management related performance criteria. Because 

of this, FEMA states that a safe room offers “nearabsolute protection” in severe weather events, an 

even higher level of protection than that provided 

by storm shelters. Examples of a FEMA residential 

and community safe room are presented in Figures 

9-2 and 9-3, respectively.

While safe rooms and storm shelters can provide the same or different levels of protection, the 

FEMA criteria for near-absolute protection can provide a different (and higher) level of protection 

depending on the design criteria used. The level of occupant protection provided by a space 

specifically designed as a safe room is intended to be much greater than the protection provided by 

buildings that comply with the minimum requirements of building codes. With respect to the storm 

shelter criteria from the ICC, the FEMA safe room criteria provide the same or slightly higher level 

“Near-absolute protection means that, 

based on our [FEMA’s] current knowledge of tornadoes and hurricanes, the 

occupants of a safe room built according to this guidance [FEMA 361] will have 

a very high probability of being protected from injury or death.”

SOURCE: FEMA 361, PG. 1-2 (2008 EDITION)

Figure 9-1: 

A hardened room in a 

residential building in 

Tuscaloosa, AL
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

of protection than the criteria set forth in the ICC 500 and consequently, the FEMA criteria can be 

said to meet or exceed the design requirements of ICC 500 in all instances. The level of protection 

provided by a safe room or storm shelter is a function of the design wind speed, resulting wind 

pressure used in designing it, and wind-borne debris impact criteria.

Figure 9-2: 

Above-ground residential 

safe room installed in a 

garage of a home in Joplin, 

MO, directly impacted by the 

tornado (rated EF4 based on 

the MAT’s observations)

Figure 9-3: 

These above-ground 

community safe rooms 

in Brookwood, AL, were 

used during the April 27 

tornado outbreak, but were 

not directly impacted by a 

tornado
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

+ Storm shelters are designed and constructed 

in accordance with ICC 500 and offer greater 

protection than traditional buildings and homes 

because they have been designed to provide lifesafety protection. However, they do not meet all the 

criteria of FEMA 320 and FEMA 361 and are not 

considered safe rooms.

+ Safe rooms are hardened structures that are 

specially designed and constructed in accordance with FEMA 320 and FEMA 361 guidelines. 

Safe rooms provide “near-absolute protection” in extreme weather events, including tornadoes 

and hurricanes. “Near-absolute protection” means that, based on our current knowledge of 

tornadoes and hurricanes, the occupants of a safe room will have a very high probability of 

being protected from injury or death per FEMA 320.

Safe rooms and storm shelters are typically interior rooms or spaces within a building, but they may 

also be entirely separate buildings or structures designed and constructed to protect their occupants 

from tornadoes or hurricanes. Safe rooms may be constructed above or below ground. Safe rooms 

and storm shelters can be used as dual-function rooms within a building or home, where the room 

may normally be used as a training room, hallway, or closet.

The fact that an engineering design standard (ICC 500) is referenced and heavily used as part 

of a much larger emergency management program shows FEMA’s commitment to use voluntary 

consensus standards to the maximum extent possible in carrying out its programs. FEMA continues 

to educate designers, emergency management officials, property owners, and people in the 

community seeking to find protection from tornados on the benefits of FEMA 320, FEMA 361, and 

ICC 500 and how they complement one another.

When compared, the technical guidance for tornado hazards is essentially the same between ICC 

500 and FEMA 361 for community storm shelters and safe rooms, but there are some differences 

when comparing criteria for hurricane hazards for wind, wind-borne debris, and flood design 

criteria. For residential applications, ICC 500 provides performance design criteria to be met. This 

allows for residential tornado and hurricane storm shelters to be designed for different wind speeds. 

In contrast, FEMA 320 guidance provides a prescriptive solution designed for the highest wind speed 

and wind-borne debris criteria shown on the tornado and hurricane hazard maps included in the 

ICC and FEMA documents. Further, the FEMA 320 criteria also specify the use of more stringent 

criteria than ICC 500. As a result, the prescriptive FEMA 320 safe room designs can be used for 

small community safe rooms, thereby expanding their applicability and usefulness.

In all cases, where differences exist, FEMA criteria are more stringent than the ICC 500 storm 

shelter criteria. Further, both the FEMA 320 and 361 documents provide important information 

about the planning, operation, and maintenance of a safe room while ICC 500 (an engineering 

standard) does not address those issues. Unfortunately, this does not diminish the reality that 

when the engineering design standard (ICC 500) and the FEMA technical guidance (FEMA 320 

and FEMA 361) provide different levels of protection it may lead to some confusion for designers, 

emergency management officials, property owners, and people in the community seeking to find or 

provide life-safety protection from tornadoes.

To date, NWS has not recorded any 

wind event exceeding the maximum 

design criteria provided in FEMA 320 

and FEMA 361 (250 mph, 3-second 

gust, 33 feet above grade).
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.2 Tornado Refuge Areas 

The MAT was able to find only a few safe rooms and 

storm shelters along the more than 300 tornado 

tracks (or damage swaths) of the April 25–28, 2011 

tornado events in the mid-south of the United States 

or in the May 22, 2011 Joplin, MO, tornado. This was 

surprising because it had been more than 10 years 

since FEMA began publishing technical guidance 

for the design and construction of safe rooms and 

storm shelters. Many people were forced to find 

any protection they could wherever they found 

themselves when the tornadoes struck.

Although some people taking refuge in areas of their homes in Alabama, Georgia, and Mississippi 

perished, the MAT believes the number of fatalities would have been significantly higher if these 

tornado refuge areas were occupied when the storms struck. The MAT observed many tornado 

refuge areas that had collapsed or filled with broken glass from windows shattered by wind-borne 

debris that would have been unsafe had they been occupied. However, for the tornado events of 

April 25–28, 2011 the NWS was able to provide long warning times and notifications. As a result, 

many people who would have taken refuge in an inappropriate place either found safer refuge or 

moved out of the path of the tornado.

The tornado that struck Joplin, MO on May 22, however, formed rapidly and descended on the 

city with little advanced warning. Numerous critical facilities, many commercial buildings, and 

thousands of homes were damaged by the tornado. There were fatalities in tornado refuge areas 

used during this event.

This section discusses the MAT’s observations of buildings (or the areas of buildings) where people 

took refuge when no safe rooms, storm shelters, or hardened areas were available. The performance 

of the buildings in the direct path, or near the path, of strong or violent tornadoes was poor, as 

expected. Residential buildings are not designed to provide resistance to wind loads or consider 

only minimal wind loads in their design. Non-residential structures, while designed to consider 

some level of wind resistance, generally do not provide resistance to extreme wind loads. For more 

detailed discussions and observations related to building performance, see Chapters 4, 5, 6, and 7 

of this report for residential buildings, commercial and industrial buildings, schools, and critical 

facilities, respectively.

9.2.1 Tornado Refuge Areas in Residences

The MAT was informed that many residents took refuge in their homes. This occurred for a number 

of reasons, including minimal warning time and the perception of their home being the safest 

location. In most cases, the homes did not have a safe room and there was no nearby community 

safe room or storm shelter. When such a place is not available within or near a home, homeowners 

are forced to take refuge in the best available spaces they can identify.

If homeowners cannot find shelter in a specifically designed safe room or storm shelter during a 

tornado, building occupants should take refuge either in the central areas of their homes or in 

The NWS and local meteorologists 

should be credited for their forecasting success in providing important and 

useful storm information that allowed 

many people to take appropriate action 

to either find a safe room or move out 

of the path of the tornadoes before the 

event struck in their community.
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the basements (if available). If no basement is available, the central area of the home is typically 

the portion most likely to survive tornado impacts and provides the best tornado refuge area in 

a home. This is evidenced by core remnants of residential buildings that survive tornado events. 

The performance of core remnants observed by the MAT is described in Section 9.2.1.1. The 

performance of basements is discussed in Section 9.2.1.2.

9.2.1.1 Core Remnants

In general, the basement is often the least vulnerable area during a tornado. However, if a house 

has no basement, the MAT’s observations indicate that the best place for an individual to go in their 

home is the central or core areas of the home. Although the location of the core varies from home 

to home, areas with multiple wall intersections, stairways, or near bathrooms or kitchens are most 

often the building core. These portions of homes typically perform better than other areas when 

exposed to extreme winds from tornadoes; areas with multiple wall intersections provide additional 

strength to resist wind loads if the walls (and sometimes ceiling systems) are connected together.

Site-Built Housing: Based on the MAT’s observations in all the impacted States, the cores of sitebuilt homes provided the most redundant portions of the structure (see Chapter 4 for detailed 

discussions on residential building performance). Figures 9-4 and 9-5 illustrate this concept. Some 

residents in site-built homes in Crescent Ridge, AL, took refuge in the core areas of their homes and 

survived the tornado event, even when their homes were largely destroyed. Unfortunately, many of 

the core remnants observed by the MAT could not protect the occupants in this hard-hit community, 

which was one of the first areas to be impacted by the Macon County Supercell Thunderstorm (see 

Figure 2-2 in Chapter 2). This single tornado was associated with 61 reported fatalities across these 

two cities, 43 of which were in the Tuscaloosa area.2 According to the FEMA JFO approximately 

one-third of the 43 people killed by this tornado were in Crescent Ridge. The NWS rated the center 

of the tornado circulation as EF4 in this portion of its track. The approximate centerline of the 

tornado damage swath is shown in Figure 9-4. This tornado struck both site-built and manufactured 

homes in the Cresent Ridge neighborhood, resulting in a significant loss of life.

Figure 9-6 shows another example of how a portion of a building may remain standing even after 

most of the building is destroyed by a violent tornado. No individuals took refuge in this home, but 

this core remnant survived the impact of the May 22, 2011 Joplin, MO, tornado. The NWS rated the 

center of the tornado circulation as EF4 in the vicinity of this building.

Manufactured Housing: Manufactured housing in Crescent Ridge, AL, did not withstand the 

tornado that struck the neighborhood. Damage in this neighborhood was ranked as EF4 by the 

MAT (see Appendix E for additional detail). Although the design and construction of manufactured 

housing improved greatly after HUD requirements were changed in 1994, manufactured housing 

is not constructed to survive a tornado event. The long, narrow dimension of the units and 

different means and methods of securing the units to foundations are a few of the factors that 

have contributed to overturning and other failures of manufactured home units. Figure 9-7 shows 

several manufactured homes in the Crescent Ridge, AL, area after the tornado. These homes were 

displaced off their foundations and also experienced significant damage to the units themselves. No 

core remnants remained.

2 NOAA’s NWS SPC, Annual U.S. Killer Tornado Statistics, http://www.spc.noaa.gov/climo/torn/fataltorn.html.
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Figure 9-4: Aerial view of tornado damage swath in Crescent Ridge, AL (approximate centerline of swath is indicated 

by red line).3 Core remnants of homes shown in Figures 9-5 are identified with red arrows. The damaged manufactured 

homes in Figure 9-7 are identified with a yellow arrow.

SOURCE: ALL AERIAL PHOTOGRAPHS ARE FROM NOAA IMAGERY (HTTP://NGS.WOC.NOAA.GOV/STORMS) UNLESS OTHERWISE NOTED

Figure 9-5: Core remnants of homes sometimes survive a tornado as shown in this photograph of site-built homes 

where a closet (red arrow in left photograph) and a bathroom behind a kitchen (red arrow in right photograph) remained 

standing after the tornado (Crescent Ridge, AL)

3 The red line in this and all similar figures is intended to represent the center of the damage swath. The track location is approximated by the 

MAT based on post-event aerial photographs. The actual centerline of circulation is offset from the centerline of the damage.
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.2.1.2 Basement Areas

Basement areas typically provide better protection than above-ground areas because one or more 

walls (or a room within the basement) are below ground and will not be affected by wind forces or 

wind-borne debris. However, basements are vulnerable to damage from the collapse of the structure 

above unless the ceiling of the basement (or the floor above) is designed to provide protection if the 

house above collapses.

Figure 9-8 shows an interior basement storage room in a Tuscaloosa, AL, home. This unique home 

was re-constructed in the 1940s from two old cabins that had been re-located to the site. Placed 

atop a hillside, the masonry foundation supporting the cabins created a walkout basement. When 

the family constructed the basement, they set aside the storage room to be used during tornadoes. 

With heavy timber construction and one wall built into the hillside, this space offered some level 

of protection. Damage in the neighborhood of this home was ranked as EF2 by the MAT (see 

Appendix E for additional detail). Although not specifically designed for protection, the family 

Figure 9-6: 

The core remnant of a home 

in Joplin, MO

Figure 9-7: 

Manufactured homes 

destroyed in Crescent Ridge, 

AL (location shown in 

Figure 9-4) 
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

occupied the basement during the tornado, and the storage room provided the family a place to 

take cover when a tornado passed over their neighborhood.

The Pleasant Grove neighborhood outside Birmingham, AL, was directly struck by a tornado 

(Figure 9-9). The NWS rated the center of the tornado circulation as EF4 in this portion of its track. 

Many homes in this neighborhood were destroyed, resulting in several fatalities.4 In several of the 

destroyed homes, residents sought refuge in their basements, but they were not always safe.

Figure 9-10 shows a home that had a heavily reinforced porch slab over a storage area in their 

basement; the slab was voluntarily constructed with reinforcing steel and with a slab depth thickness 

of 9 inches to provide protection during a tornado. The family sought refuge in the storage area 

under the front porch. The home was completely destroyed by the tornado, but the family survived 

in the portion of the walk-out basement where the reinforced concrete roof deck was placed.

Figure 9-8: 

Tornado refuge area in a 

Tuscaloosa, AL, basement

4 NOAA’s NWS SPC, Annual U.S. Killer Tornado Statistics, http://www.spc.noaa.gov/climo/torn/fataltorn.html.
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-10: 

A hardened porch slab over 

this basement helped to 

create a tornado refuge 

area that allowed this family 

to survive the tornado; 

location shown in Figure 9-9 

(Birmingham, AL) 

Figure 9-9: Aerial view of the Pleasant Grove, AL, neighborhood.

NOTE: TRACK DAMAGE CENTERLINE IS NOT IN THE FRAME SHOWN HERE.

Basement remant 

seen in Figure 9-10
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

It is important to note, however, that not all basement areas should be considered “safe” during a 

tornado just because they are below ground. According to local residents, a few doors down from 

the home shown in Figure 9-10, a fatality occurred when people sought shelter in the basement and 

the concrete floor above collapsed into the basement space.

9.2.1.3 Tornado Refuge Areas in Multi-Family Buildings or Complexes

In multi-family residential situations, it is important to 

understand the limitations for potential tornado refuge 

areas. Figure 9-11 shows a new, multi-unit residential 

complex in Tuscaloosa, AL, after it was struck directly 

by a tornado as it tracked through the city. The NWS 

rated the center of the tornado circulation as EF4 in 

this portion of its track; its track is shown as tornado 

#46 on Figure 2-2. Most of the complex was destroyed. 

The inset photograph shows an interior bathroom in a 

first floor unit of the complex. Although areas like this are often used as tornado refuge areas, the 

damage to the space and the debris inside it illustrate the limitations of such refuge areas. Though 

the bathroom may have provided a place of refuge in this portion of the building that was badly 

damaged, but did not collapse, the space was not safe. The ceiling (floor structure for the upper 

floor) blew off, a piece of framed lumber was thrown into the bathroom, and an asphalt shingle 

(red arrow) penetrated the wall. It is important to note that other similarly constructed areas were 

completely destroyed by the tornado.

Taking refuge does not guarantee 

safety or survival. While some refuge areas may survive a direct hit by 

a tornado, thereby protecting the occupants, other identical refuge areas 

may collapse and result in fatalities.

Figure 9-11: An interior bathroom (inset), often considered a 

tornado refuge area, was heavily damaged when the tornado 

struck the development of Chastain Manor. An asphalt shingle 

penetrated the wall (red arrow) (Tuscaloosa, AL).
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.2.2 Tornado Refuge in Commercial and Industrial Buildings: 

Planned Tornado Refuge Areas

The MAT visited a number of sites that 

had formally designed areas within their 

building for use during tornadoes. These 

areas performed no better than the typical 

commercial and industrial construction 

described in Chapter 5 of this report 

because they were not constructed to resist 

high wind loads. In all cases, the designated 

areas had been identified and were part 

of a formal plan, but the buildings (and 

designated areas for use during tornadoes) 

weren’t designed or constructed to provide 

additional protection. Further, the MAT did 

not find any indication that these designated 

areas had been evaluated to understand and 

document their vulnerability to high winds 

and wind-borne debris impact.

In commercial and industrial buildings, 

post-disaster assessments by the MAT and 

NSF team following the April 25–28, 2011 

and May 22, 2011 tornado events suggested that administrative officials or others involved in local 

planning often identified designated areas or tornado refuge areas without the guidance of a 

qualified architect or engineer. While it was clear that an effort was made to protect the occupants, 

many of these designated areas were not evaluated for their ability to provide resistance to or 

protection from wind and wind-borne debris and were vulnerable. These designated areas were 

located in: 

+ Large spaces, such as gymnasiums or auditoriums

+ Areas near exterior windows and doors 

+ Areas surrounded by wall systems subject to collapse in high-wind events 

Additionally, in some cases the designated areas had insufficient space for all of the building 

occupants or were in locations where it would be difficult to move occupants in a reasonable period 

of time.

9.2.2.1 Walmart (Joplin, MO )

Although not a public shelter or designated community tornado refuge area, a Walmart store in 

Joplin, MO, had a disaster plan that provided guidance on where to take refuge during a tornado. 

Over 200 people sought refuge inside the store during the May 22, 2011 tornado. The damage 

swath centerline of the tornado that devastated Joplin was located just a few hundred feet from the 

building (Figures 9-12 and 9-13). The NWS rated the center of the tornado circulation as EF4 in this 

portion of its track. Employees gathered everyone inside the store in break rooms, rest rooms, and 

In the tornado-prone region of the United States, 

many schools have designated refuge for students and faculty during tornadoes. Several of 

the schools visited by the MAT had designated 

refuge areas. The observations on the performance of tornado refuge areas in schools are 

presented in Chapter 6. An example of a school 

with a community safe room meeting the FEMA 

criteria is presented in Section 9.4.4.3.

In addition to schools, other critical facilities 

often have designated areas for use during tornadoes. The observations on the performance of 

tornado refuge areas in other critical facilities are 

presented in Chapter 7.

See also Recovery Advisories 5, 6, and 8 in 

Appendix F for additional information regarding 

refuge areas in schools and critical facilities.
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-12: Walmart store in Joplin, MO

Figure 9-13: 

Close-up view of the damage 

at the Walmart store in 

Joplin, MO

in the customer service desk area near the back of the store. Part of the store’s tornado refuge area 

was constructed of reinforced CMU walls. Once the tornado struck, the front doors and roof were 

torn away from the building and part of the roof structure collapsed (see Section 5.2.5 for further 

discussion of the building). According to a local Walmart representative, there were three fatalities 

inside the store. The fatalities occurred near the center of the store, away from the reinforced 

exterior walls of the store.

9.2.2.2 Lowe’s Home Improvement Store (Tuscaloosa, AL)

The Lowe’s Home Improvement store in Tuscaloosa, AL (Figure 9-14), was a site where individuals 

who heard the tornado warning gathered to seek refuge. Although it was not impacted by a 

tornado, the MAT visited the site. The Lowe’s store had an emergency response flipchart that clearly 

described the action to be taken by store employees during an emergency, including tornadoes 

(Figure 9-15). The tornado procedure included what to do for a tornado watch, tornado warning, 

response procedure, and post-tornado procedures.
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-14: 

Lowe’s Home Improvement 

building (Tuscaloosa, AL) 

Figure 9-15: 

Lowe’s Emergency Response 

Flipchart (Tuscaloosa, AL)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

The store manager had been advised of an updated procedure recently issued by Lowe’s corporate 

officials after a tornado struck a Lowe’s store in North Carolina just weeks before. The response 

plan originally called for customers inside the 

store to be moved to the center aisles of the 

building, away from exterior walls and windows. 

In the updated plan, employees were instructed 

to move everyone to the front of the store into 

areas with multiple walls defining the space. 

At this store location, the front of the store was 

identified in the updated response plan as the 

designated area for use during tornado events. 

These smaller rooms were identified in the 

hopes they would provide better protection for 

employees and patrons based on similar areas 

of the North Carolina store performing better 

during a tornado. This part of the store was 

primarily unreinforced CMU construction and 

drop ceiling. The MAT could not determine if 

this portion of the building had been assessed 

for use as a tornado refuge area or evaluated to 

be a best available refuge area.

During the April 27, 2011 tornado event, the Lowe’s store housed around 50 customers and residents 

from the surrounding area who came to the store seeking refuge, as well as employees at work at the 

time. The store manager moved everyone to the front area of the building and had the occupants 

congregate in the break rooms and meeting rooms. Power was lost for a short time during the 

storms, but auxiliary (generator) power turned on. Employees also had battery-powered flash lights 

to ensure they had enough light to see, as the storage rooms had no windows.

The Lowe’s emergency response plan for responding to a tornado event appeared to have been 

well executed at this store, although the building was not struck or impacted directly by a tornado. 

The store manager put the response plan into action quickly and followed it to eliminate confusion 

among the work staff.

9.2.2.3 Home Depot (Joplin, MO)

The Home Depot in Joplin, MO, was struck by a direct hit from a very intense tornado on May 

22, 2011 (Figure 9-16). The NWS rated the center of the tornado circulation as EF4 to EF5 in the 

vicinity of this building. Individuals in the area who heard the tornado warning attempted to seek 

refuge at this store. As discussed in Section 5.1.3 of this report, the roof of the store was torn off 

and the building’s massive concrete tilt-up panels collapsed, resulting in seven fatalities in different 

locations in the store.

Employees listened to the weather radio and followed the standard emergency plan put in place 

by the company. As part of the emergency plan, all doors in the store were locked in an attempt to 

secure the building and reduce the risk of inflow of air, which could compromise the roof system 

of the building by causing uplift. There were two fatalities at the front of the store. People from the 

Many existing buildings, both publicly and 

privately owned, do not have a safe room 

or storm shelter. Occupants in these buildings must either leave the building or take 

refuge in the best available tornado refuge 

area. The technical guidance in FEMA 361 

recommends that all tornado refuge areas 

be evaluated by a design professional to 

identify the vulnerability of the refuge areas to high winds and wind-borne debris 

and to evaluate the residual risk associated 

with using these areas for tornado refuge. 

Additional information on this topic is presented in FEMA Recovery Advisories 2, 5, 

and 6 issued for this event (see Appendix F).
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

surrounding area were trying to take refuge inside the building right up to the time the tornado 

struck it.

In accordance with the emergency plan, all shoppers and employees in the store were gathered in 

the employee lounge and training area at the back of the store. The MAT was unable to determine 

if this area was designated as a best available refuge area for use during tornadoes by a design 

professional or if a formal assessment of the tornado refuge area was conducted. The 28 people who 

took refuge in the training room survived the storm.

The area of the store where employees and shoppers congregated was constructed of metal stud 

framing and dry wall. This area was not a hardened structure and could have potentially been 

crushed had the tilt-up panels fallen on top of the room. Figure 9-17 shows a picture of the remaining 

structure around the training area. The wall composed of metal studs and drywall can be seen 

leaning inward (yellow arrow). The photograph also shows the tilt-up panels that collapsed outward 

beside this area (red arrow).

9.3 Hardened Structures, Rooms, and Areas 

Not Designed to Defined Criteria

This section discusses the MAT’s observations of buildings where people took refuge in hardened 

structures or portions of buildings. In all cases, the buildings were designed to provide some 

level of hardening, but the MAT was unable to obtain details of the design wind speed used, the 

debris impact criteria used, or if any operational or emergency management plans were included 

Figure 9-16: Home Depot after the May 22, 2011 tornado (Joplin, MO)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

in the design process. Further, the MAT 

noted one or more deficiencies in all 

of the hardened areas described in this 

section that prevented them from being 

categorized as safe rooms or storm shelters. 

The most common deficiency observed was 

with door assemblies; specifically, the doors 

were not capable of withstanding wind 

forces and wind-borne debris associated 

with tornadoes. When such doors fail (as occurred in several cases), the occupants are exposed to 

the tornado and are not as protected as originally intended.

Many people interviewed by the MAT had the perception that the only safe place to be during 

a tornado was in a below-ground structure. Although below-ground shelters have afforded their 

occupants reasonable protection from violent storms for centuries, this is not accurate, and aboveground safe rooms and storm shelters can also provide life-safety protection when designed and 

constructed properly. However, for either type of structure or room to protect occupants, all exposed 

portions must resist debris impacts, and the structures or rooms must have robust doors and locking 

systems that are easily operated in a high-wind environment. This means any door system used must 

be tested for wind and debris impact-resistance, or prescriptive solutions that have been shown to 

pass the FEMA and ICC 500 criteria must be used. The specifications for a prescriptive solution to 

constructing debris impact-resistant doors are presented in FEMA 320. The solution specifies using 

three hinges and three points of latching, though variations on the number of hinges attaching 

doors is becoming more common as more products are tested to the ICC criteria.

Figure 9-17: 

Tornado refuge area (training 

room) of the Home Depot. 

Note the collapsed tilt-up 

wall (red arrow) and the wall 

leaning into the refuge area 

(yellow arrow) (Joplin, MO).

The Wind Science and Engineering Research 

Center at TTU is one entity that performs testing 

on doors for use in tornado safe rooms and storm 

shelters. For more information on doors and door 

hardware that has passed the debris impact test, 

see http://www.depts.ttu.edu/weweb.
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

The advantage of above-ground hardened 

structures and rooms is that they are more 

accessible to young, old, and handicapped 

people than below-ground structures. The 

complete exterior of the safe room or storm 

shelter (including the door assembly) must be 

designed to resist the violent wind pressures as 

well as the debris impacts associated with highwind events. Doors on above-ground structures 

used for occupant protection are particularly 

vulnerable and must resist debris with minimal 

damage after impact (see Chapter 8 of ICC 500). 

The MAT observed dozens of below-ground and 

above-ground “shelters” and hardened structures 

in Alabama and Mississippi. In Joplin, MO, 

only above-ground structures and rooms were 

observed. The MAT speculates that this is because 

of the existence of old mining tunnels under 

portions of the City of Joplin, but there may be 

other reasons below-ground structures were not 

observed. Research into why a certain type of 

structure was selected for protection is beyond the 

scope of the MAT.

9.3.1 Hardened Structures for Residential Use 

The structures presented in the following sections did not meet the FEMA or ICC criteria for safe 

rooms or storm shelters. Although these structures provided some protection, the occupants were at 

risk due to the poor construction of the door assemblies or door latching systems.

9.3.1.1 Below-Ground Applications

Although constructed of a hardened concrete shell, the “shelter” shown in Figure 9-18 was protected 

by plywood doors clad with light steel, a single point locking system, and a vent system that was 

vulnerable to impacts. It is unknown how many occupants using this structure survived, but the 

adjacent home was destroyed when the tornado passed over Smithville, MS. Although the Smithville 

tornado was rated higher at different locations along its track (see Section 2.5.1.7 of this report), the 

MAT derived the tornado rating as EF2 at this location based on damage to this building.

The Hackleburg, AL, below-ground structure shown in Figure 9-19 seemed to be relatively new. 

The MAT was unable to determine how many sought refuge here, but there was evidence in the 

shelter that it was used. Damage in the neighborhood of this home was ranked as EF3 by the MAT 

(see Appendix E for additional detail). Though the structure was mostly underground and had 

a reinforced concrete roof structure, the door was constructed of wood planks and locked with a 

chain held by bent nails. This type of door and method of connection is inadequate to resist wind 

loads and wind-borne debris; occupants who took refuge here were still at risk because of the low 

quality and characteristics of this door assembly.

There are several sources for information 

on securing safe room and storm shelter 

doors. FEMA 320 provides a prescriptive 

design for door construction (with hinges 

and latching systems) that can resist wind 

and wind-borne debris associated with 

tornadoes. This solution meets the testing 

requirement of the ICC 500 for residential 

safe rooms.

Although three hinges and three latching 

mechanisms are no longer required per 

the ICC 500, most doors and systems that 

have passed the debris impact and wind 

pressure tests have multiple (or continuous) hinges and multiple latches. As of this 

publication, no single dead bolt acting as 

the lone closure mechanism has passed 

the ICC 500 tests for wind and wind-borne 

debris resistance.
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-18: Underground shelter that survived a tornado (rated EF2 based on the MAT’s observations). Inset shows the 

location of shelter (Smithville, MS).

Figure 9-19: Below-ground hardened structure used for tornado 

refuge; door and closure system are shown in the inset (rated an EF3 

based on the MAT’s observations) (Hackleburg, AL)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.3.1.2 Above-Ground Applications

A husband and wife took shelter is their above-ground concrete shelter in Smithville, MS, shown 

in Figure 9-20. Although the small town of Smithville was devastated by a tornado that reached 

EF4 intensity in places along its track, this home was on the periphery of the vortex and suffered 

little damage. The clam-shell concrete structure was anchored to the ground with steel bands and 

earth anchors. Although the concrete walls were sufficiently thick at 61⁄2 inches, the door system was 

untested, and the locking system could open when impacted by debris or subjected to high wind 

pressures. The door locking mechanism used three points of connection on the non-hinge side of 

the door (as suggested in FEMA 320), but the three individual mechanisms used to keep the door 

in the closed position were not identified as having been tested to the FEMA or ICC debris impact 

resistance criteria. Because these latching mechanism were light weight and the door did not appear 

to be reinforced around the latch points, the door was vulnerable to being forced open from wind 

or wind-borne debris. Further, this structure did not appear to be anchored to resist wind loads 

(other than the grounding force resulting from its dead weight).

The MAT observed another example of an above-ground “shelter” in Athens, AL (Figure 9-21). 

A family survived the tornado in a hardened room they had constructed within a shop building 

east of their home. The hardened room (approximately 8 feet tall, and 6 feet by 9 feet in plan) 

was constructed with a reinforced CMU wall structure and concrete roof deck. The shop building 

was totally destroyed by the tornado, as was most of their home. The NWS rated the center of the 

Figure 9-20: 

Above-ground shelter with 

untested door system; inset 

shows the inside of the door 

latch (Smithville, MS)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

tornado circulation in the vicinity of this building as EF3. The design of the structure was consistent 

with the FEMA 320 guidelines with the exception of the door assembly. The door and latching 

mechanism was not a tested assembly and had only one deadbolt; at the time of this publication, no 

door latch configuration with one bolt has passed the ICC 500 or the FEMA 361 debris impacting 

testing criteria.

Although this room successfully provided safe refuge for the family, they were still at risk from high 

winds and wind-borne debris because of the door system used. The performance of this structure 

may not have been successful if the door had been impacted by wind-borne debris that caused the 

door system to fail. Occupants are often unaware of residual risks that remain in these otherwise 

robustly constructed structures and rooms when structures intended to provide protection from 

tornadoes are not constructed to the FEMA or ICC criteria.

9.3.2 Hardened Structures Used as Community Tornado Refuge Areas

The MAT observed several hardened structures used by communities as tornado refuge areas. The 

hardened structures presented in this section did not meet the FEMA or ICC criteria for safe rooms 

or storm shelters. Although these structures provided some protection, the occupants were at risk 

Figure 9-21: 

A family shelter with a single 

deadbolt (Athens, AL)

One deadbolt
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Electrical 

boxes

because of the poor construction of the door assemblies or door latching systems. Unless otherwise 

noted, the MAT was not able to verify if these hardened structures had been evaluated by design 

professionals for vulnerabilities to high winds or use as tornado refuge areas.

9.3.2.1 Above-Ground Applications

The Town of Amory, MS, was directly struck by the tornadoes of April 25–28, 2011, but its sirens 

were sounded by their 911 facility and many took refuge in the concrete above-ground structures 

shown in Figure 9-22. These structures were not in the damage swath of the tornado that struck 

Amory. It is unknown how many residents occupied these structures during the several days when 

tornado watches were in effect. Each unit is 13 feet x 13 feet wide and 7.5 feet tall. Although conduit 

and switch receptacles for lighting were present in the concrete structures when the MAT visited, 

no wiring or fixtures had been installed. The doors were hollow metal commercial grade with three 

deadbolts, but it is unknown if they were FEMA-compliant and tested door assemblies. Although 

the intended use of these structures was clear, the MAT could not verify the design criteria used for 

these structures and if they were evaluated to any standards or guidelines for tornado protection.

Figure 9-22: Above-ground hardened structures used as community tornado refuge areas. Insets show electrical boxes 

ready for wiring and fixtures (left) and door assemblies (right) (Amory, MS).
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.3.2.2 Below-Ground Applications

In Smithville, MS, a hardened, underground structure (Figure 9-23) was designated as the 

“community shelter” to be used during tornadoes. The structure reportedly held 10 individuals 

during the April 27, 2011 tornado event, rated EF3 by the NWS. Although the structure was robust 

and constructed from reinforced concrete, the doors were inadequate and did not provide the 

appropriate level of protection. The doors were constructed of two layers of plywood with a thin 

sheet steel cladding and only one locking point. This structure also had only one vent for fresh air; 

the vent was damaged by debris during the storm.

Damaged 

vent

Door and locking system

with one dead bolt

Figure 9-23: Below-ground, hardened structure with poor door and locking system (inset on lower left) and damaged 

vent (upper inset) (Smithville, MS)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.4 Safe Rooms and Storm Shelters

The MAT observed safe rooms that were compliant with FEMA 320 and FEMA 361 criteria and 

storm shelters that were compliant with ICC 500 criteria in Alabama and Joplin, MO. Refer to 

Section 1.2 for a detailed description of the differences between safe rooms and storm shelters.

Safe rooms and storm shelters can be above-ground or below-ground. They can also be site-built 

or prefabricated structures. The MAT observed all of these types of safe rooms during the field 

assessments after the April 25–28, 2011 and May 22, 2011 tornadoes.

9.4.1 Above- and Below-Ground Alternatives

There are two general types of safe rooms and storm shelters: above-ground and below-ground. 

Both types were observed during the field observations. Both above-ground and below-ground safe 

rooms and storm shelters can be stand-alone structures away from the home or building, or they 

can be rooms or areas in the home, such as a bedroom, a bathroom, or a closet. Wherever it is 

located, it is specially designed to provide life-safety protection for the people who live in the house 

or building. Above-ground safe rooms are particularly desirable for those who have a disability or 

difficulty climbing down into a below-ground area.

Figure 9-24 shows an above-ground safe room that was added to the exterior of an existing home in 

Tuscaloosa, AL. This home was not in the path of the tornado that struck Tuscaloosa, but the safe 

room was used by the resident during the storms. The safe room was placed at-grade on the back 

porch of the home and matched the existing siding and aesthetics of the home. This particular 

design was chosen because the homeowner’s mother had limited mobility and would not be able to 

access a below-ground safe room in the event of an emergency. This safe room was constructed with 

FEMA funds.

Figure 9-25 shows an above-ground community storm shelter in Graysville, AL. The structure is 

adjacent to a church and available for residents of the surrounding area to use in the event of a 

tornado.

Figure 9-24: 

Above-ground safe room 

that matches the aesthetics 

of the home (outside 

Tuscaloosa, AL)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

A common safe room design is a stand-alone residential safe room installed below the ground surface 

outside a house or building. Small stand-alone safe rooms can be constructed to accommodate the 

occupants of one house, a few houses, or a small apartment building. Building a stand-alone safe 

room underground can be desirable because it does not take up any additional space within the 

home or building, and the grade of the surrounding land may lend itself favorably to this design. 

Figure 9-26 is an example of a below-ground safe room built into the side slope of the back yard 

of a home in Tuscaloosa, AL. This safe room, constructed in 2008 and funded in part through 

FEMA grant programs, was placed about 20 feet away from the home and could be reached quickly 

during a storm. This particular model is large enough to accommodate 10 people comfortably. It is 

a prefabricated unit, and the door and portions of the safe room that are above ground were tested 

to show compliance with FEMA 320 criteria. This safe room was occupied during the April 25–28, 

2011 tornado outbreak, but this site was not struck by a tornado.

Figure 9-25: 

Above-ground community 

storm shelter (Graysville, AL)

Figure 9-26: 

Below-ground FEMAfunded residential safe room 

(Tuscaloosa, AL)
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9.4.2 Prefabricated versus Site-Built Alternatives

Safe rooms and storm shelters can be prefabricated or site-built, depending on the needs of the 

owner and the specific site limitations. If constructed correctly to FEMA or ICC criteria, both 

types can provide life-safety protection. Safe rooms built within existing homes or as part of new 

construction projects tend to be site-built because there is usually limited access to position a 

prefabricated safe room or storm shelter. Figure 9-27 is an example of a residential site-built safe 

room constructed in the master bedroom closet of an existing home in Tuscaloosa, AL, using one of 

the designs presented in FEMA 320. The above-ground, wood-frame safe room with steel sheathing 

was used (see Drawing No. AG-06, sheet 11 of 18 [FEMA 1999b]). This safe room was constructed 

in 2002, funded in part through FEMA grant programs. The safe room was completely contained 

by the existing structure and very well concealed. The residents of this home used the safe room 

during the April 25–28, 2011 tornado outbreak, but this site was not struck by a tornado.

The MAT observed many configurations of both above- and below-ground prefabricated safe 

rooms used during the April 25–28, 2011 and May 22, 2011 tornado outbreaks. Several examples of 

prefabricated safe rooms (with space for 3 to 12 occupants) are discussed in Sections 9.4.3 and 9.4.4.

Figure 9-27: 

Site-built FEMA-funded 

residential safe room 

(Tuscaloosa, AL) 
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.4.3 Residential Safe Rooms and Storm Shelters

Many residential safe rooms were successfully used during the April 25–28, 2011 and May 22, 2011 

tornado outbreaks. All but one of the safe rooms observed were prefabricated units. Homeowners 

told the MAT they had chosen to install a prefabricated safe room because of the speed of 

installation and lower cost of the structure. When the safe rooms were constructed as in-home- and 

garage-installed safe rooms, these alternative locations provided the occupants the most protected 

access during the tornadoes as they were not required to go outdoors.

9.4.3.1 Below-Ground Applications

In Tuscaloosa, AL, four people survived an EF2 tornado (as rated by the NWS) in the below-ground 

FEMA-funded safe room shown in Figure 9-28. The grab bar to the right of the safe room was bent 

by a fallen tree that trapped the family in the safe room until a neighbor cut the tree away from the 

door. This safe room was installed in 2001 and complies with the FEMA 320 criteria for residential 

safe rooms in place at the time.

The concrete below-ground safe room shown in Figure 9-29 was in a rural area outside of Smithville, 

MS, and provided shelter for the occupants of a manufactured home. On April 27, 2011 the 

homeowner and nine other family members and neighbors, as well as one dog and two cats, took 

shelter in this FEMA-funded safe room. The shelter had a tested door assembly. Though the area 

was not struck by the storm, the occupants were comforted and protected by their safe room.

The MAT observed the below-ground garage storm shelter shown in Figure 9-30 in Huntsville, AL. 

This area of Huntsville was placed under two separate tornado warnings on April 27. The homeowner 

and his wife retreated to their storm shelter on both occasions. This house was not ultimately 

affected by the tornadoes, though it sustained damage when a tree fell on it as a result of the strong 

winds from the storm. Though not a FEMA-funded safe room, the shelter is ICC 500-compliant and 

Figure 9-28: 

Below-ground FEMAfunded residential safe room 

(Tuscaloosa, AL) 
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-29: 

FEMA-funded residential 

safe room (Smithville, MS)

Figure 9-30: 

Below-ground garage shelter 

(Huntsville, AL)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

manufactured by a member of the NSSA. The homeowner, not being an Alabama native, said that 

he feared “the infamous tornadoes of the southeast” and was intent on having a shelter. He reported 

that he felt very safe in his new storm shelter.

9.4.3.2 Above-Ground Applications

In the Village of Providence in Huntsville, AL, the MAT found the small and unique above-ground 

storm shelter shown in Figure 9-31. The shelter was not funded by FEMA, but was ICC 500-compliant 

and was constructed and installed by an NSSA member company. A husband and wife sought shelter 

here during both tornado warnings issued on April 27, 2011 for the Huntsville area.

Amidst the massive destruction of the violent tornado that struck Joplin, MO, on May 22, 2011 the 

MAT discovered the safe room shown in Figure 9-32; its location is shown in Figure 9-33. A family of 

two walked out of their safe room, only to find their home and their neighborhood totally destroyed. 

The safe room was anchored to the concrete slab where the garage once stood. The safe room door 

was locked with multiple locking points and used four hinges. This shelter design was tested at 

TTU. Installed with no FEMA or Federal funding assistance, the safe room effectively protected the 

occupants during the historic May 22, 2011 Joplin, MO, EF4 tornado event.

Figure 9-31: 

ICC 500-compliant storm 

shelter (Huntsville, AL)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-32: 

Residential safe room that 

survived the May 22, 2011 Joplin, 

MO, tornado (rated EF4 based 

on the MAT’s observations). The 

upper inset shows the inside of 

the safe room.
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-33: Proximity of the residential safe room shown in Figure 9-32 (circled in yellow in the inset) to the 

approximate centerline of the Joplin, MO, tornado damage swath (red line). The safe room was located 0.5 mile west of 

the heavily damaged St. John’s Medical Center (shown by yellow box and described in Section 7.1.4.)

TTU assisted the manufacturer of the in-residence safe room shown in Figure 9-34 in researching 

and developing its design and performed all the debris impact testing to meet the residential safe 

room criteria set forth in FEMA 320 and FEMA 361. The home and its safe room were on the 

periphery of the violent May 22, 2011 Joplin, MO, tornado. The NWS rated the center of the tornado 

circulation in the vicinity of this home as EF2. The roof structure of the home was lifted up and 

glazing damage occurred.

9.4.4 Non-Residential and Community Safe Rooms

Similar to residential safe rooms, the MAT observed both site-built and prefabricated non-residential 

safe rooms. However, for community safe rooms, the prefabricated safe rooms observed all had a 

maximum occupancy of 100 to 150 people (but often fewer). Larger community safe rooms are 

typically site-built structures. Steel panels were the predominant materials used in the prefabricated 

community safe rooms observed by the MAT, while reinforced concrete and reinforced masonry 

were the predominant materials used in the site-built community safe rooms.
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9.4.4.1 Brookwood and Phil Campbell Community Safe Rooms (AL) 

The MAT visited three community safe rooms in Alabama. The two above-ground safe rooms 

were prefabricated structures, while the one below-ground safe room was site-built with reinforced 

concrete. Although none of these safe rooms was directly hit by a tornado, they each provided safety 

and comfort to their occupants during the April 25–28, 2011 tornado outbreak.

Brookwood, AL 

In 2007, in response to past tornado activity in the town, the Town of Brookwood installed an aboveground safe room in its Town Park. Figure 9-35 shows the safe room, which is also promoted on the 

town Web site. The safe room was used by members of the community for most of the day on April 

27, 2011. The town was in the warning areas for the tornadoes that day, but was not directly struck. 

Because the safe room was in the Town Park, most residents who used the safe room drove there 

on the day of the event. Town officials stated that the safe room was filled to “standing room only” 

for a good portion of the day. Power in the town was lost several times during the day, but the safe 

room was supported by a generator (protected from wind-borne debris by a steel structure) that 

functioned properly and provided electricity to the safe room. The Brookwood safe room had a 

restroom for occupant comfort.

Figure 9-34: 

Residential safe room 

(Joplin, MO)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Phil Campbell, AL 

The community of Phil Campbell, AL, was struck by a violent tornado on April 27, 2011. The 

NWS rated the center of the tornado circulation for this tornado as EF4. Hundreds of homes were 

damaged or destroyed, and 27 lives were lost according to a local representative. On top of a hill, 

away from most of the devastation, was Phil Campbell’s FEMA-funded community safe room (Figure 

9-36), which housed 60 residents on the day of the storm. The safe room door and panel system was 

tested in the Debris Impact Test Facility at TTU and meets FEMA 361 debris impact guidelines. 

The safe room and door is heavy gauge steel and the shelter is partially buried into the hill. An 

emergency generator (located in the box outside the door of the safe room) supplies electricity for 

lighting and the mechanical ventilation system. The generator is protected by an impact-resistant 

enclosure, and the ventilation system is protected from debris impacts with heavy steel shrouds. 

Figure 9-37 shows the inside of the safe room and the seating arrangement.

The temporary communications tower shown in Figure 9-36 was installed after the tornadoes 

struck the town. The tower should not be connected to the safe room because the structure was not 

designed to provide foundation support for guy wires for a communications tower.

Figure 9-35: 

Community safe room with 

exterior and interior locking 

mechanism; inset shows the 

three-point interior locking 

system (Brookwood, AL)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-37: Interior of the community safe room shown in Figure 9-36 featuring seating, emergency lighting (green 

arrows), and ventilation (red arrows); inset is a close-up of the entrance door (Phil Campbell, AL)

Figure 9-36: 

FEMA-funded community 

safe room; guy wires for the 

temporary communications 

tower should not be attached 

to the structure (Phil 

Campbell, AL)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.4.4.2 Brookside Fire Station and Community Safe Room (Brookside, AL)

The MAT visited a below-ground community safe room constructed beneath the Brookside Fire 

Station in Brookside, AL (Figures 9-38 and 9-39). The safe room was known throughout the 

community to be at this location and was used by approximately 150 individuals during the April 

25–28, 2011 tornado outbreak. Although the town was not struck by a tornado that day, many of 

the occupants reportedly drove over 5 miles to get to the safe room after watching the day’s events 

unfold on television.

Figure 9-38: 

A large site-built, belowgrade community safe 

room is housed below this 

fire station; the red arrow 

indicates an unprotected 

generator (Brookside, AL)

Figure 9-39: 

Interior view of the wellfurnished community safe 

room shown in Figure 9-38 

(Brookside, AL) 
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

The safe room was constructed in 2008 and funded in part through FEMA grant programs. The fire 

station and other municipal functions were relocated to this site because of repetitive flooding of 

the town buildings. The safe room was designed during the fire station design process and is part of 

the building. It is constructed below grade from reinforced concrete walls with a pre-cast concrete 

roof deck. The roof deck is the floor system for the fire station offices and dispatch area located 

above in a non-hardened structure.

There are two entrances to the safe room, one of which has a lift so disabled occupants can access 

it. The structure can shelter over 300 occupants. The safe room has tools, equipment, bedding, and 

other support elements in adequate supply for the safe room occupants. Although an emergency 

generator is on site for backup power, it is not protected from wind-borne debris (red arrow in 

Figure 9-38). Figure 9-39 shows the interior of the safe room.

9.4.4.3 Seneca Intermediate School (Seneca, MO) 

After suffering damage from a tornado in May of 2008, the City of Seneca, MO, built a new 

Intermediate School (Figure 9-40). Using FEMA HMGP funding, the school designed the 

cafetorium and gymnasium as a FEMA 361 community safe room (Figures 9-41 and 9-42). This safe 

room was also constructed to comply with the new ICC 500 storm shelter standard; it was the only 

safe room visited by the MAT designed to both criteria.

Figure 9-40:

Seneca Intermediate School 

(Seneca, MO)

Though the community of Seneca, MO, was not hit by a tornado on May 22, 2011 the MAT inspected 

this new community safe room as a case study of good community safe room construction:

+ The walls are constructed from pre-cast, insulated concrete panels and the roof structure is 

constructed from precast concrete double tee’s (Figure 9-42) 

+ All doors are tested FEMA 361 assemblies (Figure 9-43) and the louvers above doors are 

protected by alcove entries (Figure 9-44)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-41: 

Seneca Intermediate School 

safe room in the cafetorium

Figure 9-42: 

Seneca Intermediate School 

gymnasium safe room

+ Elevated ventilation units are protected on the outside wall with heavy steel shrouds (Figure 

9-45)

+ The generator building was similarly constructed with heavy wall and roof construction, tested 

doors, and steel shrouds over ventilation openings (Figure 9-46)
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-44: 

Outside doors and louvers (red 

arrow) protected by alcoves at 

the Seneca Intermediate School 

community safe room

Figure 9-43: 

Doors and ventilation louvers in Seneca Intermediate School 

community safe room
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Figure 9-45: 

Elevated ventilator in the Seneca 

Intermediate School community safe room. 

Inset shows the exterior shroud.

Figure 9-46: 

Emergency generator 

building for the community 

safe room at the Seneca 

Intermediate School
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.5 Travel Time to Community Safe Rooms, Storm 

Shelters, and Tornado Refuge Areas

To better understand the time and distances that people traveled to these safe rooms, shelters and 

places of tornado refuge during the storms, the MAT interviewed the owners, operators, and some 

users of community safe rooms, storm shelters, and other areas used to take refuge from tornadoes 

(including both hardened structures and best available tornado refuge areas). The MAT interviewed 

staff at schools and commercial businesses, as well as community safe room operators. This effort was 

intended to collect data and possible gaps in knowledge that experts in social sciences or behavior 

analysis may find useful in researching travel time issues and people’s considerations when deciding 

whether to seek shelter or remain in place.

At the time of publication of this report, FEMA technical and policy guidance on safe rooms states:5

“The distance from the safe room for the at-risk population is based on a maximum walking travel 

time of 5 minutes or a maximum driving travel distance of approximately 0.5 mile... whether 

walking or driving, prospective safe room occupants must be able to safely reach the facility within 5 

minutes of receiving a tornado warning or notice to seek shelter.”

This guidance was observed to have been followed at most schools in Mississippi, Alabama, and 

Missouri visited by the MAT that had safe rooms and best available tornado refuge areas. For all 

schools discussed in Chapter 6, the tornado refuge areas could be reached by the facility, staff, and 

students within 5 minutes, and the distances to the safe rooms were 1⁄2 mile or less.

The MAT visited several commercial businesses in the tornado warning areas and along the paths 

of the April 25–28, 2011 tornadoes in Tuscaloosa and Birmingham, AL. Staff at the Hobby Lobby, 

Lowe’s Home Improvement, and Home Depot stores in Tuscaloosa said that, to the best of their 

knowledge, the people who took refuge within their facility during the event were either inside or 

near the store when they decided to take refuge in the buildings. This finding is consistent with the 

MAT’s discussions with Joplin, MO, business owners and employees after the May 22, 2011 tornado.

Unlike staff of schools and commercial businesses who reported receiving occupants from areas 

immediately adjacent to their facility, operators of community safe rooms, storm shelters, and 

tornado refuge areas outside the larger cities reported that many individuals traveled longer 

distances to seek refuge from the tornadoes. The operators of community safe rooms in Brookside, 

Brookwood, and Phil Campbell, AL, indicated that occupants reported travelling “miles” and that 

some had driven to the safe room seeking refuge; no log was kept to record where occupants came 

from. The operators of hardened structures used during the event in Smithville, MO, and Armory, 

AL, reported similar information.

While none of the MAT’s findings are conclusive about the risk and vulnerability accepted by 

individuals that travel to a safe room, storm shelter, or best available tornado refuge area (hardened 

or not), the variation in the travel patterns and the behaviors reported were not unexpected. However, 

the MAT is concerned that not all of the observed behavior was the safest reaction to an impending 

tornado event; specifically, more study is needed to quantify (if possible) how many people drove to 

5 HMA Unified Guidance, Part IX, Section C.4.1.2, page 111, http://www.fema.gov/library/viewRecord.do?id=4225.
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

a safe room or best available tornado refuge area. Further study is also needed to understand what 

risks people took, both knowingly and unknowingly, for themselves and their families when they 

decided to travel great distances within a warning area or along/across a tornado’s path, instead of 

sheltering in place when they became aware of the tornado threat.

9.6 Compliance Issues with FEMA 320, FEMA 361, and the ICC 500

The MAT observed a number of well-constructed shelters and safe rooms constructed to FEMA 

criteria, but only one that was also stated to be constructed to the ICC 500 standard. They also 

observed a number of safe rooms with compliance issues. In some cases, the safe room was compliant 

except for a minor element; unfortunately, even a small deviation from the criteria can endanger 

occupant lives. Consequently, many of the shelters and hardened structures the MAT observed were 

selected for presentation in this chapter to demonstrate that these structures could be brought into 

compliance with the FEMA and ICC criteria with only slight modifications.

Note that all the hardened structures the MAT observed were constructed to either the FEMA 320 

and FEMA 361 criteria or to unidentified or unknown criteria. The MAT identified only one storm 

shelter designed to be compliant with the ICC 500 standard; this was the Seneca Intermediate School 

community safe room in Missouri, which was designed specifically to meet both the FEMA and the 

ICC criteria (see Section 9.4.4.3). However, as the FEMA and ICC 500 criteria are very similar (and 

essentially identical for wind and wind-borne debris protection in tornado-prone areas), compliance 

issues identified in this section are evaluated based on both sets of criteria.

The following section describes ICC 500 and FEMA safe room and storm shelter design and 

construction elements that were not followed in at least one facility observed by the MAT. The 

description of each element is followed by a summary of the specific MAT observations related to 

that element. This information is provided because people may be at risk during a tornado event 

and unaware of their vulnerability.

9.6.1 Identifying Design Criteria Used for Safe Rooms and Storm Shelters 

Compliance Criteria: Wind pressure design criteria are given by different guides, codes, and 

standards. The wind pressure criteria specify how strong the safe room must be. The design wind 

speed is the primary factor in determining the magnitude of wind pressure a building is designed 

to withstand. FEMA’s safe room publications and ICC 500 use the same wind speed hazard maps 

to recommend design wind speeds ranging from 130 to 255 mph, depending on location. The only 

exception to this is for residential tornado safe rooms as described in FEMA 361, which requires 

that residential safe rooms be constructed to resist 250 mph wind speeds. The designs presented 

in FEMA 320 were designed for the most severe wind and debris condition, those associated with a 

250-mph wind speed. Therefore, a safe room designed to the FEMA criteria would be designed to 

resist tornado (or hurricane) wind speeds in any of the different regions defined by the wind speed 

hazard maps. This approach was chosen by FEMA to provide a set of designs for home owners and 

small business that would meet and exceed the design criteria regardless of geographic location. 

FEMA performed an analysis of costs and materials for each of their prescriptive designs to arrive 

at this approach. The results did not support development of separate prescriptive designs for each 

wind speed. These safe room and storm shelter design wind speeds are in contrast to the minimum 
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OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

required design wind speed of 90 mph for most tornado-prone areas of the country, as stated in the 

2009 IRC and the 2009 IBC (codes that establish the minimum requirements for residential and 

other building construction).

The FEMA 320 safe room designs reflect considerable feedback from stakeholders that preengineered prescriptive solutions are highly desirable and simplify the safe room design process. As 

such, safe room designs in FEMA 320 include easy-to-follow construction plans and specifications.

When designing a safe room, it is also critical to consider wind-borne debris load criteria. 

The “Tornado Missile Testing Requirements” in FEMA 361 are guidance for missile-resistance 

requirements for residential and community safe rooms that provide near-absolute protection.

In addition to the safe room’s structural performance requirements, the following operational, 

maintenance, and human factors must be considered for a successful safe room: electric generator, 

lighting, emergency provisions, occupancy duration, and more described in FEMA 361 and ICC 500. 

Each of these items is further elaborated in FEMA 361 and ICC 500. Not all items must be considered 

for a residential safe room, but they are especially important when designing a community safe 

room.

MAT Observation: Although most community safe room operators and residential safe room 

owners the MAT visited provided documentation of the design criteria used, the MAT did not 

observe any posted signs or labels stating the criteria to which the safe rooms were designed in any 

of the community safe rooms. Only a few of the prefabricated residential safe rooms had a label 

stating the design criteria or NSSA member compliance.

9.6.2 Accessibility to Safe Rooms and Storm Shelters

Compliance Criteria: A safe room designer should consider the time needed for occupants of a 

building to reach the safe room or storm shelter. Safe rooms and storm shelters are only useful if 

users are able to make it inside safely before a tornado strikes. The following elements should be 

considered:

+ Safe room users with disabilities may need assistance to access the safe room and may take 

longer to reach it. Wheel-chair users may require special accommodations along the route to the 

safe room to reduce the amount of time needed to reach it.

+ Clearly posted signs and labels indicating the purpose of the safe room or storm shelter and its 

location will make it easier to find.

+ It is essential that the path to the safe room remain clear to allow orderly access to it.

+ Adequate interior dimensions of the safe room and shelter to house the number of users 

expected. FEMA and ICC both recommend a square foot area per occupant to ensure an 

appropriate minimum area. The area requirements vary depending on the number of standing 

and seated occupants and the number of wheel-chair-bound occupants a community safe room 

can safely hold.
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MAT Observation: Accessibility requirements were considered in the larger community safe 

rooms visited by the MAT (Seneca Intermediate School in Missouri and the Brookside, AL, Fire 

Department community safe room). The Brookside, AL, safe room had a lift to assist disabled or 

impaired occupants with access to and from the safe room. However, the MAT could not determine 

whether the smaller Alabama community safe rooms in Phil Campbell, Brookwood, and Graysville 

had additional space for disabled occupants or whether access for them was considered.

9.6.3 Ventilation for Safe Rooms and Storm Shelters

Compliance Criteria: Tornado community and residential safe rooms should be ventilated by 

natural means or mechanical ventilation in accordance with FEMA 361 or ICC 500 for storm shelters. 

If mechanical ventilation is provided, it must be protected from the wind pressures and wind-borne 

debris criteria used for the protected space. Further, the ventilation system should be capable of 

providing the minimum mechanical ventilation rate required by local building code provisions and 

should also be connected to a backup power system in the event that primary power is lost.

MAT Observation: While all the community safe rooms the MAT observed had passive ventilation 

systems or mechanical ventilation systems, only the Seneca Intermediate School (in Missouri) 

and the Brookwood and Brookside community safe rooms (in Alabama) were observed to have 

mechanical systems protected and supported with backup power systems.

9.6.4 Toilet Facilities for Community Safe Rooms and Storm Shelters

Compliance Criteria: Safe rooms and storm shelters should contain toilets within the protected 

space. While this is not a design requirement for life-safety protection, this criterion is included to 

ensure the successful operation and management of safe rooms and storm shelters.

MAT Observation: The MAT observed that compliance with providing toilets in the safe rooms 

varied. The large safe rooms at the Seneca Intermediate School (in Missouri) and in the community 

safe room in Brookside, AL, had toilet facilities within the protected space. However, no toilets were 

observed in the smaller Alabama community safe rooms in Graysville.

9.6.5 Location and Labeling of Safe Rooms and Storm Shelters 

Compliance Criteria: Safe rooms and storm shelters should be located such that those intending 

to seek refuge in the safe room or shelter are not exposed to additional hazards while traveling to 

or occupying the shelter. Users should be able to safely reach the safe rooms or storm shelter with 

minimal travel time. Therefore, community safe rooms should be located in a central area such that 

all designated users can access it quickly. Users should not have to cross obstructions such as creeks, 

fences, busy roads, or railroad tracks to reach the shelter. Safe rooms and storm shelters should 

be located outside of floodprone areas. When possible, safe rooms should be located away from 

structures and objects that could collapse onto it, such as communications towers, roof-mounted 

equipment, and immediately adjacent multi-story buildings. Similarly, safe rooms should be located 

such that they avoid nearby electrical transmission or distribution lines that can collapse onto, or 

very near, the structure. If it is not possible for a safe room to meet any of these criteria, a design 

and/or operational solution to adequately overcome the shortcoming should be provided.
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Safe rooms and storm shelters should be accurately labeled and also identified on posted floor plans. 

This is especially important for visitors who may not know where the safe room is located or the 

extent of the protected space within a larger building. Operators of community safe rooms should 

register their safe rooms with their local emergency management agencies (sometimes it might be 

police or fire departments) with the exact coordinates of the location of the main entrance of their 

safe room.

MAT Observation: Following the April 25–28, 2011 tornado outbreak, the community of Madison, 

AL, created such a registry noting the locations of all of safe rooms and storm shelters.

9.6.6 Tools and Other Equipment within Safe Rooms and Storm Shelters 

Compliance Criteria: FEMA guidance on safe rooms recommends that tools, communication 

devices, and other ancillary equipment be stored within the safe room. This equipment is not 

intended for life-safety protection, but to support the successful operation of the safe room during 

a hazard event. Every safe room and storm shelter, both residential and community, should have a 

supply of tools to help occupants exit the safe room after an event. Since the ICC 500 is an engineering 

standard, these operational items are not discussed or required for life-safety protection.

MAT Observation: Tools were not needed by any of the community safe room occupants to exit 

after the tornado events because none of the safe rooms observed by the MAT were in structures 

destroyed by the tornadoes. However, if safe rooms had been located within the numerous damaged 

businesses visited by the MAT, the occupants would likely have had difficulties exiting the safe rooms 

since many of the buildings had completely collapsed.

In Tuscaloosa, AL, a family was trapped in their below-ground safe room when a tree fell across the 

door (see Section 9.4.3.1). The family had to wait for assistance and for the tree to be removed before 

they could leave the safe room. In another residential safe room in Smithville, MS, the latching 

mechanism was damaged by debris during the tornado and not operational from inside the safe 

room. Tools for opening such a damaged locking mechanism were not present in the safe room; 

storing such tools in a safe room is, however, recommended by in FEMA’s guidance documents.

The MAT recommends local emergency management agencies maintain a list of community 

and residential safe rooms to allow them to efficiently locate and check on the safety of the 

occupants after the storm.

Preferably, every community should have GPS 

coordinates of the main entrances for all safe 

rooms in the community. This information will 

help locate and perform rescue operations after 

an event, if needed. The presence of debris can 

make it impossible for occupants to exit a safe 

room and difficult for rescue workers to locate.

The MAT had difficulty finding some safe rooms 

located in and amongst the piles of debris on 

large properties because it did not have the exact coordinates of the main entrance.

Some cities have voluntary storm shelter / safe 

room registries so that emergency personnel can 

check on the shelter occupants without being 

notified.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 9-47

OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

9.7 Summary of Conclusions and Recommendations

Table 9-1 provides a summary of the conclusions and recommendations for Chapter 9 and provides 

section references for supporting observations. Additional commentary on the conclusions and 

recommendations is presented in Chapters 10 and 11. 

Table 9-1: Summary of Conclusions and Recommendations for Tornado Refuge Area, Hardened Area, and Safe Room 

Performance

Observations Conclusions Recommendations

ICC 500 and FEMA technical guidance 

provide similar levels of protection (see 

Terminology and Examples, Section 9.1)

Conclusion #27

Design and construction guidance 

for storm shelters and safe rooms 

is consistent, though somewhat 

different in scope. 

FEMA adds different requirements 

pertaining to using ICC 500 within the 

context of an emergency management 

program.

Recommendation #12

Continue to coordinate 

standards and 

guidance for storm 

shelters and safe room 

design. 

With the exception of the Seneca 

Intermediate School in Seneca, MO, all 

of the safe rooms and storm shelters 

inspected by the MAT, for both residential 

and community uses, were constructed 

prior to the publication of the ICC 500. 

Many of the observed safe rooms and 

storm shelters were deficient when 

measured against the ICC 500 standard.

Refer to:

•	 Hardened structures, rooms, and areas 

not designed to defined criteria (Section 

9.3)

•	 Identifying design criteria used for safe 

rooms and storm shelters (Section 9.6.1)

Conclusion #7

State of ICC 500 adoption and 

enforcement. 

Many of the observed safe rooms 

and storm shelters were deficient 

when measured against the ICC 500 

standard.

Recommendation #13

Improve performance 

of safe rooms and 

storm shelters through 

code adoption and 

enforcement.

The MAT observed many existing buildings 

that did not have:

•	 a FEMA 361-compliant safe room,

•	 an ICC 500-compliant storm shelter, 

•	 a designated evaluated by a design 

professional to be a best available refuge 

area, or

•	 a tornado refuge area

Refer to:

•	 Terminology and examples (Section 9.1)

•	 Tornado refuge areas in commercial and 

industrial buildings: Planned tornado 

refuge areas (Section 9.2.2)

Conclusion #7

State of ICC 500 adoption and 

enforcement.

Many of the observed safe rooms 

and storm shelters were deficient 

when measured against the ICC 500 

standard.

Recommendation #13

Improve performance 

of safe rooms and 

storm shelters through 

code adoption and 

enforcement.
9-48 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Observations Conclusions Recommendations

Several schools visited by the MAT had 

designated refuge areas, however, aside 

from the Seneca Intermediate School, the 

MAT did not observe any schools with 

safe rooms constructed to the ICC 500 

standard (refer to Section 9.4.4 and 9.2.2).

Conclusion #22

2010 Alabama State school tornado 

safe room requirement.

FEMA supports the State of Alabama 

Building Commission and Alabama 

House Bill 459 that requires new school 

buildings constructed after July 2010 

to provide mandatory safe spaces for 

tornado protection in all K-12 public 

schools.

Recommendation #10

Propose IBC code 

change.

Refer to Chapter 11 for 

proposed language 

for submittal to 

IBC regarding shelters in 

schools.

People may travel great distances to get 

to a community safe room or storm shelter 

which exceed the 1⁄2-mile maximum travel 

distance advocated in FEMA publications 

(refer to Section 9.5, Travel time to 

community safe rooms, storm shelters, 

and tornado refuge areas)

Conclusions #24 and #26

(#24) People traveled excessive 

distances to community shelters 

and safe rooms.

(#26) Guidance for identifying 

how to provide community-wide 

protection is lacking. There is a lack 

of guidance as to how far people can 

and should travel safely to access a 

safe room or storm shelter.

Recommendations #34

and #35

(#34) Research travel 

time to, and use of, 

safe rooms and storm 

shelters.

(#35) Locate safe 

rooms or storm 

shelters close to 

people who will use 

them.

The MAT observed areas within exiting 

non-residential buildings labeled as 

“tornado shelters.” However, these areas 

were not designed and constructed in 

compliance with FEMA 320/361 or ICC 

500 to provide a clear level of protection 

from tornadoes. While it may result from a 

lack of understanding of the terminology 

used in safe room guidance such as FEMA 

320/361 and ICC 500, such mislabeling 

may mislead and endanger potential 

occupants during a tornado event.

Refer to:

•	 Terminology and examples (Section 9.1)

•	 Location and labeling of safe rooms and 

storm shelters (Section 9.6.5)

Conclusions #8 and #28

(#8 and #28) There is a lack of 

proper labeling and signage. There 

is a lack of proper labeling and signage 

for the areas where people seek to take 

cover from tornadoes.

Recommendation #14

Submit proposed IBC 

code change.

Refer to Chapter 

11 for proposed 

language for submittal 

to IBC regarding 

identification of best 

available refuge areas.

Table 9-1: Summary of Conclusions and Recommendations for Tornado Refuge Area, Hardened Area, and Safe Room 

Performance (continued)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 9-49

OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Observations Conclusions Recommendations

The MAT observed lack of best available 

refuge areas sited in buildings:

•	 Terminology and examples (Section 9.1)

•	 Location and labeling of safe rooms and 

storm shelters (Section 9.6.5)

•	 Tornado refuge areas (Section 9.2)

•	 Identifying design criteria used for safe 

rooms and storm shelters (Section 9.6.1)

Conclusions #25, #26, and#8 and 

#28

(#25) There is a poor understanding 

of public actions/movement 

patterns during tornadoes. Public 

actions/movement patterns during 

the April 27 tornadoes and the Joplin 

tornado are not understood.

(#26) Guidance for identifying 

how to provide community-wide 

protection is lacking. Guidance is 

needed to help public to select a large, 

community safe room vs. one of the 

many smaller, dispersed safe rooms 

across a community

(#8) and (#28) 

There is a lack of proper labeling 

and signage.

Recommendations #36 

and #34 

(#36) Identify best 

available refuge areas.

(#34) Research travel 

time to, and use of, 

safe rooms and storm 

shelters.

Tornado refuge areas in large, single-story 

commercial buildings and retail buildings 

did not perform well (see Section 9.2.2).

Conclusion #37

Tornado refuge areas located 

in large, single-story buildings 

performed poorly.

Tornado refuge areas located in large, 

single-story buildings did not perform 

well

Recommendations #36 

and #37

(#36) Identify best 

available refuge areas.

(#37) Perform 

vulnerability 

assessments.

Almost none of the residential safe 

rooms and storm shelters observed by 

the MAT in the five affected States were 

registered or listed with local emergency 

management agencies or police/fire 

departments. Furthermore, the MAT had 

difficulty locating FEMA-funded safe room 

even when latitudes and longitudes were 

provided (see Section 9.6.5).

Conclusions #29 and #31

(#29) There were unregistered safe 

rooms.

(#31) Some safe rooms were difficult 

to locate with given coordinates.

Recommendation #38

Register safe rooms. 

Table 9-1: Summary of Conclusions and Recommendations for Tornado Refuge Area, Hardened Area, and Safe Room 

Performance (continued)
9-50 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

OBSERVATIONS ON TORNADO REFUGE AREAS, HARDENED AREAS, AND SAFE ROOMS

Observations Conclusions Recommendations

Many safe room owners did not coordinate 

with their local government, so first 

responders did not necessarily know 

the locations of private and individual 

safe rooms and storm shelters. Also, few 

community safe rooms were equipped 

with alternate communication systems as 

recommended in FEMA 361 (see Sections 

9.6.5 and 9.6.6).

Conclusions #36, #39, and #30

(#36) Safe room locations were not 

documented and occupants had no 

ability to communicate from within. 

In many locations, first responders 

did not know the locations of private 

and individual safe rooms and storm 

shelters. This is a concern because 

safe rooms can be hidden beneath 

debris and difficult to locate after a 

storm, and occupants may have no 

means of communication with first 

responders.

(#39) There was a lack of alternate 

means of communication in 

community safe rooms.

(#30) Safe rooms and storm shelters 

lacked tools to open or dismantle 

door if blocked. Most safe rooms 

and storm shelters did not have tools 

available should the doors and egress 

routes become damaged, inoperable, 

or blocked by debris.

Recommendations 

#39 and #40

(#39) Equip safe 

rooms, storm shelters, 

and best available 

refuge areas with tools 

to assist occupants 

when doors and 

egress routes become 

damaged, inoperable, 

or blocked by debris.

(#40) Equip safe

rooms, storm shelters, 

and best available 

refuge areas with an 

alternate means of 

communication.

Evidence of technical inadequacies and 

public misconceptions regarding tornado 

safe rooms and storm shelters.

Refer to:

•	 Above-ground applications (Sections 

9.3.1.2, 9.3.2.1, 9.4.1, 9.4.3.2)

•	 Ventilation for safe rooms and storm 

shelters (Section 9.6.3)

•	 Terminology and examples (Section 9.1)

•	 Location and labeling of safe rooms and 

storm shelters (Section 9.6.5)

•	 Hardened areas: areas designed to 

provide some protection (Section 9.1.1)

•	 Tornado refuge areas in residences 

(Section 9.2.1)

•	 Hardened structures, rooms, and areas 

not designed to defined criteria (Section 

9.3)

•	 Safe rooms and storm shelters 

(Section 9.4)

Conclusions #23, #8 and #28, #32, 

#33, #34, #35, and #38

(#23) Above-ground safe rooms 

performed as well as those 

below ground. The public has 

misconceptions that above-ground 

safe rooms are not as safe as belowground safe rooms.

(#8) and (#28) There was a lack of 

proper labeling and signage.

(#32) Safe room door quality 

observed was often inadequate.

(#33) Safe room door hardware 

observed was often inadequate.

(#34) There was a lack of adequate 

ventilation in shelters.

(#35) Safe rooms were observed 

that had inadequate or no 

anchoring.

(#38) There was inadequate doors 

and door hardware on safe rooms/

storm shelters.

Recommendation #41

Provide training. 

Table 9-1: Summary of Conclusions and Recommendations for Tornado Refuge Area, Hardened Area, and Safe Room 

Performance (concluded)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 10-1

10Conclusions of the 

2011 Tornado MAT

The conclusions in this report are based on the MAT’s damage 

observations and assessments, an evaluation of relevant codes 

and regulations, and meetings with Federal, State, and local 

officials and other interested parties. 

Discussions with subject matter experts, State emergency management agencies from the five 

affected States, the Alabama Safer Schools Initiative, and local government representatives in the 

areas hit by the tornadoes were essential in verifying data observed in the field to prepare these 

conclusions. The conclusions of this report, upon which the recommendations in Chapter 11 are 

based, are intended to assist States, communities, businesses, and individuals who are recovering 

and rebuilding from the tornadoes by providing insight into protection of life and property. 
10-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

CONCLUSIONS OF THE 2011 TORNADO MAT

10.1 Codes and Standards

This section summarizes the MAT’s conclusions related to the effectiveness of model building 

codes and standards based on performance assessments of residential buildings, commercial and 

industrial buildings, critical facilities, infrastructure, and safe rooms and storm shelters damaged 

during the spring 2011 tornado outbreak. 

The adoption and enforcement of a building code results in safer buildings and improved chances of 

survival should a tornado strike in the future. It is important to note that building code adoption will 

not prevent damage to buildings when strong tornadoes strike unless that building had extremely 

high wind design concepts applied. However, adopting and enforcing building codes and standards 

demonstrates the community’s commitment to improving the quality of design and construction 

of structures and its belief that citizens’ investment in their homes and businesses is important to 

protect. 

10.1.1 Residential Buildings

Conclusion #1 – Failure to adopt a current version of code or having no uniform code leaves 

residential buildings vulnerable to wind damage: Much of the residential damage occurred 

in municipalities that had either no adopted building code (Hackleburg, AL) or outdated codes 

(Harvest, AL [2003 IRC] and Phil Campbell, AL [1998 SBC]) at the time of the tornado strikes. At 

the time of publication of this report, current codes are the 2012 or 2009 IRC. As of the publication 

of this report, Alabama and Missouri do not require individual communities to adopt a uniform 

residential building code. Three of the 17 Alabama communities the MAT visited had no residential 

building code whatsoever, and five others reported local adoption of residential building codes that 

predated the 2009 IRC. Adopting and enforcing any model building code is better than none, but as 

a rule, the more recent the code, the better. Since its introduction in 2000, the IRC has continuously 

improved its load path provisions, as demonstrated by the expanded wall bracing section in 2006, 

and has continued to evolve in subsequent editions. 

While adopting the most recent version of the IRC does not affect existing building stock (unless 

building additions are considered), it does establish a benchmark for new construction. Furthermore, 

adopting model building codes at a statewide level protects individual communities that are unable 

to adopt newer building codes through their own community processes. In their 2012 report, 

Cultivating a State of Readiness, the Tornado Recovery Action Council of Alabama encourages the 

adoption of a statewide building code to save lives, increase cooperation between agencies, improve 

delivery of services, and reduce the negative economic impacts of future storms.

The newly published 2012 IRC contains enhanced provisions for mitigating wind damage for 

basic 90 mph (3-second gust) wind speed zones, including increased wall bottom plate-to-stud 

connections and new tables for rafter and roof truss-to-wall uplift resistance requirements, both of 

which improve a structure’s resistance to wind forces by enhancing the continuous load path. Table 

802.11 in the 2012 IRC provides prescriptive values for both low- and high-sloped roofs in wind 

Exposure Categories B and C. 

Conclusion #2 – Failure to adhere to the structural provisions of the model building code as 

written can result in buildings that are vulnerable to structural damage: Buildings are made more 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 10-3

CONCLUSIONS OF THE 2011 TORNADO MAT

vulnerable to damage when local communities weaken the structural provisions of the adopted 

model building code with amendments or do not rigorously enforce the structural provisions of 

adopted code. Allowing the continuous load path of a building to be compromised—either in the 

form of amendments or through enforcement practices—increases the likelihood of structural 

failure when buildings are exposed to high winds. 

An example of non-rigorous enforcement of structural provisions would be allowing bottom wall 

plates to be attached with concrete nails or cut nails instead of IRC-specified anchor bolts. One 

reason concrete nails are used to anchor the bottom plate is because they are much easier to use 

than anchor bolts. Use of anchor bolts requires more planning than concrete nails because anchor 

bolts have to be embedded in the foundation before the framing is erected. However, concrete 

nails provide significantly less resistance to uplift and lateral forces than 0.5-inch-diameter anchor 

bolts with 7 inches of minimum embedment spaced a maximum of 6 feet on-center, as required 

by code, and therefore the substitution of concrete nails for anchor bolts significantly weakens the 

connection of the exterior framed wall to the foundation. 

Failure of the connection between the wall bottom plate and foundation was observed in newly 

constructed residential buildings in Alabama, where concrete nails were used for bottom plate 

attachment (refer to Figure 4-30). Follow-up analysis revealed that the City of Tuscaloosa allows 

the use of concrete nails for attaching the bottom plate to foundations in lieu of using anchor bolts 

as required by the IRC. The City of Tuscaloosa continued to permit bottom plates to be nailed to 

foundations even after the April 2011 tornadoes (Figure 10-1).

The MAT also observed new residential construction in Jefferson County, AL, that was non-codecompliant in the connection of the framed wall plate to the foundation (Figure 10-2).

Figure 10-1: Concrete nails (red circles in left photograph) used in lieu of anchor bolts (absent in both photographs) 

on residential buildings under construction in the City of Tuscaloosa, AL, after the 2011 tornadoes
10-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

CONCLUSIONS OF THE 2011 TORNADO MAT

Figure 10-2: 

Lack of anchor bolts on 

recently constructed slab 

foundation in Jefferson 

County, AL. Note that an 

anchor bolt is installed at 

the corner, but cut nails are 

installed elsewhere. 

10.1.2 Commercial and Industrial Buildings

Conclusion #3 – Wind provisions of the current codes and standards are insufficient to manage 

building performance in overload events: The MAT observed numerous instances of failure that 

occurred when various levels of overload were experienced by the structure. With the exception 

of storm shelter design and construction per ICC 500, the wind load provisions of the code do not 

address tornadic events. The ASCE commentary to the wind load provisions speak to the limitations 

of the wind provisions with respect to tornadoes, but this language is not clear. 

10.1.3 Critical Facilities

Conclusion #4 – IBC-compliant facilities can be susceptible to building damage: Buildings built 

to the current IBC are still susceptible to significant building damage and disruption if struck by 

strong or violent tornadoes, as evidenced by the damage sustained by Joplin East Middle School (see 

Section 6.1.4).

Conclusion #5 – Many of the critical facilities observed lacked safe rooms and/or storm shelters: 

The MAT visited 41 critical facilities located in the path of tornado tracks or track peripheries. None 

of these facilities had an area designed as a FEMA 361 tornado safe room or an ICC 500 shelter. 1

1 Unless otherwise specified, this chapter references the 2008 versions of FEMA 320, FEMA 361, and ICC 500.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 10-5

CONCLUSIONS OF THE 2011 TORNADO MAT

First responders typically stay in their buildings to facilitate post-disaster community response and 

are at risk when there are no safe areas to go to during tornadoes (see Section 7.2).

10.1.4 Infrastructure Facilities

Conclusion #6 – Wind-displaced materials affected communications towers: The MAT observed 

that wind-displaced materials can collect on communications towers and increase the wind loads 

on those towers. Chapter 8 describes how latticed free-standing towers are vulnerable to the effects 

of wind-displaced materials that increase the tower’s exposure to wind by adhering to the tower 

surface. Two cases are summarized where those increased loads likely contributed to observed tower 

collapse. 

Section 2.6.9.1 of ANSI/TIA-222-G Structural Standard for Antenna Supporting Structures and Antennas

(2009) uses Effective Projected Area (EPA) method to determine wind loads. With the EPA method, 

the sum of the areas of antennae and their supporting structures that are perpendicular to the 

wind direction is totaled. The total projected area is first scaled by a drag coefficient. Next, the drag 

coefficient, the EPA, and the design wind speed are used to determine wind loads on the tower and 

its components. When wind-displaced materials adhere to a latticed tower, the tower’s EPA increases, 

and wind loads on the tower also increase. Presently, ANSI/TIA-222-G does not address the increase 

in EPA and wind loads from wind-displaced materials that adhere to latticed structures. There is 

no guidance in ASCE 7-10 in either the standard or the commentary that deals with the issue of 

increased loads caused by wind-displaced materials. 

10.1.5 Tornado Refuge Areas, Hardened Areas, and Safe Rooms

Conclusion #7 – State of ICC 500 adoption and enforcement: With the exception of the Seneca 

Intermediate School in Seneca, MO, all of the safe rooms and storm shelters inspected by the MAT, 

for both residential and community uses, were constructed prior to the publication of the ICC 

500. Many of the observed safe rooms and storm shelters were deficient when measured against 

the ICC 500 standard. Sections 10.6.2 and 10.6.3 describe some of the more common inadequacies 

in greater detail. Communities can improve the quality of new safe rooms and storm shelters by 

adopting and enforcing ICC 500 by itself or through the provisions of the 2009 or 2012 I-Codes. 

Those editions of the IBC (Section 423) and IRC (Section 323) require that “in addition to other 

applicable requirements in [the] code, storm shelters shall be constructed in accordance with the 

ICC/NSSA-500.”

Conclusion #8 – There is a lack of proper labeling and signage: The MAT observed areas within 

existing non-residential buildings labeled as “tornado shelters.” However, these areas were not 

designed and constructed in compliance with FEMA 320/361 or ICC 500 to provide a clear level 

of protection from tornadoes. While it may result from a lack of understanding of the terminology 

used in safe room guidance such as FEMA 320/361 and ICC 500, such mislabeling may mislead and 

endanger potential occupants during a tornado event. 
10-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

CONCLUSIONS OF THE 2011 TORNADO MAT

10.2 Performance of Residential Buildings 

The MAT inspected various degrees of damage to 

residential buildings. The primary difference between 

whether a building suffered only minor damage, such 

as loss of siding or shingles, or total destruction, such 

as a slab swept clean, was tornado strength and location 

of the building with respect to the storm swath. Simply 

put, greater wind pressures led to greater damage. An 

illustration of this difference is described in Sections 

4.2.1 and 4.2.3 using the contrast in damage between 

Chastain Manor Apartments (Tuscaloosa, AL) and 

Mercy Village Apartments (Joplin, MO). 

While these factors, as well as variables related 

to building code adoption and enforcement, and 

construction materials and methods, directly influence 

building performance, they are often beyond the 

control of individual homeowners. The best means of 

providing life-safety protection for building occupants 

is to have quick-response access to a safe room 

compliant with FEMA 361 or a storm shelter compliant 

with ICC 500 (see Section 10.6). 

Conclusion #9 – Voluntary implementation of better design and construction practices could 

mitigate damage: The MAT did not observe many instances of enhanced wind-resistant construction 

in the residences damaged by the tornadoes. As stated in Chapter 4, according to NOAA tornado 

statistics from 1950 to 2006, almost 95 percent of all recorded tornadoes were EF2 or less. Some 

of the damage observed by the MAT resulted primarily from tornadoes rated as EF2 or less or to 

buildings located in the periphery of a more severe event. This damage can be mitigated through 

voluntary implementation of recommended best practices for wind-resistant construction. 

The design wind speed in the current model building codes for all areas the MAT observed is 90 

mph. Since model building code minimum requirements for continuous load path connections 

increase with design wind speeds, designing buildings to withstand higher wind loads will increase 

their resistance to wind damage. While it is neither economical nor practical to construct an 

entire home that is resistant to tornadoes of all strengths, improved design and construction and 

implementation of details and techniques that are already required in coastal high-wind regions will 

significantly reduce property damage caused by tornadoes rated EF2 or less (i.e., estimated wind 

speeds of 135 mph or less). An example of such improved building performance was observed after 

Hurricane Katrina, where the MAT noted that buildings designed and constructed to resist wind 

loads greater than 90 mph, as prescribed in ASCE 7 and the I-codes for coastal areas, performed 

better than the general building stock (FEMA 2006). 

Implementing and enforcing current codes and standards resulted 

in enhanced building performance

in several locations, one such being 

Mercy Village Apartments in Joplin, 

MO (described in Section 4.2.3). The 

level of detailing and engineering incorporated into the construction of 

the apartment building contributed to 

its enhanced performance under tornado-force winds. 

The load paths and structural systems 

used in the construction of the Mercy 

Village project allowed the transfer of 

the high wind loads to the foundations. 

The building suffered damage, but the 

structural integrity of the gravity systems remained stable and protected 

the building inhabitants.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 10-7

CONCLUSIONS OF THE 2011 TORNADO MAT

The following conclusions focus on the types of residential building damage observed by the 

MAT that could be mitigated if enhanced wind design and construction practices already used in 

hurricane-prone regions are voluntarily applied to tornado-prone regions with lower model building 

code design wind speeds. These types of damage included: 

+ Loss of Roof and Wall Covering: Roof and wall covering blown away by high winds and uplift forces 

became wind-borne debris that endangered surrounding buildings and their occupants as 

shown in Figure 4-1. Buildings that suffered roof covering loss were often further damaged by 

water intrusion. 

+ Component Damage: Component damage, whether shattered glazing or collapsed garage doors, 

often led to other structural and non-structural damage because of increased pressurization 

and water intrusion that followed breaching of the building envelope (Figures 4-9 and 4-10). 

Unprotected glazing and wide garage doors (16 or 18 feet wide) were particularly vulnerable 

(Figures 4-7 and 4-8), as was expected from previous MAT assessments.

+ Uplift of Roof Decking: Loss of roof decking often appeared to be triggered by increased 

pressurization resulting from damaged soffits and gable end walls (Figures 4-13 and 4-16). Poor 

fastening of roof decking to the roof structure also appeared to play a role in the loss of roof 

decking as shown in Figure 4-15.

+ Loss of Roof Structure: The weak link most often identified as responsible for loss of roof structure 

was the roof-to-wall connection (Figures 4-18 through 4-22).

+ Wall Collapse: Wall collapse was observed to result from failed attachment of floor and ceiling 

systems to walls (Figures 4-23 and 4-24) and inadequate bracing of framed walls (Figures 4-25 

and 4-26).

+ Failure of Wall Bottom Plate Attachment: Foundations typically performed adequately, but in 

some instances the connection of walls to the foundation system failed because of inadequate 

connection of the bottom plate, as shown in Figures 4-27 through 4-31.

10.3 Performance of Commercial and Industrial Buildings 

The MAT noted that, during the tornado events, people came from other locations to take refuge 

in commercial buildings because they perceived them to be safer than other types of buildings. 

However, in many cases, this perception was unfounded and misguided. Although multi-story framed 

structures did not experience disproportionate damage or collapse (although there was significant 

glazing damage), single-story commercial buildings did; the MAT inspected many failures of such 

buildings. Further, not all building owners and operators 

understood that commercial structures may not be safe 

in certain environmental or climatic conditions, such 

as during violent weather. The MAT’s conclusions on 

communications and operations, as well as building 

performance as a function of design, are presented in the 

section that follows.

Refer to Section 10.1.3 (Codes and 

Standards: Critical Facilities) for 

conclusions on the susceptibility 

of IBC-compliant critical facilities.
10-8 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

CONCLUSIONS OF THE 2011 TORNADO MAT

10.3.1 Communications and Operations

Conclusion #10 – There was inadequate signage in commercial buildings: In an effort to 

increase survivability and lower injury and loss of life, building users and occupants need a better 

understanding of a building’s design capacity and limits through adequate signage. Increased 

awareness of relevant building design parameters such as importance factor, design wind speed, 

ground snow load, seismic criteria, rain fall intensity criteria, and other relevant information will 

help individuals decide where to take refuge and the attendant risks.

Conclusion #11 – Emergency operations flip charts can aid in decision making: According to 

management personnel the MAT interviewed at a Lowes in Tuscaloosa, AL, flip charts helped the 

response of the store operators during the high stress and confusion of the tornadoes event by 

providing emergency protocols. Use of a preplanned strategy helps manage the people instead of 

having to make decisions about issues that they are not trained or educated in, specifically building 

performance. The use of a tool such as a flip chart allows the store operator to rely on the best 

information available while leaving the issues of engineering and risk analysis to people with those 

skill sets.

10.3.2 Building Performance/Building Design

Conclusion #12 – URM performed poorly as primary support: Buildings that used unreinforced 

masonry in the exterior walls and primary load carrying system did not perform well (see Figure 

5-18). Unreinforced masonry should not be used in any primary load support system or any critical 

area of a building used for the protection of people. 

Conclusion #13 – Connections between primary structural members were often the initial point 

of failure: The MAT noted that the connections between primary structural members on many 

buildings were the initial point of failure of the structural systems (see Figure 5-6 and Figure 5-8). 

Puddle welds that attached the roof deck to the joists were found to have inconsistent performance. 

This is consistent with past findings of roof deck connection performance in high-wind events. 

Additionally, the performance of the primary structural member connections could be improved to 

be more robust and ductile. It is neither difficult nor expensive to increase the design load capacity 

of these connections. However, it is sometimes more involved to properly construct and inspect the 

connections.

Conclusion #14 – Lack of redundant stability systems or non-discrete structural systems 

contributed to progressive collapse: The MAT inspected several one- and two-story, large-footprint 

commercial structures with long-span roofs that suffered catastrophic failure when smaller 

portions of the structure were progressively overloaded and failed. These smaller local failures then 

progressed to larger areas of failure that then led to entire building collapse. Buildings with nonredundant structural systems that served multiple functions (such as weather barrier and stability) 

did not perform well. Such failures were observed in several locations in Alabama and Missouri. Per 

ASCE 7, buildings should be designed to not experience disproportionate collapse. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 10-9

CONCLUSIONS OF THE 2011 TORNADO MAT

10.4 Performance of Critical Facility Buildings 

The MAT visited a total of 41 critical facilities in the path of tornado tracks or track periphery 

areas across five States. The tornadoes in April and May of 2011 significantly affected many critical 

facilities, totally destroying some of them and severely interrupting the operations of several others. 

Critical facilities such as schools, healthcare facilities, police and fire stations, and EOCs are vitally 

important to communities that have been struck by tornadoes. Functional schools are needed for 

educational continuity and they are often used as space for recovery operations. Functional hospitals 

and other healthcare facilities are needed to treat injuries and provide routine ongoing care to 

the community. Functional police and fire stations and EOCs are needed to manage their normal 

mission, along with response and recovery operations after an event. 

Conclusion #15 – Glazing is susceptible to damage: Damage to critical facilities constructed since 

the adoption of the IBC is still possible because of wind-borne debris that damages the glazing and 

building envelope. Although the design wind speed for IBC-compliant facilities in the areas visited 

by the MAT is greater than EF0 speeds and only slightly below upper EF1 speeds, such facilities were 

observed to be susceptible to extensive glazing damage (as illustrated by Figures 6-26 and 10-3)2 and 

facility disruption due to wind-borne debris generated by the weaker tornadoes. IBC design wind 

speeds and glazing requirements only apply to the wind-borne debris regions in hurricane-prone 

areas along the Nation’s coastlines. 

Figure 10-3 shows a police station in Tuscaloosa, AL (see Figure 7-1 for location) that experienced 

roof covering damage and extensive glazing damage. Most of the exterior windows were impacted by 

wind-borne debris (primarily aggregate from a built-up roof). The debris chipped and cracked the 

glazing, as shown in the Figure 10-3 inset, but because the glazing was bullet resistant, the glazing 

remained in the frame. Figure 10-3 shows plywood (red arrows) placed over the damaged glazing.

Conclusion #16 – Older facilities were susceptible to damage from weak tornadoes: The MAT 

observed older critical facilities with significant wind-resistance vulnerabilities.3 Unless mitigated, 

older facilities are susceptible to considerable building damage and disruption of facility operations 

if struck by even weak tornadoes. Ringgold High School and Ringgold Middle School (see Section 

6.1.3), Webster’s Chapel Volunteer Fire Department (see Section 7.2.3), and the Smithville Police 

Department (see Section 7.3.4) are all examples of older critical facilities that demonstrated 

significant wind-resistance vulnerabilities when struck by weak tornadoes.

Conclusion #17 – There was a lack of adequate signage directing occupants to refuge areas: 

The MAT noted many critical facilities with no signage directing occupants to refuge areas in the 

building. The MAT observed some critical facilities that had tornado refuge areas identified by 

signs. In some instances, the signage indicated the refuge area was a “shelter” even though the area 

had not been designed as a FEMA 361 safe room or an ICC 500 storm shelter. Joplin East Middle 

School (see Section 6.1.4), the Fultondale Municipal Complex’s Library and “Shelter” (see Section 

7.2.1), as well as the Tuscaloosa EOC (see Section 7.3.1) all had signage that indicated the marked 

2 Although the facilities shown in Figures 6-27 and 10-3 were constructed prior to the publication of the IBC, the exterior glazing in IBCcompliant buildings is no more resistant to wind-borne debris than the glazing in older buildings in locations where the basic wind speed 

is 90 mph. 

3 Older facilities are those for which codes, standards, design, and construction practices did not adequately address non-tornadic wind 

resistance. 
10-10 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

CONCLUSIONS OF THE 2011 TORNADO MAT

MAT EF Rating: Using DI 9 

(Small Professional Building), the 

MAT selected DOD 3 (“broken 

windows, including clear story windows or skylights”) for the 

Tuscaloosa, AL, police station.1

Using the expected wind speed 

for DOD 3, the MAT derived the 

tornado rating as EF1 (86–110 

mph) based on the damage to 

this building. Hence, the estimated wind speed experienced by 

the building was not substantially above the current basic wind 

speed of 90 mph.

1. There is no DI for police stations. The type of construction listed for DI 9 is applicable to this facility.

Figure 10-3: Red arrows show plywood placed over damaged glazing at this police station; inset shows chipped glazing 

and illustrates the quantity of wind-blown roof aggregate that struck the facility. Because of the building damage, a 

mobile command vehicle (yellow arrow) was brought to the site (Tuscaloosa, AL).

refuge area was a “shelter.” However, none of these refuge areas had been designed as a FEMA 361 

safe room or an ICC 500 storm shelter.

Conclusion #18 – There was a lack of safe rooms and storm shelters in critical facilities: The 

MAT inspected 41 critical facilities in tornado tracks or along the track periphery. None of these 

facilities had an area designed as a FEMA 361 tornado safe room or an ICC 500 storm shelter. First 

responders typically stay in their buildings to facilitate post-disaster community response and are at 

risk when there are no safe areas to go to during tornadoes (see Section 7.2).
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 10-11

CONCLUSIONS OF THE 2011 TORNADO MAT

10.5 Performance of Infrastructure Facilities 

The tornadoes not only damaged buildings, but also disrupted community infrastructure. The MAT 

inspected damage to public utilities, including water distribution systems, waste water treatment 

plants, and communications towers.

Conclusion #19 – Lost utility power caused loss of 

system function: The MAT noted that when water 

treatment and distribution systems relied exclusively 

on utility power, the systems failed when utility power 

was lost. When tornadoes destroyed portions of the 

electrical utilities’ distribution systems, the reliance of 

the systems on utility power to operate lift pumps to 

fill storage tanks or booster pumps to increase water 

distribution pressures resulted in the tanks draining 

and the loss of system pressure. Both the Tuscaloosa 

Water Works in Alabama (Section 8.1.1) and the 

Smithville, MS, water treatment and distribution 

system (Section 8.1.2) were affected in this manner. 

Conclusion #20 – Guy anchors failed when struck by wind-displaced materials: The MAT 

inspected the failure of guy anchors when wind-displaced materials struck the guy wires of a guyed 

communications tower, resulting in tower collapse. With guyed structures, all anchors must function 

to make the tower structurally stable. The lack of structural redundancy inherent in guyed towers 

makes them particularly vulnerable to collapse when one or more guys or their anchors fail. The 

300-foot guyed cellular tower in Smithville, MS experienced that mode of failure (Section 8.3.2.1). 

Conclusion #21 – Wind-displaced materials affected tower performance: There were numerous 

examples of how wind-displaced materials can increase loads on communications towers. Winddisplaced materials were observed to have adhered 

to latticed free-standing towers. Once adhered, the 

wind-displaced materials increased the area of the 

latticed towers exposed to wind loads and increased 

the total wind forces on the towers themselves. While 

insufficient data were available to confirm that the 

wind-displaced materials caused tower collapse, winddisplaced material increased wind loads on the tower 

and likely contributed to tower collapse. Examples 

include:

+ A 250-foot EMS communications tower in Tuscaloosa, AL (Section 8.3.1.1) that collapsed during 

the tornado had wind-displaced materials adhered to the latticed tower. Collapse of the EMS 

tower disrupted communications and impeded response and recovery in the Tuscaloosa County.

+ A 300-foot free-standing cellular tower in Tuscaloosa, AL (Section 8.3.1.2) also collapsed. While 

there were no wind-displaced materials noted that were physically adhered to the fallen latticed 

tower, there were large amounts of debris surrounding the tower. This suggests that some winddisplaced materials may have struck the tower but were dislodged after the tower fell. 

Facilities with sufficient back-up 

power supply remained functional.

The Tuscaloosa Waste Water Treatment 

Plant (Section 8.2.1) was able to continue operations after the tornado in 

the region knocked out its local power source. The facility was equipped 

with enough emergency generators to 

sustain enough of the lift stations to 

prevent overflow or discharge of untreated effluent. 

Solid free-standing cell towers survived the event that destroyed guyed 

and latticed cell towers. One such tower, discussed in Section 8.3.1.3, did 

not collapse even though it was located near the center of the tornado track, 

where maximum winds generally occur. 
10-12 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

CONCLUSIONS OF THE 2011 TORNADO MAT

Solid free-standing towers are less affected by wind-displaced materials than other types of towers 

since their entire surface is already exposed to wind pressures and therefore the wind loads are 

not increased even when materials adhere to the towers. Solid towers are less vulnerable to winddisplaced materials since ANSI/TIA-222-G requires solid free-standing cell towers to be designed 

to resist higher wind loads (due to greater EPAs) than latticed towers. Also, since they are freestanding, solid towers do not rely on vulnerable guys and anchors for structural stability. 

The few numbers of cellular towers assessed prevent the MAT from drawing definitive conclusions 

about tower performance. However, based on the fact that solid cellular towers must be designed 

with near-maximum EPAs and do not rely on guys for support, properly designed solid cellular 

towers should perform better than latticed or guyed towers during wind events that create high 

winds and wind-displaced materials.

10.6 Performance of Tornado Refuge Areas, 

Hardened Areas, and Safe Rooms 

The MAT observed several community safe rooms and storm shelters constructed to criteria that 

have been in place since 2000, but only one that had been constructed since the release of the 

2008 safe room and storm shelter guidance. 

Numerous residential safe rooms and storm 

shelters throughout the areas were impacted by 

the tornadoes. More can be done to promote the 

design and construction of safe rooms and storm 

shelters in all building types and uses to provide 

life-safety protection during tornadoes. 

10.6.1 General

The best life-safety protection from tornadoes is a safe room or storm shelter, specifically one 

designed and tested to the FEMA criteria (FEMA 320 / FEMA 361 or the ICC 500 standard). There 

were no fatalities in any of the observed safe rooms or storm shelters, and none of the occupants of 

these specially designed structures were injured in spite of the strength of the tornadoes. Although 

the residential and community safe rooms had generally been designed, constructed, and tested 

to meet FEMA 320/361 guidelines, there were numerous compliance issues with signage, doors, 

ventilation, and square footage space allocation.

The performance of tornado refuge areas, hardened rooms, safe rooms, and storm shelters 

highlights the need for the construction of more safe rooms and storm shelters in tornado-prone 

regions. The following statements related to the use and performance of safe rooms and storm 

shelters are based solely on the MAT’s observations. Specific conclusions related to residential and 

community safe rooms and storm shelters are presented in the following sections. 

Conclusion #22 – 2010 Alabama State school tornado safe room requirement: FEMA supports 

the State of Alabama Building Commission and Alabama House Bill 459 that requires new school 

buildings constructed after July 2010 to provide mandatory safe spaces for tornado protection in all 

Refer also to Sections 10.3 (Commercial 

and Industrial) and 10.4 (Critical Facilities) 

for specific sheltering conclusions related 

to those building types.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 10-13

CONCLUSIONS OF THE 2011 TORNADO MAT

K-12 public schools. The Building Commission further identified the ICC 500 as the standard to 

which the safe spaces are to be constructed for providing protection from tornadoes. 

Conclusion #23 – Above-ground safe rooms performed as well as those below ground: Despite 

broad public perception to the contrary, above-ground safe rooms, when constructed properly, 

provide the same level of protection and perform just as well as below-ground safe rooms. 

Conclusion #24 – People traveled excessive distances to community shelters and safe rooms:

People may travel great distances to get to a community safe room or shelter, especially when they 

have ample warning time as was the case in many communities on April 27, 2011. Travel distances to 

community safe rooms and shelters on that day were reported to be between 5 and 10 miles, greatly 

exceeding the 1⁄2-mile maximum driving distance or 5-minute maximum walking time advocated by 

FEMA. Whether walking or driving, prospective safe room occupants must be able to safely reach 

the facility within 5 minutes of receiving a tornado warning or notice to seek shelter.

Conclusion #25 – There is a poor understanding of public actions/movement patterns during 

tornadoes: Based on statistics from the NOAA SPC, over 65 percent of all fatalities on April 27, 2011 

occurred in homes, 6 percent occurred in commercial/public buildings, and 3 percent occurred 

in vehicles. By comparison, 40 percent of the fatalities on May 22, 2011 in Joplin, MO, occurred in 

homes, 42 percent in commercial/public buildings, and 9 percent in vehicles. 

While the time of day and day of the week definitely influenced where people were when the tornado 

struck, it is difficult to establish if movement patterns related to sheltering were consistent during 

the April 27 tornadoes (which included both large tornadoes with atypical warning times, many 

upwards of 60 minutes as well as rapidly forming tornadoes with minimal to no warning times). 

During the Joplin tornado, which was a large tornado with warning times at or below average, a 

much higher percentage of fatalities occurred outside the home. Although greater availability of 

safe rooms or storm shelters in non-residential buildings may have prevented loss of life during 

this event (which provided less than 20 minutes warning time), behavioral studies and research are 

lacking to help explain or predict the movements of people during tornadoes.

Conclusion #26 – Guidance for identifying how to provide community-wide protection is lacking:

Based on the MAT’s observations, the determination of whether or not to protect a vulnerable 

community using a single, large safe room or storm shelter (versus smaller, dispersed safe rooms and 

storm shelters) is currently based on conjecture and anecdotal evidence. Behavior during storms 

that spawn tornadoes is not well studied. There is a lack of data and research that clearly states or 

defines the risk individuals take when they travel long distances to seek refuge during a tornado. 

Technical storm elements and social science (behavioral) issues such as warning time, presence of 

multiple funnel clouds, track variation movement patterns across the tornado path, lack of safe 

areas at current location, and the time available to make the decision to shelter or seek shelter are 

examples of inputs to the decision making process that warrant further study. Currently, there is a 

lack of consistent guidance on how to provide protection when the potential occupants are traveling 

more than 5 minutes (walking time). As such, it is up to the community to determine if they will 

support or promote the use of a single, large community safe room, dispersed smaller community 

safe rooms, or smaller private and residential safe rooms throughout the community. 

Conclusion #27 – Design and construction guidance for storm shelters and safe rooms is consistent, 

though somewhat different in scope: The ICC 500 for storm shelters and the FEMA technical 
10-14 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

CONCLUSIONS OF THE 2011 TORNADO MAT

guidance (FEMA 320 and FEMA 361) for safe rooms provide the same or nearly identical levels 

of protection for tornado hazard protection. Notable differences exist between the documents for 

hurricane hazard protection, but a review of the hurricane provisions was beyond the scope of this 

tornado MAT report. Both these documents provide important guidance and FEMA continues to 

educate designers, emergency management officials, property owners, and people in the community 

seeking to find protection from tornados on the benefits of FEMA 320, FEMA 361 and ICC 500 and 

how they complement one another. The fact that FEMA references an engineering design standard 

(ICC 500) and uses it as part of their much larger emergency management program shows FEMA’s 

commitment to use voluntary consensus standards to the maximum extent possible in carrying out 

its programs. 

ICC 500 is an engineering standard and in its first edition; it does not provide a commentary to 

support the requirements of the standard. The standard is adopted by reference by the 2009 and 

2012 I-Codes. By comparison, the technical criteria from the FEMA guidance documents—although 

not ANSI-certified consensus standards—include an extensive commentary addressing not just 

design considerations, but also operational and maintenance issues of safe rooms. While the FEMA 

documents are not adopted by the I-Codes, the FEMA criteria may be adopted by a jurisdiction 

to govern the construction safe room and storm shelters. The authority having jurisdiction must 

clearly state who is responsible for reviewing and accepting the design of and construction of a safe 

room or storm shelter to ensure compliance with the technical criteria or standard.

Conclusion #28 – There is a lack of proper labeling and signage: There were areas within existing 

non-residential buildings labeled as “tornado shelters.” However, these areas were not designed and 

constructed in compliance with FEMA 320/361 or ICC 500 to provide a clear level of protection 

from tornadoes. Such labeling may result from a lack of understanding of the terminology used in 

safe room guidance (such as FEMA 320/361 and ICC 500). This labeling can, however, mislead and 

endanger potential occupants during a tornado event. 

Conclusion #29 – There were unregistered safe rooms: There is a potential for people to become 

trapped in their safe rooms (see Section 9.4.3.1). While most community safe rooms and storm 

shelters are managed by local or county governments (as they are public facilities), almost none of 

the residential safe rooms and storm shelters observed by the MAT in the five affected States were 

registered or listed with local emergency management agencies or police/fire departments.

Conclusion #30 – Safe rooms and storm shelters lacked tools to open or dismantle door if blocked: 

Most safe rooms and storm shelters did not have tools available to open or dismantle the door from 

within should egress routes become damaged, inoperable, or blocked by debris. 

Conclusion #31 – Some safe rooms were difficult to locate with given coordinates: The MAT had 

difficulty locating FEMA-funded safe rooms even when latitudes and longitudes were provided. It 

seemed that coordinates were either incorrect or outdated, and had not been verified in the field 

prior to the tornado. 

10.6.2 Residential Safe Rooms and Storm Shelters

There were design and construction issues observed with the residential safe rooms, storm shelters, 

and tornado refuge areas assessed by the MAT. For best available tornado refuge areas, it is difficult 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 10-15

CONCLUSIONS OF THE 2011 TORNADO MAT

to ensure that “above code” improvements are implemented correctly. The MAT observed numerous 

attempts to construct hardened rooms that were misidentified as “tornado shelters” where voluntary 

compliance with the criteria and standards from FEMA and ICC was not achieved. An opportunity 

exists for communities to enable improved compliance with the safe room and storm shelter criteria 

by adopting the ICC 500 as a minimum standard for storm shelter construction (alone or along with 

adoption of the latest edition of the IRC). 

All of the safe rooms or storm shelters inspected by the MAT during the field visits were constructed 

prior to any adoption of the 2009 I-codes and ICC 500, which require building departments to be 

involved in the design, construction, and installation of safe rooms and storm shelters. However, there 

were numerous discrepancies noted between the observed construction and the FEMA guidance 

documents on safe rooms or the ICC 500 criteria, that going forward, need to be corrected. The 

most common deficiencies in the residential safe rooms and storm shelters noted during the field 

assessments are described below.

Conclusion #32 – Safe room door quality observed was often inadequate: Doors that did not meet 

the FEMA or ICC criteria were the most dominant deficiency in residential safe rooms. Door quality 

was lacking in many observed residential safe rooms and storm shelters. Many of the doors would 

not pass the debris impact tests from FEMA 320/361 and ICC 500, and many that were installed 

had not been tested to show compliance with the criteria. The presence of substandard doors places 

occupants at risk. If substandard doors fail, the occupants in these areas can be exposed to wind 

and wind-borne debris.

Conclusion #33 – Safe room door hardware observed was often inadequate: Door hardware, 

specifically latching mechanisms, was observed to be inadequate in many older shelters and 

hardened rooms (but also in some new storm shelters and safe rooms). FEMA 320 requires three 

hinges and three latches. FEMA 361 recommends six points of connection (typically three hinges 

and three latching mechanisms), but allows for other alternatives if the door and door hardware are 

tested to meet stated debris impact criteria. ICC 500 requires only that the door and door hardware 

be tested to meet stated debris impact criteria. Most of the older doors (both above- and belowground) installed in hardened rooms and older shelters had inadequate latching; these doors 

performed with varying levels of success during the storms. 

Conclusion #34 – There was a lack of adequate ventilation in shelters: Ventilation pipes and vents 

were altered or removed in many older below-ground shelters. This is an unsafe practice and places 

occupants at risk.

Conclusion #35 – Safe rooms were observed that had inadequate or no anchoring: A few 

prefabricated safe rooms were installed but not anchored to a foundation; specifically, the structures 

observed were heavy, precast concrete safe rooms. Although these safe rooms/storm shelters are 

massive and stated by sellers and manufactures to be FEMA- and ICC-compliant structures, they 

must still be restrained to resist high wind forces. The MAT was unable to obtain documentation to 

show these structures were adequately anchored to resist overturning. 

Conclusion #36 – Safe room locations were not documented and occupants had no ability to 

communicate from within: Many tons of debris can be blown on top of or around a safe room 

or storm shelter during a tornado. Many safe room owners did not coordinate with their local 

government, so first responders may not have known the locations of private and individual safe 
10-16 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

CONCLUSIONS OF THE 2011 TORNADO MAT

rooms and storm shelters. Furthermore, safe room and storm shelter occupants were not always able 

to communicate with first responders from within their safe rooms and storm shelters when egress 

was disabled or blocked by debris. 

10.6.3 Community Safe Rooms, Storm Shelters, and Tornado Refuge Areas

There were design and construction issues with the community safe rooms, storm shelters, and 

tornado refuge areas inspected by the MAT. The MAT deployed after the April 25–28, 2011 

tornadoes observed numerous safe rooms and storms shelters where voluntary compliance with the 

criteria and standards from FEMA and ICC was not achieved. An opportunity exists to improve 

compliance with the safe room and storm shelter criteria by adopting the ICC 500 and a minimum 

standard for storm shelter construction (alone or along with adoption of the latest edition of the 

IRC). Further, the few non-stand-alone designated “tornado shelters” or designated refuge areas 

the MAT observed were in portions of buildings that were not constructed to any higher level of 

protection than the other portions of the building. The MAT could not verify if any of these areas 

had been evaluated or assessed for their vulnerability to tornadoes prior to their use as a tornado 

refuge area.

All of the safe rooms and storm shelters inspected by the MAT during the field assessments were 

constructed prior to any adoption of the 2009 I-codes and ICC 500 (in which building departments 

would have been required to be involved in the design, construction, and installation of the 

structures). The lone exception was the Seneca Intermediate School in Seneca, MO (see Section 

9.4.4.3). The most common shortcomings of tornado refuge areas and deficiencies in the community 

safe rooms and storm shelters noted during the field assessments are described below.

Conclusion #37 – Tornado refuge areas located in large, single-story buildings performed poorly:

Tornado refuge areas in large, single-story commercial buildings and retail buildings did not 

perform well. Although some winds were at or above design wind speeds, disproportionate collapses 

(and almost complete collapses) occurred in several instances (refer to Section 10.3). Although 

emergency planning efforts by building owners and operators identified specific areas to be used 

during a tornado event, the MAT could not verify whether any of these areas were defined as best 

available refuge areas by design professionals who specifically identified vulnerability to wind and 

wind-borne debris.

Conclusion #38 – There was inadequate doors and door hardware on safe rooms/storm shelters:

Some FEMA-funded community safe rooms were observed to have inadequate doors and door 

hardware, similar to problems the MAT observed with residential safe rooms and storm shelters. 

This is a compliance issue that building departments would have been required to evaluate during 

the design, construction, and installation of the structures had the construction of these protected 

spaces been required by the State or local building code. 

Most tornado refuge areas the MAT observed also had doors that would not pass the FEMA/ICC 

criteria (tests) for wind and debris-impact resistance. These weak doors and door systems place 

occupants at risk during a tornado.

Conclusion #39 – There was a lack of alternate means of communication in community safe 

rooms: Few community safe rooms were equipped with alternate communication systems as 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 10-17

CONCLUSIONS OF THE 2011 TORNADO MAT

recommended in FEMA 361. Where alternative means of communication were observed, not all safe 

rooms provided backup power for these systems in the event power was lost during the event.

10.7 EF Scale

At each site visited, the MAT independently determined an EF scale rating based on one of the 28 

DIs and DOD described in A Recommendation for an Enhanced Fujita Scale (TTU 2006), which was 

officially adopted by NOAA/NWS and first used in February of 2007. Information on the EF scale 

is provided in Chapter 2 and Appendix E. The following conclusions relate to the EF scale rating 

system based on the MAT’s observations.

Conclusion #40 – DI lists are incomplete: To effectively use the EF scale, the construction description 

should reasonably match the building or structure being rated. There were some types of buildings, 

such as fire stations, that did not have specifically assigned DIs. Therefore, the MAT used DI 14 

(Automobile Service Building) or DI 21 (Metal Building System), depending on which construction 

type was most closely approximated, to rate fire stations. By contrast, schools are accounted for 

reasonably well in the existing format, and are separated into DI 15 (Elementary School) and DI 16 

(Junior or Senior High School). 

Conclusion #41 – DOD categories are inadequate for specific DIs: For some of the current 28 

DIs, there are up to 12 DOD indicators, allowing the user to choose the specific level of damage 

based on observations. However, for some DIs, such as free-standing towers, there are only two 

DOD indicators. Freestanding communications towers (DI 25) were rated by the MAT. The existing 

format of the EF scale only lists three DODs under DI 25, which limits the number of estimated wind 

speeds that can be deduced. While free-standing towers have a limited number of possible failure 

modes and related DODs, other DIs such as DI 5 (Apartments, Condominiums, and Townhouses) 

have more DODs to better rate tornado wind speeds. 

Conclusion #42 – The process for assessing varying DODs in the same DI is not well explained 

in EF guidance: Large buildings, such as Ringgold High School in Ringgold, GA, often exhibited 

marked differences in damage from one portion of the building to another because the tornado 

only struck a portion of the building. The lack of guidance for how to assess large buildings where 

only a portion of the building is struck can make the application of the EF scale different among 

different users. For example, DI 16, DOD 5, is for “... significant loss of roofing material (>20%) ...” 

If only one end of a large building is struck, the roof covering damage in that area could exceed 

20 percent, but could be less than 20 percent of the total for the entire roof area. In this case, if 

the DOD were applied only to the portion of the building that was struck, then DOD 5 would be 

applicable. But if the DOD was applied to the entire building, then DOD 2 would be applicable 

(assuming the only damage was to the roof covering). 

Conclusion #43 – Order of DOD choices for DI 2 (One- and Two-Family Residences) in the EF 

rating scale does not follow observed damage patterns: As noted in Chapter 4, most residences 

rated by the MAT followed the order of DODs prescribed by the EF scale closely, with the exception 

of DOD 5 (Entire House Shifts off Foundation). It was very unusual for DOD 5 to precede DOD 6. 

In the one documented case (Figure 4-17), the observed residence was older construction. 
10-18 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

CONCLUSIONS OF THE 2011 TORNADO MAT

Conclusion #44 – Photographs of DODs would aid in determining EF ratings: A Recommendation for 

an Enhanced Fujita Scale (TTU 2006) does not include photographs for each of the DOD indicators, 

making it difficult for users to accurately interpret the guidance and evaluate structure damage. 

10.8 Post-Tornado Imagery

Following the tornadoes, the NWS released aerial photographs and rated the intensity of the 

tornadoes along the tracks in certain locations. The following conclusions relate to the post-tornado 

imagery and the MAT’s observations. These conclusions are not based on field observations, but 

rather the MAT’s observations in developing this report and working with the information collected 

in the field.

Conclusion #45 – Post-tornado NWS aerial photographs were helpful in conducting damage 

analysis: The NOAA post-tornado aerial photographs were helpful to the MAT. The photographs 

provide context for wind performance of a given building with respect to building location within 

or on the periphery of the tornado track. The aerial photographs also show other damage in the 

vicinity of a given building. The view from the air provided insights that could not be discerned 

from ground-based observations. 

Conclusion #46 – EF contours provided by NWS were useful: Having EF contours of the track 

was helpful to the MAT. Where contours were provided, a direct comparison between the NWS EF 

contour rating and the MAT EF rating for a specific building could be made. Development of EF 

contours is also important for risk modeling of facilities and other structures such as nuclear power 

plants, safe rooms, and power transmission lines. 

Conclusion #47 – Accuracy of EF ratings used to develop track contours is important: For risk 

modeling, in addition to developing EF contours, it important that the EF ratings for the contours 

be accurate. Accurate wind speed determination is difficult for two reasons: 1) there is some 

uncertainty of the wind speed for given DODs, and 2) accurate selection of the wind speed between 

the lower- and upper-bound speeds associated with the DODs requires specialized knowledge. The 

MAT derived an EF rating for several buildings; the MAT’s ratings for most of these buildings were 

different from the NWS track rating or contour rating in the vicinity of the building. The difference 

may be a function of the MAT’s specialized knowledge of structural performance. 
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 11-1

11Recommendations of the 

2011 Tornado MAT

The tornadoes of April 25–28, 2011 and May 22, 2011 

were devastating in their intensity, severity, and loss of life 

and property.

While the events of April and May 2011 cannot be undone, the affected communities can commit to 

planning for future tornadoes through promoting sustainable and tornado-resistant construction. 

The recommendations in this report are based solely on the MAT’s observations, assessments, 

analysis, and conclusions. These recommendations are intended to assist individuals, communities, 

and businesses through the reconstruction process and to help reduce future damage and impacts 

from other tornadic wind events.

At a minimum, as communities begin to rebuild homes, businesses, and critical facilities, there are 

several ways they can reduce the effects of future tornadoes, including:

+ Design buildings to the most current building codes and engineering standards to improve 

building performance and reduce damage 
11-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS OF THE 2011 TORNADO MAT

+ Construct residential and community safe rooms to provide safe refuge in the event of a strong 

or violent wind storm or tornado

Specific recommendations are included in the following subsections. Mitigating future losses, 

however, will not be accomplished by simply reading this report; mitigation is achieved when a 

community actively seeks and applies methods and approaches that will lessen the DOD, injuries, 

and loss of life in future tornadoes. For example, the Tornado Recovery Action Council of Alabama 

is encouraging the adoption of a statewide building code to mitigate future losses (2012). These 

recommendations can be used across the United States and for other disasters, as applicable, to 

prepare, plan, and design for mitigating deaths and damages in similar hazard events. 

11.1 Codes and Standards

This section provides MAT recommendations related to codes and standards intended to improve 

building performance of residential, commercial, industrial, and critical facilities. In addition to 

property protection, the MAT provides recommendations for requirements related to personal 

protection. 

11.1.1 Residential Buildings

Recommendation #1 – Adopt and enforce current model 

building codes: State and local officials should adopt and 

enforce a current edition of a model building code (current 

codes at the time of publication of this report are the 2012 or 

2009 IRC, Figure 11-1) for all new residential construction. 

The minimum requirements of the code should be kept intact, 

including the criteria set forth in ASCE 7, the ICC 500, and 

Chapter 3 of the IRC. Where the State is deficient in model code 

adoption, the local jurisdictions should adopt and enforce the 

latest model building codes. Some jurisdictions may qualify for 

HUD Community Development Block Grants and FEMA HMGP 

opportunities to establish inspection departments. 

As an interim step to code adoption, engineers should design and builders should build to the latest 

model building codes. Designers, builders, and owners should consider voluntary implementation 

of these codes in jurisdictions where they are not adopted by government authorities.

Recommendation #2 – Increase emphasis on code compliance: Where codes are in place, more 

emphasis should be placed on code compliance. Homebuilders and code enforcement agencies 

should consider developing an active education and outreach program with contractors to emphasize 

the importance of code compliance for wind resistance. 

Recommendation #3 – Maintain and rigorously enforce the adopted model building code since 

amendments or lax enforcement practices may weaken the continuous load path of the building:

Minimum requirements of the IRC and IBC that specify prescriptive connections along the critical 

load path from roof, through walls, into floor systems, and into the foundation should not be 

Figure 11-1: IBC/IRC
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

weakened through local amendments or enforcement practices. Weakening the critical load path 

threatens the integrity of buildings and endangers their occupants unnecessarily. 

11.1.2 Commercial and Industrial Buildings

Recommendation #4 – Include failure states and survivability in building codes and standards: 

For a coherent design approach, structural loads need to be addressed and presented in a clear, 

consistent philosophy of design. Failure states and building survivability also need to be addressed 

in the codes. Wind design provisions important for building resistance to high-wind events such as 

tornadoes should be discussed in ASCE 7, and wind design methodologies should be developed for 

use by practitioners. 

Recommendation #5 – Change risk category for large-footprint commercial structures with 

long-span roofs to Risk Category III in ASCE 7-10: Classify one- and two-story, large-footprint 

commercial structures with long-span roofs as Risk Category III under ASCE 7-10 to protect the 

large number of people that may occupy these structures at any given time. 

Recommendation #6 – Improve design approach in ASCE 7 and IBC to address risk consistently 

across hazards: The codes and standards need a coherent approach to risks, threats, and hazards. 

The ASCE 7 standard does not have a clearly articulated design approach as part of the document. 

If clear and consistent designs with predictable and acceptable performance are to be achieved 

our codes and standards must clearly state the basis for their development and implementation. 

Therefore, the MAT recommends that ASCE 7 and IBC undertake the task of capturing a better 

design approach that treats risk consistently across hazards. Part of the code and standard 

performance objective must be to prevent building collapse even in extreme events. A building may 

be rendered a complete functional and economic loss, but it should not collapse. This area of code 

improvement implies a more sophisticated approach that is partially captured by the development 

of performance-based design methods. Performance-based design methods should be expanded to 

more areas of ASCE 7 and the IBC, particularly as they relate to the wind hazard. 

Recommendation #7 – ASCE 7 should improve the commentary on code limitations: The current 

codes and standards that govern building design do not clearly express how they handle tornado 

loads. The narrative that explains the limitations does not clearly state what elements of tornado risk 

or exposure are covered. ASCE 7 should make clear, unambiguous statements in the commentary 

about code limitations. These statements should clarify whether tornadoes are dealt with in the 

process, and if not, why. The commentary discussion needs to objectively explain the rationale for 

the decision. 

Recommendation #8 – Clarify risk tolerance in ASCE 7 and IBC: ASCE 7 and the IBC should 

begin the discussion of risk tolerance so that probability-based design of building performance can 

be better understood, communicated and implemented. 

Recommendation #9 – Include best practices for wind design in IBC: The IBC should develop 

a best practices section for wind design similar to the seismic portion of the code. This section 

can incorporate details and systems that enhance building performance in extreme wind events. 

Expansion of this discussion may incorporate concepts that are familiar to seismic designers and 

also address progressive collapse. Best practices for extreme wind design include redundancy of the 
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

MWFRS, ductility of connections, alternate load paths, design for load reversal, robust perimeter 

element design, continuity of boundary elements, good connectivity, and inclusion of discrete 

MWFRS components.

11.1.3 Critical Facilities

Recommendation #10 – Propose IBC code change: The MAT recommends submitting the 

following IBC code change proposal regarding schools: 

“In areas where the shelter design wind speed for tornadoes per Figure 304.2(1) of 

ICC 500 (2008) is 250 mph, all new kindergarten through 12th grade schools with 50 

or more occupants in total, per school, shall have a FEMA 361-compliant safe room 

or an ICC 500-compliant storm shelter.” 

Recommendation #11 – Propose IBC code change: Submit the following IBC code change 

proposal regarding fire and police stations, 911 call centers, and EOCs: 

“In areas where the shelter design wind speed for tornadoes per Figure 304.2(1) of 

ICC 500 (2008) is 250 mph, all new 911 call stations, emergency operation centers, 

and fire, rescue, ambulance, and police stations shall have a FEMA 361-compliant 

safe room or an ICC 500-compliant storm shelter.” 

11.1.4 Tornado Refuge Areas, Hardened Areas, and Safe Rooms

Recommendation #12 – Continue to coordinate standards and guidance for storm shelters and 

safe room design: The ICC and FEMA should continue to work together to establish standards and 

guidance that are complementary. There are design elements based on emergency management 

considerations in the FEMA guidance related to the operations and maintenance of storm shelters 

or safe rooms that are not appropriate for inclusion in the ICC 500, as it is an engineering standard. 

As FEMA programs continue to fund the design and construction of safe rooms, there are valuable 

lessons in engineering and construction, in addition to the operational aspects of its safe room 

program, that could be incorporated into the ICC standard. 

The primary reason to keep the FEMA guidance and ICC 500 documents separate is to ensure 

that emergency management considerations receive appropriate attention during design and 

construction. While most technical elements in the documents are the same, some remain different. 

These few differences, less notable in the tornado hazard areas as compared to the hurricane 

hazard areas, need to be understood and explained to designers, emergency management officials, 

property owners and managers, and people in communities seeking protection from tornadoes. This 

outreach is necessary to minimize potential confusion that may exist. As the ICC enters its next cycle 

of standards development, it should develop a commentary for the ICC 500 ICC 500 that discusses 

assumptions and limitations of the standard. Further, as FEMA continues to provide guidance in its 

publications and policies, ICC and FEMA should continue to work together to develop a common 

message on life-safety protection from tornadoes.
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

Recommendation #13 – Improve performance of safe rooms and storm shelters through code 

adoption and enforcement: The 2009 and newer versions of both the IBC and IRC require 

compliance with the ICC 500 for any plan-designated storm shelter. The ICC 500 includes testing 

standards for storm shelter and safe room components. Components for newly constructed 

storm shelters and safe rooms, including elements such as doors, door hardware, ventilation, and 

anchorage, should be verified as compliant with ICC 500 as part of enforcing the aforementioned 

model building codes. 

Recommendation #14 – Submit proposed IBC code change: The MAT recommends submitting the 

following IBC code change proposal regarding identification of best available refuge areas: 

“For new buildings that do not incorporate a FEMA 361-compliant safe room or an 

ICC 500-compliant shelter, the floor plan shall indicate the best available refuge 

area(s).

+ “The best available refuge area(s) shall be capable of accommodating the 

building’s occupant load based on the allowable square footage per occupant 

prescribed in ICC 500.

+ “When signage is provided to identify the refuge area, the terminology should 

read: “Best Available Refuge Area.

+ “Exception: If building occupants have access to a community FEMA 

361-compliant safe room or an ICC 500-compliant shelter, this provision is not 

applicable.”

11.2 Residential Construction

Recommendation #15 – Implement voluntary best practices to mitigate damage to one- and twofamily residential buildings: The MAT recommends implementing the voluntary best practices for 

one- and two-family residential construction listed in this section and described further in Appendix 

G; these best practices will greatly reduce tornado damage to new and rebuilt one- and two-family 

residential buildings that are exposed to wind loads associated with weaker (i.e., EF0, 1, and 2) 

tornadoes. Since the decision to implement best practices for enhanced building performance is 

cost-based, and therefore ultimately lies with the consumer (prospective homeowner), the MAT 

recommends that designers and builders offer enhanced performance option packages for new 

residential buildings. These options should be clearly presented so that the potential homeowner 

understands that improved wind resistance does not equate to “windproof.” 

The guidance for improved building performance presented in Appendix G is intended solely for 

enhanced property protection and should not be construed in any way as an alternative to sheltering. 

Consequently, occupants of residential buildings in tornado-prone regions should have a tornado 

emergency operations plan in place, and whenever possible, have practiced this plan through drills 

to quickly access their safe room, storm shelter, or best available storm refuge. 
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

Prescriptive guidance is provided in Appendix G, per specific sections referenced below, to enhance 

performance of components, cladding, and critical load path connections observed to have failed 

during the spring 2011 tornado events. The prescriptive guidance in Appendix G is intended to:

+ Improve roof and wall coverings per Section G.3.1 

+ Increase awareness of glazing damage and strengthen garage doors per Section G.3.1

+ Strengthen roof decking (sheathing) attachment per Section G.3.2

+ Strengthen roof-to-wall connections per Section G.3.2

+ Improve wall performance through sheathing attachment, hold-down installation, and better 

top plate splicing per Section G.3.3 

+ Improve wall-to-floor connections and bottom plate attachment per Section G.3.3 

11.3 Commercial and Industrial Construction

For new commercial and industrial buildings, the MAT recommends that architects and engineers 

consider the following approaches to improve building performance related to communications 

and operations, and to detailing and connections. 

11.3.1 Occupant Notification and Operations

Recommendation #16 – Install a storm shelter or safe room or identify best available refuge areas 

in large-footprint buildings: In buildings where there can be a significant number of people, there 

should be a designated area that has been evaluated for its vulnerability to damage from tornadic 

winds and wind-borne debris where occupants can take refuge during a high-wind event. This space 

could be a break room, an office, or any other space with sufficient floor space for the occupants. 

Because best available refuge areas do not guarantee safety, the space should be designed to FEMA 

361 or ICC 500 criteria.1

Recommendation #17 – For all public buildings, install signage in a conspicuous place at 

building entrances (similar to maximum occupancy signs from the fire department): The resulting 

information may lead to the decision to abandon a structure and find more suitable refuge in 

certain situations. Signs should: 

+ Include relevant building design parameters such as importance factor, design wind speed, 

ground snow load, seismic criteria, rain fall intensity criteria, and if the building is constructed 

from URM.

+ Prominently display “Best Available Storm Refuge Area – Maximum Occupancy of” with the 

maximum occupancy on the sign.

1 This chapter references the 2008 versions of FEMA 320 and 361, as well as ICC 500, unless another date is specified.
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

+ Be of similar size and placement as the occupancy limitation signs currently used and placed in 

all buildings. 

Recommendation #18 – Place decision-making check lists or flip charts in prominent locations: 

Such check lists or flip charts help people make critical decisions in times of high stress and are a 

preferred method of ensuring that consistent and good decisions are made in high-stress situations. 

Checklists or flip charts should be located where building occupants can easily find them. An 

example of a flip chart is shown in Figure 9-15. 

11.3.2 Detailing and Connections

Recommendation #19 – Do not use URM in primary or critical support areas of a building: All 

masonry used in a building as a support wall or shear wall should be reinforced and tied into the 

adjacent structural elements to ensure ductile and robust performance in overload conditions, as 

URM has been known to fail in extreme events. URM is not allowed in parts of the country that are 

subject to increased seismic performance requirements due to its poor behavior in extreme events 

and insufficient ductility (FEMA 2009). The MAT recommends that all masonry for retail and 

commercial buildings be reinforced. This will ensure positive connections and a clear load path that 

is not dependent on gravity alone for the integrity of the building during an extreme wind event. 

Critical areas of buildings lacking reinforcement should be upgraded to include reinforcement and 

a continuous load path.

Recommendation #20 – Use screws in deck-to-joist connections instead of puddle welds: Several 

past MAT studies and damage assessments from FEMA, as well as other FEMA guidance documents, 

recommend the use of screws instead of puddle welds in the deck-to-joist connection. (See FEMA 

342; FEMA P-424; FEMA 543, Design Guide for Improving Critical Facility Safety from Flooding and High 

Winds: Providing Protection to People and Buildings [2007]; and FEMA 577, Design Guide for Improving 

Hospital Safety in Earthquakes, Floods, and High Winds: Providing Protection to People and Buildings [2007], 

for more context.) The screws provide a more reliable and consistent connection than puddle welds 

and have been shown to perform better in high-wind events. The MAT recommends the use of 

screws in accordance with observed failures during spring 2011 deployment and past FEMA reports 

and assessments. 

Recommendation #21 – Include enhancements to building connections beyond the code 

requirements: Design improvements can be achieved in new construction by incorporating 

enhancements that go beyond code requirements. Improving the performance of building 

connections is a low-cost improvement that can increase design strength and ductility. Until better 

criteria are established by a rational means, design non-residential buildings as Risk Category III 

structures under ASCE 7-10.

Recommendation #22 – Incorporate redundancy in the MWFRS: To reduce high-wind damage 

to buildings with long-span roofs and tall walls and limit the progression of a failure, building 

designers should incorporate redundancy in the MWFRS. Specifically:

+ Design redundant features to limit the area supported by each element to a relatively uniform 

shape (aspect ratio no greater than 2). 
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

+ Limit the maximum area supported by a bracing system to 40,000 square feet. The area should 

be large enough that it does not severely affect building operations and flow. 

+ Design redundant support, or minimize deflections, such that a column or wall could be 

damaged and the structural system would not collapse.

+ Provide lateral load resistance in tall walls with more than one means of support at both the top 

and bottom of the walls.

+ Account for the break in continuity at the expansion/contraction joint when designing the 

MWFRS wall system.

Recommendation #23 – Incorporate more redundancy in the design of large-footprint buildings:

To limit the extent of a progressive collapse from failure of a small element or from a non-redundant 

system, more redundant systems should be incorporated into the design of large-footprint buildings. 

The limiting area should be large enough to permit use of the space without substantially affecting 

the operations and flexibility of the facility. Single-purpose structural stability systems should also 

be considered. Additional ductility and continuity measures at the perimeter of the structure would 

allow load distribution to other elements in the event of massive overloads (see Figure 5-48).

Recommendation #24 – Use discrete structural systems in large, long-span buildings: To improve 

building performance, designers should consider solutions that provide for discrete service of 

components. For example, a building can be designed so that it could lose the roof and not lose 

stability from the loss of the diaphragm critical to the MWFRS. Although such solutions may add 

construction cost by removing efficiency of design, they will result in a more robust, redundant 

system. The greater construction costs may be regained in lower risk and loss profiles. 

An example of such a design would be installing a roof deck that provides weather protection, but 

is separated from the MWFRS and not used as the shear diaphragm. Another example would be 

including a wall system that does not provide vertical support and shear resistance, but acts solely as 

an environmental barrier. Such a wall could be lost, and the MWFRS would not be compromised. 

11.4 Critical Facilities

Design enhancements can be made to both existing critical facilities and those in the planning 

stage that can be incorporated into the construction documents. Design enhancements beyond IBC 

requirements are necessary to minimize damage from tornadoes. Design enhancements (including 

provisions pertaining to electrical power and communications) are also necessary to ensure COOP 

after a tornado strike. 

The MAT prepared several Tornado Recovery Advisories in the wake of the April 25–28, 2011 and 

May 22, 2011 tornado events. FEMA Recovery Advisory No. 5, Critical Facilities Located in Tornado-Prone 

Regions: Recommendations for Facility Owners (Appendix F), provides recommendations for owners of 

critical facilities. FEMA Recovery Advisory No. 6, Critical Facilities Located in Tornado-Prone Regions: 

Recommendations for Architects and Engineers (Appendix F), provides recommendations for architects 

and engineers. These recommendations pertain to both existing and new critical facilities. The 
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

recommendations address best available refuge areas, safe rooms, strengthening new facilities to 

minimize tornado damage, and enhancements to avoid interrupted operations. 

The MAT’s key recommendations for improving the performance and operation of existing and 

new critical facilities during and after a tornado are described below (refer also to the Recovery 

Advisories in Appendix F).

11.4.1 Existing Critical Facilities

Recommendation #25 – Perform a vulnerability assessment: A team of architects and engineers 

should perform a high-wind vulnerability assessment of existing facilities. Findings from such an 

assessment can lay the groundwork for planning and budgeting capital improvement projects and 

for developing contingency plans that address facility disruptions that result from a tornado or other 

natural hazard event, as illustrated in Figure 11-2. Figure 11-2 shows a collapsed CMU/brick veneer 

wall and collapsed roof structure at Joplin High School (see also Section 6.1.5).

Figure 11-2: 

Collapse of exterior CMU/

brick veneer wall and roof 

collapse at the Joplin High 

School (Joplin, MO). The wall 

debris fell into the corridor.

Recommendation #26 – Identify best available refuge areas: Best available refuge areas should be 

identified in all critical facilities that do not have areas designed and constructed as safe rooms or 

storm shelters. Best available refuge areas do not guarantee safety; they are, however, the safest areas 

available for building occupants. A design professional familiar with tornado risk should assess 

existing buildings and identify the best available refuge areas. Once identified, the locations of the 

best available refuge areas should be clearly marked with a permanent sign that reads “Best Available 

Refuge Area.”
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

11.4.2 New Critical Facilities

Recommendation #27 – Include safe rooms in design of new facilities: One or more safe rooms 

should be incorporated into new designs to provide occupant protection. FEMA 361 provides 

comprehensive guidance for the design of safe rooms. If a safe room is not incorporated, the 

architect or engineer should identify the best available refuge area(s), and specify that those area(s) 

should have a permanent sign that reads “Best Available Refuge Area.” 

Recommendation #28 – Enhance building design to better withstand tornadoes: By using design 

strategies and building materials that are used in hurricane-prone regions, critical facilities can be 

built to be more wind resistant to most tornadoes (i.e., EF0–EF3). Detailed recommendations for 

three levels of enhancement to minimize building damage are given in FEMA Recovery Advisory 

No. 6. 

Recommendation #29 – Strengthen facilities to remain operational: For critical facilities that 

should remain operational if struck by a violent tornado (i.e., EF4 and EF5), designers should follow 

the detailed recommendations related to the MWFRS, the building envelope, HVAC, water, sewer, 

and emergency power provided in FEMA Recovery Advisory No. 6. 

If, because of the additional expense, the owner determines that a critical facility does not need to 

be operational if struck by a violent tornado, then this reduced building performance should be 

clearly considered and addressed in emergency operations plans. Other critical facilities (that are 

not expected to be impacted by the same tornado) should be identified from which to continue 

critical operations. Appropriate planning, emergency plans, and cooperative agreements, typically 

referred to as COOP Plans, should be put in place. For facilities such as EOCs that are determined to 

be critical in providing effective emergency response, owners should budget facility enhancements 

to avoid interrupted operations even if struck by violent tornadoes.

11.5 Infrastructure Facilities 

The MAT assessed the performance of water treatment facilities, water distribution facilities, 

wastewater treatment facilities, and communications towers. It is important that these facilities stay 

operational after a disaster to provide clean water, sanitation, and communications for the people 

and emergency responders of the community. The following are recommendations for enhancing 

infrastructure performance based on the MAT’s observations. 

Recommendation #30 – Work collaboratively to better understand the risks of wind-displaced 

materials on communications towers: The authors of ANSI/TIA-222, Structural Standard for Antenna 

Supporting Structures and Antennas (2005), should investigate the risks that wind-displaced materials 

pose to communications towers and develop methods in that standard to address those risks. 

Recommendation #31 – Work collaboratively to better understand the effects of wind-displaced 

materials on latticed structures: The ASCE should provide commentary in Chapter 29 of ASCE 

7 on the effects of wind-displaced materials clinging to latticed structures so that designers can 

consider the possible increases in wind loads on those structures.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT 11-11

RECOMMENDATIONS OF THE 2011 TORNADO MAT

Recommendation #32 – Provide an alternate electrical source: For water distribution systems that 

are fed only from utility power systems and that rely on electrically driven pumps to fill storage tanks 

or boost system pressures, alternate power supplies should be provided. Alternate power supplies 

may be from on-site standby generators or from temporary portable generators brought to the site 

after an event. If temporary portable generators are used, provisions should be installed to allow 

operators to quickly and safely connect the generators to the pump stations before tanks drain or 

system pressures significantly affect operations.

Recommendation #33 – Work collaboratively to better understand communications tower 

performance: Stakeholders should collaborate to better understand tower performance.

11.6 Tornado Refuge Areas, Hardened Areas, and Safe Rooms

Safe rooms are the best means of providing nearabsolute protection for individuals who are attempting 

to take refuge during a tornado. Whether a safe room is 

constructed by a homeowner for protection of his or her 

family or is constructed as a group or community safe 

room, all safe rooms should be designed and constructed 

in accordance with either FEMA 320 or FEMA 361. 

The following are recommendations for personal 

protection based on the MAT’s observations and 

conclusions.

Recommendation #34 – Research travel time to, and 

use of, safe rooms and storm shelters: Travel time and 

safe room use research should be sponsored by FEMA, NIST, NSF, NWS, or other Federal entities 

who have the resources to investigate both the technical and social science issues that are part of 

the decision-making process of where and how to take shelter from a tornado. How far individuals 

will travel to find a safe place or shelter from tornadoes is a topic that is not well documented, 

and as a result, people may be making decisions to find shelter during an event in which there is 

no time (due to a short warning time period). This complex issue requires further study to better 

answer the question of how to provide safe rooms, storm shelters, and safe places of refuge at the 

community level and how to most effectively communicate needed tornado response activities to 

their community. 

Recommendation #35 – Locate safe rooms or storm shelters close to people who will use them: 

Safe rooms and storm shelters should be provided as close to the specific population being protected 

as possible. This reduces the risk to occupants who have to walk, run, drive, or otherwise travel 

to the safe room or storm shelter. Safe rooms within the actual building where the occupants are 

located provide life-safety protection while minimizing the risk to individuals who are attempting to 

access the space. 

Recommendation #36 – Identify best available refuge areas: Best available refuge areas should be 

identified in all non-residential buildings that do not have safe rooms. Best available refuge areas 

Safe rooms and storm shelters constructed in compliance with FEMA 

guidance and ICC 500 provide 

life-safety protection to building 

occupants. Refer to Sections 11.3 

(Commercial and Industrial) and 

11.4 (Critical Facilities) for specific 

sheltering recommendations related to those building types. Also, 

refer to Recovery Advisory Nos. 2, 

3, and 4 in Appendix F. 
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

do not guarantee safety; they are, however, the safest areas available within the existing space for 

building occupants. 

A design professional familiar with tornado risk analysis should assess existing buildings and identify 

the best available refuge areas. Once identified, the location(s) of the best available refuge area(s) 

should be clearly marked with a permanent sign. This sign should not use the term “shelter” or “safe 

room” since those terms should be used only for areas that meet the criteria set forth in FEMA 320, 

FEMA 361, or ICC 500. If a design professional is not used to identify the space, the area should be 

referred to only as a tornado refuge area. Tornado refuge areas offer the least amount of protect 

from a tornado and may not offer any better protection than typical construction.

Recommendation #37 – Perform vulnerability assessments: For existing, non-residential buildings, 

a team of architects and engineers should perform a vulnerability assessment. Findings from such 

an assessment can lay the groundwork for planning and budgeting capital improvements and for 

developing contingency plans that address facility disruptions that result from a natural hazard 

event.

Recommendation #38 – Register safe rooms: All safe rooms, storm shelters, and refuge areas 

within a community should be registered or noted on a list with local emergency management and 

first responders. The coordinates for the primary entrance to the safe room, storm shelter, or best 

available refuge area should be provided to help responders locate the structures in the event debris 

has hidden them or buildings, street signs, etc. have been destroyed. This applies to FEMA-funded 

safe rooms as well.

Recommendation #39 – Equip safe rooms, storm shelters, and best available refuge areas with 

tools to assist occupants when doors and egress routes become damaged, inoperable, or blocked 

by debris: All safe rooms, storm shelters, and best available refuge areas should be equipped with 

whatever tools are necessary for occupants to open or dismantle the door from inside in the event 

that egress is blocked or the door is damaged.

Recommendation #40 – Equip safe rooms, storm shelters, and best available refuge areas with an 

alternate means of communication: Safe room and storm shelter owners and operators should plan 

for potential disruptions to both wired and wireless communications systems. Community safe rooms 

and storm shelters in particular may require backup power to operate alternate communication 

systems. 

Recommendation #41 – Provide training: Training on tornado safe rooms, storm shelters, and 

refuge areas needs to be expanded for professional organizations and should continue for public 

officials, emergency managers, building owners/operators, and the public. This training should 

include both technical issues, such as how to perform a vulnerability assessment and identify the 

best available area for storm refuge in an existing building, as well as non-technical issues, such as 

travel time and decision-making during tornado warnings as discussed in this report.
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

11.7 EF Scale

Based on the MAT’s observations and conclusions about the current EF scale provided in A 

Recommendation for an Enhanced Fujita Scale (TTU 2006), the MAT recommends that the EF scale 

guidance be modified as follows:

Recommendation #42 – Add DIs: While the current 28 DIs encompass most buildings, some 

common building types, such as fire stations and churches, are not included. The MAT recommends 

that guidance on the EF scale be updated by adding DIs for common building types that are not 

currently included

Recommendation #43 – Increase the number of DOD categories for specific DIs: The MAT 

recommends that the DODs for all DIs be reevaluated for consistency and expanded upon where 

appropriate. Specifically, the number of DODs for communications towers needs to be increased. 

Any updates should be reflected in published guidance on the EF scale. 

Recommendation #44 – Provide additional guidance for DOD assessment when only a portion 

of a large building is struck: For large buildings where only a portion of the building is struck, 

guidance should be provided that instructs users on the appropriate DOD selection. Any updates 

should be reflected published guidance on the EF scale.

Recommendation #45 – Modify EF scale DI 2 (One- and Two-family Residences): Based on the 

MAT’s observations for DI 2 (One- and Two-family Residences), DOD 5 (“entire house shifts off 

foundation”) was rarely witnessed, unlike DODs 4 and 6, and should be eliminated from the list of 

DODs.

Recommendation #46 – Provide photographs with DOD descriptions in EF rating guidance: The 

MAT recommends that photographs be added to published guidance on the EF scale to illustrate 

each DOD in each DI.

11.8 Post-Tornado Imagery

Based on the MAT’s observations and conclusions about the current methods for capturing posttornado imagery and using graphics to display tornado intensity, the MAT recommends that the 

process be modified as follows:

Recommendation #47: NOAA should capture post-tornado aerial photographs: When tornado 

damage is potentially greater than EF3, the MAT recommends that NOAA shoot aerial photographs 

soon after the event. Opportunities to coordinate post-tornado aerial photograph missions between 

FEMA and NOAA to better capture perishable forensic evidence should be explored.

Recommendation #48 – NWS should develop EF contours: The MAT recommends that the NWS 

develop EF contours for all tracks that are rated.
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RECOMMENDATIONS OF THE 2011 TORNADO MAT

Recommendation #49 – NWS should enhance the determination of EF ratings at individual 

structures by including a design professional as part of the QRTs: QRTs were deployed to many 

of the sites visited by the MAT in spring 2011, but only the Birmingham, AL area QRT included an 

engineer. The MAT recommends that a design professional be included in NWS QRTs to improve 

damage analysis of individual structures after a tornado and to support the documentation of NWS 

tornado ratings.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT A-1

AAcknowledgments

The Federal Emergency Management Agency would like to acknowledge the contributions of the following people 

to the Mitigation Assessment Team study of the areas affected by the tornadoes of Spring 2011:

FEMA Contributors

Jacob Anderson

Gerald Bonney

Lisa Booth

Gregory Bosko

Sandy Bridges

Michael A. Brown

Ronald Broxton

Michael F. Byrne, FCO DR-1971

Luletha Cheatham

Fellece Coleman

Roger Faris

Richard Flinn

Katy Goolsby-Brown

Tara Hallmark

Donna Hamilton

Aaron Hartwell

Auco Ho

Sandra Knight, Ph.D., PE

Edward Laatsch, PE

Lois Lopez

Patricia McArthur

Elaine McNeil

Laura McSweeney

Winfield W. Montague, FCO DR-1972

Ray Morgan

Patrick L. Neichter, PE

Jose Francisco Oporto

Wesley Parker

Gloria Phillips

Terry Quarles, FCO DR-1972

Carl Rea

Christopher Smith

Jonathan “Ed” Smith

Mark South

Jody Springer

Gary Swagart, PE

John Synnott

Gracia Szczech, FCO DR-1973

Norman Thidemann

Evelyn Tirado

Elizabeth Turner, FCO DR-1980 

John Van Zweden

Maria Vorel

James Walke, PE

Darrell Walker

Ronald C. Wanhanen, PE

Steiner Wilanger

Charles Williams

Lynda Williams

Gregory Wilson
A-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

ACKNOWLEDGMENTS

Other Contributors

Mattie Banks

Birmingham Nursing and Rehabilitation Center, Birmingham, AL

Gary Box

Business Retention and Expansion Coordinator, Joplin Chamber of Commerce, Joplin, MO

John Brook

Fire Marshal, City of Tuscaloosa, Tuscaloosa, AL

Donald Burgess, Ph.D. 

National Weather Service

Chris Canoles

Senior Director, Loss Prevention, The Home Depot

Gregory Carbin

Warning Coordination Meteorologist, National Weather Service, Norman, OK

Bill Coulbourne, PE

Director, Wind and Flood Hazard Mitigation, Applied Technology Council

Thang Dao, Ph.D.

Post-Doctoral Scholar, University of Alabama, Tuscaloosa, AL

Shane Daugherty

Director, Tuscaloosa Environmental Services, Tuscaloosa, AL

John De Block

Warning Coordination Meteorologist, National Weather Service, Birmingham, AL

Gary Ehrlich

Program Manager, Structural Codes & Standards, National Association of Home Builders, 

Upper Marlboro, MD

Jennifer Erixon

Senior Vice President, Real Estate Development and Asset Management, Mercy Housing 

Mountain Plains, Joplin, MO

Mathew Francis, PE

URS Group, Inc., Germantown, MD

Gary Goggins

Meteorologist, National Weather Service, Birmingham, AL

Barry Gooden

Warning Coordination Meteorologist, National Weather Service, Atlanta, GA

Andrew Graettinger, Ph.D.

Associate Professor, Civil, Construction, and Environmental Engineering, University of 

Alabama, Tuscaloosa, AL

David Grau, Ph.D.

Assistant Professor, Civil, Construction and Environmental Engineering, University of Alabama, 

Tuscaloosa, AL
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT A-3

ACKNOWLEDGMENTS

Billy Green

Deputy Director, Tuscaloosa County Emergency Management Agency, Tuscaloosa, AL

Rakesh Gupta, Ph.D.

Professor, Wood Engineering and Mechanics, Oregon State University, Corvallis, OR

Darwin Hathcock

Chief of Police, Smithville Police Department, Smithville, MS

Samuel Hensen, PE

Engineering Manager, Simpson Strong Tie, McKinney, TX

Larry Holcomb

Director of Maintenance, Bradley County Schools, Cleveland, TN

Ben Jennings, PE

Structural Engineer, J&M Engineering, Springfield, MO

Jeff Johnson

Executive Director of Facilities, Tuscaloosa City Schools, Tuscaloosa, AL

Michael Johnson

Director of Buildings, Joplin School District, Joplin, MO

Omar Kapur

URS Group, Inc., Germantown, MD

Vassiliki Koumoudis

URS Group, Inc., Germantown, MD

Erica Kuligowski, Ph.D.

National Institute of Standards and Technology, Gaithersburg, MD

James G. LaDue

Meteorologist, Warning Decision Training Branch, National Weather Service, Norman, OK

Kayed I. Lakhia, AIA, LEED AP, CFM

URS Group, Inc., Boca Raton, FL

Eric Letvin, PE, Esq., CFM

National Institute of Standards and Technology, Gaithersburg, MD

Philip Line, PE

Director, Structural Engineering, American Wood Council, Leesburg, VA

Julie Liptak

Greenhorne & O’Mara, Laurel, MD

Phyllis Little

Director, Cullman County Emergency Management Agency, Cullman, AL

Frank Lombardo

National Institute of Standards and Technology, Gaithersburg, MD

Bobbie Misner

Greenbriar Nursing Home, Joplin, MO
A-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

ACKNOWLEDGMENTS

John Moyers

Tennessee Emergency Management Agency, Nashville, TN

Robert Norton

Regional Vice President, Support Services/Facilities, St. John’s Health System, Springfield, MO

Richard Okulski

Warning Coordination Meteorologist, National Weather Service, Memphis, TN

Lynn Iliff Onstot

Public Information Officer, City of Joplin Public Affairs, Joplin, MO

Kelly Park, Ph.D.

Structural Engineer, Hazard Mitigation Department, Greenhorne & O’Mara, Laurel, MD

Shiling Pei, Ph.D., PE

Assistant Professor, Structural Engineering, South Dakota State University, Brookings, SD

Clif Penick

City Facility Manager, Tuscaloosa, AL

Long Phan

National Institute of Standards and Technology

David O. Prevatt, Ph.D., PE

Assistant Professor, Civil and Coastal Engineering, University of Florida, Gainesville, FL

Damon Raines

Director of Operations, Catoosa County Public Schools, Catoosa County, GA

Mitch Randles

Fire Chief, Joplin Fire Department, Joplin, MO

Brian Readling, PE

Senior Engineer, APA – The Engineered Wood Association, Charlotte, NC

Denia Reese

Superintendent, Catoosa County Public Schools, Catoosa County, GA

Thomas Reynolds, PE

URS Group, Inc., Germantown, MD

David Roberts

Director of Construction, DCH Regional Medical Center, Tuscaloosa, AL

Jeff Roberts

Tuscaloosa Fire Station 4, Tuscaloosa, AL

Steve Runnels

Warning Coordination Meteorologist, National Weather Service, Springfield, MO

Thomas Schmidlin, Ph.D.

Professor, Department of Geography, Kent State University, Kent, OH

Corey Schultz, AIA

PBA Architects, Wichita, KS
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT A-5

ACKNOWLEDGMENTS

Adrienne Sheldon, PE, CFM

URS Group, Inc., Germantown, MD

Tilt-Up Concrete Association 

National Disaster Task Force, Mount Vernon, IA

Tuscaloosa County, AL, Sheriff’s Office

Bryan Wert, PE

Branch Engineer, Simpson Strong Tie Co., Inc.

Steve Wilmoth, Ph.D.

Superintendent of Schools, Seneca R-7 School District, Seneca, MO

Jimmy Yeung, Ph.D., PE

Greenhorne & O’Mara, Laurel, MD

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT B-1

BReferences

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B-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

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Engineers, Recovery Advisory 6, Recovery Advisories from the Tornado MATs for Alabama, 

Mississippi, Tennessee, Georgia, and Missouri. August.

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Tennessee, Georgia, and Missouri. July.

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Advisories from the Tornado MATs for Alabama, Mississippi, Tennessee, Georgia, and 

Missouri. August.

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Missouri. August.

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Recovery Advisories from the Tornado MATs for Alabama, Mississippi, Tennessee, Georgia, 

and Missouri. June.

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from the Tornado MATs for Alabama, Mississippi, Tennessee, Georgia, and Missouri. June.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT B-3

REFERENCES

FEMA, 2011h. Safe Rooms: Selecting Design Criteria, Recovery Advisory 2, Recovery Advisories from 

the Tornado MATs for Alabama, Mississippi, Tennessee, Georgia, and Missouri. June.

FEMA, 2011i. Tornado Risks and Hazards in the Southeastern United States, Recovery Advisory 1, 

Recovery Advisories from the Tornado MATs for Alabama, Mississippi, Tennessee, Georgia, 

and Missouri. June.

FEMA. 2010a. Design Guide for Improving School Safety in Earthquakes, Floods, and High Winds. FEMA 

P-424. December. 

FEMA. 2010b. Pre-Mitigation Assessment Team Report – Mississippi Tornado Outbreak, April 23rd – 

24th: Damage and Safe Room Performance Observations, Recommendations, and Conclusions.

Unumbered publication. July.

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April 30.

FEMA. 2009b. Tornado Protection: Selecting Refuge Areas in Buildings. FEMA P-431. October.

FEMA. 2009c. Unreinforced Masonry Buildings and Earthquakes: Developing Successful Risk Reduction 

Programs. FEMA P-774. October.

FEMA. 2008a. Design and Construction Guidance for Community Safe Rooms. FEMA 361. August. 

Second Edition.

FEMA. 2008b. Hazard Mitigation Assistance for Safe Rooms, Mitigation Interim Policy MMR-2-07-1, 

March 7.

FEMA. 2008c. Taking Shelter From the Storm: Building a Safe Room For Your Home or Small Business.

FEMA 320. August. Third Edition.

FEMA. 2007a. Design Guide for Improving Critical Facility Safety from Flooding and High Winds: Providing 

Protection to People and Buildings. FEMA 543. January.

FEMA. 2007b. Design Guide for Improving Hospital Safety in Earthquakes, Floods, and High Winds: 

Providing Protection to People and Buildings. FEMA 577. June.

FEMA. 2006. Hurricane Katrina in the Gulf Coast: Mitigation Assessment Team Report, Building 

Performance Observations, Recommendations, and Technical Guidance. FEMA 549. July.

FEMA. 2000. Design and Construction Guidance for Community Shelters. FEMA 361. July. First Edition.

FEMA. 1999a. Building Performance Assessment Team Report: Oklahoma and Kansas, Midwest Tornadoes of 

May 3, 1999. FEMA 342. October.

FEMA. 1999b. In-Residence and Small Business Safe Room Designs. Drawing No. AG-06, sheet 11 of 18.

FEMA. 1999c. Taking Shelter from the Storm: Building a Safe Room Inside Your House. FEMA 320. 

October. Second Edition.

FEMA. 1998. Taking Shelter from the Storm: Building a Safe Room Inside Your House. FEMA 320. 

October. First Edition.

FEMA. 1990. Tornado Protection: Selecting and Designing Safe Areas in Buildings. FEMA TR-83B. June.

FEMA. 1980. Interim Guidelines for Building Occupant Protection From Tornadoes and Extreme Winds. 

TR-83A. September.
B-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

REFERENCES

Fujita, T.T. 1971. Proposed characterization of tornadoes and hurricanes by area and intensity. Satellite and 

Mesometeorology Research Project Report 91, the University of Chicago: Chicago, IL.

Hamilton County, TN. Undated. “Hamilton County Building & Zoning.” http://www.hamiltontn.

gov/inspect, accessed May 1, 2012.

ICC (International Code Council). 2012a. International Building Code. Birmingham, AL.

ICC. 2012b. International Residential Code for One- and Two-Family Dwellings. Birmingham, AL.

ICC. 2009a. International Building Code. Birmingham, AL.

ICC. 2009b. International Residential Code for One- and Two-Family Dwellings. Birmingham, AL.

ICC. 2008. Standard for Residential Construction in High-Wind Regions, ICC 600. Birmingham, AL.

ICC. 2003a. International Building Code. Birmingham, AL.

ICC. 2003b. International Residential Code for One- and Two-Family Dwellings. Birmingham, AL.

ICC. Undated. Alabama Code Adoption Information. http://www.iccsafe.org/gr/Documents/

al.htm, accessed May 1, 2012.

ICC and NSSA (National Storm Shelter Association). 2008. Standard for the Design and Construction of 

Storm Shelters, ICC 500. Birmingham, AL.

Jefferson County, AL. 2011. “ORDINANCE NO. 1800, An ordinance to adopt a Building Code 

for Jefferson County, Alabama.” http://jeffconline.jccal.org/inspectionservices/main/ISBuildingCode.pdf.

Natural Disaster Taskforce. 2012. Analysis of the Damage from Historic Tornado in Joplin, Missouri, 

U.S.A. on May 22, 2011, a Report to the Technical Committee of the Tilt-Up Concrete 

Association: Mount Vernon, IA. Report 201-12-01. January 12.

NOAA (National Oceanic and Atmospheric Administration). 2012. 2011 Tornado Fatality 

Information. National Weather Service, Storm Prediction Center, Severe Weather Database, 

updated in January 2012. http://www.spc.noaa.gov/climo/torn/2011deadlytorn.html.

NOAA. 2011. Storm Prediction Center Warning Coordination Meteorologist’s Page. National Weather 

Service, Storm Prediction Center. http://www.spc.noaa.gov/wcm.

NOAA. 2007a. NOAA Service Assessment on Enterprise Tornado Demonstrates Need to Build Hazard 

Resilient Communities. November 29. Available at: http://www.noaanews.noaa.gov/

stories2007/20071129_tornado.html.

NOAA. 2007b. Service Assessment: Tornadoes in Southern Alabama and Georgia on March 1, 2007.

National Weather Service. November. Available at: http://www.nws.noaa.gov/os/

assessments/pdfs/AL-GA_tornadoes07.pdf.

Prevatt, David O.; Coulbourne, William; Graettinger, Andrew; Pei, Shiling; Gupta, Rakesh; and 

Grau, David. 2011a. The Joplin Tornado of 2011 – Damage Survey and Case for Tornado-Resilient 

Codes. September 26.

Prevatt, David O.; van de Lindt, John W.; Graettinger, Andrew; Coulbourne, William; Gupta, 

Rakesh; Pei, Shiling; Hensen, Samuel; and Grau, David. 2011b. Damage Study and Future 

Direction for Structural Design Following the Tuscaloosa Tornado of 2011. July 27.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT B-5

REFERENCES

Simmons K.M. and D. Sutter. 2011. The Economic and Societal Impacts of Tornadoes. Boston: American 

Meteorological Society.

State of Missouri, Division of Facilities Management. 2007. Designer Information Packet. State 

of Missouri, Office of Administration, Division of Facilities Management, Design and 

Construction. April. http://oa.mo.gov/fmdc/dc/fmdc_dip/index.htm. 

SBCCI (Southern Building Code Congress International). 1998. Standard Building Code. 

Janesville, WI.

SBCCI. 1994. Standard Building Code. Janesville, WI.

SBCCI. 1991. Standard Building Code. Janesville, WI.

Tilt-Up Concrete Association. 2012. Analysis of Damage from Historic Tornado in Joplin, Missouri, U.S.A. 

on May 22, 2011, a Report to the Technical Committee of the Tilt-Up Concrete Association 

by the Natural Disaster Task Force. Report 201-12-01. January 12.

Tornado Recovery Advisory Council of Alabama. 2012. Cultivating a State Of Readiness: Our Response 

to April 27, 2011. January. http://tracalabama.org/wp-content/uploads/2012/01/

TRAC_Report.pdf.

Town of Smithville, MS. “Long-Term Recovery, Smithville Recovery News, Building Permits.” Last 

modified June 21, 2011. https://sites.google.com/site/smithvilleltcr/hot-news-1/headline1, 

accessed May 1, 2012.

TTU (Texas Tech University). 2004. A Recommendation for an Enhanced Fujita Scale, Submitted to 

The National Weather Service and Other Interested Users, June 2004, Wind Science and 

Enginering Center, Texas Tech University: Lubbock, TX. 

TTU. 2006. A Recommendation for an ENHANCED FUJITA SCALE (EF-Scale), Submitted to The 

National Weather Service and Other Interested Users, October 10, 2006, Revision 2, Wind 

Science and Enginering Center: Lubbock, TX.

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT C-1

CAcronyms

Acronym Definition

ASCE American Society of Civil Engineers

ASTM ASTM International

ATC Applied Technology Council

BOCA Building Code Administrators International

C&C components and cladding

CAPE Convective Available Potential Energy

CDT Central Daylight Time

CMU concrete masonry unit

COOP Continuity of Operations

CWA County Warning Area

dbZ decibels of Z

DHS U.S. Department of Homeland Security

DI damage indicator

DOD degree of damage

EF Enhanced Fujita

EHI Energy Helicity Index

EIFS exterior insulation and finishing systems

EMA Emergency Management Agency
C-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

ACRONYMS

EMS Emergency Management System

EOC Emergency Operations Center

EPDM ethylene propylene diene monomer

FAR false alarm ratio

FEMA Federal Emergency Management Agency

FIMA Federal Insurance and Mitigation Administration

HMGP Hazard Mitigation Grant Program

HVAC Heating, ventilation, and air-conditioning

HSS hollow structural steel

IBC International Building Code

ICBO International Conference of Building Officials

ICC International Code Council

ICU intensive care unit

IRC International Residential Code

ISO Insurance Services Office

LASD Los Angeles Sherriff’s Department

LSU Louisiana State University

LTVT long-track violent tornadoes

MAT Mitigation Assessment Team

mb Millibar

MGD million gallons per day

mph miles per hour

mrh mean roof height

MRI mean recurrence interval

MWFRS Main Wind Force Resisting System

NOAA National Oceanic and Atmospheric Administration 

NSF National Science Foundation

NSSA National Storm Shelter Association

NWS National Weather Service

OSB oriented strand board

OSU Oregon State University
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT C-3

ACRONYMS

PDS particularly dangerous situation

PEMB pre-engineered metal building

PMAT Pre-Mitigation Assessment Team

psi pounds per square inch

QLCS quasi-linear convective system

QRT Quick Response Team

SBC Standard Building Code

SBCCI Southern Building Code Congress International

SDSU South Dakota State University

SPC Storm Prediction Center

SRH Storm-Relative Helicity

TTU Texas Tech University

UA University of Alabama

UF University of Florida

URM unreinforced masonry

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT D-1

DGlossary

Accessory structures: Accessory structures are also called appurtenant structures. An accessory 

structure is a structure on the same parcel of property as a principal structure and the 

use of which is incidental to the use of the principal structure. For example, a residential 

structure may have a detached garage or storage shed for garden tools as an accessory 

structure. Other examples of accessory structures include gazebos, picnic pavilions, 

boathouses, small pole barns, storage sheds, and similar buildings.

Advection: The transfer of a property of the atmosphere, such as heat, cold, or humidity, by the 

horizontal movement of an air mass.

Base reflectivity: One of the three fundamental quantities (along with base [radial] velocity and 

spectrum width) that a Doppler radar measures. Reflectivity is related to the power, or 

intensity, of the reflected radiation that is sensed by the radar antenna. Base reflectivity is 

expressed on a logarithmic scale in units called dBZ (decibels of Z, where Z represents the 

energy reflected back to the radar). The term “base” refers to the product being “basic,” 

with little advanced processing performed on the data. Base reflectivity is related to rainfall 

intensity (e.g., drop size and rainfall rate) and hail size (for large values of reflectivity).

Basic wind speed: Three-second gust wind speed at 33 feet above the ground in Exposure C. 

(Exposure C is flat open terrain with scattered obstructions having heights generally 

less than 30 feet. See “Exposure category.”) Note: Since 1995, American Society of Civil 

Engineers (ASCE) standard ASCE 7 has used a 3-second peak gust measuring time. A 

3-second peak gust is the maximum instantaneous speed with a duration of approximately 

3 seconds. A 3-second peak gust wind speed could be associated with either a given 

windstorm (e.g., a particular storm could have a 40-mph peak gust speed), or a design level 

event (e.g., the basic wind speed prescribed in ASCE 7). 
D-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

GLOSSARY

Best available refuge area: Per Federal Emergency Management Agency (FEMA) 431, Tornado 

Protection: Selecting Refuge Areas in Buildings (2009), a “best available refuge area is” an 

area in an existing building that have been deemed by a qualified architect or engineer to 

likely offer the greatest safety for building occupants during a tornado. It is important to 

note that, because these areas were not specifically designed as tornado safe rooms, their 

occupants may be injured or killed during a tornado. However, people in the best available 

refuge areas are less likely to be injured or killed than people in other areas of a building. 

Bond beam: A structural member along the top of a bearing wall used to support and distribute 

roof loads. Bond beams are either reinforced concrete or reinforced masonry units. 

Bow echo: A bow-shaped line of convective storm cells that is often associated with swaths of 

damaging straight-line winds and small tornadoes.

Building: A walled and roofed structure. A building includes not only the structure, but also the 

non-structural elements that complete a building, including walls, roof, glazing, interior 

finishes, and exterior finishes.

Building envelope: The entire exterior surface of a building, including roof and wall covering, 

exterior glazing and doors, skylights, and other components enclosing the building.

Building footprint: Land area occupied by the building.

Communications tower: A structure that supports antennae for cellular phones, Emergency 

Management Services, fire, police, and other critical functions.

Components and cladding (C&C): ASCE 7-10 describes C&C as elements of the building 

envelope that do not qualify as part of the Main Wind Force Resisting System (MWFRS). 

These elements include roof sheathing, roof coverings, exterior siding, windows, doors, 

soffits, fascia, and chimneys and include components of some MWFRS elements such as the 

chords of roof trusses.

Continuous load path: The condition required to resist loads acting on a building. The continuous 

load path starts at the point or surface where loads are applied (i.e., the building envelope), 

moves through the building, continues through the foundation, and terminates where the 

loads are transferred to the soils that support the building.

Convective Available Potential Energy (CAPE): One of two important parameters necessary to 

predict long-track violent tornadoes (LTVTs). High CAPE values represent an unstable 

atmosphere and are associated with warm weather and sunny skies. Locations in the midsouth experience their highest CAPE values during the summer months.

Corbel: A structural feature resembling a bracket that projects from a wall and supports a beam 

or ceiling. 

Critical facility: A facility that is essential for the delivery of vital services or protection of a 

community. Critical facilities include, but are not limited to, hospitals, emergency operation 

centers, fire and police stations, schools, and primary utility facilities. Critical facilities are 

Category III and IV buildings as defined in ASCE 7.

Cyclogenesis: The development or strengthening of a circulating area of low pressure in the 

atmosphere which results in the development of a cyclone.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT D-3

GLOSSARY

Damage indicator (DI): A category for buildings, structures, and trees used to estimate wind 

speeds on the Enhanced Fujita (EF) scale. The EF scale currently has 28 DIs, each of which 

have several degrees of damage (DODs).

Debris rowing: A phenomenon that occurs when wind-borne debris is spread in straight lines as a 

result of a tornado.

Degree of damage (DOD): Numbered level of damage for each DI used in estimating wind speeds 

on the EF scale. For each DI, several DODs are identified, increasing sequentially from 

slight visible damage to complete destruction of the particular DI.

Design wind speed: see “Basic wind speed.”

Diffluent zone: An area where wind spreads laterally in a fan-like pattern from a central axis 

parallel to the flow along the axis.

Emergency Operations Center (EOC): The physical location at which the coordination of 

information and resources to support incident management (on-scene operations) activities 

normally takes place. An EOC may be a temporary facility or may be located in a more 

central or permanently established facility, perhaps at a higher level of organization within 

a jurisdiction. EOCs may be organized by major functional disciplines (e.g., fire, law 

enforcement, and medical services), by jurisdiction (e.g., Federal, State, regional, tribal, city, 

county), or some combination thereof.

Energy Helicity Index (EHI): An index that incorporates CAPE and Storm Relative Helicity 

(SRH), two important parameters in the prediction of LTVTs.

Enhanced code construction: Construction that exceeds minimum building code requirements. 

Also commonly referred to as “Code-Plus” and “Fortified.” The exact meaning varies 

geographically because different States and communities have adopted and amended 

different building codes, or different editions of those codes, and thus have different 

minimum design and construction requirements.

Enhanced Fujita (EF) scale: A tornado strength rating model implemented by the National 

Weather Service (NWS) in 2007 that has six categories, from zero to five, representing 

damage from increasing wind speeds. The EF scale is an improvement of the previous Fujita 

scale that better relates wind speeds to levels of damage observed after a tornado. The EF 

scale contains 28 DIs for the type of building, structure or tree; each DI includes DODs, 

which are damage descriptors associated with an expected estimated wind speed. 

Exposure Category: Wind exposure categories defined in ASCE 7 based on the terrain and 

obstructions surrounding a building. There are three exposure categories: Exposure 

Category B is for buildings in urban/suburban areas surrounded by low- to mid-rise 

buildings and/or wooded areas; Exposure Category C is for buildings in open terrain with 

scattered obstructions having heights generally less than 30 feet (includes the shoreline 

in hurricane-prone regions); and Exposure Category D is for buildings at the shoreline 

(except in hurricane-prone areas) with wind flowing over open water for at least 1 mile.

Federal Emergency Management Agency (FEMA): Independent agency created in 1979 to provide 

a single point of accountability for all Federal activities related to disaster mitigation and 

emergency preparedness, response, and recovery. 
D-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

GLOSSARY

Federal Insurance and Mitigation Administration (FIMA): A component of FEMA which 

manages the National Flood Insurance Program (NFIP) and other programs designed to 

reduce future losses from natural disasters to homes, businesses, schools, public buildings, 

and critical facilities.

Funnel cloud: As defined by the National Oceanic and Atmospheric Administration (NOAA), a 

condensation funnel extending from the base of a cloud, associated with a rotating column 

of air that is not in contact with the ground. This is different from a tornado because it is 

not in contact with the ground and does not have a debris cloud.

Gable end wall: The vertical triangular end of an exterior wall above the eave line formed under a 

gable roof.

Glazing: Glass or transparent or translucent plastic sheet used in windows, doors, and skylights.

Guy wire: A tensioned cable used to add stability to a structure, such as a tower.

Hardened area: Areas that are designed and constructed to provide some level of protection, 

but do NOT necessarily meet International Code Council (ICC) / National Storm Shelter 

Association (NSSA) Standard for the Design and Construction of Storm Shelters (ICC 

500) criteria or FEMA guidelines. These areas are commonly referred to by builders and 

homeowners as “shelters.”

Hip roof: A roof type composed of four sloping sides. A hip roof does not have any gable ends.

Hook echo: A radar reflectivity pattern characterized by a hook-shaped extension of a 

thunderstorm echo, usually in the right-rear part of the storm (relative to its direction of 

motion). A hook is often associated with a mesocyclone and indicates favorable conditions 

for tornado development.

Importance Factor: A multiplier that accounts for the degree of hazard to human life and 

damage to property. Importance Factors are given in ASCE 7-05 and earlier versions of 

the standard. Note: In ASCE 7-10, the Importance Factor was eliminated for wind loads 

because the degree of hazard to human life and property damage is accounted for by 

selecting the proper wind speed map.

Jet streak: The region in the jet stream where the wind speeds are highest.

Linear bow echo: A large convective system shaped like an archery bow on the radar; systems with 

this shape can produce severe straight-line winds and occasionally tornadoes.

Long-track violent tornado (LTVT): A strong tornado that stays on the ground for a relatively long 

time, creating a long track.

Low-sloped roofs: A category of roofs generally made of weatherproof membrane installed on 

slopes of 3:12 or less.

Main Wind Force Resisting System (MWFRS): ASCE 7-10 defines the MWFRS as an assemblage 

of structural elements designed to provide support and stability for the overall structure. 

The MWFRS consists of the foundation; floor supports (e.g., joists, beams); columns; roof 

rafters or trusses; and bracing, walls, and diaphragms that help transfer loads. 

Masonry infill wall: A wall consisting of either steel or concrete frames with masonry inset 

between the openings.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT D-5

GLOSSARY

Mean recurrence interval (MRI): An estimate of time between events with a common level of 

intensity; an estimate of the amount of time that would elapse between two wind events of 

the same strength.

Mesoscale: A meteorological phenomenon larger than microscale and storm-scale cumulus 

systems, but smaller than synoptic weather-scale systems; 10 to 1,000 kilometers in 

horizontal extent. 

Mitigation: Any sustained action taken to reduce or eliminate long-term risk to people and 

property from hazards and their effects.

Multiple vortex structure: A type of tornado in which two or more columns of spinning air have a 

common center of rotation.

National Oceanic and Atmospheric Administration (NOAA): An agency within the United States 

Department of Commerce that specializes in the conditions of the oceans and atmosphere. 

NOAA reports daily weather forecasts, severe storm warnings, and climate monitoring to 

fisheries management, coastal restoration, and supporting marine commerce entities.

National Weather Service (NWS): One of six agencies in NOAA that produce weather, hydrologic, 

and climate forecasts and warnings for the United States, its territories, adjacent waters, and 

ocean areas for the protection of life and property and the enhancement of the national 

economy.

Near-absolute protection: The level of protection for which, based on our current knowledge of 

tornadoes and hurricanes, the occupants of a safe room will have a very high probability of 

being protected from injury or death.

Occupancy Category: For the purpose of applying the environmental loads of flood, wind, snow, 

earthquake, and ice, buildings and other structures are classified in ASCE 7-05 into one of 

four Occupancy Categories based on how they are used. Category I buildings are those that 

pose low hazard to human life if failure occurs; essential facilities are classified as Category 

IV. In ASCE 7-10, these are now called “Risk Categories.”

Particularly dangerous situation (PDS): A type of watch issued that implies an increased risk of 

severe and life-threatening weather, such as a major tornado outbreak.

Prescriptive measures: Guidance that has been predetermined and calculated for specific 

circumstances.

Primary structural system: A structural system that supports the building against all lateral and 

vertical loads.

Quasi-linear convective system (QLCS): A group of thunderstorms in a linear arrangement; also 

known as a “squall line.” Development of a QLCS depends on the cold pool produced by 

the storm and the environmental shear. The movement of the two components creates 

horizontal velocity that can create tornadoes. 

Redundancy: The practice of using system components that, when another critical component 

fails, can resist the loads of the first component as well as its own; redundancies increase the 

reliability of structural performance.

Retrofit: Any change or combination of adjustments made to an existing building that is intended 

to reduce or eliminate damage to that building from natural hazards.
D-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

GLOSSARY

Right mover: A thunderstorm that moves appreciably to the right relative to the main steering 

winds and to other nearby thunderstorms. Right movers are typically associated with a high 

potential for severe weather. (Supercells are often right movers.)

Risk Category: A term defined in ASCE 7-10 based on the risk to human life, health, and welfare 

associated with potential damage or failure of the building. These Risk Categories dictate 

which design event MRI is used when calculating the building’s resistance to these events. 

In ASCE 7-05, these are called “Occupancy Categories.”

Roof assembly: An assembly of interacting roof components including roof deck, vapor retarder 

(if present), insulation, and membrane or primary weatherproof roof covering.

Roof deck: The structural component of a roof assembly that supports the roof system.

Roof system: A system of interacting roof components generally consisting of a membrane or 

primary roof covering and roof insulation (not including the roof deck) designed to 

weatherproof and sometimes improve the building’s thermal resistance.

Safe room: A specially designed hardened structure that meets FEMA criteria and provides “nearabsolute protection” from extreme wind events. The level of protection provided by a safe 

room is a function of the design wind speed and resulting wind pressure used in designing 

it, and of the wind-borne debris load criteria. To be considered a safe room, the structure 

must be constructed as detailed in the prescriptive plans in FEMA 320, Taking Shelter From 

the Storm: Building a Safe Room For Your Home or Small Business (2008), (for homes and small 

businesses) or designed and constructed to FEMA 361, Design and Construction Guidance 

for Community Safe Rooms (2008), (for communities) guidelines. FEMA 361 also contains 

guidance for homes and small businesses.

Shortwave trough: Also called “shortwave.” A disturbance in the middle or upper part of the 

atmosphere that induces upward motion ahead of it. If other conditions are favorable, the 

upward motion can contribute to thunderstorm development ahead of a shortwave trough. 

Sill plate: The bottom of the wall that provides the connection point between the wall and the 

foundation below. 

Squall line event: According to NOAA, a squall line event is a line of active thunderstorms, 

either continuous or with breaks, including contiguous precipitation areas resulting from 

thunderstorms.

Steep-slope roof: A category of roofing that generally includes water-shedding types of roof 

coverings installed on slopes exceeding 3:12.

Storm Relative Helicity (SRH): One of two important parameters necessary to predict LTVTs. 

High SRH values promote rotating updrafts and are associated with wind shear (changing 

wind speed and wind direction with height in the atmosphere).

Storm relative radial velocity: Base velocity with the average motion of all storm centroids 

subtracted out. Storm relative radial velocity can be useful in finding mesocyclones or other 

circulation patterns. It is characterized on the Doppler radar by a tight couplet of green and 

blue colors moving toward the radar and red and orange colors moving away.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT D-7

GLOSSARY

Storm shelter: Structures, buildings, or portions thereof designed and constructed to meet 

International Code Council (ICC) standard ICC-500 guidelines and provide life-safety 

protection from extreme weather events, such as tornadoes and hurricanes. Unlike safe 

rooms, storm shelters do not meet all FEMA criteria and are not considered to offer “nearabsolute protection” in these weather events. Storm shelters can be for homes, small 

businesses, or communities.

Structure: A part of a building or a freestanding constructed element, such as a roof system, tower, 

or platform. 

Supercell: According to NOAA, potentially the most dangerous of the convective storm types. 

Storms possessing this structure have been observed to generate the vast majority of longlived strong and violent (F2 to F5) tornadoes, as well as downburst damage and large hail. 

It is defined as a thunderstorm consisting of one quasi-steady to rotating updraft that may 

exist for several hours.

Synoptic weather observation: A surface weather observation of sky cover properties, such as, the 

state of the sky, cloud height, atmospheric pressure (reduced to sea level), temperature, dew 

point, wind speed and direction, amount of precipitation, and other special phenomena 

made periodically for the same area.

Tilt-up wall construction: A type of construction during which pre-cast panels, usually concrete, 

are lifted (tilted) into place on a concrete foundation. These walls may be self-supporting 

or part of a steel load-bearing framework. 

Tornado: A violently rotating column of air, often visible as a funnel cloud, suspended from a 

cumuliform cloud or underneath a cumuliform cloud.

Tornado outbreak: An event that occurs when 6 or more tornadoes occur within approximately 24 

hours in the same region from the same synoptic-scale weather system.

Tornado track: The path that the tornado follows or is predicted to follow.

Tornado refuge area: Any location where people go to seek cover during a tornado. Tornado 

refuge areas may have been constructed to comply with basic building code requirements 

(that do not consider tornado hazards). These areas may also have continuous load paths, 

bracing, or other features that increase resistance to wind loads. It is important for people 

to know that such an area may not be a safe place to be when a tornado strikes and they still 

may be injured or killed during a tornado event. 

Tributary area: The area of the floor, wall, roof, or other surface that is supported by the element. 

The tributary area is formed by one-half the distance to the adjacent element in each 

applicable direction.

Trough: An elongated region of relatively low atmospheric pressure often associated with fronts, 

but not usually associated with a closed circulation.

Uplift: An upward force caused by winds perpendicular to the uplift direction caused by a sudden 

change in wind direction caused by an object blocking the airstream (i.e., a building). 

Uplift can occur on structural and non-structural components from wind forces.

Velocity couplet: A tornado vortex signature that appears on the Doppler radar as side-by-side 

velocities—one inbound and one outbound. It is also known as “gate-to-gate shear.”
D-8 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

GLOSSARY

Vortex: The core of the tornado. In this region of the tornado, the winds are complicated and 

include the peak at-ground wind speeds, but are dominated by the tornado’s strong 

rotation. It is in this region that strong upward motions occur that carry debris upward, as 

well as around the tornado.

Vulnerability assessment: An assessment that is focused on building and operational weaknesses 

when impacted by a particular hazard event. Results of the assessment would be used to 

determine what mitigation activities would most likely reduce the vulnerability.

Wedge structure: A profile formed by a large single-vortex tornado that resembles a wedge stuck 

in the ground. Sometimes a wedge can be so wide that it appears to be a large block of lowhanging clouds.

Wind-borne debris (missiles): Debris that becomes airborne during a wind event. 

Wind field: The spatial three-dimensional pattern of winds in a region.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT E-1

EEF Scale Summary

Currently, tornado intensity is classified using the “Enhanced Fujita” (EF) scale, which improves upon 

the original Fujita scale. The Fujita scale, originally developed by Dr. Tetsuya T. Fujita in 1971 (Fujita 

1971), provided a method to rate tornado intensity by examining the affected area. Since there was 

no reliable method to accurately determine the wind speed of a tornado, the method allowed people 

to distinguish between weak and strong tornadoes using the damage caused by the tornado. The 

Fujita scale was updated and superseded by the EF scale, published in 2004 in A Recommendation 

for an Enhanced Fujita Scale (TTU 2004) and clarified in 2006 (TTU 2006).1 The 2006 revision to 

this document clarified the steps in assigning an EF scale rating to a tornado event. More detailed 

information can be found at the TTU Wind Science and Engineering Research Center Web site.2

The EF scale is an important factor considered by architects and engineers in their evaluation of 

damage following a tornado. Its use has made it easier to distinguish those areas that are outside of 

the center of the tornado circulation and which experience lesser wind speeds; these are areas where 

wind-resistant design practices may reduce damage. It was important for the Mitigation Assessment 

Team (MAT) to document the EF scale rating at each damaged building it visited, as the increased 

clarity provided by the EF scale allows the MAT to better evaluate and recommend wind-resistant 

design practices that may be applicable for certain wind speeds.

The EF scale is presented similarly to the original Fujita scale. The EF scale includes six categories, 

from 0 to 5, that represent increasing degrees of wind damage (see Figure E-1). The wind speed 

correlation estimates for each category were improved upon from the estimates used in the original 

Fujita scale. Table E-1 shows the relationship between the 3-second gust speeds of the original Fujita 

scale and the EF scale. 

1 Available online from TTU at http://www.depts.ttu.edu/weweb/Pubs/fscale/EFScale.pdf.

2 TTU Wind Science and Engineering Research Center Web site, www.wind.ttu.edu.
E-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

EF SCALE SUMMARY

Incredible: Strong frame houses are lifted from 

foundations, reinforced concrete structures are 

damaged, automobile-sized missiles become airborne, 

trees are completely debarked.

Devastating: Well-constructed houses are destroyed, 

some structures are lifted from foundations and blown 

some distance, cars are blown some distance, large 

debris becomes airborne.

Severe: Roofs and some walls are torn from 

structures, some small buildings are destroyed, nonreinforced masonry buildings are destroyed, most 

trees in forest are uprooted.

Considerable: Roof structures are damaged, mobile 

homes are destroyed, debris becomes airborne, 

(missiles are generated), large trees are snapped or 

uprooted.

Moderate: Roof surfaces are peeled off, windows are 

broken, some tree trunks are snapped, unanchored 

mobile homes are overturned, attached garages may 

be destroyed.

Light: Chimneys are damaged, tree branches are 

broken, shallow-rooted trees are toppled.

Figure E-1: The EF scale is based on level of typical observed damage
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT E-3

EF SCALE SUMMARY

Table E-1: Wind Speeds Used in Fujita Scale Compared to EF Scale

Fujita Scale Fujita Scale: 3-Second Gust (mph) EF Scale EF Scale: 3-Second Gust (mph)

F0 45–78 EF0 65–85

F1 79–117 EF1 86–110

F2 118–161 EF2 111–135

F3 162–209 EF3 136–165

F4 210–261 EF4 166–200

F5 262–317 EF5 Over 200

mph = miles per hour; EF = Enhanced Fujita

The EF scale uses 28 damage indicators (DIs) to categorize building use and type of construction 

(Table E-2). Each DI includes damage description categories; each is assigned a number termed 

the degree of damage (DOD), and each has a damage description associated with an expected 

estimated wind speed. Table E-3 shows an example of the DOD and damage descriptions for a singlefamily residence. The DOD includes the expected wind speed that would most likely produce the 

observed damage. Photographs are included in the supporting documentation for the EF scale in A 

Recommendation for an Enhanced Fujita Scale (TTU 2006) to assist investigators.

Table E-2: EF Scale Damage Indicators

DI No. Damage Indicator (DI) Use

1 Small Barns or Farm Outbuildings (SBO)

Residential

2 One- to Two-Family Residences (FR12)

3 Manufactured Home – Single Wide (MHSW)

4 Manufactured Home – Double Wide (MHDW)

5 Apartments, Condos, Townhouses [three stories or less] (ACT)

6 Motel (M)

Commercial

and Retail

Structures

7 Masonry Apartment or Motel Building (MAM)

8 Small Retail Building [fast food restaurant] (SRB)

9 Small Professional Building [e.g., doctor’s office, branch bank] (SPB)

10 Strip Mall (SM)

11 Large Shopping Mall (LSM)

12 Large, Isolated Retail Building [e.g., K-Mart, Wal-Mart] (LIRB)

13 Automobile Showroom (ASR)

14 Automobile Service Building (ASB)

15 Elementary School [single story; interior or exterior hallways] (ES) Schools

16 Junior or Senior High School (JHSH)

17 Low-Rise Building [1–4 stories] (LRB)

Professional

Buildings

18 Mid-Rise Building [5–20 stories] (MRB)

19 High-Rise Building [more than 20 stories] (HRB)

20 Institutional Building [e.g., hospital, government, or university] (IB)
E-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

EF SCALE SUMMARY

DI No. Damage Indicator (DI) Use

21 Metal Building Systems (MBS)

Metal Buildings 

and Canopies 22 Service Station Canopy (SSC)

23 Warehouse Building [tilt-up walls or heavy timber construction] (WHB)

24 Transmission Line Towers (TLT)

25 Free-Standing Towers (FST) Towers/Poles

26 Free-Standing Light Poles, Luminary Poles, Flag Poles (FSP)

27 Trees: Hardwood (TH) Vegetation 28 Trees: Softwood (TS)

EF = Enhanced Fujita, DI = damage indicator

SOURCE: RECOMMENDATION FOR AN ENHANCED FUJITA SCALE (TTU 2006)

Table E-3: Example – EF Scale DOD for DI No. 2 (Single-Family Residence)

DOD Damage Description

Lower- and UpperBound Wind Speed 

Range (3-second 

gust in mph)

Expected Wind 

Speed 

(3-second gust 

in mph)

1 Threshold of visible damage 53–80 65

2 Loss of roof covering material (<20%), gutters, and/or 

awning; loss of vinyl or metal siding 63–97 79

3 Broken glass in doors and windows 79–114 96

4 

Uplift of roof deck and loss of significant roof covering 

material (>20%); collapse of chimney; garage doors 

collapse inward; failure of porch or carport 

81–116 97

5 Entire house shifts off foundation 103–141 121

6 Large sections of roof structure removed; most walls remain 

standing 104–142 122

7 Exterior walls collapsed 113–153 132

8 Most walls collapsed except small interior rooms 127–178 152

9 All walls collapsed 142–198 170

10 Destruction of engineered and/or well-constructed 

residence; slab swept clean 165–220 200

EF = Enhanced Fujita, DOD = degree of damage, DI = damage indicator

(a) The differences between “expected,” “upper bound,” and “lower bound” wind speeds are relatively complex. When assessing typical 

DIs, professionals familiar with wind effects on buildings and familiar with building sciences should be consulted.

SOURCE: RECOMMENDATION FOR AN ENHANCED FUJITA SCALE (TTU 2006)

After a tornado event, assessment teams rate the intensity of the tornado based on observed damage 

to individual buildings, structures, or other DIs (as shown in Table E-2) using damage descriptions 

for each DI (such as the example shown in Table E-3) to determine the appropriate DOD. Structures 

along the path of a tornado may be assigned several different EF ratings ranging from EF0 to EF5, 

based on their location within the center of the tornado circulation. Several DIs must be considered 

when assigning an EF scale rating for a tornado event; therefore, although the EF rating assigned 

Table E-2: EF Scale Damage Indicators (concluded)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT E-5

EF SCALE SUMMARY

to individual structures may vary along the path of a tornado, 

the overall tornado intensity is assigned a single rating. For 

archival purposes, a tornado is officially labeled by the NWS 

according to its highest intensity along its path.

The EF scale is still evolving and may be revised based on field 

observations made by post-tornado assessment teams. For instance, the MAT noted in its report that 

the EF scale currently does not include listings for all possible DIs, nor does it include photographic 

documentation of all DODs (refer to Section 10.7 and Section 11.7 of the MAT report). A focus of the 

MATs and other storm researchers is to provide additional data that can be incorporated in future 

updates and refinements to the EF scale and the EF methodology.

Using the EF methodology, the MAT evaluated buildings it visited. The EF ratings given by the MAT 

for sites visited in Alabama, Georgia, Mississippi, and Tennessee are shown in Table E-4 and for Joplin, 

MO, in Table E-5. Characteristics such as building age, code built to, siting, construction methods, 

etc. can affect the amount of damage caused by a tornado; these characteristics can therefore cause 

a deviation (either lower or higher) between the observed damage and resulting DOD rating and the 

expected wind speed assigned in the EF scale.

Table E-4: MAT EF Ratings for Sites Visited in Alabama, Georgia, Mississippi, and Tennessee

MAT EF Scale Ratings by Location: AL, GA, MS, TN

Municipality Location Latitude Longitude

Analysis

DI DOD EF Rating

Alabama

Athens McCulley Mill Road residence 

near shelter 34.76957 -86.8635 2 6 2

Birmingham Apartment building 33.53808 -86.8907 5 4 2

Cullman

3rd Street NE historic residence 34.17959 -86.8325 2 7 2

Three-story church/school 34.17846 -86.8339 20 7 2

Hackleburg

Ray Road residence adjacent to 

Hackleburg Community Shelters 34.28556 -87.8208 2 8 3

Hackleburg Police Station 34.27583 -87.8272 9 8 2

Hackleburg School Complex: 

Elementary, Junior High, and 

High School

34.28111 -87.8331 15 7 2

Hackleburg Fire Department 34.27556 -87.8275 21 3 1

Harvest

Doris Avenue single-family home 

adjacent to manufactured home 34.82223 -86.7746 2 2 0

Placid Drive residence #1 34.83972 -86.7347 2 4 1

Placid Drive residence #2 34.84028 -86.7350 2 6 2

Doris Avenue single-wide 

manufactured home 34.82216 -86.7741 3 7 1

Lockhart Road double-wide 

manufactured home 34.81996 -86.7711 4 1 0

To assign an accurate EF scale 

ranking to a tornado event, 

several DIs must be rated.
E-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

EF SCALE SUMMARY

MAT EF Scale Ratings by Location: AL, GA, MS, TN

Municipality Location Latitude Longitude

Analysis

DI DOD EF Rating

Alabama (continued)

Fultondale Residential neighborhood 33.60716 -86.7947 2 6 1

Fultondale Fire Station 33.60909 -86.7995 21 3 1

Phil 

Campbell

Stalcup Circle residences 34.34583 -87.7075 2 6 2

Phil Campbell Middle and High 

School 34.34944 -87.7078 16 8 2

Pleasant 

Grove

Safe Room at 10th Street 

residence 33.48378 -86.9874 2 2 0

6th Way residence 33.49162 -86.9818 2 8 4

12th Street residence #1 33.48031 -86.9975 2 9 4

12th Street residence #2 33.48035 -86.9988 2 9 4

12th and 13th Streets residences 33.48030 -86.9975 2 10 4

Rainsville

Plainview Schools:

High school 34.48156 -85.8222 16 3 1

Elementary school 34.48156 -85.8222 15 5 1

Tuscaloosa

5th Street residence 33.21083 -87.4831 2 2 0

Two-family residences:

Building 40 33.18619 -87.5522 2 3 1

Main structure on 10th 

Avenue 33.18482 -87.5523 2 8 3

Crescent Lane residence on top 

of ridge 33.21556 -87.4886 2 9 4

Hardened area “shelter” at 16th 

Street E residence 33.19662 -87.5317 2 9 4

Manufactured housing park:

Unit B 33.20566 -87.4927 3 3 0

Unit A 33.20566 -87.4927 3 7 1

Apartment buildings at 5th 

Avenue E 33.19377 -87.5301 5 2 1

LaRocca Nursing Home 33.21063 -87.4925 5 4 2

Chastain Manor Apartments:

Townhouses (one-story) 33.21199 -87.4954 5 4 3

Townhouses (two-story) 33.21193 -87.4945 5 6 4

Apartment building behind Fire 

station 4 33.20632 -87.5097 5 5 3

Tuscaloosa Police Station 33.20689 -87.5039 9 3 1

Retail stores “A” and “B” 33.19993 -87.5240 12 7 4

Table E-4: MAT EF Ratings for Sites Visited in Alabama, Georgia, Mississippi, and Tennessee (continued)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT E-7

EF SCALE SUMMARY

MAT EF Scale Ratings by Location: AL, GA, MS, TN

Municipality Location Latitude Longitude

Analysis

DI DOD EF Rating

Alabama (concluded)

Tuscaloosa

(concluded)

Armed Forces Reserve Center:

Building behind main 

building with service bays 33.18652 -87.5515 14 4 1

Low-rise building 33.18676 -87.5514 17 4 1

Alberta Elementary School 33.20796 -87.5025 15 10 4

University Place Elementary 

School 33.19301 -87.5393 16 10 3

Fitness center 33.20053 -87.5217 21 7 3

Curry Building city complex EOC 33.17961 -87.5629 23 7 3

Communications Tower at 35th 

Street 33.17793 -87.5637 25 3 2

Georgia

Ringgold

Middle school 34.92238 -85.1127 16 6 1

High school 34.92234 -85.1130 16 6 1

Mississippi

Smithville

Brasfield Lane residence 

adjacent to below-ground shelter 34.06278 -88.4072 2 6 2

Gum Street residence in front of 

old cellar/shelter 34.07111 -88.3917 2 6 2

Below-ground shelter at Poplar 

Street residence 34.07083 -88.3958 2 9 4

Community shelter at 

manufactured housing park at 

Commerce and Dunlap Streets

34.06972 -88.3997 3 9 3

Police Station 34.06889 -88.3982 9 8 3

Fire Station 34.06722 -88.3981 21 3 1

Cell tower 34.06444 -88.4103 25 2 3

Tennessee

Cleveland Blue Springs Elementary School 35.08809 -84.9094 15 6 1

Table E-4: MAT EF Ratings for Sites Visited in Alabama, Georgia, Mississippi, and Tennessee (concluded)
E-8 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

EF SCALE SUMMARY

Table E-5: MAT EF Scale Ratings for Sites Visited in Joplin, MO

MAT EF Scale Ratings by Location: Joplin, MO

Location Latitude Longitude

Composite

DI DOD EF Rating

Safe Room at Alabama Avenue residence 37.06656 -94.4861 2 4 1

Safe Room at Adele Avenue residence 37.0614 -94.5391 2 9 3

Mercy Village Apartments 37.06009 -94.5263 5 3 2

Greenbriar Nursing Home 37.06294 -94.5209 9 9 3

Walmart 37.0729 -94.4716 12 6 4

Home Depot 37.06958 -94.4744 12 7 4

East Joplin Middle School 37.06764 -94.4489 16 7 2

Joplin High School 37.06757 -94.5054 16 11 3

Ozark Center for Autism - Jackson Ave 37.06397 -94.5218 17 5 3

St. John’s Medical Center 37.05933 -94.5322 20 10 3

St. Paul’s United Methodist Church 37.06271 -94.5441 21 3 1
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT F-1

FRecovery Advisories for 

the Spring 2011 Tornadoes

FEMA has prepared a series of new Recovery Advisories (RAs) that present guidance for safe room 

and refuge areas, facility operations, and the design and reconstruction of buildings in areas subject 

to tornadoes. Eight advisories have been prepared and are included in this appendix:

RA1. Tornado Risks and Hazards in the Southeastern United States

RA2. Safe Rooms: Selecting Design Criteria

RA3. Residential Sheltering: In-Residence and Stand-Alone Safe Rooms

RA4. Safe Rooms and Refuge Areas in the Home

RA5. Critical Facilities Located in Tornado-Prone Regions: 

Recommendations for Facility Owners

RA6. Critical Facilities Located in Tornado-Prone Regions: 

Recommendations for Architects and Engineers

RA7. Rebuilding and Repairing your Home After a Tornado

RA8. Reconstructing Non-Residential Buildings After a Tornado

These advisories are also available online at http://www.fema.gov/library/viewRecord.do?id=4723

Tornado Risks and Hazards in the Southeastern United States HSFEHQ-11-J-0004, 0005 / June 2011 Page 1 of 6

Purpose and Intended Audience

The purpose of this Tornado Recovery Advisory is to provide background on the tornado hazard in the 

Southeast. The general population, homeowners and renters, policy makers, local officials, builders, and 

building departments should understand that tornado occurrence in the Southeast is not a rare event. In fact, 

of the top 20 States in tornado frequency, 5 are in the Southeast. 

This advisory also identifies FEMA resources that can be used to help design and construct portions of almost 

any building type (including residences) to provide safe refuge from tornadoes, or to help minimize damage 

caused by these wind events.

This Recovery Advisory Addresses:

" Recent events

" Tornado occurrence outside “Tornado Alley”... 

how great is the risk? 

" Assessing your risk

" Can a building survive a tornado? Yes!

" Weather radios

Recent Events

In the late afternoon of April 27, 2011, a large 

outbreak of tornadoes struck Mississippi, 

Tennessee, Alabama, and portions of Georgia. The 

National Oceanic and Atmospheric Administration 

(NOAA) estimated there were approximately 190 

tornadoes that touched down between 8:00 a.m. 

EDT April 27 and 8:00 a.m. EDT April 28, a record high for a single storm system. Three of the tornadoes 

were rated by the National Weather Service (NWS) as EF5, 11 were rated at EF4, 21 at EF3, and the 

remainder at EF2 and below on the Enhanced Fujita Scale. Fatalities for the events in April totaled 3611 and 

hundreds more were injured, making April 27th the fourth deadliest day for tornadoes on record.2 Total damage 

estimates are still being compiled from this event, but early estimates are that the insured loss for the storms 

could reach $6 billion, with Alabama accounting for 70 percent of that loss.3

On May 22, 2011, Joplin, Missouri, a town of 50,000 people, was devastated by a large tornado. NWS 

estimated that the tornado was an EF5 (greater than 200 mph) tornado. At the time of publication of this 

Recovery Advisory, 141 people from Joplin have been confirmed dead and 750 people reported as injured. 

The Joplin tornado is the deadliest single tornado since modern recordkeeping began in 1950 and is ranked 

eighth among the deadliest tornadoes in U.S. history.4 Total damage estimates could reach $3 billion.5

1 NOAA, 2011. http://www.spc.noaa.gov/climo/torn/fataltorn.html accessed 5/27/11

2 NOAA, 2011. http://www.noaanews.noaa.gov/april_2011_tornado_information.html accessed 5/17/11

3 Gow, Lauren. May 17, 2011. “US tornado insured losses could reach $6bn” in Global Reinsurance

4 SOURCE: http://www.crh.noaa.gov/sgf/?n=event_2011may22_summary accessed 5/27/11

5 SOURCE: http://money.cnn.com/2011/05/24/news/economy/tornado_joplin/index.htm accessed 5/27/11

TORNADO RECOVERY ADVISORY RA1, June 2011

Tornado Risks and Hazards 

in the Southeastern 

United States

The National Weather Service uses the 

Enhanced Fujita Scale (EF Scale) to categorize 

tornado severity based on observed damage. 

The scale ranges from EF0 to EF5. See 

http://www.spc.noaa.gov/efscale for further 

information on the EF Scale. 

EF Scale 3-Second Gust Speed (mph)

EF0 65–85

EF1 86–110

EF2 111–135

EF3 136–165

EF4 166–200

EF5 Over 200
Tornado Risks and Hazards in the Southeastern United States HSFEHQ-11-J-0004, 0005 / June 2011 Page 2 of 6

Tornado Occurrence Outside “Tornado Alley”... How Great Is the Risk?

“Tornado Alley” is an area of the heartland of the United States known for its tornado activity. Although the 

exact extent of Tornado Alley can be debated, most scientists agree that Texas, Oklahoma, and Kansas are 

well known for tornado risk and make up a large portion of Tornado Alley. 

What most people may not be aware of is the amount of tornadic activity outside of Tornado Alley. FEMA 

Region IV has eight States subject to tornadoes and six subject to hurricanes (refer to Figure 1 and Table 1).

Although hurricanes 

have received most 

of the attention in 

recent years in the 

Southeast, the threat 

and risk of tornadoes 

is real. Table 1 below 

shows the number of 

tornadoes occurring 

in each of the States 

in FEMA Region IV. 

A total of 11,629 

tornadoes were 

recorded by NOAA’s 

Storm Prediction 

Center for the 60-year 

study period from 

1950 through 2010. 

Between 2000 and 

2010, Alabama alone 

experienced 636 

tornadoes.

Except for in the 

States of Mississippi 

and Alabama, 

tornadoes occurring 

in the Southeast are 

typically weak to moderately strong (EF0, 

EF1, EF2, and EF3 tornadoes). However, 

these weaker tornadoes can be as deadly 

as the stronger (EF4 or EF5) tornadoes. 

For example, more than 50 of the 78 

deadliest tornadoes that occurred in Florida 

between 1882 and 2007 were EF3 or 

weaker. Further, tornadoes are not always 

single events; sometimes several tornado 

outbreaks result from a large storm system.

In addition to the April 27, 2011, outbreak, 

other notable outbreaks in the Southeast 

include:

The Super Outbreak of April 3–4, 1974

" 148 tornadoes responsible for 330 

fatalities

" Approximately 5,484 injuries

" Approximately $600 million (1975 dollars) 

in damages

" Tornadoes affected 13 States from Alabama to Michigan

Figure 1: Average number of tornadoes per year in FEMA Region IV and Tornado Alley

States

in FEMA 

Region IV

Total Tornado 

Occurrences 

(1950–2010)

Total 

Fatalities 

(1950–2010)

Total Injuries 

(1950–2010)

Fatality 

Rank

Alabama 1,695 441 6,808 4

Florida 3,052 161 3,307 16

Georgia 1,381 190 4,059 14

Kentucky 741 180 3,310 15

Mississippi 1,790 443 6,223 2

North Carolina 1,116 114 2,536 17

South Carolina 894 60 1,693 23

Tennessee 960 399 5,114 5

TOTAL 11,629 1,988 33,050

Values do not include Spring 2011 tornadoes. 

SOURCE: TornadoHistoryProject.com, which compiles NOAA Storm Prediction Center 

data found at http://www.spc.noaa.gov/wcm/#data

Table 1: Tornado occurrences in FEMA Region IV
Tornado Risks and Hazards in the Southeastern United States HSFEHQ-11-J-0004, 0005 / June 2011 Page 3 of 6

The Carolinas Outbreak of March 28, 1984

" 22 tornadoes responsible for 57 fatalities

" Approximately 1,250 injuries

" Approximately $200 million (1984 dollars) in damages

" 37 percent of fatalities occurred in manufactured homes

The Palm Sunday Outbreak of March 27, 1994

" 27 tornadoes responsible for 42 fatalities

" Approximately 491 injuries

" Approximately $107 million (1994 dollars) in damages

" Tornadoes hit Alabama, Georgia, South Carolina, and North Carolina

The Enterprise, Alabama Tornado of March 1, 2007

" 8 fatalities and 50 injuries in Enterprise High School

" The fatalities occurred when walls and roof structure collapsed onto 

a group of students huddled in the hallway in a crouched position

" Tornado estimated at an EF4

Assessing Your Risk

To determine if you have a low, moderate, or high tornado risk, use the Frequency map (Figure 2) to determine 

how many tornadoes were recorded per 2,470 square miles for the area where your building is located. Find 

the row in Table 2 that matches that number. Next, look at the Wind Speed map (Figure 3) and note the design 

wind speed (130 mph, 160 mph, 200 mph, 250 mph) for your building location. Find the matching column in 

Table 2 and find the box that lines up with both the number of tornadoes 

per 2,470 square miles in your area and your wind speed. The color in 

that box tells you the level of your risk from extreme winds and helps 

you decide whether to build a safe room. A safe room is the preferred 

method of wind protection in high-risk areas.

Example: If your building is located in Birmingham, Alabama, you would 

see that Birmingham is in an area shaded red on the Frequency map 

(Figure 2). According to that map, the number of tornadoes per 2,470 

square miles in the Birmingham area is >15. On the Wind Speed map 

(Figure 3), Birmingham is within the dark blue area, identified by the 

map key with a design wind speed of 250 mph. The box in the Risk 

Table (Table 2) where the frequency >15 row and the 250 mph wind 

speed column meet is shaded dark blue, which shows that the building 

is in an area of high risk.

Can a Building Survive a Tornado? Yes!

Tornado safe rooms can be designed and constructed to protect occupants from winds and wind-borne 

debris associated with all tornadoes (EF0–EF5). Buildings designed and constructed above basic code 

requirements (aka “hardened” buildings) and newer structures designed and constructed to modern, hazardresistant codes can resist the wind load forces from weak tornadoes (EF1 or weaker). Furthermore, even when 

stronger tornadoes strike, not all damage is from the rotating vortex of the tornado. Much of the damage 

is from straight-line winds rushing toward and being pulled into the tornado itself. Many newer homes and 

commercial buildings designed and constructed to modern codes, such as the International Residential Code

and International Building Code (2009 editions and newer), have load paths that better resist high-wind forces 

(specified in building codes for hurricane resistance) and may survive without structural failure. The damage 

to these newer homes and buildings is often to the cladding and exterior systems: roof covering, roof deck, 

exterior walls, and windows. 

For most building uses, it is economically impractical to design the entire building to resist tornadoes. 

However, portions of buildings can be designed as safe rooms to provide occupant protection from tornadoes. 

For information on designing safe rooms to resist the strongest tornadoes and hurricane events, see the 

Tornado Recovery Advisory RA2 titled “Safe Rooms: Selecting Design Criteria” (updated in 2011). For 

residential safe rooms, see the Tornado Recovery Advisory RA3 titled “Residential Sheltering: In-Residence 

and Stand-Alone Safe Rooms” (updated in 2011). 

Note that some areas of low 

or moderate risk, shown as 

pale blue or medium blue on 

Table 2, are within the region 

of the United States that is 

also subject to hurricanes (see 

Figure 3). If you live in this 

hurricane-prone region, your 

risk is considered high even if 

Table 2 shows a moderate or 

low risk.

In 2010, the Alabama Building 

Commission passed a bill 

(Act 2010-746 Safe Space) 

requiring that all new K-12 

school construction projects 

awarded after July 1, 2010, 

provide a storm shelter that 

complies with the ICC-500 

storm shelter standard. This 

was in large part due to the 

tragic events of March 1, 2007, 

when a tornado destroyed the 

Enterprise High School, killing 

7 students and 1 teacher.
Tornado Risks and Hazards in the Southeastern United States HSFEHQ-11-J-0004, 0005 / June 2011 Page 4 of 6

Number of Tornadoes 

per 2,470 Square Miles 

(see Figure 2)

Design Wind Speed (see Figure 3)

130 mph 160 mph 200 mph 250 mph

<1 LOW Risk LOW Risk « LOW Risk « MODERATE Risk

1–5 LOW Risk MODERATE Risk « HIGH Risk HIGH Risk

6–10 LOW Risk MODERATE Risk « HIGH Risk HIGH Risk

11–15 HIGH Risk HIGH Risk HIGH Risk HIGH Risk

>15 HIGH Risk HIGH Risk HIGH Risk HIGH Risk

LOW Risk – Sheltering from 

high winds is a matter of 

preference.

MODERATE Risk – Shelter 

should be considered for 

protection from high winds.

HIGH Risk – Shelter is 

the preferred method of 

protection from high winds.

Table 2: Levels of risk during high-wind events

Figure 2: Frequency of recorded F3, F4, and F5 tornadoes (1950–2006)

NOTE: Due to the level of detail and size of the map, if the reader is uncertain of their 

location, or they find they live on or very near one of the delineation lines, they should 

use the highest adjacent Design Wind Speed or Tornado Frequency number. 

SOURCE: FEMA 320, Taking Shelter From the Storm: Building a Safe Room For Your Home 

or Small Business, August 2008, 3rd Edition

FEMA Region IV

Unless a building has a specifically designed safe room, or occupants have access to a community safe room 

nearby, building owners should work with a qualified architect or engineer to identify the best available refuge 

areas in the building. For more information on best available refuge areas, see Tornado Protection: Selecting 

Refuge Areas in Buildings (FEMA P-431, 2009) and the Extreme-Wind Refuge Area Evaluation Checklists in 

Design and Construction Guidance for Community Safe Rooms (FEMA P-361, Appendix B1, 2008).
Tornado Risks and Hazards in the Southeastern United States HSFEHQ-11-J-0004, 0005 / June 2011 Page 5 of 6

Weather Radios

Everyone living or working in tornado-prone areas should have a weather radio at their home or place of work. 

A weather radio is particularly important for those living in areas that do not have storm warning sirens.

The NOAA Weather Radio (NWR) is a nationwide network of radio stations broadcasting continuous weather 

information directly from a nearby NWS office. NWR broadcasts NWS warnings, watches, forecasts, and other 

hazard information 24 hours a day, as well as post-event information for all types of hazards, both natural and 

technological.

NOAA Weather Radios are available at electronics stores across the country and range in cost from $25 up to 

$100 or more, depending on the quality of the receiver and number of features. The NWS does not endorse 

any particular make or model of receiver. 

Features to look for in a NOAA Weather Radio

" The most desirable feature is an alarm tone. This allows you to have the radio turned on, but silent until a 

special tone is broadcast before watch and warning messages of an imminent life-threatening situation.

" Specific Area Message Encoding (SAME) technology, a NOAA Weather Radio feature available since the mid1990s, is capable of providing detailed, area-specific information. Unlike other NOAA Weather Radios, the 

SAME feature will filter out alerts that do not affect your immediate area.

Figure 3: Tornado safe room design wind speeds in the United States

SOURCE: FEMA 361, Design and Construction Guidance for Community Safe Rooms, August 2008, 2nd Edition
Tornado Risks and Hazards in the Southeastern United States HSFEHQ-11-J-0004, 0005 / June 2011 Page 6 of 6

" The NOAA Weather Radio should be operated on batteries when electrical service may be interrupted. Look 

for radios with an AC adapter and battery compartment.

" The radio should be tunable to all seven NWR frequencies. For the latest list of frequencies and transmitter 

locations, check the NOAA Weather Radio Web site http://www.weather.gov/nwr.

" The hearing and visually impaired can receive watches and warnings by connecting weather radio alarms to 

other kinds of attention-getting devices, like strobe lights, pagers, bed-shakers, personal computers, and 

text printers.

Automated Spanish translation systems are available for use on transmitters serving a significant Hispanic 

population to broadcast Spanish translations of all emergency weather and natural hazard messages 

immediately after the official Emergency Alert System (EAS) warning is issued. For more information in 

Spanish, please visit the NOAA Web site http://www.weather.gov/nwr/indexsp.htm.

Other Methods to Receive Forecasts, Watches, and Warnings:

" Tune in to your local radio and television stations for the latest weather forecasts, watches, and warnings. 

In the event of power loss, battery-operated weather radios can be an interim solution to receive forecasts, 

watches, and warnings. 

" NWS products and services are also available on the Internet at http://www.weather.gov/nwr. Delivery of 

data across the Internet, however, cannot be guaranteed because of potential interruption of service. 

" Another low-cost method for receiving the NWS’s essential information is available on a wireless data 

system called the Emergency Managers Weather Information Network (EMWIN). This system presents 

the information directly on your home or office computer. Users may set various alarms to be alerted to 

particular information, whether for their local area or adjacent areas. For more information, visit the EMWIN 

Web site http://www.weather.gov/emwin/index.htm.

FEMA is in the process of introducing the Personal Localized Alerting Network (PLAN), which will allow 

customers with certain types of mobile devices, such as smartphones, to receive emergency alerts specific 

to their location. Some cities are planned to be online by the end of 2011, and large portions of the United 

States should have the service by mid-2012. This service will enable certain national, State, and local 

agencies to send customers alerts for public safety emergencies like tornado warnings and watches. 

Customers with PLAN-capable devices will be notified by text message of emergencies relevant to their 

geographic area.

National Weather Service StormReady Program

In addition to the guidance and outreach offered by FEMA, the National Weather Service has established the 

StormReady Program to help communities prepare for extreme weather events. The StormReady Program, 

established in 1999, helps communities establish the communication and safety skills and awareness 

to reduce impacts from extreme events. This is done by strengthening local safety programs and helping 

communities with advanced planning, education, and awareness. Through this program, the National Weather 

Service also provides a number of publications and other forms of information on various types of natural 

hazards. Visit http://www.stormready.noaa.gov for more information. 

Useful Links and Resources

Taking Shelter from the Storm: Building a Safe Room For Your Home or Small Business (FEMA 320), August 

2008, 3rd Edition. http://www.fema.gov/library/viewRecord.do?id=1536

Design and Construction Guidance for Community Safe Rooms (FEMA 361) August 2008, 2nd Edition. 

http://www.fema.gov/library/viewRecord.do?id=1657

Tornado Protection: Selecting Refuge Areas in Buildings (FEMA P-431), FEMA, October 2009, 2nd Edition. 

http://www.fema.gov/library/viewRecord.do?id=1563

National Storm Shelter Association (NSSA). http://www.NSSA.cc

ICC/NSSA Standard for the Design and Construction of Storm Shelters (ICC-500), June 2008. http://www.

iccsafe.org/Store/Pages/Product.aspx?id=8850P08_PD-X-SS-P-2008-000001
Safe Rooms: Selecting Design Criteria HSFEHQ-11-J-0004, 0005 / June 2011 Page 1 of 8

Purpose and Intended Audience 

The intended audience for this Tornado Recovery Advisory is anyone involved in the planning, policy-making, 

design, construction, or approval of safe rooms, including designers, emergency managers, public officials, 

policy or decision-makers, building code officials, and home or building owners. Homeowners and renters 

should also refer to the Tornado Recovery 

Advisory No. 3 titled “Residential 

Sheltering: In-Residence and Stand-Alone 

Safe Rooms” (updated in 2011). The 

purpose of this advisory is to identify 

the design guidance, code requirements, 

and other criteria that pertain to the 

design and construction of safe rooms 

for tornadoes and hurricanes. Different 

safe room and storm shelter criteria offer 

different levels of protection to safe room 

occupants. 

This Recovery Advisory Addresses: 

" How safe room construction is different 

from typical building construction 

" Structural systems 

" Wind-borne debris resistance 

" Safe rooms vs. storm shelters

" Selecting refuge areas in buildings 

How Safe Room Construction is Different from Typical Building Construction 

A safe room is typically an interior room, space within a building, or an entirely separate building, designed 

and constructed to protect its occupants from tornadoes or hurricanes. Safe rooms are intended to provide 

near-absolute protection against both wind forces and the impact of wind-borne debris. The level of occupant 

protection provided by a space specifically designed as a safe room is intended to be much greater than the 

protection provided by buildings that comply with the minimum requirements of building codes. Until the 2009 

International Codes adopted the International Construction Code/National Storm Shelter Association (ICC/

NSSA) Standard for the Design and Construction of Storm 

Shelters (ICC-500), the model building codes did not cite 

design and construction criteria for life safety for sheltering, 

nor do they provide design criteria for tornado-resistant 

construction. Information about the ICC shelter criteria and 

FEMA safe room criteria that provide life-safety protection 

can be found in other guidance documents referenced in this 

recovery advisory.

TORNADO RECOVERY ADVISORY RA2, June 2011

Safe Rooms: 

Selecting Design Criteria

The term “hardened” refers to 

specialized design and construction 

applied to a room or building to allow it 

to resist wind pressures and wind-borne 

debris impacts during a high-wind event 

and serve as a shelter.

Community safe room being constructed to FEMA 361 criteria in Wichita, KS.
Safe Rooms: Selecting Design Criteria HSFEHQ-11-J-0004, 0005 / June 2011 Page 2 of 8

Safe rooms typically fall into two categories: residential safe rooms and community (non-residential) safe 

rooms. 

" There are two general types of residential safe rooms: in-residence safe rooms and stand-alone safe 

rooms, located adjacent to or near a residence. An in-residence safe room is a small, specially designed 

(“hardened”) room, such as a bathroom or closet, designed as a place of refuge for the people who live 

in the house. A stand-alone residential safe room is similar in function and design, but it is a separate 

structure installed outside the house, either above or below the ground surface. Refer also to Tornado 

Recovery Advisory No. 3 titled “Residential Sheltering: In-Residence and Stand-Alone Safe Rooms” (updated in 

2011). 

" A community safe room is intended to protect a larger number of people: anywhere from approximately 16 

to several hundred individuals. Community safe rooms include not only public safe rooms but also private 

safe rooms for businesses and other organizations. 

" Guidance on designing and constructing safe rooms can be found in FEMA 320, Taking Shelter from 

the Storm: Building a Safe Room For Your Home or Small Business (2008) and FEMA 361, Design and 

Construction Guidance for Community Safe Rooms (2008).

Structural Systems 

The primary difference in a building’s structural system when designed for use as a safe room, rather than for 

conventional use, is the magnitude of the wind forces that it is designed to withstand. 

Buildings are designed to withstand a certain wind speed (termed “basic [or design] wind speed”) based 

on historic wind speeds documented for different areas of the country. The highest design wind speed used 

in conventional construction is near the coastal areas of the Atlantic and Gulf Coasts and is in the range of 

140–150 mph, 3-second gust in most locations. By contrast, the design wind speed recommended by FEMA1

for safe rooms in these same areas is in the range of 200–250 mph, 3-second gust; this design wind speed 

is intended to provide “near-absolute protection.” 

Wind pressures are generally calculated as a function of the square of the design wind speed. As a result, the 

structural systems of a safe room are designed for forces up to almost eight times higher than those used 

for typical building construction. Consequently, the structural systems of a safe room (and the connections 

between them) are very robust. 

Wind-Borne Debris Resistance 

Wind-borne debris, commonly referred to as missiles, causes many of the injuries and much of the damage 

from tornadoes and hurricanes. Windows and the glazing in exterior doors of conventional buildings are not 

required to resist wind-borne debris, except for buildings 

in wind-borne debris regions.2 Impact-resistant glazing can 

either be laminated glass, polycarbonate, or shutters. The 

American Society of Civil Engineers (ASCE) Standard 7 

missile criteria were developed to minimize property damage 

and improve building performance; they were not developed 

to protect occupants. To provide occupant protection, the 

criteria used in designing safe rooms include substantially 

greater wind-borne debris loads and will be detailed later in 

this recovery advisory. 

The roof deck, walls, and doors of conventional construction 

are also not required by the building code to resist windborne debris. However, the roof deck and walls around a safe room space, and the doors leading into it, must 

resist wind-borne debris if the space inside is to provide occupant protection. Additional information regarding 

the different levels of wind-borne debris loads is provided below. 

1 FEMA 361, Design and Construction Guidance for Community Safe Rooms, Second Edition (August 2008)

2 ASCE 7, American Society of Civil Engineers Standard 7, Minimum Design Loads for Buildings and Other Structures (2010)

If glazing is present in a tornado safe 

room, it should be protected by an 

interior-mounted shutter that can be 

quickly and easily deployed by the safe 

room occupants, or be designed to 

resist the wind-borne debris impact and 

wind pressure tests cited in FEMA 361 

and prescribed in ICC-500, Chapter 8.
Safe Rooms: Selecting Design Criteria HSFEHQ-11-J-0004, 0005 / June 2011 Page 3 of 8

Safe Rooms vs. Storm Shelters 

Safe rooms and storm shelters provide different 

levels of protection depending on the design criteria 

used. The level of protection provided by a safe room 

is a function of the design wind speed (and resulting 

wind pressure) used in designing it, and of the windborne debris load criteria. In addition to FEMA 320 

and FEMA 361, the International Construction Code/

National Storm Shelter Association (ICC/NSSA)

Standard for the Design and Construction of Storm 

Shelters (ICC-500) provides design and construction 

criteria for storm shelters. FEMA’s safe room criteria 

and ICC-500’s storm shelter criteria are similar, with 

a few differences such as citing with respect to flood 

hazards and the horizontal missile impact test speed 

for the hurricane hazard. While the two criteria are 

similar, FEMA changed the name of its guidance 

from “shelters” to “safe rooms” when ICC-500 was 

released to avoid confusion. In addition, FEMA 361, 

which was updated at the same time ICC-500 was 

released, references ICC-500 for certain criteria in 

the design and construction of a safe room, such 

as testing standards for missile impact and wind 

pressure resistance. 

Design wind speed and wind pressure criteria: Wind 

pressure criteria are given by different guides, codes, 

and standards. The wind pressure criteria specify 

how strong the safe room must be. The design 

wind speed is the major factor in determining the 

magnitude of the wind pressure that the building 

is designed to withstand. In FEMA’s safe room 

publications and ICC-500, the same wind speed 

hazard maps are used to recommend design 

wind speeds ranging from 130 to 255 mph. The 

2009 International Residential Code and the 2009 

International Building Code, which establish the 

minimum requirements for residential and other 

building construction, include design wind speeds 

ranging from 90 to 150 mph throughout most of 

the country. Table 1 provides a comparison of safe 

room/shelter design criteria options. 

Wind-borne debris load criteria: Table 2 presents 

wind-borne debris criteria given in various guides, 

codes, and standards. Table 2 shows the different 

test missiles and the corresponding momentum 

they carry with them as they strike a safe room. The 

first entries on the table (Tornado Missile Testing 

Requirements) are the FEMA missile guidance for 

residential and community safe rooms that provide 

near-absolute protection.

HMGP funds were used for this Public Safety Complex 

constructed so that the entire facility is compliant with FEMA 

361 criteria. Robert J. Curry Public Safety Complex, Gulfport, MS.

HMGP-funded community safe room constructed in the 

basement of a new fire station in Brookside, AL.
Safe Rooms: Selecting Design Criteria HSFEHQ-11-J-0004, 0005 / June 2011 Page 4 of 8

Title or Name of Document Code, Regulation, Standard, 

or Statute?

Wind 

Hazard Wind Map

FEMA Safe Room Publications: 

FEMA 320 Taking Shelter from the Storm: 

Building a Safe Room For Your Home or 

Small Business (2008) 

FEMA 361 Design and Construction 

Guidance for Community Safe Rooms 

(2008) 

FEMA guidance document, not a 

code or standard. “Best Practice” 

for high-wind safe rooms 

Tornado and 

Hurricane 

FEMA 320: Hazard map, maximum wind hazard 

speed of 250 mph used for design 

FEMA 361: Map with four wind speed zones for 

design (wind mri2 is 10,000–100,000 years). This 

map is often referred to as the “FEMA 361 map” 

International Code Council/National 

Storm Shelter Association (ICC/NSSA)

High Wind Shelter Standard (ICC-500)

Consensus standard for shelter 

design and construction. 

Incorporated by reference into the 

2009 IBC and IRC. 

Tornado and 

Hurricane 

Tornado: Uses FEMA 361 map 

Hurricane: Uses revised ASCE 7 map with 

contours at 10,000 year mri with minimum 

shelter design wind speed of 160 mph, maximum 

approximately 255 mph 

Florida State Emergency Shelter Program 

(SESP) – Florida’s interpretation of the 

American Red Cross (ARC) 4496 Guidance. 

Note: shelters in this category range from 

EHPA-recommended design levels, shown 

in this row, to the code requirement levels 

(next row), to the ARC 4496 requirements 

(see below). 

Guidance in the Florida Building 

Code (FBC) “recommending” 

above-code requirements for 

EHPAs. See also Appendix G of the 

Florida SESP report for detailed 

design guidance. 

Hurricane FBC map, based on ASCE 7-05 (maps basically 

equivalent); mri is 50–100 years in coastal areas 

and adjusted with importance factor 

ASCE 7-10 2010 edition of ASCE standard 

on minimum design loads for 

buildings and other structures. 

Hurricane ASCE 7-10 departs from previous editions and 

provides multiple wind maps for various “building 

risk categories” (which are based on occupancy 

type). The maps have wind speeds based on 

different mri. 

FBC 2000, IBC/IRC 2000 through 2009, 

ASCE 7-98 through 2005

Building code and design 

standards for regular (nonshelter) buildings. Some 

additional guidance is provided in 

commentary. 

Hurricane ASCE 7 has its own wind speed map based 

on historical and probabilistic data; mri is 

50–100 years in coastal areas and adjusted with 

importance factor 

Institute for Business and Home Safety 

(IBHS) Fortified Home Program – intended 

as guidance to improve the performance of 

residential buildings during natural hazard 

events, including high-wind events. Not 

considered adequate for sheltering. 

Guidance provided to improve 

performance of regular (nonshelter) buildings in high winds 

Tornado and 

Hurricane 

ASCE 7 or modern State building code map 

FBC EHPAs – code requirements for public 

“shelters” (FBC Section 423.25) 

Statewide code requirements for 

EHPAs 

Hurricane The minimum requirement is based on ASCE 7 

(maps basically equivalent); mri is 50–100 years 

in coastal areas and adjusted with importance 

factor; the missile impact criteria for openings, 

walls, and roof as provided in SSTD 12,3 must 

also be met

Building Codes: Pre-2000 Building code and design 

standards for regular (non-shelter) 

buildings 

Hurricane Each of the older codes used their own published 

wind contour maps 

ARC 4496 Standards for Hurricane 

Evacuation Shelter Selection

Guidance for identifying buildings 

to use as hurricane evacuation 

shelters 

Hurricane ASCE 7-98 or ANSI A58 structural design criteria

Other: Information for selecting areas of 

refuge/last resort 

Guidance from FEMA and others 

for selecting best-available refuge 

areas 

Tornado and 

Hurricane 

None 

NOTES:

1. The wind shelter guidance and requirements shown here are presented from highest to least amount of protection provided

2. Mean recurrence intervals (mri) for wind speeds maps are identified by the code or standard that developed the map. Typically, the mri for nonshelter construction in non-hurricane-prone areas is 50 years and in hurricane-prone regions, approximately 100 years.

3. Standard Building Code/Standard 12 – Test Standards for Determining Resistance from Windborne Debris

Table 1. Wind Safe Room/Shelter Design and Construction Codes, Standards, Guidance Comparison1 (page 1 of 2)
Safe Rooms: Selecting Design Criteria HSFEHQ-11-J-0004, 0005 / June 2011 Page 5 of 8

Table 1. Wind Safe Room/Shelter Design and Construction Codes, Standards, Guidance Comparison1 (page 2 of 2)

Wind Design Coefficient 

Considerations4,5, Debris Impact Criteria6 Remarks 

FEMA 320: N/A – prescriptive design 

guidance for maximum hazard 

FEMA 361: Use FEMA 361 wind speed 

map with four zones. Calculate pressures 

using ASCE 7 methods and use I=1.0, 

Kd=1.0, Exposure C, no topographic 

effects, GCpi=+/-0.55 (this will account for 

atmospheric pressure change [APC]) 

Test all safe rooms with the representative 

missile (missile speed dependent on site 

design wind speed):

FEMA 320: 15 lb 2x4 at 100 mph (horizontal) 

and 67 mph (vertical)

FEMA 361 Tornado: 15 lb 2x4 at 80-100 mph 

(vertical) and 2/3 of this speed (horizontal)

FEMA 361 Hurricane: 9 lb 2x4 at 0.1 times 

the wind speed (horizontal) and 0.5 times the 

wind speed (vertical) 

FEMA 320: Intent is to provide “near-absolute protection.” No 

certification is provided. 

FEMA 361: Intent is to provide “near-absolute protection.” Safe 

room operations guidance is provided. Occupancy issues are 

addressed. Wall section details provided. No certification is 

provided. 

Tornado: Use FEMA 361 wind speed 

map. Calculate pressures using ASCE 7 

methods and use I=1.0, Kd=1.0, Exposure 

C with some exceptions, Kzt=need not 

exceed 1.0, GCpi=+/-0.55 or +/-0.18+APC 

Hurricane: Use revised ASCE 7 map and 

methods and use I=1.0, all other items as 

per ASCE 7, no APC consideration required. 

Test shelters with representative missile 

(missile speed dependent on site design wind 

speed): 

Tornado: 15 lb 2x4 at 80–100 mph (vertical) 

and 2/3 of this speed (horizontal). Hurricane:

9 lb 2x4 at 0.1 times the wind speed 

(horizontal) and 0.4 times the wind speed 

(vertical) 

Intent is to provide a standard for the design and construction of 

high-wind shelters. Will not use term “near-absolute protection.” 

Occupancy, ventilation, and use issues are also addressed. 

Shelter operations guidance is provided in the commentary 

only (commentary is a separate document—not a consensus 

document). 

Recommends that designer add 40 mph 

to basic wind speed identified on map, 

Exposure C, I=1.15, Kd=1.00, GCpi as 

required by design (typically +/-0.18), but 

recommends +/-0.55 for tornado shelter 

uses.

In wind-borne debris region (120 mph+): 

Small – pea gravel; Large – 9 lb 2x4 at 75 

mph (horizontal), up to 60 feet above grade, 

but recommends 15 lb 2x4 at 50 mph 

(horizontal) 

The building, or a portion of a building, is defined as an essential 

facility and as a shelter. Designer is required to submit signed/

sealed statement to building department and State offices 

stating the structure has been designed as a shelter (EHPA plus 

added recommended criteria). 

Method is basis of most wind pressure 

calculation methods. All items in design 

process are site-specific. Unlike ASCE 

7-05, ASCE 7-10 does not use importance 

factor in wind calculation. 

Uses the same reference as ASCE 7-05 for 

debris impact criteria (ASTM E 1996), with 

wind zones modified to account for higher 

basic wind speeds (see C26.10 of ASCE 7-10 

for more information).

The 2009 model I-codes reference ASCE 7-05. However, ASCE 

7-10 will be referenced in the 2012 IBC. The 2010 Florida 

Building Code references ASCE 7-10. 

Method is basis of most wind pressure 

calculation methods. All items in design 

process are site-specific. Use I=1.15 for 

critical and essential facilities.

In wind-borne debris region (120 mph+): 

Small – pea gravel; Large – 9 lb 2x4 at 34 

mph (horizontal) and areas > 130 mph: 9 

lb 2x4 at 55 mph (horizontal), up to 60 feet 

above grade. Note: 2006 IBC requires the 

9-lb 2x4 (large) missile to be tested at 55 

mph for critical and essential facilities 

Code requires increased design parameters only for buildings 

designated as critical or essential facilities. 

Based on regional hazards, 

recommendations are provided to improve 

and strengthen the load path and the 

performance of the building exterior.

Window and glazing protection is 

recommended for most hurricane-prone 

areas, not just areas with a basic wind speed 

of 120 mph and greater.

This program provides design and construction guidance to 

improve building performance for high-wind events. Compliance 

will likely improve building performance but does not imply that 

the building is safe or that it is appropriate to use as a shelter. 

Use basic wind speed at site as identified 

on FBC wind speed map, use exposure at 

site, use Category III (Essential Buildings), 

use wind loads in accordance with ASCE 7. 

Use the missile impact criteria for the building 

enclosure, including walls, roofs, glazed 

openings, louvers, and doors, per SBC/SSTD 

12. 

The building or a portion of a building is defined as an essential 

facility and as an EHPA. Designer is required to submit signed/

sealed statement to building department and State offices 

stating the structure has been designed as an EHPA. 

Typically these older codes provided a 

hurricane regional factor for design wind 

speeds, but little attention was paid to 

components and cladding 

Not required for all buildings. Where required, 

the Standard Building Code7 developed and 

recommended debris impact standards for 

use in hurricane-prone regions.

These codes specified limited hazard-resistant requirements. 

Some guidance was provided with SSTD 10 from SBCCI for the 

design and construction of buildings in high-wind and hurricaneprone regions. Buildings constructed to these early codes were 

not required to have structural systems capable of resisting wind 

loads. 

None None Provides guidance on how to select buildings and areas of a 

building for use as a high-wind shelter or refuge area. Does 

not provide or require a technical assessment of the proposed 

shelter facility. 

None None Best available refuge areas should be identified in all buildings 

without shelters. FEMA 431, Tornado Protection: Selecting 

Refuge Areas in Buildings, provides guidance to help identify the 

best available refuge areas in existing buildings. Because best 

available refuge areas are not specifically designed as shelters, 

their occupants may be injured or killed during a tornado or 

hurricane. 

NOTES (continued): 

4. ASCE 7-05 Building Design Loads for Buildings and Other Structures (2005) is the load determination standard referenced by the model building codes. 

The wind design procedures used for any shelter type in this table use one of the wind design methods as specified in ASCE 7-05, but with changes to 

certain design coefficients that are identified by the different codes, standards, or guidance summarized in this table. 

5. From ASCE 7 method: I = importance factor; Kd = wind directionality factor; GCpi = internal pressure coefficient 

6. Roof deck, walls, doors, openings, and opening protection systems must all be tested to show resistance to the design missile for the FEMA, ICC, and 

FL EHPA criteria

7. From the Southern Building Code Congress International, Inc. (SBCCI)
Safe Rooms: Selecting Design Criteria HSFEHQ-11-J-0004, 0005 / June 2011 Page 6 of 8

Guidance, Code, or Standard Criteria 

for the Design Missile Debris Test Speed (mph)

Large Missile 

Specimen

Momentum at 

Impact (lbf s)

Tornado Missile Testing Requirements 

FEMA 320/FEMA 361 100 (maximum)

80 (minimum)

15# 2x4

15# 2x4

68

55

International Code Council (ICC) ICC-500 Storm Shelter 

Standard 

100 (maximum)

80 (minimum)

15# 2x4

15# 2x4

68

55

Hurricane Missile Testing Requirements 

FEMA 320/FEMA 361 128 (maximum)

80 (minimum)

9# 2x4

9# 2x4

53

33

ICC 500 Storm Shelter Standard 102 (maximum)

64 (minimum)

9# 2x4

9# 2x4

42

26

Florida State Emergency Shelter Program (SESP) Criteria 

and Emergency Operations Center (EOC) Design Criteria

50 (EOC recommended)

55 (EHPA recommended)

34 (EHPA minimum)

15# 2x4

9# 2x4

9# 2x4

34

23

14

IBC/IRC 2009, ASCE 7-10, Florida Building Code, ASTM E 

1886/E 1996 

55

34

9# 2x4 

9# 2x4

23

14

NOTES:

IBC/IRC – International Building Code/International Residential Code

lbf-s – Pounds (force) seconds

EHPA – Enhanced Hurricane Protection Area

Table 2. Wind-Borne Debris Criteria

Using Wind Shelter Design and Construction Codes: An Example 

Table 3 shows comparative data for two locations using the design criteria presented in Table 1. Where 

no guidance is provided for sheltering or basic construction, “N/A” (not applicable) is stated. Where the 

requirement is not required, “Not required” is stated.

Selecting Refuge Areas in Buildings

Building owners should be aware of any existing public shelters near their building. For instance, new schools 

in many States are required to include an ICC-500-compliant storm shelter. If no sheltering options are 

located nearby, building owners should consider whether their building can be retrofitted for a shelter or safe 

room. While it is recommended that a safe room be installed, this may not solve the immediate problem of 

needing to identify the best available refuge areas in a building. 

During severe weather, building occupants should be moved to a location in the building that is protected 

from potential wind-borne debris and the least susceptible to collapse. While these areas do not provide 

near-absolute protection (unless designed as safe rooms), they may limit the number of occupants injured or 

killed. Appropriate refuge areas should be identified by architects, engineers, or design professionals familiar 

with FEMA 361 (2008) and FEMA P-431, Tornado Protection: Selecting Refuge Areas in Buildings (2009). These 

refuge areas are usually interior locations with short-span roof systems, reinforced masonry walls, and no 

glass openings. 

Post-disaster assessments following April 2011 Tornado Outbreak demonstrated that administrative 

officials or others involved in local planning efforts often identified refuge areas without the guidance of an 

experienced design professional. While it was clear that an effort was made to protect the occupants, many 

of these refuge areas were located in large spaces—such as gymnasiums or auditoriums—or in areas near 

exterior windows and doors. Additionally, many of the selected refuge areas were observed to be surrounded 

by wall systems subject to collapse in high-wind events. In some cases, the refuge areas had insufficient 

space for all of the building occupants, or were in locations which would be difficult to move the occupants 

to in a reasonable period of time. While there were no reports of fatalities in the refuge areas studied, it 

was likely because the areas were not occupied when the storms struck because many of refuge areas had 

collapsed or filled with broken glass from windows shattered by wind-borne debris.

Administrative officials interviewed in several communities after the April 2011 Tornado Outbreak indicated 

that they had been unable to obtain the expertise of a design professional in selecting the appropriate refuge 

area. The reason cited was liability concerns on the part of the design professional. To ease this concern, 
Safe Rooms: Selecting Design Criteria HSFEHQ-11-J-0004, 0005 / June 2011 Page 7 of 8

Shelter Design Standard, 

Code, or Document Data1

Example Location # 1: 

Miami, FL 

Example Location #2:

Joplin, MO 

FEMA 361 2

Design wind speed 200 mph (tornado)

225 mph (hurricane) 250 mph

Pressure on windward wall 107 psf3 (tornado)

135 psf (hurricane) 167 psf

Pressure on roof section 239 psf (tornado, suction)

303 psf (hurricane, suction) 374 psf (suction)

Test missile momentum at impact 61 lbf -s (tornado)

46 lbf -s (hurricane) 68 lbf -s

ICC-500

Design wind speed 200 mph (tornado) 

225 mph (hurricane) 250 mph

Pressure on windward wall 107 psf (tornado) 

135 psf (hurricane) 167 psf

Pressure on roof section 239 psf (tornado, suction) 

303 psf (hurricane, suction) 374 psf (suction)

Test missile momentum at impact 61 lbf -s (tornado) 

37 lbf -s (hurricane) 68 lbf -s

FBC EHPA/SESP (using + 

40 mph recommendation)

Design wind speed 186 mph N/A

Pressure on windward wall 106 psf N/A

Pressure on roof section 238 psf (suction) N/A

Test missile momentum at impact 34 lbf -s N/A

ASCE 7-10 

(ASTM E 1996)

Design wind speed 170 mph 115 mph

Pressure on windward wall 77 psf 35 psf

Pressure on roof section 173 psf (suction) 79 psf (suction)

Test missile momentum at impact 14 lbf -s Not required

ASCE 7-05/IBC 2009 

(ASTM E 1996) 4,5

Design wind speed 150 mph 90 mph

Pressure on windward wall 69 psf 25 psf

Pressure on roof section 155 psf (suction) 56 psf (suction)

Test missile momentum at impact 14 lbf -s Not required

IBHS

Design wind speed 150 mph 90 mph

Pressure on windward wall 69 psf 25 psf

Pressure on roof section 155 psf (suction) 56 psf (suction)

Test missile momentum at impact 14 lbf -s Not required

FBC EHPA

Design wind speed 146 mph N/A

Pressure on windward wall 66 psf N/A

Pressure on roof section 147 psf (suction) N/A

Test missile momentum at impact 23 lbf -s N/A

Pre-2000 Building Codes

Design wind speed 140 mph and less 90 mph and less

Pressure on windward wall < 40 psf (varies) < 15 psf (varies)

Pressure on roof section < 120 psf (varies) < 45 psf (varies)

Test missile momentum at impact Not required by all codes Not required

ARC 4496

Design wind speed N/A N/A

Pressure on windward wall N/A N/A

Pressure on roof section N/A N/A

Test missile momentum at impact N/A N/A 

Areas of Last Resort

Design wind speed Unknown Unknown

Pressure on windward wall Unknown Unknown

Pressure on roof section Unknown Unknown

Test missile momentum at impact Not required Not required

NOTES: 

1. Wind pressures were calculated based on a 40-foot x 40-foot square building, with a 10-foot eave height and a 10-degree roof pitch, partially enclosed

2. For a combined tornado/hurricane safe room, the more restrictive criteria apply. FEMA 320 criteria are based on a 250-mph wind speed regardless 

of location

3. psf – Pounds per square foot; lbf -s – Pounds (force) seconds

4. Non-storm shelter wind design criteria

5. IBC/IRC 2000, 2003, and 2006 editions and ASCE 7-98 have similar wind design criteria

Table 3. Design Criteria Comparison
Safe Rooms: Selecting Design Criteria HSFEHQ-11-J-0004, 0005 / June 2011 Page 8 of 8

engineers are encouraged to add the following information and qualifiers to their contract and their findings 

report: 

" The identified area should be considered by building owners as only a “best available area of refuge” and 

occupants could still be injured or killed

" The findings should include: 

" The level of testing completed during the identification of the area 

" The total number of occupants the area can hold

" The approximate maximum safe wind speed for the best available refuge area

" The timeframe before which the area should be re-evaluated

" An outline of potential modifications that could be made to the structure to improve its performance in 

high-wind events

" State that changes to the building may make the refuge area no longer the best available refuge area 

Agreement between the client and the design professional on these points may ease some of the liability 

concerns. Administrators and facilities managers for buildings with large occupancies should also review 

FEMA P-431 (2009) and the refuge area evaluation checklists presented in Appendix B of FEMA 361.

Operating a Safe Room 

In addition to the safe room’s structural performance requirements, the following operational, maintenance, 

and human factors criteria must be considered for a successful safe room:

" Standby power (e.g., generator) 

" Protection of critical support systems such as a generator

" Occupancy duration

" Ventilation

" Minimum square footage per occupant

" Egress

" Distance and travel time for occupants traveling to the safe room

" Access for disabled occupants

" Special needs requirements

" Lighting

" Emergency provisions (food, water, sanitation management, emergency supplies, communication equipment)

" Operations and maintenance plans for the safe room

Each of these items is further elaborated in FEMA 361 and ICC-500. Not all items must be considered for a 

residential safe room, but they are especially important when designing a community safe room. 

Useful Links and Shelter Resources 

Taking Shelter from the Storm: Building a Safe Room For Your Home or Small Business (FEMA 320), August 

2008, 3rd Edition http://www.fema.gov/library/viewRecord.do?id=1536

Design and Construction Guidance for Community Safe Rooms (FEMA 361), August 2008 2nd Edition 

http://www.fema.gov/library/viewRecord.do?id=1657

Tornado Protection: Selecting Refuge Areas in Buildings (FEMA P-431), October 2009 2nd Edition http://www.

fema.gov/library/viewRecord.do?id=1563

ICC/NSSA Standard for the Design and Construction of Storm Shelters, International Code Council and the 

National Storm Shelter Association (ICC-500), June 2008 http://www.iccsafe.org/Store/Pages/Product.

aspx?id=8850P08_PD-X-SS-P-2008-000001#longdesc

National Storm Shelter Association (NSSA); http://www.NSSA.cc
Residential Sheltering: In-Residence and Stand-Alone Safe Rooms HSFEHQ-11-J-0004, 0005 / June 2011 Page 1 of 6

Residential Sheltering: 

In-Residence and 

Stand-Alone Safe Rooms

Purpose and Intended Audience 

The purpose of this advisory is to inform homeowners, renters, apartment building owners, and manufactured 

home park owners about in-residence and stand-alone safe rooms. 

This Recovery Advisory Addresses: 

" Consider a safe room for your home 

" In-residence safe room construction and retrofitting options 

" Recommendations for sheltering options for when you cannot place a safe room within your home 

" Safe room doors

" Refuge areas 

" Emergency supply kits and weather radios

" Registering your safe room with local officials 

Consider a Safe Room for Your Home

The purpose of having a safe room in or near your home is to protect you and your family from injury or death 

from extreme winds. Safe rooms are intended to allow occupants to survive tornadoes and hurricanes with 

little or no injury. To determine your exposure to tornadoes, refer to FEMA 320, Taking Shelter from the Storm: 

Building a Safe Room For Your Home or Small Business (2008). This publication can help you decide whether 

to construct a safe room to protect you and your family from injury or death during a tornado or hurricane. 

Additional information is provided in the Tornado 

Recovery Advisory (RA) No. 1 titled “Tornado Risks 

and Hazards in the Southeastern United States” 

(updated in 2011). 

After determining that you live in a tornado- or 

hurricane-prone region, it is important to understand 

the risks. Most homes, even new ones constructed 

according to current building codes, do not provide 

adequate protection for occupants seeking refuge 

from tornadoes. A tornado or hurricane can cause 

much greater wind and wind-borne debris loads 

on your house than those on which building code 

requirements are based. Only specially designed and 

constructed safe rooms, which are voluntarily built 

above the minimum code requirements, offer nearabsolute protection during a tornado or hurricane. 

In-Residence Safe Room Construction and Retrofitting Options

Constructing a safe room within your home puts it as close as possible to your family. While a safe room on 

the exterior of your home may provide adequate protection, it does require your family to be exposed to the 

TORNADO RECOVERY ADVISORY RA3, June 2011

Safe rooms should not be constructed where 

flood waters have the potential to endanger 

occupants within the safe room. Safe rooms 

in areas where flooding may occur during 

hurricanes should not be occupied during a 

hurricane. However, occupying such a safe room 

during a tornado may be acceptable if the safe 

room will not be flooded by rains associated 

with other storm and tornado events. Consult 

your local building official or local National Flood 

Insurance Program representative to determine 

whether your home, or a proposed stand-alone 

safe room site, is susceptible to local, riverine, 

or coastal flooding.
Residential Sheltering: In-Residence and Stand-Alone Safe Rooms HSFEHQ-11-J-0004, 0005 / June 2011 Page 2 of 6

weather elements while traveling 

to the safe room. A safe room 

may be either installed during 

the initial construction of a home 

or retrofitted afterward. As long 

as the design and construction 

requirements and guidance 

are followed, the same level of 

protection is provided by either 

type of safe room. 

New Construction

FEMA 320 contains detailed 

drawings and specifications 

that can be used by a builder 

or contractor to construct a 

safe room in your home. The 

designs provided are for safe 

rooms constructed of wood, 

masonry, or concrete. All of 

them are designed to resist 

250 mph (3-second gust) wind 

speeds and impacts from windborne debris. Pre-fabricated 

safe rooms are also available for 

installation when first building 

your home. The basic cost to 

design and construct a safe room 

during the construction of a new 

house is approximately $6,000; 

larger, more refined, and more 

comfortable designs may cost 

more than $15,000. 

It is relatively easy and cost 

effective to add a safe room 

when first building your home. 

For example, when the home is 

constructed with exterior walls 

made from concrete masonry 

units (CMU, also commonly 

known as “concrete block,” 

see sketch this page ), the 

protection level in FEMA 320 can 

be achieved by strengthening 

the safe room area’s exterior 

walls with additional steel 

reinforcement and grout. The 

safe room is easily completed by 

adding interior walls constructed 

of reinforced CMU, a concrete 

roof deck over the safe room, 

and a special safe room door, as 

shown under construction in the 

bottom photograph.

CMU was used for the exterior walls at this house under construction (New Smyrna 

Beach, FL).

Sketch of floor plan showing location of safe room area in house.

View of an in-residence safe room under construction. Steel reinforced and fully 

grouted CMU surround the safe room space (New Smyrna Beach, FL).
Residential Sheltering: In-Residence and Stand-Alone Safe Rooms HSFEHQ-11-J-0004, 0005 / June 2011 Page 3 of 6

Retrofitting Existing Houses

FEMA 320 contains general guidance for retrofitting a house by adding 

a safe room. Building a safe room in an existing house will typically 

cost 20 percent more than building the same safe room in a new house 

while under construction. Because the safe room will be used for life 

safety, and because your home might be exposed to wind loads and 

debris impacts it was not designed to resist, an architect or engineer 

should be employed to address special structural requirements, even if 

inclusion of an architect or engineer in such a project is not required by 

the local building department. 

Recommendations for Sheltering When You Cannot Place 

a Safe Room Within Your Home

There are many reasons that homeowners or renters may not be able 

to install a safe room within their home. These could include lack of 

permission (the resident does not own the home or does not have 

rights to modify or change the home), lack of available space, or lack of 

technical or economic practicality. In those cases, a stand-alone safe 

room can be designed and constructed outside of a residence. Standalone safe rooms can provide the same level of protection against high 

winds and wind-borne debris as in-residence safe rooms. 

Small Stand-Alone Safe Rooms

Some site-built homes, and most manufactured homes, do not lend themselves to the structural 

modifications and retrofitting required to install or construct an in-residence safe room. In these instances, a 

stand-alone safe room may be constructed (either above grade, partially above grade or below grade) near the 

residence. Small stand-alone safe rooms can be constructed to accommodate the occupants of one house, 

a few houses, or a small apartment building. The photograph from Tuscaloosa, AL, shows how a stand-alone 

safe room provides refuge for the residents. 

Community Safe Rooms

A community safe room can be 

constructed to accommodate 

the occupants of several 

apartments or homes (sitebuilt or manufactured homes). 

The small safe room designs in 

FEMA 320 were revised in 2008 

and expanded for applications 

of up to 16 individuals and are 

suitable for use by business, 

public facilities, and others when 

a small, community safe room is 

desired. The design criteria for 

these prescriptive designs are 

presented in FEMA 361, Design 

and Construction Guidance for 

Community Safe Rooms (2008). 

For additional information about 

community safe rooms, refer to 

the Tornado Recovery Advisory No. 

2 titled “Safe Rooms: Selecting 

Design Criteria” (updated in 

2011). Many different types of 

safe rooms can be designed and 

View of a pre-fabricated safe room that serves a residence (Tuscaloosa, AL).

The design drawings provided 

in FEMA 320 are also 

appropriate for use in small 

businesses, fire and police 

stations, and other public 

areas where small groups 

of people may be seeking 

life-safety protection from 

extreme winds and wind-borne 

debris.

For more information about 

pre-fabricated and standalone safe rooms and storm 

shelters, contact the National 

Storm Shelter Association 

(http://www.nssa.cc)
Residential Sheltering: In-Residence and Stand-Alone Safe Rooms HSFEHQ-11-J-0004, 0005 / June 2011 Page 4 of 6

constructed to meet the needs of 

small or large groups of residents. 

A safe room may be constructed 

to be used solely as a shelter or 

it may be designed as a multi-use 

building, such as a clubhouse, 

school, or recreation center. A safe 

room may also be constructed 

above-grade, below-grade, or 

partially below-grade as shown in 

the photograph from Brookwood, 

AL. Selecting the right type of safe 

room will be a collective decision 

made by the residents, funding 

agencies, and property owners 

and managers. For information on 

community safe rooms for larger 

populations, including planning 

and operational issues, see 

FEMA 361. 

Safe Room Doors

When building a safe room, it is very important to pay 

extra attention to the safe room door. Door construction 

has been found to be a common weakness in safe rooms’ 

ability to withstand high wind pressures and missile 

impacts. Door failures are typically due to the type of 

door construction and door hardware. Standard door 

construction that meets minimum code requirements is 

not sufficient to withstand the extreme wind forces and 

the wind-borne debris impacts often seen in extreme 

wind events. It is imperative that the walls, ceilings, and 

doors of a safe room be able to withstand the impacts of 

missiles carried by extreme winds. 

Safe room doors are tested by laboratories for their 

ability to withstand the pressures associated with highwind events and missile impacts. To meet the criteria set 

forth in FEMA 320 for residential and small community 

safe rooms, doors must resist wind pressures and windborne debris impacts in tests set forth in the International 

Construction Code/National Storm Shelter Association 

(ICC/NSSA) Standard for the Design and Construction 

of Storm Shelters (ICC-500), for a 250 mph safe room 

design wind speed and impacts from a 15-pound 2x4 

sawn lumber member traveling horizontally at 100 mph 

(additional design restrictions apply). 

Research by the NSSA has shown that steel doors with 

14-gauge (or heavier) skins are able to withstand the 

standard missile impact test. Such doors in widths up 

to 3 feet, typical of what is found in a residential safe 

room, are capable of withstanding wind loads associated 

with wind speeds up to 250 mph when they are latched 

with three hinges and three deadbolts. At the time of 

this publication, there has not been a wood door that 

has successfully passed the pressure or missile impact 

View of a partially below-grade community safe room (Brookwood, AL). 

Photograph of safe room door with three deadbolts and 

three hinges.
Residential Sheltering: In-Residence and Stand-Alone Safe Rooms HSFEHQ-11-J-0004, 0005 / June 2011 Page 5 of 6

tests using the design criteria for 

250 mph winds. Testing has been 

performed on various sized doors, 

and guidance on choosing an 

appropriate safe room door can be 

found in Appendix F of FEMA 361 

(2008).

Refuge Areas

Occupants of dwellings that 

do not have in-residence safe 

rooms or access to stand-alone 

or community safe rooms should 

identify the best available refuge 

area in their home before an 

emergency happens. When people 

identify and take refuge in the best 

available space within a building, 

they are less likely to be injured 

or killed. However, it is important 

to remember that “best available 

refuge areas” are not specifically 

designed as safe rooms, so 

occupants can be injured or killed 

during a tornado or hurricane 

event if the high winds breach the 

building. 

The lowest floor of a building is 

usually the safest. Upper floors 

receive the full strength of the 

winds. Occasionally, tornado 

funnels hover near the ground but 

hit only upper floors. Belowground 

space is almost always the 

safest location for a refuge area. 

The following criteria should be 

considered when identifying the 

best available refuge area in your 

home: 

" Choose a location that is large 

enough for all the residents of 

the home. It is recommended 

that each person be provided 

with a minimum of 5 square feet of space in the refuge area. Additional space will need to be accounted 

for if the residents of the home are wheelchair users or bedridden. Guidance is provided in FEMA P-431, 

Tornado Protection: Selecting Refuge Areas in Buildings (2009).

" Avoid locations with high ceilings. These spaces often have long-span roofs that can collapse under the 

forces imposed by tornado winds.

" Choose the lowest floor of the residence. A basement is preferable, or first floor if there is no basement). 

" Avoid taking refuge in basements with exterior doors or large windows (i.e., walk-out basement). If no other 

viable option exists, take shelter in a basement area that is away from windows and exterior doors. 

" Choose a small interior room without windows (i.e., none of the room’s walls is an exterior wall), such as a 

bathroom or closet, preferably with only one door. 

Avoid selecting a refuge area that is near a masonry chimney (Moore, OK). 

View of remnants of an interior room of a house that survived a strong tornado 

(Tuscaloosa, AL).
Residential Sheltering: In-Residence and Stand-Alone Safe Rooms HSFEHQ-11-J-0004, 0005 / June 2011 Page 6 of 6

" Choose a room located away from masonry chimneys, trees, or power poles. 

" Keep the room relatively free of clutter so you and the other residents can enter and remain in the room for up 

to several hours. 

Homeowners and renters should also refer to the Tornado Recovery Advisory No. 2 titled “Safe Rooms: 

Selecting Design Criteria” (updated in 2011).

Emergency Supply Kits and Weather Radios 

FEMA 320 includes information on preparing a family emergency plan and an emergency supply kit for a 

shelter. Further, all individuals living or working in tornado-prone areas should have a battery-powered weather 

radio in their home or place of work. For more information about weather radios, see Tornado Recovery 

Advisory No. 1 titled “Tornado Risks and Hazards in the Southeastern United States” (updated 2011). 

Registering Your Safe Room with Local Officials

FEMA recommends that the local fire department, local emergency management agency (EMA), and other 

relevant local officials be given the location of the safe room. Providing the latitude and longitude coordinates 

of the entrance to the safe room to local officials can be vital in post-disaster recovery efforts. In the event 

that debris is surrounding or on top of the safe room, this will allow them to check on the safe room to make 

sure the occupants are not trapped inside. 

Useful Links and Resources

Taking Shelter from the Storm: Building a Safe Room For Your Home or Small Business (FEMA 320), 

August 2008, 3rd Edition http://www.fema.gov/library/viewRecord.do?id=1536

Design and Construction Guidance for Community Safe Rooms (FEMA 361), August 2008, 2nd Edition 

http://www.fema.gov/library/viewRecord.do?id=1657

Tornado Protection: Selecting Refuge Areas in Buildings (FEMA P-431), FEMA, October 2009, 2nd Edition 

http://www.fema.gov/library/viewRecord.do?id=1563

National Storm Shelter Association (NSSA); http://www.NSSA.cc
Safe Rooms and Refuge Areas in the Home HSFEHQ-11-J-0004, 0005 / June 2011 Page 1 of 2

Purpose and Intended Audience 

The intended audience for this Tornado Recovery 

Advisory is homeowners or home builders. 

Homeowners and renters should also refer to the 

Tornado Recovery Advisory No. 3 titled “Residential 

Sheltering: In-Residence and Stand-Alone Safe 

Rooms” (updated in 2011). The purpose of this 

advisory is to identify the different types of safe 

rooms and provide a brief overview of areas of 

refuge. 

This Recovery Advisory Addresses: 

" How safe room construction is different from 

typical home construction 

" Which guidance should be followed 

" What constitutes a safe room 

" Refuge areas in the home 

How Safe Room Construction is Different from Typical Home Construction 

A residential safe room is a space, either within a home or an entirely separate structure, designed and 

constructed to protect its occupants from tornadoes or hurricanes. The safe room may be located above 

or below ground. Safe rooms are intended to provide protection against both wind forces and the impact 

of wind-borne debris. Near-absolute life-safety protection is the level of occupant protection provided by a 

space specifically designed as a safe room and 

constructed to meet criteria set forth by FEMA; 

this is much greater than the protection provided 

by buildings that comply with the minimum 

requirements of building codes. Although the FEMA 

guidance on safe rooms has been available since 

1998, building codes did not begin to provide 

design and construction criteria for life-safety 

protection from wind events until 2009. When 

constructed to meet the criteria set forth in the building codes, hardened areas are called storm shelters. 

Design criteria for storm shelters are similar to criteria for safe rooms, but differences do exist. Information 

about safe room criteria and storm shelter criteria can be found in other guidance documents referenced 

in this recovery advisory. A slightly higher level of protection is provided when safe rooms are constructed 

to meet the FEMA criteria, and owners may be eligible for FEMA grant programs to fund the design and 

construction of the safe room.

Safe rooms typically fall into two categories: residential safe rooms and community (non-residential) safe 

rooms. 

A safe room is a room or structure specifically 

designed and constructed to resist wind pressures 

and wind-borne debris impacts during an extremewind event for the purpose of providing life-safety 

protection.

TORNADO RECOVERY ADVISORY RA4, June 2011

Safe Rooms and Refuge 

Areas in the Home

An example of an above-ground, in-residence safe room that 

successfully protected two people (Joplin, MO).
Safe Rooms and Refuge Areas in the Home HSFEHQ-11-J-0004, 0005 / June 2011 Page 2 of 2

" Residential Safe Rooms: There are two general 

types of residential safe rooms: in-residence safe 

rooms and stand-alone safe rooms (located adjacent 

to, or near, a residence). An in-residence safe room is 

a small, specially designed (“hardened”) room, such 

as a bathroom or closet that is intended to provide 

a protected area for the people who live in the 

house. A stand-alone safe room is similar in function 

and design, but it is a separate structure installed 

outside the house, either above or below the ground 

surface. FEMA guidance is available in FEMA 320, 

Taking Shelter from the Storm: Building a Safe Room 

For Your Home or Small Business (2008).

" Community Safe Rooms: Some areas construct 

community safe rooms that provide protection for 

a large number of people—from 16 to as many as 

several hundred individuals. Criteria for designing 

and constructing a safe room can be found in 

FEMA 361, Design and Construction Guidance for 

Community Safe Rooms (2008). 

The following should be considered when 

identifying the best available refuge area in 

your home:

" Choose a location that is large enough for all the 

residents of the home to be seated. Account for 

additional space if the residents of the home are 

wheelchair users or bedridden.

" Choose the lowest floor of the residence. A 

basement is preferable, or first floor if there is 

no basement. Below-ground space is almost 

always the safest location for a refuge area.

" Choose a small interior room without windows 

(i.e., none of the room’s walls is an exterior 

wall), such as a bathroom or closet, preferably 

with only one door. 

" Choose a room located away from masonry 

chimneys, trees, or power poles. 

" Avoid locations with high ceilings. These spaces 

often have long-span roofs that can collapse 

under the forces imposed by tornado winds. 

" Avoid taking refuge in basements with exterior 

doors or large windows (i.e., walk-out basement). 

If no other viable option exists, choose an area 

that is away from windows and exterior doors. 

" Keep the room relatively free of clutter so you 

can remain in the space for up to several hours.

A small area located inside a detached garage used as a 

refuge area during a tornado (Athens, AL).

Selecting Refuge Areas in the Home

If there are no hardened areas within or 

near a home to use during high wind events, 

homeowners should consider whether their 

house can be retrofitted for a safe room. If 

this is not a viable option, homeowners should 

identify the best available refuge areas in their 

home. People in manufactured homes should 

seek shelter in a community safe room.

Useful Links and Safe Room 

Resources 

Taking Shelter from the Storm: Building a Safe 

Room For Your Home or Small Business (FEMA 

320), August 2008, 3rd Edition http://www.

fema.gov/library/viewRecord.do?id=1536

Design and Construction Guidance for 

Community Safe Rooms (FEMA 361), August 

2008, 2nd Edition 

http://www.fema.gov/library/viewRecord.

do?id=1657

ICC/NSSA Standard for the Design and 

Construction of Storm Shelters, International 

Code Council and the National Storm 

Shelter Association (ICC-500), June 2008 

http://www.iccsafe.org/Store/Pages/

Product.aspx?id=8850P08_PD-X-SS-P-2008-

000001#longdesc

Additional information from FEMA Building 

Science can be found at http://www.fema.gov/

rebuild/buildingscience and http://www.fema.

gov/plan/prevent/saferoom
Recommendations for Facility Owners HSFEHQ-11-J-0004, 0005 / July 2011 Page 1 of 5

Purpose and Intended Audience 

Critical facilities are emergency operations centers (EOCs), fire and police stations, hospitals, nursing homes, 

schools, and other buildings that are essential for the delivery of vital services or protection of a community. 

Tornado damage investigations and other research have shown us techniques for protecting occupants of 

critical facilities struck by tornadoes, as well as maintaining continuity of operations for those facilities. 

The 2011 tornadoes that struck the southeast United States specifically highlighted the importance of 

properly selecting the best available refuge area in existing facilities as well as the importance of minimizing 

collapse hazards, such as tree fall and other nearby objects. The purpose of this advisory is to inform critical 

facility owners of enhancements that can be made both to existing facilities and those still in the planning 

stage. With this awareness, facility owners can budget for desired enhancements and request that these 

enhancements be incorporated into the construction documents. 

This Recovery Advisory Addresses:

● Best available refuge areas 

● Tree fall and other collapse hazards 

● Safe rooms 

● Strengthening new facilities to minimize damage 

from tornadoes

● Enhancements to avoid interrupted operations 

Existing Buildings 

Critical facility owners should hire the services of 

a qualified architect or engineer to evaluate their 

existing building. The evaluation should determine 

whether the facility adequately protects occupants, 

operations, and the facility itself from tornadoes 

and other appropriate hazards. The evaluation 

should identify the best available refuge areas in 

the existing facility. Any needed enhancements can 

be incorporated into capital improvement planning 

and budgeting. Lack of adequate planning can 

result in loss of operation and possible loss of life 

when buildings are inadequately hardened or lack a 

best available refuge area for occupants (Figure 1). 

Best Available Refuge Areas

In regions of the United States subject to 

tornadoes, identifying the best available refuge 

areas within buildings is essential for the safety of 

building occupants. Safe rooms specifically designed 

TORNADO RECOVERY ADVISORY RA5, July 2011

Critical Facilities Located in Tornado-Prone Regions:

Recommendations for 

Facility Owners

Figure 1: An EOC in Tuscaloosa, AL, that saw a loss of operations 

but remained intact even though the story above it collapsed 

(Tornado 2011)

PHOTO COURTESY OF THE TUSCALOOSA COUNTY SHERIFF’S OFFICE.
Recommendations for Facility Owners HSFEHQ-11-J-0004, 0005 / July 2011 Page 2 of 5

and constructed to resist wind-induced forces and 

the impact of wind-borne debris provide the best 

protection. However, findings from investigations 

of past tornadoes show that many critical facilities 

contain rooms or areas that may afford some 

degree of protection from all but the most extreme 

tornadoes (i.e., an EF4 and EF5 tornado). The 

best available refuge areas should be identified 

in buildings that do not have areas designed and 

constructed to serve as safe rooms. Giving building 

occupants a best available refuge area in a building 

greatly reduces the risk of injury or death. Best 

available refuge areas do not guarantee safety; they 

are, however, the safest areas available for building 

occupants. 

Interior areas with short-span roof systems, such 

as corridors and small rooms (e.g., restrooms), are 

often the best available refuge areas. However, as 

shown in Figure 2, this is not always the case. It 

is therefore recommended that owners of critical 

facilities hire a qualified architect or structural 

engineer familiar with tornado risk analysis to 

assess existing buildings and identify the best 

available refuge areas. 

The architect’s or engineer’s systematic review 

of a building may reveal some problems (such as 

doors with glass vision panels) within the best 

available refuge area that can be economically 

mitigated to improve the refuge area. Areas that 

include such doors or other problems could still be 

considered the best available refuge areas despite 

the vulnerability of the glass. However, known 

problems should be addressed to the extent 

possible. Examples of corrective actions include 

replacing any doors that contain windows or 

replacing the existing glazing with impact-resistant 

glazing.

Collapse Hazards

Collapse hazards can include parts of the 

building, communication towers and equipment, 

chimneys, poles, and trees. Collapses can break 

windows and rupture roof coverings of critical 

facilities, damage components such as emergency 

generators and HVAC equipment needed for the 

operation of a critical facility, and cause structural 

damage to buildings (Figure 3). Collapse hazards 

must be addressed in design and sheltering 

decisions to avoid injuries or death and to ensure 

operational requirements of a critical facility are 

met. Potential collapse hazards can be evaluated 

using the checklists in Appendix B of FEMA 361, 

Design and Construction Guidance for Community 

Safe Rooms (2008) and the results can be used to 

evaluate the best available refuge areas. 

Guidance documents for identifying best available 

refuge areas are referenced in FEMA Recovery 

Advisory No. 6, Critical Facilities in Tornado-Prone 

Regions: Recommendations for Architects and 

Engineers.

Figure 2: Debris in an elementary school restroom in Tuscaloosa, 

AL (Tornado 2011)

Enhanced Fujita Scale

EF0 65–85 mph winds

EF1 86–110 mph

EF2 111–135 mph

EF3 136–165 mph

EF4 166–200 mph

EF5 >200 mph
Recommendations for Facility Owners HSFEHQ-11-J-0004, 0005 / July 2011 Page 3 of 5

Proper maintenance and placement of trees 

will minimize damage to critical facilities and 

surrounding buildings. Trees should be placed 

such that the distance between the critical facility 

and the tree is greater than the height the tree will 

reach when it is fully grown. Trees with wounds, 

decay, structural defects, known internal trunk 

voids, severed roots, and soil compaction are prime 

targets for storm damage. These defects are often 

a result of damage from a lawnmower or weed 

trimmer and can be avoided with proper, careful 

lawn maintenance. 

New trees should be planted at the correct depth. Trees planted too deep can develop stem girdling, where 

the tree roots encircle the stem and weaken it just below the ground, making it more likely to snap off at 

the stem-girdled point in the event of a forceful wind. In addition, mature trees should be pruned to correct 

defects, such as multiple leaders and weak branch attachments. Prune trees as soon as the defect is 

detected because younger trees will heal faster from the pruning.

New Buildings and Additions to Existing Buildings

During planning and budgeting for a new facility or making additions to existing facilities, a designer or space 

planner normally helps the facility owner develop a program for types of spaces, size of space, equipment 

needed, parking, and many other elements. For critical facilities in areas prone to tornadoes, owners should 

consider building safe rooms, strengthening their facility to minimize damage, and enhancing their facility to 

avoid interruption of operations (see also Recovery Advisory No. 6 for the associated design and construction 

guidance).

Safe Rooms

All new critical facilities should include one or more safe rooms (depending on facility size) to provide 

occupant protection. When adding on to an existing facility that does not have a safe room, facility owners 

should budget for a safe room within the addition (see Figure 4). If possible, the safe room should be sized to 

accommodate the number of occupants in the existing building and the addition. 

Safe rooms are typically dual-function rooms. During normal times, the safe room may function as a training 

room, restroom, hallway, or other such purpose. When tornadoes threaten, the specially designed and 

Figure 3: Collapse of a large communications 

tower onto a building in Joplin, MO 

(Tornado 2011)

Vulnerability assessment of existing facilities:

Most existing critical facilities are vulnerable to 

damage if struck by tornadoes. The damage may 

result in minor inconvenience or it may necessitate 

shutting down the facility. Facilities struck by an 

EF4 or EF5 tornado will normally not be operational 

unless the facility was designed to remain 

operational if struck. 

A vulnerability assessment can be conducted by 

a team of architects and engineers. Findings from 

such an assessment can lay the groundwork for 

planning and budgeting capital improvements or 

developing contingency plans that address facility 

disruption.
Recommendations for Facility Owners HSFEHQ-11-J-0004, 0005 / July 2011 Page 4 of 5

constructed safe room serves to 

protect the building occupants. 

The additional cost of making a 

room serve a dual function as 

a safe room varies. Excluding 

interior finishes and furnishings 

in the safe room area, a cost 

of $200 per square foot for 

budgeting is usually sufficient 

to cover design fees and 

construction.1

Safe rooms afford building 

occupants near absolute 

protection. However, facility 

operations that are housed 

outside of a safe room are 

normally susceptible to tornado 

damage and disruption. To 

minimize damage or to ensure 

continuity of operations, 

additional design and 

construction measures are 

needed as recommended below.

Strengthening New Facilities to Minimize Damage from Tornadoes

By using design strategies and building materials that are used in 

hurricane-prone regions2, facilities can be built to be more resistant 

to tornadoes. Therefore, facility owners should consider budgeting 

for strengthening new buildings or additions to minimize damage and 

disruption from nearby weak and strong tornadoes and from violent 

tornadoes that are on the periphery of the facility. With appropriate 

strengthening and selection of building materials and systems, the 

cost of tornado repairs and the potential for disruption of operations 

(see Figure 5) will likely be reduced. Even when constructing a facility 

using stronger systems, a safe room should be included in the facility to 

protect occupants during an EF4 or EF5 tornado that strikes the facility. 

Enhancement to Avoid Interrupted Operations 

Designing a facility to ensure it will remain operational if struck by a 

violent tornado is expensive. Therefore, when considering the costs and 

benefits of designing for continuity of operations, it may be more cost 

effective to design to minimize building damage and/or provide safe 

rooms. If, because of the additional 

expense, the owner determines 

that a critical facility does not need to be operational if struck by a 

violent tornado, then this reduced building performance should be clearly 

considered and addressed in emergency operations plans. Other critical 

facilities should be identified (that are not expected to be impacted by 

the same tornado) from which to continue critical operations. Appropriate 

planning, emergency plans, and agreements should be put in place. For 

facilities such as Emergency Operations Centers that are determined 

to be critical in providing effective emergency response, owners should 

budget facility enhancements to avoid interrupted operations even if 

struck by violent tornadoes.

1 Section 2.3 and Table 2-4 in FEMA 361 (2008), provides additional information on safe room costs.

2 For more information on constructing buildings hurricane-prone regions, refer to FEMA P-424, Design Guide for Improving School Safety in 

Earthquakes, Floods, and High Winds (2010); FEMA 543, Design Guide for Improving Critical Facility Safety from Flooding and High Winds (2007); and 

FEMA 577, Design Guide for Improving Hospital Safety in Earthquakes, Floods, and High Winds (2007).

Figure 4: The addition to this school was designed to serve as a safe room (Wichita, KS)

If Federal funding for the 

design and construction 

of a safe room is sought, 

the technical information in 

FEMA 361 (2008) must be 

adhered to as part of the 

funding requirements of the 

FEMA safe room policy. FEMA 

policy on the eligibility of 

the design and construction 

of safe rooms for Federal 

funding is provided in 

FEMA Mitigation Interim 

Policy MRR-2-09-1, Hazard 

Mitigation Assistance for Safe 

Rooms, dated April 30, 2009.

Specific design recommendations pertaining to continuity 

of operations are provided 

in FEMA Recovery Advisory 

No. 6, Critical Facilities in 

Tornado-Prone Regions: 

Recommendations for 

Architects and Engineers.
Recommendations for Facility Owners HSFEHQ-11-J-0004, 0005 / July 2011 Page 5 of 5

Useful Links and Resources

2007 Tornado Recovery Advisories. FEMA. 2007. http://www.fema.gov/library/viewRecord.do?id=2631

Hazard Mitigation Assistance for Safe Rooms FEMA. April 2009. Mitigation Interim Policy, MRR-2-09-1. 

http://www.fema.gov/library/viewRecord.do?id=3634

HMA Unified Guidance FY 10. FEMA. 2009. http://www.fema.gov/library/viewRecord.do?id=3649

HMA Unified Guidance FY 11. FEMA. 2010. http://www.fema.gov/library/viewRecord.do?id=4225

Recovery Advisory No. 6, Critical Facilities in Tornado-Prone Regions: Recommendations for Architects and 

Engineers. FEMA. 2011. 

Taking Shelter from the Storm: Building a Safe Room For Your Home or Small Business (FEMA 320). August 

2008, 3rd Edition. http://www.fema.gov/library/viewRecord.do?id=1536

Design and Construction Guidance for Community Safe Rooms (FEMA 361). August 2008, 2nd Edition. 

http://www.fema.gov/library/viewRecord.do?id=1657

Design Guide for Improving School Safety in Earthquakes, Floods, and High Winds (FEMA P-424). December 

2010, Second Edition. http://www.fema.gov/library/viewRecord.do?id=1986

Tornado Protection: Selecting Refuge Areas in Buildings (FEMA P-431). October 2009, Second Edition. 

http://www.fema.gov/library/viewRecord.do?id=1563

Design Guide for Improving Critical Facility Safety from Flooding and High Winds (FEMA 543). January 

2007. http://www.fema.gov/library/viewRecord.do?id=2441

Design Guide for Improving Hospital Safety in Earthquakes, Floods, and High Winds (FEMA 577). June 

2007. http://www.fema.gov/library/viewRecord.do?id=2739

ICC/NSSA Standard for the Design and Construction of Storm Shelters (ICC-500), June 2008. http://www.

iccsafe.org/Store/Pages/Product.aspx?id=8850P08_PD-X-SS-P-2008-000001 

Figure 5: Most of the exterior glass in this Joplin, MO, hospital was 

broken (Tornado 2011)

Vulnerability assessment of new 

facilities: As part of the planning 

process for new facilities, other 

natural hazards (flood, seismic, 

and wildfire) should be considered 

in addition to the tornado hazard. 

FEMA P-424 (2010), 543 (2007), 

and 577 (2007) provide guidance on 

conducting vulnerability assessments. 

If the building design does not ensure 

continuity of operations, contingency 

plans should be developed that 

address facility disruption. 

Specific design recommendations for minimizing 

building damage are provided in FEMA Recovery 

Advisory No. 6, Critical Facilities in Tornado-Prone 

Regions: Recommendations for Architects and 

Engineers.

Multi-hazard Design

This Recovery Advisory addresses the tornado hazard. However, critical facilities may be damaged—

and continuity of operations may be impaired—by 

other natural hazards such as flooding, seismic 

events, and wildfire. When performing vulnerability 

assessments and design work on critical facilities, all natural hazards that can affect the facility 

should be considered and accounted for. 

Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 1 of 10

Purpose and Intended Audience 

Critical facilities are emergency operations centers 

(EOCs), fire and police stations, hospitals, nursing 

homes, schools, and other buildings that are essential for the delivery of vital services or protection of 

a community. Tornado damage investigations and 

other research have helped to identify techniques 

for protecting occupants of critical facilities struck by 

tornadoes, as well as maintaining continuity of operations for those facilities. The 2011 tornadoes that 

struck the southeast United States specifically highlighted the importance of properly selecting the best 

available refuge areas in existing facilities as well as 

the importance of minimizing collapse hazards, such 

as tall trees and other nearby objects. 

The purpose of this advisory is to inform architects 

and engineers of design enhancements that can 

be made to both existing facilities and facilities in 

the planning stage. With this awareness, desired 

enhancements can be incorporated into construction 

documents.

The interim information in this Recovery Advisory is 

intended to assist during the recovery and redevelopment of tornado-damaged areas and to minimize 

future tornado damage and interruption of operations. This information was developed because of 

the lack of design guidance on this topic. 

This Recovery Advisory Addresses: 

● Existing Buildings 

● Best available refuge areas 

● Tree fall and other collapse hazards 

● New Buildings and Additions to Existing Buildings 

● Safe rooms 

● Strengthening new facilities to minimize 

damage from tornadoes 

● Enhancements to avoid interrupted operations 

TORNADO RECOVERY ADVISORY RA6, August 2011

Critical Facilities Located in 

Tornado-Prone Regions: 

Recommendations for 

Architects and Engineers 

Standard of Care

Critical facilities have facility and operational 

requirements that should be met in addition to 

building code requirements. Building codes do 

not stipulate expected building performance for 

tornadoes. The designer should discuss expectations for acceptable building damage, operational 

requirements, and occupant safety with the facility 

owner to ensure the full range of solutions for any 

special requirements is considered.
Vulnerability Assessment of Existing Facilities

Most existing critical facilities are vulnerable to 

damage if struck by tornadoes. The damage may 

result in minor inconvenience or it may necessitate shutting down the facility. Facilities struck by 

a violent (EF4 and EF5) tornado will normally not 

be operational unless the facility was designed to 

remain operational if struck. 

A vulnerability assessment can be conducted by 

a team of architects and engineers. Findings from 

such an assessment can lay the groundwork for 

planning and budgeting capital improvements or 

developing contingency plans that address facility 

disruption.

Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 2 of 10

FEMA’s MRR-2-09-1, Hazard Mitigation Assistance for Safe Rooms, dated April 30, 2009, sets forth eligibility 

requirements for Pre-Disaster Mitigation Program and Hazard Mitigation Grant Program safe room projects and 

requires adherence to FEMA 361. Also refer to the appropriate State Hazard Mitigation Officer for additional 

information (http://www.fema.gov/about/contact/shmo.shtm).

Existing Buildings 

Although safe rooms specifically designed and 

constructed to resist wind-induced forces and the 

impact of wind-borne debris provide the best protection, buildings can have rooms or areas that afford 

some degree of protection from all but the most extreme tornadoes (i.e., an EF4 or EF5 tornado on the 

Enhanced Fujita scale). In buildings that do not have 

areas designed and constructed to serve as safe 

rooms, the goal of the architect or engineer should 

be to select the best available refuge areas. Giving building occupants a best available refuge area 

in a building greatly reduces the risk of injury or 

death. Best available refuge areas do not guarantee

safety; they are, however, the safest areas available 

for building occupants. Interior areas with shortspan roof systems, such as corridors and small 

rooms (e.g., restrooms), are often best available 

refuge areas. However, as shown in Figures 1 and 

2, this is not always the case. It is therefore recommended that qualified architects or engineers 

familiar with tornado risk analysis follow the guidance in FEMA P-431, Tornado Protection: Selecting 

Refuge Areas in Buildings (2009), and the checklists in Appendix B of FEMA 361, to identify best 

available refuge areas. It is recommended that the 

best available refuge area(s) have a permanent 

sign installed that states “Tornado Refuge Area.”

An architect’s or engineer’s systematic review of 

a building may reveal some problems (such as 

doors with glass vision panels as shown in Figure 

3) within the best available refuge area that can be 

economically mitigated to improve the refuge area. 

Terminology: Safe Rooms and Shelters

“Safe rooms” are defined as buildings or portions thereof that comply with FEMA 361, Design and Construction Guidance for Community Safe Rooms (2008). 

“Shelters” are defined as buildings or portions thereof that comply with International Code Council (ICC), 

ICC 500, ICC/NSSA Standard on the Design and Construction of Storm Shelters (2008). 

FEMA 361 and the ICC 500 criteria are quite similar. All safe room criteria in FEMA 361 meet the shelter requirements of the ICC 500. However, a few design and performance criteria in FEMA 361 are more 

restrictive than those in the ICC 500. 

A summary of the primary differences between FEMA 361 and ICC 500 is presented in Recovery Advisory 

No. 2, Safe Rooms: Selecting Design Criteria (June 2011). The 2009 edition of the International Building 

Code (IBC) references ICC 500 for the design and construction of hurricane and tornado shelters. However, although ICC 500 specifies shelter criteria, it does not require shelters. 

Figure 1: Debris in a school corridor in Joplin, MO (2011 Tornado) 
Collapse Hazards

Position poles, towers, and trees with trunks 

larger than 6 inches in diameter away from new 

buildings, additions to existing buildings, and 

primary site access roads so that they do not 

hit or block access to the facility if they topple.

Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 3 of 10

Areas that include such doors or other problems could still be considered the best available refuge areas despite the vulnerability of the glass. However, known problems should be addressed to the extent possible. An 

example of a corrective action would be to replace doors that have vision panels with new door/vision panel 

assemblies that resist the test Missile E load specified in ASTM E 1996, when tested in accordance with 

ASTM E 1886. For more information on the test Missile E, see Section 6.3.3.3 of FEMA P-424, Design Guide 

for Improving School Safety in Earthquakes, Floods, and High Winds (2010). 

When evaluating critical facilities to determine the best 

available refuge areas, architects and engineers should 

identify potential collapse hazards using the checklists in Appendix B of FEMA 361. Collapse hazards can 

include parts of the building, communication towers 

and equipment, chimneys, poles, and trees that can 

damage buildings with light-frame construction, break 

windows, and rupture roof coverings (Figures 4 and 5). 

Refer also to Recovery Advisory No. 5, Critical Facilities 

in Tornado-Prone Regions: Recommendations for Facility 

Owners (2011). 

Figure 2: Collapsed concrete masonry unit (CMU) walls at a 

Joplin, MO, school restroom (2011 Tornado) 

Figure 3: Broken vision panel at an elementary school corridor in 

Tuscaloosa, AL (2011 Tornado) 

Figure 4: Collapse of a large communications tower onto a 

building in Joplin, MO (2011 Tornado) 

Figure 5: Tree-fall damage at a critical facility in Tuscaloosa, 

AL (2011 Tornado) 
Flood Hazards

See FEMA 361 Sections 3.2.1, 3.6, and 4.4.3 for 

information regarding flood hazards.

FEMA Design Guides

Wind design recommendations for critical facilities 

located both inside and outside of hurricane- and 

tornado-prone regions can be found in the following FEMA publications: 

● FEMA P-424, Design Guide for Improving School 

Safety in Earthquakes, Floods, and High Winds 

(2010)

● FEMA 543, Design Guide for Improving Critical 

Facility Safety from Flooding and High Winds

(2007) 

● FEMA 577, Design Guide for Improving Hospital 

Safety in Earthquakes, Floods, and High Winds 

(2007) 

Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 4 of 10

New Buildings and Additions to Existing Buildings

Architects and engineers designing new critical facilities or additions to existing facilities should consider 

including a safe room to protect occupants, making enhancements that will minimize building damage, and 

designing the facility to remain operational even if it is struck by a violent tornado.

Safe Rooms 

For all new critical facilities, the facility design should incorporate one or more safe rooms (depending on facility size) to provide occupant protection. When adding on to an existing facility that does not have a safe room, 

incorporate safe rooms within the addition. Size the safe room to accommodate the number of occupants in 

the existing building and the addition. Note that if temporary buildings will be used to accommodate increases 

in occupancy (for example, schools with portable classrooms), space should be designed in the safe room to 

account for these potential changes in safe room occupancy. 

FEMA 361 provides comprehensive guidance for the design of safe rooms, as well as for quality assurance 

and quality control for their design and construction. FEMA 320, Taking Shelter from the Storm: Building a Safe 

Room for Your Home or Small Business (2008), 

provides prescriptive solutions for safe rooms that 

will shelter 16 or fewer occupants. If a safe room is 

not incorporated, it is recommended that the architect or engineer identify the best available refuge 

area(s) and that a permanent sign be installed that 

states “Tornado Refuge Area.”

Minimizing Building Damage by Enhancing Building Resistance

By using design strategies and building materials 

that are used in hurricane-prone regions, critical 

facilities can be built to be more resistant to most 

tornadoes (i.e., EF0–EF3). FEMA’s design guide series (see textbox) provides recommendations for facilities located outside of hurricane-prone regions; 

these recommendations should be considered 

minimum baseline recommendations for all critical 

facilities. The design guides also provide abovebaseline recommendations for facilities located 

within hurricane- and tornado-prone regions. 

New buildings and building additions can be 

strengthened to minimize building damage and disruption from weak (EF0–EF1) and strong (EF2–EF3) 

tornadoes that pass directly over the facility, and 

from violent (EF4–EF5) tornadoes on the periphery 

of the facility. With appropriate strengthening and 

selection of building materials and systems, the 

cost of tornado repairs and the potential for disruption of operations will likely be reduced. When strengthening buildings, it is recommended that a safe room(s) 

also be included in the critical facility to protect occupants in case a violent tornado (i.e., EF4 or EF5) passes 

over or near the facility. 

Enhancement Levels 

FEMA recommends three enhancement levels. As the enhancement level increases, so does the level of 

protection from damage, disruption, and cost. Note that none of the enhancement levels ensure continuity of 

services such as electrical power or communications (see Continuity of Operations below). Table 1 provides a 

summary of the provisions to minimize building damage by enhancement level. 
Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 5 of 10

Level 1 Enhancements

Weak tornadoes (EF0 and EF1) have wind speeds 

that are below or somewhat above the 90-mph 

basic wind speed,1 which is the design wind speed 

throughout most of the continental United States. 

Hence, buildings that comply with the International 

Building Code should exhibit good structural, door, 

and wall performance when struck by weak tornadoes. However, weak tornadoes can generate 

wind-borne debris that can break unprotected glazing and puncture many types of door, wall, and roof 

assemblies, which can result in significant interior 

damage and disruption. When the Level 1 enhancement recommendations are followed, the potential 

for debris and water to enter the building, if struck 

by weak tornadoes, is low. 

Level 1 Enhancement Recommendations: In 

addition to the baseline recommendations in the 

FEMA P-424, 543, and 577 chapters that discuss 

high winds, design the roof deck, exterior doors, 

exterior glazing, and exterior walls to resist complete 

penetration by the test Missile E specified in ASTM 

E 1996. In addition, follow the roof system recommendations in P-424 (Section 6.3.3.7), 543 (Section 

3.4.3.4), or 577 (Section 4.3.3.8) for hurricane-prone 

regions to reduce the potential for wind-borne debrisinduced roof leakage. Figure 6 shows one of the 

recommended roof systems: sprayed polyurethane 

foam (SPF) over structural concrete. The strong 

tornado that struck this building did not debond the 

SPF from the concrete. Although wind-borne debris 

caused numerous gouges in the foam, the building 

did not leak because gouged SPF is not susceptible 

to leakage unless the foam is completely penetrated.

For fire stations, it is additionally recommended 

that apparatus bay doors and their connections to 

the structure be designed for a basic wind speed 

of 150 mph (plus an importance factor of 1.15).2

Brick veneer, aggregate roof surfacing, roof pavers, 

slate, and tile cannot be effectively anchored to 

prevent them from becoming missiles if a strong or 

violent tornado passes near a building with these 

components. To reduce the potential number of missiles, and hence reduce the potential for building damage and injury to people, it is recommended that these 

materials not be specified for critical facilities in tornado-prone regions.

Level 2 Enhancements

Strong tornadoes (EF2 and EF3) have wind speeds that are below or near the Level 2 enhancements design 

wind speed. Hence, when Level 2 recommendations are followed, buildings should not experience structural 

failure or door or wall collapse when struck by strong tornadoes. However, debris from an EF3 tornado may 

penetrate the building and result in extensive interior water and perhaps wind damage. 

1 The 90-mph basic wind speed is based on the 2005 edition of American Society of Civil Engineers ASCE 7, Minimum 

Design Loads for Buildings and Other Structures. If ASCE 7-10 is used, the equivalent basic wind speed for Risk Cat- egory III and IV buildings is 120 mph. 

2 The 150-mph basic wind speed is based on ASCE 7-05. If ASCE 7-10 is used, the equivalent basic wind speed for 

Risk Category III and IV buildings is 200 mph. (Note: The importance factor is built into the ASCE 7-10 maps; hence, 

the 1.15 importance factor is not used in the ASCE 7-10 pressure calculation equation.)

Brick Veneer

If brick veneer is selected, the veneer should not 

be depended on to resist debris because of the 

high potential for collapse of the veneer.

Figure 6: Although struck by a strong tornado, the SPF roof 

system of this Plainfield, IL, building did not blow off (1990 

Tornado)

Enhancement 

Levels Recommendations

Level 1

● Resist test Missile E

● Special roof system

● Avoid listed roof and wall coverings 

● Design fire station apparatus bay doors 

for a basic wind speed of 150 mph

Level 2 ● Level 1 enhancement recommendations

● Design for basic wind speed of 150 mph

Level 3 ● Level 2 enhancement recommendations

● Special roof deck and exterior walls

Table 1: Summary of Provisions to Minimize Building Damage by 

Enhancement Level
Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 6 of 10

Level 2 Enhancement Recommendations: The facility should be designed to incorporate Level 1 enhancements and to a basic wind speed of 150 mph (plus an importance factor of 1.15) for the main wind-force 

resisting system (MWFRS), the building envelope, and rooftop equipment. 

Note: The basic wind speed in south Florida is nearly 150 mph, and as a result, numerous products and systems are available that have been tested for pressures associated with this wind speed. 

Level 3 Enhancements

With incorporation of Level 3 enhancements, penetration of the roof deck or walls by EF3 debris is 

unlikely, but debris may penetrate doors or glazing. 

Designing with Level 3 enhancements also minimizes the potential for interior water and wind damage 

from strong tornadoes. However, significant interior 

damage could occur (though not within the safe 

room) if the core of a violent tornado (EF4 or EF5) 

passes over or near the building.

Level 3 Enhancement Recommendations: Facility 

design should incorporate Levels 1 and 2 enhancements as well as the following:

● Roof deck – A minimum 4-inch-thick, cast-in-place, 

reinforced concrete deck is the preferred deck. 

Other recommended decks include minimum 

4-inch-thick structural concrete topping over steel 

decking and precast concrete with an additional 

minimum 4-inch-thick structural concrete topping. 

● Exterior walls – A minimum 6-inch-thick, cast-inplace concrete wall reinforced with #4 rebar at 

12 inches on center each way is the preferred 

wall. Other recommended walls are a minimum 

8-inch-thick, fully grouted CMU reinforced vertically with #5 rebar at 40 inches on center and 

minimum 6-inch-thick precast concrete that is 

reinforced equivalent to the recommendations for 

cast-in-place walls.

Note that the above reinforcing recommendations 

are based on wind-borne debris resistance. More 

reinforcing steel may be required in the wall to 

carry wind loads, depending on the design and 

geometry of the wall. 

The benefit of the Level 3 enhancement deck 

recommendation is illustrated by the fire station 

shown in Figure 7, which was struck by a strong 

tornado. The apparatus bay doors collapsed (red 

arrow), and all of the unprotected glazing was broken. However, the walls and cast-in-place concrete 

roof deck remained in place. Interior damage was 

substantial as a result of the glazing failures. If the 

Level 3 enhancement door, glazing, and rooftop 

equipment recommendations had been followed, 

this station would likely have had little, if any, 

interior damage. The adjacent unreinforced CMU 

apartment building (red circle) experienced blow off 

of the wood roof structure and collapse of some 

exterior CMU walls. 

Figure 7: Fire station with a cast-in-place concrete roof deck in 

Tuscaloosa, AL. The apparatus bay doors (red arrow) collapsed and 

the adjacent building (red circle) was damaged (2011 Tornado). 

Hospitals and Nursing Homes

Designing to at least the Level 1 enhancement 

recommendations is particularly important for 

hospitals and nursing homes. Designing these 

facilities to the Level 3 enhancement recommendations is preferable. Sometimes tornado warning time is ample for occupants to reach a safe 

room; however, at times an approaching tornado 

is not noticed until a few minutes before it strikes. 

In those instances with little or no warning of an 

impending tornado strike, maintaining building 

envelope integrity is crucial to providing protection 

to patients, residents, and staff, and to minimizing 

disruption of services.

Figure 8: Collapse of the second-floor roof structure, interior walls, 

and exterior walls of a school in Tuscaloosa, AL (2011 Tornado) 
Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 7 of 10

The performance of the fire station in Figure 7 is in stark contrast to the school shown in Figure 8, which did 

not have any of the Level 1, 2, or 3 enhancements. The school was struck by the same strong tornado as the 

fire station, but the school’s steel deck/steel joist roof structure blew away, and the exterior CMU/brick veneer 

walls and interior walls on the second floor collapsed. 

Continuity of Operations 

Designing a facility to ensure it will remain operational 

if struck by a violent tornado is expensive. Therefore, 

when considering the costs and benefits of designing for continuity of operations, designing to minimize 

building damage and/or provide safe rooms may be 

more cost effective. Facilities such as EOCs that are 

determined to be critical in providing effective emergency response should be designed to avoid interrupted operations even if struck by violent tornadoes. The 

following practices will reduce the chances of interrupted operations related to building damage or loss 

of municipal utilities (i.e., water, sewer, and electrical 

power). 

Follow Recommendations in FEMA 361

If the entire facility must remain operational, FEMA 

361 recommendations should be applied to the entire building. However, if only a portion of the building 

must remain operational, the recommendations can 

be applied only to that portion.

Figure 9 shows an example of an EOC (red oval) 

located in a portion of the first floor of a large building.3 The collapsed second floor of this facility did not 

need to remain operational; hence, if a similar facility 

were being constructed, designing the second floor in 

accordance with FEMA 361 would not be necessary.

Avoid Water Leakage 

Critical facilities can be housed either on a top 

floor, with a roof overhead, or a bottom or intermediate floor with another story overhead. Avoiding 

water leakage is important for both scenarios. For 

critical facilities with a roof overhead, either of the 

following options is recommended:

● A modified bitumen roof membrane that is torch-applied to a primed concrete roof deck. Over this membrane, apply roof insulation, gypsum roof board, and another roof membrane as recommended in FEMA 

P-424 (Section 6.3.3.7), 543 (Section 3.4.3.4), or 577 (Section 4.3.3.8). 

● A minimum 4-inch-thick SPF roof system over a concrete roof deck. The SPF should be coated rather than 

protected with an aggregate surfacing.

For critical facilities with a floor slab overhead, as shown in Figure 9, collapse of an upper level could allow 

water to leak into the critical facility. If water-sensitive equipment or operations are within the critical facility, 

the following is recommended.

● Design a false ceiling between the equipment or operations and the floor slab above. Design a waterproof 

membrane over the top of the false ceiling to prevent leakage into the water-sensitive area below.

3 The building shown in Figure 9 was not FEMA 361 compliant.

Figure 9: An EOC in Tuscaloosa, AL, that remained intact even 

though the story above it collapsed (Tornado 2011) 

Vulnerability Assessments

As part of the planning process for new facilities, 

other natural hazards (flood, seismic, and wildfire) 

should be considered in addition to the tornado 

hazard. FEMA P-424, 543, and 577 provide guidance on conducting vulnerability assessments. If 

the building design does not ensure continuity of 

operations, contingency plans should be developed 

that address facility disruption. 
Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 8 of 10

Design to Protect the Heating, Ventilation, and Air Conditioning

FEMA 361 provides recommendations pertaining to protecting heating, ventilation, and air conditioning (HVAC) 

equipment for safe rooms. Safe rooms, however, are normally occupied for relatively short durations, whereas 

critical facilities are normally needed for continuous long-term operation after a tornado. Therefore, additional 

provisions for ventilation and/or cooling may be required depending on facility operational requirements.

Maintaining functioning HVAC equipment in facilities that must either remain operational during an 

event or be able to be made operational shortly 

after an event can be challenging. Portions of 

commercial HVAC systems are typically inside the 

building, but portions that transfer heat to the 

environment are located outside and are, therefore, 

vulnerable to damage from wind and wind-borne 

debris (Figures 10 and 11).

To protect HVAC components outside buildings 

from horizontal wind-borne debris, wind- and debrisresistant walls can be designed around the equipment. Vertical debris protection is more difficult to 

achieve. Baffling, as shown in FEMA 361 (Section 

3.3.2.e and Figure 7-12) to protect doors from direct debris impact, can be used to prevent damage 

to exterior equipment. However, baffling can restrict 

air flow and thereby reduce the cooling capacity of 

HVAC equipment. The effects of baffling should be 

considered in the system design.

Geothermal loops transfer heat to the earth and 

are, therefore, protected from wind and wind-borne 

debris. Although retrofitting existing systems to use 

geothermal loops is often not practical, installing 

geothermal systems during original construction 

can produce HVAC systems that meet the wind 

pressure and wind-borne debris criteria in FEMA 

361.

An alternative to protecting equipment from debris 

is to rely on a temporary system, especially in situations when cooling is not needed immediately after an event. In this scenario, portable chiller units, 

cooling towers, or DX units could be brought to the 

site if a tornado damages the equipment. If temporary systems will be used, facility owners should source 

the equipment in advance, and design professionals should specify preinstallation for the power and control 

connections, as well as the associated piping and duct connections. 

Ensure Water Supply

Depending on facility operational requirements, drinking water or other water needs (such as for hand washing 

and fire protection) may be satisfied by stored water bottles, a water storage tank within the facility, or a well 

that is protected by an enclosure that meets the wind pressure and wind-borne debris criteria in FEMA 361.

Ensure Sewer Service

FEMA 361 recommends self-contained, chemical-type receptacles/toilets to provide sewer service for safe 

rooms. However, the recommendations in FEMA 361 may be inadequate for critical facilities that do not have 

to access to functional municipal sewer service for days or weeks after a tornado. For these facilities, a 

temporary storage tank that can be pumped out by a local contractor should be designed. 

FEMA has observed critical facilities that were flooded by backflow from surcharged sewer systems as a result 

of loss of electrical power to sewage lift stations or storm-damaged sewage treatment plants. Sewer backflow 

valves can be installed in the sewage discharge line to avoid this problem. However, because sewage will also 

Figure 10: ACC units vulnerable to wind and wind-borne debris

Figure 11: Cooling tower vulnerable to wind and wind-borne 

debris
Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 9 of 10

not be able to leave the building from the primary discharge line, provisions should be made for diversion to a 

temporary storage tank.

Make Provisions for Emergency Power

FEMA 361 provides recommendations pertaining to emergency power. However, because critical facilities may 

have to rely on emergency generators for several days or weeks after a tornado, designers of critical facilities 

should also refer to the electrical power recommendations in FEMA P-424 (Section 6.3.5.1). Following these 

recommendations will minimize the loss of needed emergency power (see Figures 12 and 13). These recommendations also pertain to dual fuel generators.4

4 After a tornado, main natural gas lines may need to be turned off to prevent fires. If a critical facility has a gas-fired 

generator, it may not be operational unless it has a secondary diesel fuel source. 

Figure 12: This Joplin, MO, building housing the switchgear 

(red arrow) and emergency generator (Figure 13) collapsed 

(2011 Tornado) 

Figure 13: The steel deck/steel joist roof structure and 

unreinforced CMU walls of this Joplin, MO, building collapsed 

onto the emergency generator (2011 Tornado) 

Minimizing Operational Disruption in Hospitals

Hospitals present special challenges because of the need for glazing in patient rooms. The following 

options should be considered to minimize disruption of operations in hospitals.

Adhere to FEMA 361: To ensure continuity of operations, designers could follow the recommendations 

provided in Continuity of Operations above, including specifying that the entire building, including all exterior glazing, meet the tornado wind-borne debris and wind pressure criteria in FEMA 361. 

Note: The test missile used for safe room design has much greater momentum than test Missile E 

(68 versus 22 pounds force per second). Glazing assemblies that have passed the Missile E testing 

are readily available, and a few assemblies are available that meet the tornado test missile. Known assemblies that have passed the tornado test missile requirement employ polycarbonate glazing. In some 

assemblies, a pane of glass is on the exterior side of the polycarbonate. The glass protects the outer 

surface of the polycarbonate from scratches, but the inner surface is susceptible to scratching. 

Note: Safe rooms that have a few small windows protected by a shutter on the inside of the room have 

been designed. However, expecting a shutter within each patient room to always be closed before a 

tornado event is impractical. 

Implement Level 3 enhancement recommendations: To minimize operational disruption, the Level 3 

enhancement recommendations could be implemented in patient rooms, lobbies, and other areas where 

exterior glazing is necessary. In other areas of the facility (such as the emergency room, lab, radiology 

department, surgery department, and the physical plant), the recommendations provided in Continuity of 

Operations above could be implemented. By taking this approach, some exterior glazing might be 

breached if a violent tornado passed over or near the hospital, but much of the facility would have a high 

potential of remaining operational. 
Critical Facilities Located in Tornado-Prone Regions HSFEHQ-11-J-0004, 0005 / August 2011 Page 10 of 10

Useful Links and Resources

Recovery Advisories from the Tornado MATs for Alabama, Mississippi, Tennessee, and Georgia. FEMA. 2011. 

Available from: http://www.fema.gov/library/viewRecord.do?id=4723. 

● Tornado Recovery Advisory No. 1 – Tornado Risks and Hazards in the Southeastern United States

● Tornado Recovery Advisory No. 2 – Safe Rooms: Selecting Design Criteria

● Tornado Recovery Advisory No. 3 – Residential Sheltering: In-Residence and Stand-Alone Safe Rooms

● Tornado Recovery Advisory No. 4 – Safe Rooms and Refuge Areas in the Home

● Tornado Recovery Advisory No. 5 – Critical Facilities Located in Tornado-Prone Regions: Recommendations for 

Facility Owners. 

Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business (FEMA 320), August 

2008, Third Edition. http://www.fema.gov/library/viewRecord.do?id=1536.

Design and Construction Guidance for Community Safe Rooms (FEMA 361), August 2008, Second Edition. 

http://www.fema.gov/library/viewRecord.do?id=1657.

Design Guide for Improving School Safety in Earthquakes, Floods, and High Winds (FEMA P-424), December 

2010, Second Edition. http://www.fema.gov/library/viewRecord.do?id=1986.

Tornado Protection: Selecting Refuge Areas in Buildings (FEMA P-431), October 2009, Second Edition. 

http://www.fema.gov/library/viewRecord.do?id=1563.

Design Guide for Improving Critical Facility Safety from Flooding and High Winds (FEMA 543), January 

2007. http://www.fema.gov/library/viewRecord.do?id=2441.

Design Guide for Improving Hospital Safety in Earthquakes, Floods, and High Winds (FEMA 577), June 2007. 

http://www.fema.gov/library/viewRecord.do?id=2739.

ICC/NSSA Standard on the Design and Construction of Storm Shelters, International Code Council (ICC) and 

National Storm Shelter Association (NSSA) (ICC 500), June 2008, Country Club Hills, IL. http://www.iccsafe.

org/Store/Pages/Product.aspx?id=8850P08_PD-X-SS-P-2008-000001#longdesc.
Rebuilding and Repairing Your Home After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 1 of 5

Purpose and Intended Audience 

The purpose of this advisory is to identify which standard of construction should be used when repairing 

houses damaged in high-wind events (see Figure 1). The intended audience for this Tornado Recovery Advisory 

is homeowners or home builders. The advisory explains how to determine which building code is appropriate, 

describes how to incorporate best practices into construction, and lists resources for installing residential 

safe rooms. Homeowners and renters should also refer to Tornado Recovery Advisory No. 3, Residential 

Sheltering: In-Residence and Stand-Alone Shelters (updated in 2011).

This Recovery Advisory Addresses: 

● Determining the Appropriate Building Code

● Incorporating Best Practices 

● Protecting Building Occupants by Installing 

Residential Safe Rooms 

Determining the Appropriate Building Code 

Building codes are used in many jurisdictions as 

a minimum standard of construction practice to 

provide occupants with an improved level of safety 

from natural hazards, fire, and poor air quality. 

Building codes are instituted when either the 

State or a local jurisdiction adopts them. Most 

building codes are based on one of the current 

prevailing model building codes published by the 

International Code Council (ICC). 

Houses constructed in hurricane-prone regions 

may be constructed to the ICC 600, Standard for 

Residential Construction in High-Wind Regions, in 

addition to the International Residential Code. ICC 

600 provides a prescriptive approach for building 

and repairing houses in regions where the design wind speed is above 90 mph (3-second gust) and, for some 

construction methods, up to 150 mph. Even if the design wind speed for your location is 90 mph or less, 

designing to the ICC 600 standard may improve the performance of your house in a high-wind event such as a 

weak tornado. Although constructing to a higher standard may not eliminate all damage to the building, it may 

reduce damage from high-wind storm events.

While building codes can be adopted at the State, county, or local jurisdiction (city) level, in some areas of 

the United States, no building codes are adopted or enforced. Where building codes are not adopted and 

enforced, residential construction quality may not be ensured by plan reviewers or a building inspector. In 

these areas, the building owner should hire a qualified professional to conduct inspections and verify that 

the work is being done properly.

TORNADO RECOVERY ADVISORY RA7, August 2011

Rebuilding and Repairing 

Your Home After a 

Tornado

Figure 1: A house that lost large sections of the roof and the 

garage due to internal pressurization.
Rebuilding and Repairing Your Home After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 2 of 5

Incorporating Best Practices 

Best practices are design or construction practices that go beyond the minimum code requirements of 

the latest model codes to improve building performance. An example of a best practice is adding metal 

connectors to a structure to improve the transfer of loads through the house from the roof system to the 

foundation. Construction details and material selection can result in a house with improved resistance to 

wind pressures and wind-borne debris. Resources for best practices include the ICC 600 standard and FEMA 

P-499, Home Builder’s Guide to Coastal Construction (FEMA 2010), which is a technical fact sheet series 

for improving house performance in high-wind regions. The FEMA P-499 fact sheets are appropriate for use 

throughout the country, and they provide best practice recommendations for a variety of building systems.

Best practices can be incorporated not only into new construction, but also into existing homes. Houses 

can be retrofitted either as part of the repair process, such as when replacing the roof covering, or as part 

of an independent retrofit project. FEMA P-804, Wind Retrofit Guide for Residential Buildings (FEMA 2010), 

describes how to improve a house’s performance during high-wind events. The guide outlines three levels of 

building performance and describes groups of retrofits that can reduce damage to a house. In addition, proper 

application of the retrofit packages described in FEMA P-804 may result in insurance premium rate reductions 

in certain areas of the country.

When constructing a new home or repairing a damaged house, certain practices should be considered. 

Table 1 lists building components that are commonly observed to fail during high-wind events and provides 

recommended practices to avoid these failures. The failure of these components often results in damage from 

wind-blown rain and, in some cases, pressurization of the house, which may lead to the loss of walls or the 

entire structure. While this list is not all-inclusive, it addresses some of the most common and inexpensive 

preventive measures.

Table 1. Upgrades to Prevent Common Building Component Failures

Building Component Typical Failure Recommended Practice

Asphalt Shingles Shingles blown off in high-wind events, exposing the 

roof to wind-blown rain 

Use shingles rated for 90+ mph wind and use 

a minimum of four nails per shingle; preferred 

use is six nails per shingle (Source: FEMA 

P-499, Fact Sheet 7.3)

Windows and Doors Windows and doors can be dislodged from the walls Make sure windows and doors are properly 

shimmed and nailed into the framed opening 

using nails of sufficient length to tie the 

window and door frames into the adjacent 

studs (Source: FEMA P-499, Fact Sheet 6.1)
Rebuilding and Repairing Your Home After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 3 of 5

Building Component Typical Failure Recommended Practice

Baseplate or Sillplates Uplift of the wall systems and shear failures Make sure there are anchor bolt connections 

between the plate and the foundation at least 

every 4 feet (Source: FEMA P-499, Fact Sheet 

4.3)

Roof-to-Wall Connections Uplift of the roof systems and either significant 

damage or loss of the entire roof

Ensure there is a continuous load path 

from the roof to the foundation using metal 

connectors that are approved for use with the 

applicable basic wind speed (Source: FEMA 

P-499, Fact Sheets 4.1, 4.2, and 4.3)

Sheathing Penetration of fiberboard sheathing and rigid 

insulation board by wind-borne debris in even weak 

tornadoes 

Use oriented-strand board (OSB) or plywood 

to prevent penetration from wind-borne debris 

and racking (Source: FEMA 342, Chapter 8)

Garage Doors Buckling of doors either outward or inward Select doors designed for higher wind speeds 

(Source: FEMA P-804, Chapter 4) 
Rebuilding and Repairing Your Home After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 4 of 5

Building Component Typical Failure Recommended Practice

Brick Veneer Brick veneers pull away from the wall systems Attach veneers with brick ties to the wall 

framing at adequate spacing as shown in 

FEMA P-499 (Source: FEMA P-499, Fact Sheet 

5.4)

Vinyl Siding Vinyl siding pulls off wall sheathing Use vinyl siding rated for high wind 

applications and attach it to the wall framing 

as noted in FEMA P-499 (Source: FEMA 

P-499, Fact Sheet 5.3)

Gable End Walls Gable end walls collapse or rotate, causing loss 

of the roof system, causing failure of hinges and 

possibly large sections of the building, and causing 

walls to buckle 

Improve the gable end wall bracing details 

with additional connections and by improving 

the load path with additional framing and 

metal connectors (Source: FEMA P-804, 

Chapter 4)

Protecting Building Occupants by Installing Residential Safe Rooms 

When reconstructing after a tornado event, homeowners may want to consider installing a residential safe 

room to protect building occupants in the event of a future tornado. A safe room can be an interior room, a 

space within a building, or an entirely separate building designed and constructed to protect its occupants 

from tornadoes and hurricanes. Safe rooms are intended to provide protection against both wind forces and 

the impact of wind-borne debris. 

Additional information on safe rooms can be found in Recovery Advisory No. 3, Residential Safe Rooms: 

In-Residence and Stand-Alone Safe Rooms (updated in 2011).
Rebuilding and Repairing Your Home After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 5 of 5

Useful Links and Resources

2011 Tornado Recovery Advisories. FEMA. 2011. http://www.fema.gov/library/viewRecord.do?id=4723

Recovery Advisory No. 3, Residential Safe Rooms: In-Residence and Stand-Alone Safe Rooms. FEMA. 2011. 

http://www.fema.gov/library/viewRecord.do?id=4723

Recovery Advisory No. 5, Critical Facilities Located in Tornado-Prone Regions: Recommendations for 

Facility Owners. FEMA. 2011. http://www.fema.gov/library/viewRecord.do?id=4723 

Taking Shelter from the Storm: Building a Safe Room for Your Home or Small Business (FEMA 320). August 

2008, Third Edition. http://www.fema.gov/library/viewRecord.do?id=1536

Midwest Tornadoes of May 3, 1999: Observations, Recommendations, and Technical Guidance (FEMA 342). 

October 1999. http://www.fema.gov/library/viewRecord.do?id=1423

Home Builder’s Guide for Coastal Construction (FEMA P-499). December 2010, Second Edition. 

http://www.fema.gov/rebuild/mat/mat_fema499.shtm

Wind Retrofit Guide for Residential Buildings (FEMA P-804). December 2010. 

http://www.fema.gov/library/viewRecord.do?id=4569

Standard for Residential Construction in High-Wind Regions. ICC 600, International Code Council (ICC). 

2008. Country Club Hills, IL. 

International Residential Code for One- and Two-Family Residences (IRC) ICC. 2009. Country Club Hills, IL.

ICC/NSSA Standard for the Design and Construction of Storm Shelters (ICC-500), June 2008. 

http://www.iccsafe.org/Store/Pages/Product.aspx?id=8850P08_PD-X-SS-P-2008-000001

Reconstructing Non-Residential Buildings After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 1 of 7

Purpose and Intended Audience 

The purpose of this advisory is to identify which standard of construction should be considered for repairing 

buildings damaged in high-wind events (see Figure 1). The intended audience for this Tornado Recovery Advisory is architects, engineers, builders, and building owners. This advisory explains how to determine which 

building code is appropriate, incorporating best practices into construction, common building failures and how 

to avoid them, and resources for installing shelters and safe rooms. 

This Recovery Advisory Addresses: 

● Determining the appropriate building code 

● Incorporating best practices 

● Common building failures and recommendations 

to mitigate them

● Protecting building occupants by installing 

shelters and safe rooms 

Determining the Appropriate Building Code 

Building codes are used in many jurisdictions as 

a minimum standard of construction practice to 

provide occupants with an improved level of safety 

for natural hazards, fire, and air quality. Building 

codes are instituted when either the State or a 

local jurisdiction adopts them. Most building codes 

are based on a model building code. 

The current prevailing model building code is the family of International Building Codes produced by the International Code Council (ICC). Codes are typically updated on a predetermined cycle of reviews. Codes from the 

ICC are updated on a 3-year cycle, and most governmental bodies are using a code based on the 2003, 2006, 

or 2009 ICC building codes. At the time of this 

publication, the 2012 ICC building codes have been 

published, but few local jurisdictions have adopted 

this version of the code yet. Building codes typically 

use a performance approach, which means that 

construction practices are based on a specific building’s design and location. In addition to construction 

methods, building codes also usually dictate administrative practices such as permitting, reviews, and 

inspections.

Design loads are calculated using design standards 

or other design guidance referenced by the codes. 

With only a few exceptions, the International Building Code (IBC) requires the use of American Society 

TORNADO RECOVERY ADVISORY RA8, August 2011

Reconstructing 

Non-Residential Buildings 

After a Tornado

Standard of Care

Critical facilities have facility and operational 

requirements that should be met in addition to 

building code requirements. Building codes do not 

stipulate expected building performance for tornadoes. The designer should discuss expectations 

regarding acceptable building damage, operational 

requirements, and occupant safety with the facility 

owner to ensure the full range of requirements is 

considered.

Figure 1: A business damaged by roof damage and water intrusion 

from a weak tornado
Reconstructing Non-Residential Buildings After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 2 of 7

of Civil Engineers (ASCE) 7, Minimum Design Loads for Buildings and Other Structure, to calculate wind and 

other loads on buildings. 

Even if there is no building code enforced in the jurisdiction where you are building, it is still important to 

construct to a building code to provide a minimum standard of care. While building permits in these areas 

may be required, building inspections may not be conducted, and it may be necessary to hire a qualified 

professional to conduct inspections to verify that the work is being done properly. The latest version of the 

International Codes (2012) is recommended as a minimum code.

Incorporating Best Practices 

Best practices are design or construction practices that go beyond minimum code requirements to improve 

building performance. Four options should be considered for increasing the design loads on buildings: increasing the occupancy category, increasing the design wind speed, designing as a partially enclosed building, or 

designing as if in a hurricane-prone region. Each of these methods will effectively result in a building that can 

withstand higher wind pressures and/or improve debris impact resistance. Increasing the building occupancy 

category typically only results in minimal increases in wind resistance; the other methods will improve building 

performance more substantially.

Increasing Design Wind Speed: ASCE 7 promulgates the minimum loading requirements for building design. 

To improve wind resistance, higher wind loads can be calculated using the calculations in ASCE 7. For an 

Occupancy Category II building in a non-hurricane-prone area, the standard design wind speed is 90 mph, but 

increasing the design wind speed to 115 mph will result in a 63 percent increase in velocity pressures and be 

consistent with similar buildings using the ASCE 7-10 wind speeds. In addition to using a higher design standard for loads, improved construction methods and materials can also improve building performance. Even 

small practices—such as slightly increasing reinforcing steel sizes and increasing development and lap splice 

lengths—can greatly improve building performance.

Designing as a Partially Enclosed Building: In most cases, buildings are designed to function as an enclosed 

structure, meaning that it is designed to only allow minimal air into the building even during a high wind event. 

Once windows or doors are broken by windborne debris, wind pressures can greatly increase and cause 

significant structural damage to the building. Designing exterior and load-bearing walls, roof systems, and the 

foundation to resist the increased wind pressures will result in significant improvements to the building structure performance. The recent edition of the International Building Code has tables and charts for these wind 

speeds and wind pressures that can aid in building detailing. 

Designing as if in a Hurricane-Prone Region: The design strategies and building materials used in hurricaneprone areas result in buildings that are more resistant to most tornadoes (i.e., Enhanced Fujita [EF] 0–EF3). 

With appropriate strengthening and selection of building materials and systems, both the potential for disruption of operations and the cost of repairs after a tornado event can be reduced. If the costs associated with 

loss of function or business interruption are significant, then a higher standard of construction may be appropriate. Building performance can also be improved with engineering techniques introduced through some of 

the observations noted for critical facilities (see Recovery Advisory No. 6, Critical Facilities Located in TornadoProne Regions: Recommendations for Architects and Engineers [FEMA 2011] for additional information).

Common Building Failures and Recommendations to Mitigate Them

Table 1 describes the typical failures observed after the 2011 tornadoes. The table also provides recommended practices to reduce these failures in buildings subjected to weak tornadoes and minimize them for 

buildings on the periphery of stronger tornadoes.
Reconstructing Non-Residential Buildings After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 3 of 7

Table 1. Building Failures and Recommendations

Building Component Typical Failure Recommended Practice

Superstructure

Pre-Engineered Buildings Failure of endwall trusses and endwall truss bracing. Size the endwall trusses to resist wall loads 

and verify that anchor bolts are sized to resist 

lateral loading. (Source: FEMA 489)

Masonry Buildings Collapse of unreinforced masonry walls. Fully grout walls and increase reinforcement 

to resist lateral loads and uplift loads on the 

roof system. (Source: FEMA P-424)

Roof Coverings and Roof Systems

Ballasted Roofs Ballasted roof systems can become wind-borne 

debris and damage surrounding objects.

Select an alternative ballasting system 

or fully adhere ballast to the roof system. 

(Source: FEMA P-424)
Reconstructing Non-Residential Buildings After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 4 of 7

Building Component Typical Failure Recommended Practice

Roof Truss Connections Loss of roof trusses from uplift loads. Trusses 

typically fail at the connection with the wall system, 

either through poor grouting of anchor bolts or insufficient embedment.

Improve connection of roof trusses to prevent 

failure from uplift loads. Verify that the load 

path is continued through the wall system 

into the foundation. (Source: FEMA P-424)

Double Tee Connections Double tees shift due to uplift loads and failures at 

angle iron welds or insufficient anchor bolts, allowing 

the double tee to slip off the corbel.

Ensure that anchor bolts provide sufficient 

strength to prevent uplift. (Source: FEMA 

P-424)

Gable End Walls Insufficient attachment of gable end walls results in 

building pressurization, loss of the roof system, and 

possibly large sections of the building.

Improve the gable end wall bracing details 

with additional connections and strengthen 

the load path. (Source: FEMA P-804)
Reconstructing Non-Residential Buildings After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 5 of 7

Building Component Typical Failure Recommended Practice

Building Envelope

Metal Sheeting Loss of wall coverings due to insufficient girts. Increase framing between trusses to reduce 

loads on metal sheeting. Increase metal 

sheeting thickness to resist the potential for 

pulling off connectors. (Source: FEMA 489)

Brick Veneer Wall failures resulting from insufficient brick ties. Increase number of brick ties, properly attach 

ties to the wall system, and sufficiently embed ties into the brick veneer. (FEMA P-499, 

Fact Sheet 5.1)

Exterior Insulation and 

Finishing System (EIFS)

Loss of large sections of EIFS due to impact of windborne debris.Reduce vulnerability of EIFS by using it in 

locations that are high enough to prevent 

damage from wind-borne debris. (Source: 

FEMA 424)

Rooftop Equipment Damage to rooftop equipment, typically by windborne debris or as a result of insufficient anchorage.Protect exterior equipment from wind-borne 

debris. Evaluate connections to rooftop or 

slab. (Source: FEMA 424)
Reconstructing Non-Residential Buildings After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 6 of 7

Building Component Typical Failure Recommended Practice

Roll-up Door Systems Buckling of roll-up door systems, typically due to either positive or negative pressures. Door tracks and 

rollers can fail in high winds.

Specify a door system for a higher wind 

speed than the minimum required by code. 

(Source: FEMA 489)

Two common building types that failed in the recent tornadoes were masonry buildings and pre-engineered buildings. Both of these building types are common and have aspects that put them at risk of significant damage in 

high-wind events. 

Masonry Buildings: Masonry buildings can be 

constructed as either reinforced or unreinforced 

masonry. The most common failure noted is with 

unreinforced masonry walls. The lack of reinforcement makes them particularly susceptible to collapse. Unreinforced walls are commonly observed 

in older construction, but numerous examples of 

more recently constructed buildings that contained little or no reinforcement were observed 

after the 2011 tornadoes. Due to the lack of 

rigidity, unreinforced masonry walls tend to bow 

and collapse in high-wind events. The lack of reinforcement also makes the roof system particularly 

susceptible to uplift. 

Failure of reinforced masonry walls is also not 

uncommon. The failures noted after the 2011 

tornadoes were because the wall systems either 

contained too little reinforcement or insufficient 

splices or development lengths in the bars. The 

walls failed in large sections and pulled away from 

the foundation or slab due to insufficient splice 

designs. Poor connections between roof systems 

and wall systems were also noted to cause failure 

of reinforced masonry walls.

Pre-Engineered Buildings: Pre-engineered buildings can sustain significant loss of exterior sheeting, 

and in some cases, failure of the frame. Exterior 

sheeting should be sufficiently supported to resist 

deflection from high winds; additional girts and 

purlins may be required. Increasing the thickness 

of the exterior sheeting can reduce the potential 

for sheeting pulling off connectors. Endwall trusses 

of pre-engineered buildings should be designed to 

resist wall loads, and anchor bolts should be sized to 

resist uplift from high wind loads.

Figure 2: Example of a masonry wall detail, incorporating many 

construction best practices. Source: FEMA P-424, Design Guide for 

Improving School Safety in Earthquakes, Floods, and High Winds 

(FEMA 2010)
Reconstructing Non-Residential Buildings After a Tornado HSFEHQ-11-J-0004, 0005 / August 2011 Page 7 of 7

Protecting Building Occupants by Installing Shelters and Safe Rooms 

When reconstructing after a tornado event, building 

owners may want to consider installing a safe room 

or shelter to protect occupants in the event of a 

future tornado. The distinction between a safe room 

and a shelter is described in the following text box. 

More information on the construction of safe rooms 

can be found in the FEMA 2011 Recovery Advisory 

No. 2, Safe Rooms: Selecting Design Criteria.

Useful Links and Resources: 

Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers (ASCE), 2005. 

ASCE Standard ASCE/SEI 7-05.

Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers (ASCE), 2010. 

ASCE Standard ASCE/SEI 7-10.

Recovery Advisories from the Tornado Mitigation Assessment Teams (MATs) for Alabama, Mississippi, 

Tennessee, and Georgia. FEMA. 2011. Available from: http://www.fema.gov/library/viewRecord.do?id=4723.

● Recovery Advisory No. 1, Tornado Risks and Hazards in the Southeastern United States

● Recovery Advisory No. 2, Safe Rooms: Selecting Design Criteria

● Recovery Advisory No. 6, Critical Facilities Located in Tornado-Prone Regions: Recommendations for Architects 

and Engineers

Taking Shelter from the Storm: Building a Safe Room For Your Home or Small Business (FEMA 320), August 

2008, 3rd Edition. http://www.fema.gov/library/viewRecord.do?id=1536

Design Guide for Improving School Safety in Earthquakes, Floods, and High Winds (FEMA P-424), 2010. 

http://www.fema.gov/library/viewRecord.do?id=1986

Building Performance Assessment Report. Oklahoma and Kansas, Midwest Tornadoes of May 3, 1999 – 

Observations, Recommendations and Technical Guidance (FEMA 342), October 1999. http://www.fema.gov/

library/viewRecord.do?id=1423

Design and Construction Guidance for Community Safe Rooms (FEMA 361), August 2008, 2nd Edition.

http://www.fema.gov/library/viewRecord.do?id=1657

Home Builder’s Guide for Coastal Construction (FEMA P-499), December 2010, Second Edition. 

http://www.fema.gov/rebuild/mat/mat_fema499.shtm

Wind Retrofit Guide for Residential Buildings (FEMA P-804), December 2010. http://www.fema.gov/library/

viewRecord.do?id=4569

ICC/NSSA Standard for the Design and Construction of Storm Shelters (ICC-500), June 2008. http://www.

iccsafe.org/Store/Pages/Product.aspx?id=8850P08_PD-X-SS-P-2008-000001

International Building Code (IBC), ICC. 2009. Country Club Hills, IL.

A shelter (including safe rooms) is typically an 

interior room, space within a building, or an entirely separate building, designed and constructed to 

protect occupants from tornadoes or hurricanes. 

Shelters are intended to provide protection against 

both wind forces and the impact of wind-borne 

debris. 

TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-1

GRecommendations for 

One- and Two-Family 

Residential Buildings

G.1 Purpose and Audience

This appendix provides prescriptive guidance for enhanced construction techniques to improve 

performance of wood-frame residential structures when impacted by tornadoes rated EF2 or less. 

Accordingly, the following guidance addresses only the effects of increased wind loading resulting 

from tornadoes and does not consider other loading conditions such as seismic, snow, flood, or 

any other loads. The intended users of this appendix are building designers, homebuilders, and 

homeowners in the tornado-prone regions of the United States. The use of this guidance is intended 

to be coordinated with recommendations of the building design professional to produce a complete 

building design resistant to anticipated loads. 

One of the goals of the committee that developed this appendix was to make the guidance simple 

and cost effective, and thereby foster mitigation. The building performance of one- and two-family 

residential wood-frame buildings during a high-wind event will be significantly elevated over codelevel practices through the voluntary implementation of guidance provided in this appendix. While 

implementing the following guidance is voluntary, the Mitigation Assessment Team (MAT) strongly 

advises users to take a comprehensive approach to incorporating enhancements as applicable to 

ensure continuity of the building’s load path. 

The following guidance is not intended to replace the governing building code, as it does not 

address all aspects of construction. Instead, enhanced construction techniques presented in this 
G-2 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

section should be implemented in accordance 

with provisions of the governing building code 

to enhance building performance during highwind events. If a building code has not been 

adopted by the authority having jurisdiction, 

then enhanced construction techniques in this 

appendix should be implemented in accordance 

with the requirements of the current version of 

the International Residential Code (IRC). 

While implementing the voluntary mitigation 

actions proposed in this appendix for one- and 

two-family residential buildings will greatly 

enhance their performance when impacted by 

tornadoes rated EF2 or less, there is no substitute 

for a personal protection plan that includes 

access to a safe room in the event of a tornado 

emergency. 

G.2 Background and 

Applicability

The guidance in this appendix is adapted from existing guidance for high-wind regions. The 

primary sources referenced are Technical Fact Sheets from Federal Emergency Management Agency 

(FEMA) P-499, Home Builder’s Guide to Coastal Construction (2010), the Wood Frame Construction 

Manual (WFCM) Guide to Wood Construction in High Wind Areas for One- and Two-Family Dwellings, 130 

mph, Exposure B (AWC 2006), and the International Code Council’s (ICC’s) ICC 600-2008, Standard 

for Residential Construction in High-Wind Regions. These documents provide guidance for high-wind 

resistance that, when implemented in high-wind hazard areas in accordance with the applicable 

building code, result in enhanced performance for one- and two-family residential buildings. 

It is important to note, however, that important 

differences exist between hurricanes and 

tornadoes. Hurricane-force winds affect broad 

areas of coastline, and the probability of their 

site-specific occurrence is better understood than 

that of tornadoes. Strengthening buildings by 

maintaining load path continuity and reinforcing 

connections has proven successful for mitigating 

hurricane wind damage and provides a good 

model for mitigating tornado wind damage. 

In areas with relatively low mapped wind speeds, 

one way to reduce damage caused by tornadoes 

rated EF2 or less is to design to higher wind 

speeds. Because of the current lack of standards 

The guidance for improved building performance presented in this appendix is 

intended solely for enhanced property protection and should not be construed in any 

way as an alternative to sheltering.

The guidance in Appendix G is intended 

to strengthen new construction. FEMA 

P-804, Wind Retrofit Guide for Residential 

Buildings, provides guidance on retrofitting 

existing residential buildings to reduce 

their vulnerability to damage from highwind events and wind-driven rain intrusion. 

Users should note that grant opportunities 

described in FEMA P-804 may not be 

available for homes located outside of 

hurricane-prone regions.

Basic mapped wind speeds in ASCE 7-10 for 

Category II structures (residential buildings) 

are higher than those in ASCE 7-05 because they represent ultimate wind speeds 

or strength-based design wind speeds. 

Load factors for wind in ASCE 7-10 are also 

different from those in ASCE 7-05. In ASCE 

7-10, the wind load factor in the load combinations for strength design is 1.0; in ASCE 

7-05, the load factor is 1.6. The allowable 

stress design load factor in the load combinations for wind is 0.6; in ASCE 7-05, the 

load factor is 1.0.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-3

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

or guidance on designing to loads associated with tornado events, and to facilitate complementary 

design of buildings or parts of buildings that fall outside the scope of this appendix, the wind 

pressures in Appendix G are based on an ASCE 7-05 wind speed of 130 mph (3-second gust) using 

Exposure Category B. Exposure Category B includes urban and suburban areas, wooded areas, 

and other terrain with numerous closely spaced obstructions the size of single-family dwellings. 

Residential buildings in Exposure Category C, which is defined as open terrain with scattered 

obstructions, are outside the scope of this appendix.

As noted in Chapter 4, tornadoes rated EF2 or less often damage window and door glazing in 

residential buildings, which can lead to increased pressurization of the building. Although the 

prescriptive solutions presented in this appendix maintain the assumption of an enclosed building 

consistent with the primary sources referenced above, this condition is unlikely to be met for wind 

speeds in excess of 110 mph (ASCE 7-05, 3-second gust) unless impact-resistant glazing is installed 

(described more fully in Section G.3.1.4, Glazing (Doors and Windows). For added protection of 

building structures without impact-resistant glazing that are subject to wind speeds in excess of 100 

mph (3-second gust), a designer may choose to design for higher wind speeds or increased pressures 

associated with a partially enclosed building classification as described in ASCE 7. 

The guidance in this appendix related to roof-to-wall, wall systems and connections is limited to the 

following:

+ One- and two-family wood-frame residential buildings with no more than two stories.

+ Mean roof heights (Hmax) and roof spans (Wmax) limitations as shown in Figure G-1. Continuous 

load path elements that are addressed in this appendix are also shown on Figure G-1.

+ Percentage of full-height wall sheathing and building aspect ratios, as described in Tables G-6 

and G-7.

+ Openings in floors and ceilings that are the lesser of 12 feet or half the relative building 

dimension. Vaulted or cathedral ceilings are outside the scope of this appendix.

+ Load bearing exterior wall height limited to 10 feet. Refer to Section 4 (Walls) of Wood Frame 

Construction Manual (WFCM) Guide to Wood Construction in High Wind Areas for One- and Two-Family 

Dwellings, 130 mph, Exposure B for complete wall framing schedules.1

The enhanced construction techniques described in this appendix are considered applicable 

for buildings with dimensions and characteristics outside the scope of those listed above, but 

the building design process must consider modifications to account for differences in building 

dimensions and characteristics.

1 The American Wood Council guide is available at http://www.awc.org/pdf/WFCM_130-B-Guide.pdf.
G-4 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

G.3 Discussion of Recommendations

The following recommendations include construction specifications and details for enhanced 

building performance related to the following building components and systems:

G.3.1 Building Envelope Components

+ Roof coverings

+ Wall coverings

+ Masonry veneer attachment

Figure G-1: Load path elements and height and width limitations for residential buildings covered in Appendix G

ADAPTED: COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-5

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

+ Glazing (doors and windows)

+ Garage doors

G.3.2 Roof Systems and Connections

+ Roof decking and decking attachment

+ Soffits

+ Roof-to-wall connections

G.3.3 Wall Systems and Connections

+ Sill plate attachment

+ Wall sheathing

+ Top plate splices

+ Openings in walls

+ Wall-to-floor connections

G.3.1 Building Envelope Components

The following section provides guidance for roof coverings, wall coverings, masonry veneer 

attachment, glazing (doors and windows), and garage doors.

G.3.1.1 Roof Coverings

The performance of asphalt shingle roof coverings can be improved by following the guidance in 

Technical Fact Sheet 7.3, “Asphalt Shingle Roofing for High Wind Regions,” found in FEMA P-499, 

Homebuilder’s Guide to Coastal Construction (2010). Specific information includes physical properties of 

the shingle to consider when selecting a product and the effectiveness of different wind-resistanceratings for asphalt shingles. Proper shingle installation at eaves, rakes, hips, and ridges are also 

illustrated along with fastener guidelines. Other Technical Fact Sheets in P-499 also provide relevant 

guidance: Technical Fact Sheet 7.4, “Tile Roofing for High Wind Regions,” and Technical Fact Sheet 

7.6, “Metal Roof Systems in High-Wind Regions,” provide similar high-wind region guidance for 

installing tile and metal roofs, respectively, and Technical Fact Sheet 7.2, “Roof Underlayment for 

Asphalt Shingle Roofs,” recommends best practices for installing roof underlayment for asphalt 

shingle roofs to act as an enhanced secondary water barrier. 

G.3.1.2 Wall Coverings

The performance of wall coverings and sidings in high winds can be improved by following the 

recommendations in FEMA P-499, Technical Fact Sheet 5.3, “Siding Installation in High Wind 

Regions;” it covers vinyl, wood, and fiber cement siding. Figures are included that depict key 

differences between vinyl siding rated for high winds and standard vinyl siding. The proper method 

of fastening to achieve the desired performance is also illustrated. Detailed guidance includes 

figures showing how to install both wood siding and fiber cement siding.
G-6 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

G.3.1.3 Masonry Veneer Attachment

The performance of masonry brick veneer can be improved by following the guidelines in FEMA 

P-499 Technical Fact Sheet 5.4, “Attachment of Brick Veneer in High-Wind Regions.” The Fact Sheet 

includes figures that show poor versus good installation techniques and includes recommended 

vertical spacing of brick ties with 8d ring shank nails based on wind speed. Users should select a 

wind speed of 130 mph for brick ties and attachment to be consistent with other guidance provided 

in this appendix. 

G.3.1.4 Glazing (Doors and Windows)

Section 301.2.1.2 of the 2009 and 2012 IRC requires glazed openings to be protected from impact in 

areas designated as wind-borne debris regions, which are located along hurricane-prone coastlines. 

To protect glazing from wind-borne debris impact, the IRC specifies the use of impact-resistant 

coverings, such as shutters, and impact-resistant glazing. Shutters are not a practical option in 

tornado-prone regions because of the lead time needed to cover the glazed openings. While impactresistant glazing may be cost prohibitive for elective installation in non-coastal tornado-prone 

regions, homeowners should be aware that glazing products that provide greater protection against 

risk associated with wind-borne debris are available. Specifically, wind-borne debris risks incurred 

without impact-resistant glazing include damage from water intrusion, injury from incoming missiles 

and shattered glazing, and a decreased level of performance because of increased pressurization.

FEMA P-499 Technical Fact Sheet 6.2, “Protection of Openings – Shutters and Glazing,” provides 

guidance for the use of impact-resistant glazing. To qualify as impact-resistant, the glazing has to 

comply with the testing requirements specified in ASTM E1886 and ASTM E1996 or other approved 

test methods and performance criteria. There are two typical kinds of precut impact-resistant 

glazing: laminated glazing systems and polycarbonate systems: 

+ Laminated glazing systems typically consist of assemblies fabricated with two or more panes of glass 

and an interlayer of a polyvinyl butyral (or equivalent) film laminated into the glazing assembly. 

During impact testing, the laminated glass in the system can fracture, but the interlayer must 

remain intact to prevent water and wind from entering the building. 

+ Polycarbonate systems typically consist of plastic resins molded into sheets that provide lightweight, 

clear glazing panels with high impact-resistance qualities. The strength of the polycarbonate 

sheets is much higher than non-laminated glass (i.e., more than 200 times stronger) and acrylic 

sheets or panels (i.e., more than 30 times stronger).

While protection from impact is important, glazing must also resist wind pressures. Wind pressure 

resistance of glazing can be improved by installing glazing products designed to resist the design 

pressures shown in Table G-1. For the glazed components to perform as rated, they must be installed 

in accordance with manufacturer’s installation instructions. The supplier should provide verification 

that window and door products are rated to meet or exceed the positive and negative pressures in 

Table G-1 and that the test values comply with one of the following testing standards: 

+ ANSI/AAMA/NWWDA 101/I.S.2

+ ANSI/AAMA/WDMA 101/I.S.2/NAFS
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-7

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

+ ANSI/WDMA/CSA 101/I.S.2/A440

+ Florida Building Code Testing Protocol TAS 202

Products must be permanently labeled or marked to facilitate verification.

Table G-1: Recommended Design Pressures for Doors and Windows 

Minimum Window Size Pressure (psf)* Minimum Door Size Pressure (psf)*

2 ft 4 in. x 5 ft 30.2, -32.8 (-40.3) 2 ft 6 in. x 7 ft 29.4, -32 (-38.7)**

2 ft 4 in. x 7 ft 29.5, -32.1 (-39.0) 3 ft x 7 ft 29.0, -31.6 (-38.0)

2 ft 8 in. x 5 ft 29.9, -32.5 (-39.8) 5 ft x 7 ft 28.1, -30.7 (-36.2)

2 ft 8 in. x 7 ft 29.2, -31.8 (-38.4) 6 ft x 7 ft 27.7, -30.2 (-35.3)

psf = pounds per square foot ft = feet in. = inches

* Pressures for doors and windows are derived from Table 602(1) of ICC 600 (2008) for 130 mph 3-second gust. 

** Number in parentheses represents the applicable negative pressure when the component is installed within 4 ft of wall

corner. 

G.3.1.5 Garage Doors

The performance of garage door openings can be greatly improved by installing enhanced pressureresistant overhead garage doors in accordance with the following (per ICC 600-2008 Table 602(3) 

for 130 mph 3-second gust):

+ Single garage doors (minimum size 7 feet high x 9 feet wide) should resist minimum design 

pressures of +26.7 psf, -30.2 psf.2

+ Double doors (minimum size 7 feet high x 16 feet wide) should resist minimum design pressures 

of +25.6 psf, -28.5 psf.

Pressure-rated garage doors should comply with the testing standards of ANSI/DASMA 108. 

Although some manufacturers provide wind speed and exposure ratings for their products, labels 

on many garage doors do not include wind speed or wind pressure ratings. While ANSI/DASMA 

108 does not require wind speed or wind pressure ratings to be included on the product labeling, 

it does require that the positive and negative pressure used in testing be recorded on the ANSI/

DASMA 108 Test Report Form and that the model number, description, and operating hardware be 

documented. If the label attached to the door does not list the positive and negative pressure rating, 

consult the Test Report Form to determine whether the garage door meets the minimum design 

pressures indicated above. 

In addition to the door itself, practical guidance on the issue of track depth (enough to avoid wheels 

pulling out of the track) and proper fastening of the track to the framing at each end of the door 

2 Single and double garage door pressures listed assume minimum 2-foot wall length at each end of door opening. 
G-8 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

opening is provided in DASMA TDS 156 and 161. Both Technical Data Sheets and other guidance 

related to garage access systems are available at the DASMA Web site.3

G.3.2 Roof Systems and Connections

The following section provides guidance for roof systems and connections, roof decking and decking 

attachment, soffits, and roof-to-wall connections

G.3.2.1 Roof Decking and Decking Attachment

The performance of roof decking—also referred to as roof sheathing—can be improved by following 

the guidance in FEMA P-499 Fact Sheet 7.1, “Roof Sheathing Installation.” Fact Sheet 7.1 provides 

guidance on roof decking and roof decking attachment. Insufficient fastening can lead to total 

building failure in a high-wind event. During wind loading, the highest uplift forces occur at the 

roof corners, edges, and ridgelines. 

FEMA P-499 Fact Sheet 7.1 states that wood structural panel sheathing with a minimum thickness of 

15/32 inch is typically required for roof decking in coastal high-wind areas. Wood structural panel 

sheathing may be either oriented strand board (OSB) or plywood. Sheathing panels should be rated 

“Exposure 1” or better. 

The sheathing panels should be installed with consecutive rows staggered by half the panel length 

as shown in FEMA P-499 Fact Sheet 7.1. Sheathing panels should be no shorter than 4 feet long. 

Unless otherwise indicated by the panel manufacturer, leave a 1/8-inch gap between panel edges to 

allow for expansion due to changes in moisture content.

An 8d common nail (shank diameter of 0.131 inch, length of 21⁄2 inches) is the minimum size for 

fastening sheathing panels. Additionally, full round heads are recommended to reduce the potential 

for head pull-through. Deformed-shank (i.e., ring- or screw-shank) nails provide a cost effective 

performance improvement over smooth-shank nails and are recommended for fastening the roof 

sheathing to the framing. Wood structural panel roof sheathing should be attached to roof framing 

with 8d ring shank nails spaced at 6 inches on center (o.c.) at panel edges and at intermediate 

framing. For roof sheathing within 4 feet of gable ends, fasteners should be spaced at 4 inches o.c. 

at panel edges and at intermediate framing. Roof sheathing should also be attached at 4 inches o.c. 

to blocks shown with Connector S in Table G-3. Top surface of full-height block should be in-plane 

with top surface of rafter or truss.

Proper fastener spacing is imperative on all sheathing panels. Loss of just one panel in a high-wind 

event can lead to total building failure. The builder should visually inspect work after installation 

to ensure that fasteners have hit the framing members. If the building design specifications require 

installing fasteners at less than 3 inches o.c., they should be staggered. To limit occurrence of splitting 

of roof framing members, 3-inch nominal roof framing members should be used at adjoining panel 

edges for fastener spacing less than 3 inches o.c., as required per 2012 IBC Section 2306.2.

3 The Door and Access Systems Manufacturers Association International Web site, http://www.dasma.com/pubtechdata.asp.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-9

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

FEMA P-499 Technical Fact Sheet 7.1 provides further guidance on preserving the integrity of roof 

decking around ridge vents and ladder framing at gable overhangs. 

G.3.2.2 Soffits

Soffits are particularly vulnerable to damage from high wind pressures at the edges of the building 

envelope. Loss of the soffit material can cause accelerated building damage due to pressurization 

of the attic envelope. Soffit failure can be mitigated by implementing the installation guidance 

in FEMA P-499 Fact Sheet 7.5, “Minimizing Water Intrusion through Roof Vents in High-Wind 

Regions.”

G.3.2.3 Roof-to-Wall Connectors

Each roof truss and rafter should be attached to 

the framed wall double top plate with a connector 

designed to resist the loads for the corresponding roof 

truss or rafter span and spacing. Table G-3 includes 

recommended hardware and hardware configurations 

(including blocks shown on Connector S) to resist uplift 

and shear forces along with the number and type of nails 

required to resist lateral loads associated with each roof 

span and truss or rafter spacing condition. 

If the connectors specified in Table G-2 are unavailable, 

users should refer to the uplift capacity values provided 

in Table G-4 to determine the required capacity for 

alternate hardware. All three connection categories 

listed in Table G-3—Uplift (per Connector E, F, G, H, 

and I), Shear (per Connector S and blocks) , and Lateral 

(per truss or rafter to plate attachment nailing)—are 

required at each roof member. For example, roof truss 

members spaced at 24 inches on center and spanning 

32 feet would require, per Table G-3: Connector H, 

Connector S (with blocks), and three 16d sinker toe nails.

Table G-2 specifies the model numbers and installation specifications 

for connectors identified throughout 

this appendix; it is also referenced 

in Tables G-6, G-7, G-10, G-12, 

G-13, and G-14.

WARNING

Roof-to-wall connection failure appeared to accelerate damage to 

whole structures inspected by the 

MAT; this type of failure is a critical 

initiation phase of progressive collapse during a tornado.

Recent research at Iowa State 

University has found a 2–3 times increase over hurricane wind speeds 

in uplift pressure due to the inflow 

and updraft of tornado winds. The 

possible increase in uplift pressure 

has not been accounted for in any 

of the pressure values shown in this 

appendix.4

4 “Tornado-Induced Wind Loads on a Low-Rise Building,” Dr. Partha Sarkar, Journal of Structural Engineering, 2010.
G-10 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Table G-2: Connector Selection and Installation 

Connector

Type

Simpson Strong-Tie Co. USP Structural Connectors

Model Number Total Number (and 

Size) of Fasteners Model Number Total Number (and 

Size) of Fasteners

A CS20 (10d common) RS250 (10d common)

B CS16 (10d common) RS150 (10d common)

C A34 8 (8d ×11⁄2) MP34 8 (8d ×11⁄2)

D A35 12 (8d ×11⁄2) MPA1 12 (8d ×11⁄2)

E H2.5A 10 (8d ×11⁄2) RT7 10 (8d ×11⁄2)

F H8 10 (10d ×11⁄2) RT8A 10 (10d ×11⁄2)

G LTS12 12 (10d ×11⁄2) RT8A 10 (10d ×11⁄2)

H MTS12 14 (10d ×11⁄2) MTW12 14 (10d ×11⁄2)

I H10A 18 (10d ×11⁄2) MTW12 14 (10d ×11⁄2)

J MTS12 14 (10d ×11⁄2) RT8A 10 (10d ×11⁄2)

K MTS12 14 (10d ×11⁄2) MTW12 14 (10d ×11⁄2)

L H2.5A 10 (8d ×11⁄2) RT3A 8 (8d ×11⁄2)

M SSP 4 (10d common) RT3A 8 (8d ×11⁄2)

N SP4 6 (10d ×11⁄2) 6 10d ×11⁄2 SPT4 6 (10d ×11⁄2)

O SPH4 10 (10d ×11⁄2) SPTH4 10 (10d ×11⁄2)

P HTT5 26 (16d ×21⁄2*) PHD4A 10 (WS3 1⁄4×3 screws)

Q HDU11-SDS2.5 30 (SDS 1⁄4×21⁄2 screws) PHD8 24 (WS3 1⁄4×3 screws)

R HD9B** 3 ( -inch bolts) UPHD8*** 24 (WS3 1⁄4×3 screws)

S RBC 12 10d ×11⁄2 RBC 12 (10d ×11⁄2)

* Substitution of 16d common nail is acceptable

** Must be fastened to minimum of three studs

*** Must be fastened to minimum of three studs or 4×4

Note: Because not all contractors are familiar with the type of structural connectors shown in Appendix G tables, the names of two 

companies that manufacture connectors have been included. This list of companies is not, however, exhaustive. Additionally, this list 

is not intended to express a preference for those manufacturers and/or their products by the United States government nor is it an 

endorsement of those manufacturers and/or their products.

SOURCE: RANDY SHAKELFORD, PE (PERSONAL COMMUNICATION)
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-11

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Table G-3: Roof-to-Wall Connector Requirements 

Roof Framing Span (ft) Connections Required 

in Addition to Uplift Connector 24 28 32 36

Truss or Rafter 

Spacing

Connector Type*

(Uplift)

Connector 

Type* 

(Shear)

Truss or Rafter-to-Plate 

Attachment (Lateral)

16 in. o.c. E F F G S** Three 10d sinker toe nails**

24 in. o.c. H H H I S** Three 16d sinker toe nails**

 

 

 Connector E Connector F (G Similar) Connector H Connector I Connector S**

in. = inch ft = feet o.c. = on center

* Reference Table G-2 for model number and fasteners

** Uplift connector not shown for clarity. Connector S with blocking between rafters or trusses should be used in addition to uplift 

connectors and truss or rafter to plate attachment nail schedule. 

SOURCE (NOT INCLUDING HARDWARE SPECIFICATIONS): COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA

Table G-4: Roof-to-Wall Connection Loads

Roof Framing Span (ft)

24 28 32 36

Truss or Rafter 

Spacing Uplift (lb) Shear (lb) Lateral (lb)

16 in. o.c. 442 499 247 611 109 247

24 in. o.c. 664 748 370 917 164 370

in. = inch ft = feet o.c. = on center lb = pounds

SOURCE: COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA

G.3.3 Wall Systems and Connections

The following section provides guidance for sill plate attachment, wall sheathing, top plate splices, 

openings in walls, and wall-to-floor connections

G.3.3.1 Sill Plate Attachment 

To strengthen the connection between the sill plate and foundation, the treated sill plate should be 

attached to masonry or concrete foundations with 5/8-inch-diameter anchor bolts and 0.229-inch 

x 3-inch x 3-inch washers in accordance with Table G-5 and installed as shown in Figure G-2. To 

determine the appropriate building aspect ratio required, refer to the image in Table G-5. 
G-12 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Table G-5: Anchor Bolt Spacing Guide

Foundation 

Supporting:

Stemwall Foundation

Aspect Ratio (L/W) Slab-on-Grade 

Foundation

1.00 1.25 1.50 1.75 2.00 2.25

5/8-in. Anchor Bolt Spacing

One story 58 in. 51 in. 43 in. 36 in. 32 in. 28 in. 24 in.

Two-story 40 in. 32 in. 27 in. 23 in. 20 in. 18 in. 24 in.

in. = inches

SOURCE: COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA

G.3.3.2 Wall Sheathing

All framed walls, including gable end walls, should be continuously sheathed with wood structural 

panels having a minimum nominal thickness of 7/16 inch. According to APA’s Building for High 

Wind Resistance in Light-Frame Wood Construction (2011, page 3), “the most effective way to provide 

lateral and uplift continuity is to attach adjacent wall sheathing panels to one another over common 

framing.” In order to determine the attachment schedule for wood structural panels, the following 

information must be determined from the construction drawings:

1. Building aspect ratio (see figures embedded in Tables G-6 and G-7).

2. Percentage of full height sheathing in the wall to be constructed by dividing the total length 

of that wall not containing openings (i.e., wall sections sheathed over full height) by the total 

wall line length. 

The next step is to use Table G-6 or G-7 to find the required attachment schedule, hold-down 

hardware, and bottom plate-to-frame connector for information determined in Steps 1 and 2. Table 

G-6 and Table G-7 provides the attachment schedule for 7/16-inch OSB wall sheathing, wall holddown hardware, and wall bottom plate to frame hardware. Note that the percentages indicated 

in Tables G-6 and G-7 are the maximum allowed for the selected aspect ratio and attachment 

schedule; wall conditions with percentages for the closest spaced attachment schedule in excess of 

those shown are outside the scope of the guidance in this appendix. While the performance of 

residential buildings outside the scope of these limits and provisions may be enhanced through the 

most conservative guidance in this appendix, a registered design professional should be consulted.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-13

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Figure G-2: Anchor bolt installation guide

SOURCE: COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA
G-14 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Table G-6: Percentage of Full-Height Sheathing in Maximum Building Dimension (Length)

Shear Wall Line Beneath Building Aspect 

Ratio (L/W) Percent Full-Height Sheathing on Each Exterior Wall Line

Roof and Ceiling

1.00 43% 34% 28%

1.25 36% 28% 23%

1.50 31% 24% 20%

1.75 27% 21% 17%

2.00 24% 18% 15%

2.25 22% 17% 14%

Roof, Ceiling, and One 

Floor

1.00 78% 65% 56%

1.25 68% 55% 47%

1.50 60% 48% 41%

1.75 54% 43% 36%

2.00 49% 38% 32%

2.25 44% 35% 29%

Attachment 

Schedule for

7/16-in. Wood 

Structural Panel 

Sheathing, Plate-toFloor, and Hold-down 

Requirements at 

Each Wall End

Edge nail spacing

(8d common nail) 6-in. o.c. 4-in. o.c. 3-in. o.c.

Field nail spacing 

(8d common nail) 6-in. o.c. 6-in. o.c. 6-in. o.c.

Bottom plate-to-floor 

shear connection 

(16d common nails)

436 plf 

(3/ft)

590 plf 

(3/ft)

730 plf 

(4/ft)

Hold-down loads and 

model #

4,360 lb 

Connector P*

5,900 lb

Connector Q*

7,300 lb

Connector R*

 

 Connector P (Simpson) Connector Q** Connector R (Simpson)

in. = inches o.c. = on center ft = foot plf = pounds per linear foot

* Refer to Table G-2 for model number and fasteners

** Connector P and R (United Steel Products [USP]) are similar to Connector Q

SOURCE (NOT INCLUDING HARDWARE SPECIFICATIONS): COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-15

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Table G-7: Percentage of Full-Height Sheathing in Maximum Building Dimension (Width)

Shear Wall Line Beneath Building Aspect 

Ratio (L/W) Percent Full-Height Sheathing on Each Exterior Wall Line

Roof and Ceiling

1.00 43% 34% 28%

1.25 51% 41% 34%

1.50 58% 47% 40%

1.75 65% 53% 45%

2.00 71% 58% 50%

2.25 76% 63% 54%

Roof, Ceiling, and One 

Floor

1.00 78% 65% 56%

1.25 89% 75% 65%

1.50 98% 83% 73%

1.75 NP 91% 81%

2.00 NP 98% 87%

2.25 NP NP 93%

Attachment Schedule 

for 7/16-in. Wood 

Structural Panel 

Sheathing, Plate-toFloor, and Hold-down 

Requirements at Each 

Wall End

Edge nail spacing 

(8d common nail) 6-in. o.c. 4-in. o.c. 3-in. o.c.

Field nail spacing 

(8d common nail) 6-in. o.c. 6-in. o.c. 6-in. o.c.

Bottom plate-to-floor 

shear connection 

(16d common nails)

436 plf 

(3/ft)

590 plf 

(3/ft)

730 plf 

(4/ft)

Hold-down loads and 

model #

4,360 lb

Connector P*

5,900 lb

Connector Q*

7,300 lb

Connector R*

 

 Connector P (Simpson) Connector Q** Connector R (Simpson)

NP = Not Permitted in. = inches o.c. = on center ft = foot plf = pounds per linear foot

* Refer to Table G-2 for model number and fasteners

** Connector P and R (United Steel Products [USP]) are similar to Connector Q

SOURCE (NOT INCLUDING HARDWARE SPECIFICATIONS): COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA
G-16 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Given:

+ One-story house with building length (L) = 60 feet, building width (W) = 30 feet

+ Both 30-foot-long framed walls contain one 3-foot-wide door and one 6-foot-wide double 

window

Find:

+ Sheathing attachment schedule for 30-foot-long walls

+ Hold-down hardware for 30-foot-long walls

Solution:

1. Find the sheathing attachment schedule

+ Determine building aspect ratio: L: W = (60 feet:30 feet) = 2

+ Determine percent full-height sheathing (P) in wall using the given values: 

W = Building width in feet = 30 feet

T = Total width of openings in wall in feet = 3 feet + 6 feet = 9 feet 

P = − =  −



 





[ ] W T [ ]

W

30 9

30 = 0.70, or 70 percent

+ Using Table G-7 (for (W)) select the row in the upper portion of the table showing the 

building aspect ratio (L/W) = 2.00, as determined above. 

+ Find the appropriate column for wall sheathing nailing pattern using the percentage for 

the full-height sheathing calculated above, where P = 70 percent.

Select the second column (58 percent < 70 percent < 71 percent) to determine the nailing 

schedule, which for this example is 4-inch spacing of edge nails and 6-inch spacing of field 

nails (8d common nails). 

2. Find the recommended hold-down hardware

+ Find the hold-down hardware for the column indicated in the previous section. As shown 

in Table G- 7, Connector Q is recommended for each wall end that has a minimum 

required capacity of 5900 pounds when installed per manufacturer’s installation 

instructions. 

+ Using the row in the same column labeled “Bottom plate-to-floor shear connection (16d 

common nails),” determine the plate-to-floor shear load connection. For this example, 

three 16d common nails per foot are required to transfer shear loads between the bottom 

plate of the wall and the solid floor band.

EXAMPLE
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-17

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

G.3.3.3 Top Plate Splices

To maintain the integrity of framed walls when a top plate splice is required, attach the double top 

plates together per Table G-8. Please note that the maximum roof span of 36 feet (per Figure G-1) 

and the maximum aspect ratio of 2.25 (per Tables G-5, G-6, and G-7) limit overall building length 

to a maximum of 81 feet.

Table G-8: Top Plate Splice Guide 

Splice Length

Building Dimension of Wall Containing Top Plate Splice (ft)

24 28 32 36 40 50 60 70 80

Number of 16d Common Nails per Each Side of Splice

2 ft 8 NP NP NP NP NP NP NP NP

4 ft 8 10 12 14 16 NP NP NP NP

6 ft 8 10 12 14 16 20 24 NP NP

8 ft 8 10 12 14 16 20 24 28 32

ft = feet NP = Not permitted 

SOURCE: COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA

G.3.3.4 Openings in Walls

Wall openings disrupt the continuous load path required to transfer wind forces through framed 

walls. Enhanced building performance of framed walls is achieved by installing uplift connector 

hardware around wall openings. Headers and plates at wall openings should be attached to the 

framed wall studs at each end with connectors designed to resist the uplift and lateral loads shown 

in Table G-9 for the corresponding header spans. Table G-9 also shows the number of full-height 

studs required at each end. Install hardware around framed wall openings as recommended in 

Table G-10. Please refer to Table G-2 for hardware specifications.

Table G-9: Connection Loads at Each End of Exterior Wall Headers

Header Span Number of FullHeight Studs Uplift Load (lb) Lateral Load (lb)

3 ft 2 689 278

4 ft 2 918 370

5 ft 3 1,148 463

6 ft 3 1,377 555

8 ft 3 1,836 740

10 ft 4 2,295 925

lb = pounds ft = feet

SOURCE: COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA
G-18 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Table G-10: Connector Requirements at Each End of Exterior Wall Headers

Header Span Number of 

Full-Height Studs

Uplift Connector 

Type* (#)** Lateral Connector Type

3 ft 2 A (10) C

4 ft 2 A (12) C

5 ft 3 B (14) D

6 ft 3 B (18) D

8 ft 3 A × 2 (12 each) C × 2

10 ft 4 B × 2 (14 each) D × 2

ft = feet

* Refer to Table G-2 for model number and fasteners 

** (#) = Number of nails required in each end of strap

SOURCE: ADAPTED (WITHOUT HARDWARE SPECIFICATIONS) COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-19

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

G.3.3.5 Wall-to-Floor Connection

Table G-11 shows the uplift and lateral loads to resist between the top plate and framed wall stud 

based on stud spacing and roof span. As previously noted in the section on wall sheathing, APA 

recommends attaching adjacent wall sheathing panels to one another, over common framing, to 

provide lateral and uplift continuity. To this end, wood wall sheathing panels should be extended 

upward from the first-floor walls and downward from the second-floor walls to meet at the midpoint 

of the second-floor band joist. Likewise, the wood wall sheathing panels from the first-floor walls 

should be extended downward to lap the sill plate at the foundation level. Connector requirements 

to resist wall-to-wall uplift loads are shown in Tables G-12 to G-14, and hardware specifications 

are shown in Table G-2. The number of 16d common nails (through single plate adjacent to stud) 

required to resist lateral loads is shown in Tables G-12 to G-14. 

Table G-11: Top Plate-to-Stud-Connection Loads

Roof Framing Span (ft) 

Lateral (lb)

Stud Spacing

24 28 32 36

Uplift (lb)

12-in. o.c. 331 375 416 458 185

16-in. o.c. 442 499 555 611 247

24-in. o.c. 664 748 833 917 370

in. = inches ft = feet lb = pounds

SOURCE: COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA

Table G-12: Top Plate-to-Stud Connector Requirements

Roof Framing Span (ft) Lateral

Stud Spacing

24 28 32 36 No. of 16d 

Common Nails 

Connector Type* (end-nailed)

12-in. o.c. E E E E 2

16-in. o.c. E F F J 2

24-in. o.c. K K K I 3

in. = inches ft = feet o.c. = on center

* Refer to Table G-2 for model number and fasteners

SOURCE: ADAPTED (WITHOUT HARDWARE SPECIFICATIONS) COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA
G-20 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Table G-13: Stud-to-Stud Connection Requirements

Roof Framing Span (ft) Lateral

Stud Spacing

24 28 32 36 No. of 16d 

Common Nails 

Number of 10d Common Nails in Connector A (end-nailed) *

12-in. o.c. 4 4 6 6 2

16-in. o.c. 6 6 6 8 2

24-in. o.c. 8 8 10 10 3

in. = inches ft = feet o.c. = on center 

* Install half the nails in each end of the strap to studs. Cut strap cut to length so that required number of nails can be installed in each 

end. Refer to Table G-2 for model number and fasteners.

SOURCE: ADAPTED (WITHOUT HARDWARE SPECIFICATIONS) COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-21

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

Table G-14: Stud-to-Bottom Plate Connector Requirements

Roof Framing Span (ft) Lateral

Stud Spacing

24 28 32 36 No. of 16d 

Common Nails 

Connector Type* (end-nailed)

12-in. o.c. L L M M 2

16-in. o.c. M M N N 2

24-in. o.c. N N N O 3

in. = inches ft = feet o.c. = on center 

* Refer Table G-2 for model number and fasteners.

SOURCE: ADAPTED (WITHOUT HARDWARE SPECIFICATIONS) COURTESY, AMERICAN WOOD COUNCIL, LEESBURG, VA
G-22 MITIGATION ASSESSMENT TEAM REPORT TORNADO OUTBREAK OF 2011

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

G.4 References

ANSI/AAMA/NWWDA (American National Standards Institute/American Architectural 

Manufacturers Association/National Wood Window and Door Association). 1997. Voluntary 

Specifications for Aluminum, Vinyl (PVC) and Wood Windows and Glass Doors, ANSI/AAMA/

NWWDA 101/I.S.2.

ANSI/AAMA/WDMA (Window and Door Manufacturers Association). 2002. Voluntary Performance 

Specification for Windows, Skylights and Glass Doors, ANSI/AAMA/WDMA 101/I.S.2/NAFS.

ANSI/DASMA (Door & Access Systems Manufacturers Association). 2005. Standard Method 

for Testing Sectional Garage Doors and Rolling Doors: Determination of Structural 

Performance Under Uniform Static Air Pressure Difference, ANSI/DASMA 108.

ANSI/WDMA/CSA (Canadian Standards Association). 2005. NAFS – North American 

Fenestration Standard/Specification for Windows, Doors, and Skylights, ANSI/WDMA/

CSA 101/I.S.2/A440.

APA (The Engineered Wood Association). 2011. Building for High Wind Resistance 

in Light-Frame Wood Construction. August. http://www.apawood.org/level_c.

cfm?content=pub_searchresults&pK=Form%20M310&pF=Yes.

ASCE. 2005. Minimum Design Loads of Buildings and Other Structures. ASCE Standard ASCE 7-05.

ASTM International. 2009. Standard Specification for Performance of Exterior Windows, Curtain Walls, 

Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes, ASTM E1996. 

West Conshohocken, PA.

ASTM International. 2005. Standard Test Method for Performance of Exterior Windows, Curtain 

Walls, Doors, and Impact Protective Systems Impacted by Missile(s) and Exposed to Cyclic Pressure 

Differentials, ASTM E1886. West Conshohocken, PA.

AWC (American Wood Council). 2006. Wood Frame Construction Manual (WFCM): Guide to Wood 

Construction in High Wind Areas for One- and Two-Family Dwellings, 130 mph, Exposure B. In 

cooperation with the International Code Council. American Forest & Paper Association, 

Inc.: Washington, DC.

DASMA. 2003. Connecting Garage Door Jambs to Building Framing. Technical Data Sheet 161. 

Cleveland, OH. December 2.

DASMA. 2001. Wood Horizontal and Vertical Back Jamb Detail Guidelines. Technical Data Sheet 156. 

Cleveland, OH. August 1.

FEMA. 2010a. “Asphalt Shingle Roofing for High Wind Regions,” Technical Fact Sheet 7.3, Home 

Builder’s Guide to Coastal Construction. FEMA P-499. December.
TORNADO OUTBREAK OF 2011 MITIGATION ASSESSMENT TEAM REPORT G-23

RECOMMENDATIONS FOR ONE- AND TWO-FAMILY RESIDENTIAL BUILDINGS

FEMA. 2010b. “Attachment of Brick Veneer in High Wind Regions,” Technical Fact Sheet 5.4, Home 

Builder’s Guide to Coastal Construction. FEMA P-499. December.

FEMA. 2010c. Home Builder’s Guide to Coastal Construction. FEMA P-499. December.

FEMA. 2010d. “Metal Roof Systems in High-Wind Regions,” Technical Fact Sheet 7.6, Home Builder’s 

Guide to Coastal Construction. FEMA P-499. December.

FEMA. 2010e. “Minimizing Water Intrusion through Roof Vents in High-Wind Regions,” Technical 

Fact Sheet 7.5, Home Builder’s Guide to Coastal Construction. FEMA P-499. December.

FEMA. 2010f. “Protection of Openings – Shutters and Glazing,” Technical Fact Sheet 6.2, Home 

Builder’s Guide to Coastal Construction. FEMA P-499. December.

FEMA. 2010g. “Roof Sheathing Installation,” Technical Fact Sheet 7.1, Home Builder’s Guide to Coastal 

Construction. FEMA P-499. December.

FEMA. 2010h. “Roof Underlayment for Asphalt Shingle Roofs,” Technical Fact Sheet 7.2, Home 

Builder’s Guide to Coastal Construction. FEMA P-499. December.

FEMA. 2010i. “Siding Installation in High Wind Regions,” Technical Fact Sheet 5.3, Home Builder’s 

Guide to Coastal Construction. FEMA P-499. December.

FEMA. 2010j. “Tile Roofing for High-Wind Areas,” Technical Fact Sheet 7.4, Home Builder’s Guide to 

Coastal Construction. FEMA P-499. December.

FEMA. 2008. Design and Construction Guidance for Community Safe Rooms. FEMA 361. August. 

Second Edition.

ICC. 2012. International Residential Code for One- and Two-Family Dwellings. Birmingham, AL.

ICC. 2009. International Residential Code for One- and Two-Family Dwellings. Birmingham, AL.

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