FEMA

Risk Management Series

Design Guide for Improving Critical Facility Safety 
from Flooding and High Winds

FEMA 543 / January 2007 


Any opinions, findings, conclusions, or recommendations 
expressed in this publication do not necessarily reflect the views of 
FEMA. Additionally, neither FEMA or 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.


FOREWORD AND ACKNOWLEDGMENTS 
BACKGROUND

On August 29, 2005, Hurricane Katrina caused extensive 
damage to the coast along the Gulf of Mexico, resulting 
in an unprecedented relief, recovery, and reconstruction 
effort. This reconstruction presents a unique opportunity to rebuild 
the communities and public infrastructure using the latest 
hazard mitigation techniques proven to be more protective of lives 
and property. 

Critical facilities comprise all public and private facilities deemed 
by a community to be essential for the delivery of vital services, 
protection of special populations, and the provision of other services 
of importance for that community. This manual concentrates 
on a smaller group of facilities that are crucial for protecting the 
health and safety of the population: health care, educational, and 
emergency response facilities.

The Design Guide for Improving Critical Facility Safety from Flooding 
and High Winds (FEMA 543) was developed with the support of 
the Federal Emergency Management Agency (FEMA) Region 
IV in the aftermath of Hurricane Katrina. This manual recommends 
incorporating hazard mitigation measures into all stages 
and at all levels of critical facility planning and design, for both 
new construction and the reconstruction and rehabilitation of 
existing facilities. It provides building professionals and decisionmakers 
with information and guidelines for implementing 
a variety of mitigation measures to reduce the vulnerability to 
damage and disruption of operations during severe flooding and 
high-wind events. The underlying theme of this manual is that 
by building more robust critical facilities that will remain operational during 
and after a major disaster, peoples lives and the 
communitys vitality can be better preserved and protected. 

This manual is a part of FEMAs Risk Management Series, which 
provides guidelines for mitigating against multiple hazards. The 
series emphasizes mitigation best practices for specific building 
uses, such as schools, hospitals, higher education buildings, 
multi-family dwellings, commercial buildings, and light industrial 
facilities. 

OBJECTIVES

The poor performance of many critical facilities in the affected 
areas was not unique to Hurricane Katrina. It was observed in numerous 
hurricanes dating back more than three decades. Several 
reasons may explain this kind of performance. In many cases the 
damaged facilities were quite old and were constructed well before 
the introduction of modern codes and standards. Some of 
the older facilities were damaged because building components 
had deteriorated as a result of inadequate maintenance. Many facilities 
occupy unsuitable buildings that were never intended for 
this type of use. Some newer facilities suffered damage as a result 
of deficiencies in design and construction or the application of inappropriate 
design criteria and standards.

The primary objective of this manual is to assist the building 
design community and local officials and decisionmakers in 
adopting and implementing sound mitigation measures that will 
decrease the vulnerability of critical facilities to major disasters. 

The goals of this manual are to:

-- Present and recommend the use of building design features 
and building materials and methods that can improve the 
performance of critical facilities in hazard-prone areas during 
and after flooding and high-wind events. 
-- Introduce and provide guidelines for implementing flooding 
and high-wind mitigation best practices into the process of 
design, construction, and operation and maintenance of 
critical facilities. 

SCOPE 

To aid in the reconstruction of the Gulf Coast in the wake of 
Hurricane Katrina, this manual presents an overview of the principal 
planning and design considerations for improving the 
performance of critical facilities during, and in the aftermath of, 
flooding and high-wind events. It provides design guidance and 
practical recommendations for protecting critical facilities and 
their occupants against these natural hazards. The focus is on the 
design for new construction, but this manual also addresses rehabilitation 
of existing critical facilities. It presents incremental 
approaches that can be implemented over time to decrease the 
vulnerability of buildings, but emphasizes the importance of incorporating 
the requirements for mitigation against flooding and 
high winds into the planning and design of critical facilities from 
the very beginning of the process. 

The material and recommendations contained in this manual are 
applicable to many facilities, but address primarily the following 
critical facilities:

-- Schools
-- Health Care Facilities
-- Fire Stations
-- Police Stations
-- Emergency Operation Centers (EOCs)

The information presented in this manual provides a comprehensive 
survey of the methods and processes necessary to protect 
critical facilities from natural hazards, but is necessarily limited. 
It is not expected that the reader will be able to use this information 
directly to develop plans and specifications. It is intended as 
an introduction to a broader understanding of the fundamental 
approaches to risk mitigation planning and design. This will help 
building officials and professionals move on to the implementation 
phase that involves consultants, procurement personnel, and 
project administrators, with a better grasp of the task in front of 
themimproving the safety and welfare of their communities. 

TARGET AUDIENCE

This manual describes various mitigation measures that have been 
successful in the past and could be implemented quickly, especially 
in areas recovering from a disaster. The intended audience comprises 
the people who own, operate, design, build, and maintain 
critical facilities in hazard-prone areas. This includes planning, 
building design, and construction professionals working for private 
organizations, State and local government officials working in 
the building sector, and relevant technical and management personnel 
involved with the operation of critical facilities. 

TRAINING

In tandem with the publication of this manual, FEMA has developed 
a companion training course targeted to building design 
professionals and facility managers interested in improving the 
functionality of critical facilities in natural disasters. For transfer of 
its content, FEMA will promote a series of workshops directed at 
these professionals and others involved in planning, design, construction, 
rehabilitation, and management of critical facilities in 
areas exposed to flooding and high winds.

The training course emphasizes the best practices in mitigating 
against flooding and winds hazards. It is organized around a series 
of exercises, starting with vulnerability analysis, and progressing 
through assessment of risks, assessment of building systems performance 
(especially the effects of physical damage on the facilitys 
functionality), and the selection of appropriate mitigation measures 
to be incorporated into the design of critical facilities.

The expansive scope of reconstruction activities in the aftermath 
of Hurricane Katrina requires that this course be initially offered 
and delivered only to affected communities in the Gulf States. 
However, the relevance and usefulness of this course extends far 
beyond the hurricane-prone regions, to areas exposed to other 
wind hazards, as well as areas subject to all types of coastal and riverine 
flooding. 

ORGANIZATION AND CONTENTS

This manual is divided into four main chapters. 

Chapter 1 presents an overview of the principal design considerations 
to help owners, managers, and designers when 
determining the location, building characteristics, and hazard resistance 
of critical facilities. It outlines the basic principles and 
design tools for improving the safety of critical facilities exposed 
to flooding and high winds. It also provides guidelines for facility 
managers and building professionals on how to coordinate the 
process of planning and design of critical facilities.

Chapter 2 discusses the nature of flood forces and their effects 
on buildings. It outlines the procedures for risk assessment, 
and describes current mitigation methods for reducing the effects 
of flooding. It underlines the need to avoid high-risk areas 
for the construction of new critical facilities, and encourages 
the application of mitigation measures when critical facilities 
must remain in high-risk areas. This chapter provides extensive 
review of the requirements of the National Flood Insurance 
Program (NFIP), model building codes and other standards, 
as well as new FEMA policy updates resulting from the experiences 
of Hurricanes Katrina and Rita.

Chapter 3 discusses the effects of wind forces on the structural 
and nonstructural building components of critical facilities. By reviewing 
numerous examples of wind-induced damage to these 
facilities, it points out the best practices pertaining to new construction 
and rehabilitation of existing facilities. It concentrates 
on building components most critical for protecting the uninterrupted 
operation of critical facilities and provides detailed 
guidelines for improving their design and construction in hurricane- 
and tornado-prone areas.

Chapter 4 discusses the performance of hospital, schools, and 
emergency response facilities (i.e., EOCs, and police and fire 
rescue stations) during Hurricane Katrina. This chapter emphasizes 
the lessons learned about the adverse effects on the 
functionality of critical facilities arising from damage to buildings 
and contents, especially the ways that various types of physical 
damage disrupted their operations.

Appendix A contains a list of acronyms and Appendix B contains a 
glossary of terms that appear in this manual. Appendix C contains 
an overview of the FEMA grant programs available for funding 
construction or rehabilitation of critical facilities. 

ACKNOWLEDGMENTS

The preparation of this document was sponsored by FEMA 
Region IV. It has been developed based on the work of several recent 
publications (as listed below), new insights from the Katrina 
Mitigation Assessment Teams in the field, and other sources of information 
on Hurricane Katrina. The principal and contributing 
authors of the following documents are gratefully acknowledged: 
FEMA 424, Design Guide for Improving School Safety in Earthquakes, 
Floods, and High Winds; FEMA 489, Mitigation Assessment Team 
Report for Hurricane Ivan in Alabama and Florida; FEMA Region 
IV, Hurricane Mitigation: A Handbook for Public Facilities; FEMA 
Region X, Earthquake Hazard Mitigation Handbook for Public 
Facilities; Structural Engineers Association of Washington (SEAW) 
Commentary on Wind Provisions (Volumes 1 and 2); and other reference 
documents presented in Chapter 1. 

For this manual, the following individuals are acknowledged:

Authors:

Rebecca C. Quinn, RCQuinn Consulting, Inc. 

Thomas L. Smith, TLSmith Consulting

Bogdan Srdanovic, URS

William Coulbourne, URS

Jon Heintz, ATC

Lisa Scola, PBS&J

Wilbur H. Tusler, Consultant

Douglas A. Ramirez, PBS&J

William Brown, PBS&J

Pedro Escobar, PBS&J

Shaddy Shafie, PBS&J

Scott Sundberg, URS

Milagros Nanita Kennett, FEMA, Project Officer, Risk 
Management Series Publications

Contributors:

Shabbar Saifee, FEMA, Project Monitor

Eric Letvin, URS, Project Manager

Mark Matulik, Consultant

Lawrence Frank, URS

John Squerciati, Dewberry

Wanda Rizer, design4impact 

Mike Robinson, PBS&J 

Manuel Perotin, PBS&J

Susan Patton, URS

Rob Fernandez, URS

Janet Frey, URS

The authors and editors gratefully acknowledge the invaluable assistance 
and advice provided by the following reviewers:

Christopher Arnold, Building Systems Development Inc.; 
Ronald B. Bailey, Bailey Engineering Corp.; Bob Baker, BBJ 
Environmental Solutions, Inc.; Ron A. Cook, University of Florida; 
Jim Fields; Doug Fitts, St. Louis County Public Works; Lois Forster, FEMA; David 
Godschalk, University of North Carolina; 
Neil Grigg, Colorado State University; John Ingargiola, FEMA; 
Philip Keillor, American Society of Flood Plain Managers; Leon 
Kloostra; Richard Kuchnicki, International Code Council; 
Lawrence Larson, ASFPM; Sheila McKinley, Christopher B. Burke 
Engineering; Nancy McNabb, NFPA; Elliott Mittler; Ann Patton, 
Ann Patton Company; Dan Powell, FEMA; Dennis Quan, FEMA; 
Jim Rossberg, ASCE; Michael P. Sheerin, TLC Engineering for 
Architecture; Emil Simiu, NIST; Robert Slynn, University of 
Florida; Alan Springett, FEMA; Thomas Sputo, University of 
Florida; Jim Tauby; Anton TenWolde; Scott Tezak, URS; David 
Underwood; Wallace A. Wilson.

This manual will be revised periodically and FEMA welcomes 
comments and suggestions for improvements in future editions. 
Please send your comments and suggestions via e-mail to: 
RiskManagementSeriesPubs@dhs.gov


TABLE OF CONTENTS

FOREWORD AND 
Acknowledgments.................................................................
.......i
Background......................................................................
....................................................i

Objectives......................................................................
......................................................ii

Scope 
................................................................................
.................................................iii

Target 
Audience........................................................................
..........................................iv

Training 
................................................................................
..............................................iv

Organization and 
Contents........................................................................
.........................v

Acknowledgements................................................................
.............................................vi

Chapter 1 Critical facility design 
considerations.............................1-1
1.1 
Introduction....................................................................
.................................................1-1

1.1.1 Critical 
Facilities......................................................................
..........................1-2

1.1.2 Hurricane 
Katrina.........................................................................
....................1-3

1.2 Hazard 
Mitigation......................................................................
........................................1-7

1.2.1 Hazard Mitigation for Critical 
Facilities...........................................................1-7

1.2.2 Site Selection 
................................................................................
....................1-8

1.2.3 Facility Design 
................................................................................
.................1-10

1.3 Performance-Based 
Design..........................................................................
......................1-14

1.3.1 
Background......................................................................
................................1-14

1.3.2 Prescriptive vs. Performance-Based 
Design...................................................1-15

1.3.3 The Process of Performance-Based Design of Critical 
Facilities..................1-16

1.3.4 Acceptable Risk and Performance 
Levels......................................................1-17

1.3.5 Performance-Based Flood Design 
.................................................................1-22

1.3.6 Performance-Based High-Wind Design 
........................................................1-23

1.4 
References......................................................................
...............................................1-25

Chapter 2 Making Critical facilities safe from flooding...........2-1
2.1 General Design 
Considerations..................................................................
...........................2-1

2.1.1 Nature and Characteristics of 
Flooding...........................................................2-1

2.1.1.1 Probability of Occurrence or 
Frequency.......................................2-7

2.1.1.2 Hazard Identification and Flood 
Data..........................................2-9

2.1.1.3 Design Flood Elevation 
...............................................................2-15

2.1.1.4 Advisory Base Flood Elevation 
....................................................2-16

2.1.2 Flood 
Loads...........................................................................
..........................2-17

2.1.2.1 Design Flood Depth 
.....................................................................2-18

2.1.2.2 Design Flood Velocity
Riverine.................................................2-19

2.1.2.3 Design Flood Velocity
Coastal...................................................2-20

2.1.2.4 Hydrostatic 
Loads.........................................................................2-
21

2.1.2.5 Hydrodynamic 
Loads...................................................................2-23

2.1.2.6 Debris Impact 
Loads.....................................................................2-25

2.1.2.7 Erosion and Localized 
Scour.......................................................2-27

2.1.3 Floodplain Management Requirements and Building Codes 
.....................2-28

2.1.3.1 Overview of the 
NFIP...................................................................2-29

2.1.3.2 Summary of the NFIP Minimum Requirements ........................2-31

2.1.3.3 Executive Order 11988 and Critical Facilities 
............................2-33

2.1.3.4 Scope of Model Building Codes and Standards ........................2-34

2.2 Critical Facilities Exposed to Flooding 
................................................................................
.2-37

2.2.1 Evaluating Risk and Avoiding Flood 
Hazards................................................2-37

2.2.1.1 Benefits/Costs: Determining Acceptable 
Risk............................2-38

2.2.1.2 Identifying Flood Hazards at Critical Facilities 
Sites..................2-40

2.2.1.3 Critical Facilities as Emergency Shelters 
....................................2-40

2.2.2 Vulnerability: What Flooding Can Do to Existing Critical 
Facilities............2-41

2.2.2.1 Site 
Damage..........................................................................
........2-42

2.2.2.2 Structural 
Damage........................................................................2-
43

2.2.2.3 Nonstructural 
Damage.................................................................2-46

2.2.2.4 Utility System 
Damage..................................................................2-49

2.2.2.5 Contents 
Damage.........................................................................2
-52

2.3 Requirements and Best Practices in Special Hazard 
Areas.......................................................2-55

2.3.1 Risk Reduction in A Zones 
..........................................................................2-55

2.3.1.1 Site 
Modifications...................................................................
......2-55

2.3.1.2 Elevation 
Considerations.............................................................2-58

2.3.1.3 Flood-Resistant Materials 
............................................................2-62

2.3.1.4 Dry Floodproofing Considerations 
.............................................2-64

2.3.2 Risk Reduction in V Zones 
..........................................................................2-68

2.3.2.1 Elevation 
Considerations.............................................................2-69

2.3.2.2 Flood-Resistant Materials 
............................................................2-70

2.3.3 Risk Reduction in Coastal A Zones 
............................................................2-70

2.3.4 Risk Reduction in Hurricane Storm Surge Areas 
.........................................2-72

2.3.5 Risk Reduction for Related 
Facilities.............................................................2-73

2.3.5.1 Access Roads 
................................................................................
2-73

2.3.5.2 Utility Installations 
.......................................................................2-74

2.3.5.3 Potable Water and Wastewater 
Systems.......................................2-76

2.3.5.4 Storage Tank Installations 
...........................................................2-77

2.3.5.5 Accessory Structures 
....................................................................2-77

2.4 Risk Reduction for Existing Critical 
Facilities......................................................................
...2-78

2.4.1 
Introduction....................................................................
.................................2-78

2.4.2 Site Modifications 
................................................................................
...........2-79

2.4.3 Additions 
................................................................................
.........................2-81

2.4.4 Repairs, Renovations, and 
Upgrades..............................................................2-82

2.4.5 Retrofit Dry Floodproofing 
............................................................................2-83

2.4.6 Utility Installations 
................................................................................
..........2-84

2.4.7 Potable Water and Wastewater 
Systems..........................................................2-86

2.4.8 Other Damage Reduction Measures 
.............................................................2-87

2.4.9 Emergency 
Measures........................................................................
...............2-88

2.5 Checklist for Building Vulnerability of Flood-Prone Critical 
Facilities..............................................2-91

2.6 References and Sources of Additional 
Information....................................................................2
-100

Chapter 3 Making Critical facilities safe from High wind.........3-1
3.1 General Design 
Considerations..................................................................
...........................3-1

3.1.1 Nature of High 
Winds...........................................................................
............3-2

3.1.2 Probability of 
Occurrence......................................................................
...........3-5

3.1.3 Wind/Building 
Interactions....................................................................
.........3-8

3.1.4 Building 
Codes...........................................................................
.....................3-18

3.1.4.1 Scope of Building 
Codes..............................................................3-18

3.1.4.2 Effectiveness and Limitations of Building Codes.......................3-
19

3.2 Critical Facilities Exposed to High 
Winds...........................................................................
...3-23

3.2.1 Vulnerability: What High Winds Can Do to Critical 
Facilities......................3-23

3.2.1.1 Types of Building 
Damage...........................................................3-23

3.2.1.2 Ramifications of 
Damage.............................................................3-26

3.2.2 Evaluating Critical Facilities for Risk From High 
Winds...............................3-29

3.2.2.1 New 
Buildings.......................................................................
........3-29

3.2.2.2 Existing 
Buildings.......................................................................
..3-30

3.3 Critical Facility Design 
Considerations..................................................................
...............3-32

3.3.1 General Design 
Considerations..................................................................
....3-32

3.3.1.1 Site 
................................................................................
................3-33

3.3.1.2 Building 
Design..........................................................................
....3-34

3.3.1.3 Construction Contract 
Administration.........................................3-40

3.3.1.4 Post-Occupancy Inspections, Periodic Maintenance, 
Repair, and 
Replacement...............................................................3-41

3.3.2 Structural 
Systems.........................................................................
...................3-42

3.3.3 Building Envelope 
................................................................................
..........3-48

3.3.3.1 Exterior 
Doors...........................................................................
...3-48

3.3.3.2 Windows and 
Skylights.................................................................3-53

3.3.3.3 Non-Load-Bearing Walls, Wall Coverings, and Soffits................3-56

3.3.3.4 Roof 
Systems.........................................................................
........3-71

3.3.4 Nonstructural Systems and 
Equipment..........................................................3-81

3.3.4.1 Exterior-Mounted Mechanical Equipment.................................3-
82

3.3.4.2 Exterior-Mounted Electrical and Communications 
Equipment.......................................................................
.............3-90

3.4 Best Practices in Hurricane-Prone 
Regions.........................................................................
..3-98

3.4.1 Site and General Design 
Considerations.....................................................3-100

3.4.2 Structural Systems 
................................................................................
.........3-101

3.4.3 Building Envelope 
................................................................................
........3-102

3.4.3.1 Exterior Doors 
...........................................................................3-102

3.4.3.2 Windows and Skylights 
..............................................................3-103

3.4.3.3 Non-Load-Bearing Walls, Wall Coverings, and Soffits .............3-106

3.4.3.4 Roof Systems 
..............................................................................3-
107

3.4.4 Nonstructural Systems and 
Equipment........................................................3-114

3.4.4.1 Elevators 
................................................................................
....3-114

3.4.4.2 Mechanical 
Penthouses..............................................................3-115

3.4.4.3 Lightning Protection Systems 
(LPS).........................................3-115

3.4.5 Municipal Utilities 
................................................................................
........3-120

3.4.5.1 Electrical Power 
.........................................................................3-121

3.4.5.2 Water Service 
.............................................................................3-
122

3.4.5.3 Sewer Service 
..............................................................................3-
123

3.4.6 Post-Design Considerations 
.........................................................................3-124

3.4.6.1 Construction Contract Administration 
....................................3-124

3.4.6.2 Periodic Inspections, Maintenance, and Repair .....................3-124

3.5 Best Practices in Tornado-Prone 
Regions.........................................................................
........3-126

3.6 Remedial Work on Existing 
Facilities......................................................................
...........3-132

3.6.1 Structural 
Systems.........................................................................
.................3-134

3.6.2 Building Envelope 
................................................................................
........3-137

3.6.2.1 Sectional and Rolling 
Doors......................................................3-137

3.6.2.2 Windows and 
Skylights...............................................................3-138

3.6.2.3 Roof 
Coverings.......................................................................
.....3-141

3.6.3 Exterior-Mounted 
Equipment......................................................................3
-144

3.6.3.1 Antenna (Communications 
Mast).............................................3-144

3.6.3.2 Lightning Protection 
Systems....................................................3-145

3.7 Checklist for Building Vulnerability of Critical Facilities Exposed to High 
Winds........................3-147

3.8 References and Sources of Additional Information 
..............................................................3-153

Chapter 4 Observations on the Performance of 
Critical 
facilities......................................................................
........................................4-1
4.1 
Introduction....................................................................
.................................................4-1

4.2 Health Care 
Facilities......................................................................
....................................4-3

4.2.1 
Background......................................................................
....................................4-3

4.2.2 Effects of 
Flooding........................................................................
.......................4-5

4.2.3 Effects of High 
Winds...........................................................................
...............4-6

4.2.4 Site 
Design..........................................................................
..................................4-6

4.2.5 Architectural 
Design..........................................................................
..................4-9





4.2.6 Building 
Envelope........................................................................
.....................4-11

4.2.7 Utility Plumbing 
Systems.........................................................................
..........4-16

4.2.8 Mechanical and Electrical 
Systems...................................................................4-18

4.2.10 Communications 
Systems.........................................................................
.........4-21

4.2.11 Nonstructural and Other 
Systems....................................................................4-23

4.2.12 
Summary.........................................................................
....................................4-25

4.3 Educational Facilities 
................................................................................
.......................4-26

4.3.1 
Background......................................................................
..................................4-26

4.3.2 Effects of 
Flooding........................................................................
.....................4-28

4.3.3 Effects of High 
Winds...........................................................................
.............4-29

4.3.4 Site 
Selection.......................................................................
...............................4-30

4.3.5 Architectural 
Design..........................................................................
................4-32

4.3.6 Structural 
Systems.........................................................................
.....................4-34

4.3.7 Building 
Envelope........................................................................
.....................4-35

4.3.8 Utility 
Systems.........................................................................
...........................4-39

4.3.9 Mechanical and Electrical 
Systems...................................................................4-39

4.3.10 Nonstructural and Other 
Systems....................................................................4-40

4.3.11 Equipment and Auxiliary 
Installations............................................................4-42

4.3.12 
Summary.........................................................................
....................................4-43

4.4 Emergency Response Facilities 
................................................................................
............4-45

4.4.1 
Background......................................................................
..................................4-45

4.4.2 Effects of 
Flooding........................................................................
.....................4-47

4.4.3 Effects of High 
Winds...........................................................................
.............4-48

4.4.4 Site 
Selection.......................................................................
...............................4-48

4.4.5 Architectural 
Design..........................................................................
................4-51

4.4.6 Structural 
Systems.........................................................................
.....................4-54

4.4.7 Building 
Envelope........................................................................
.....................4-56

4.4.8 Utility Plumbing 
Systems.........................................................................
..........4-61

4.4.9 Mechanical and Electrical Systems 
..................................................................4-62

4.4.10 Communications 
Systems.........................................................................
.........4-65

4.4.11 Equipment and Auxiliary 
Installations............................................................4-66

4.4.12 
Summary.........................................................................
....................................4-67

APPENDICES

Appendix A 
Acronyms........................................................................
....................................A-1

Appendix B Glossary of 
Terms...........................................................................
......................B-1

Appendix C FEMA Mitigation 
Programs........................................................................
............C-1

Public Assistance (Section 
406)............................................................................
C-4

Hazard Mitigation Grant Program (Section 
404)...............................................C-7

Pre-Disaster Mitigation (Section 203) 
.................................................................C-8

Flood Mitigation Assistance 
Program...................................................................C-9

[End of Front Matter]

1.1 INTRODUCTION

This chapter introduces the role of hazard mitigation in the 
planning, design, and construction of critical facilities. It 
describes the way building design determines how well a 
critical facility is protected against natural hazard risks, specifically 
the risks associated with flooding and high winds. Critical 
facilities, and the functions they perform, are the most significant 
components of the system that protects the health, safety, 
and well-being of communities at risk. 

The devastating effects of recent hurricanes, especially Hurricane 
Katrina, underscored the vulnerability of coastal areas of the 
United States, the fastest growing regions of the country. The population 
pressure and the aggressive coastal development in areas 
subject to hurricanes and coastal storms created the conditions 
that require careful consideration of the effects of natural hazards 
on the sustainability of this development. One of the most important 
determinants of the sustainability of coastal communities is 
the reliability of their physical and social infrastructure. The communities 
that cannot rely on their own critical infrastructure are 
extremely vulnerable to disasters. This is why the design of critical 
facilities to improve their resistance to damage, and their ability 
to function without interruption during and in the aftermath of 
hazard events, deserves special attention. 

To ensure safe and uninterrupted operation of critical facilities, 
which is vital in the post-disaster period, facility owners must incorporate 
a comprehensive approach to identify hazards and avoid them when feasible. In 
cases when exposure to hazards is unavoidable, it is recommended that they build 
new facilities, or rehabilitate the existing ones to resist the forces and 
conditions associated with these hazards. 

1.1.1 Critical Facilities

In general usage, the term critical facilities is used to describe 
all manmade structures or other improvements that, because of 
their function, size, service area, or uniqueness, have the potential 
to cause serious bodily harm, extensive property damage, or 
disruption of vital socioeconomic activities if they are destroyed, 
damaged, or if their functionality is impaired. 

Critical facilities commonly include all public and private facilities 
that a community considers essential for the delivery of vital 
services and for the protection of the community. They usually 
include emergency response facilities (fire stations, police stations, 
rescue squads, and emergency operation centers [EOCs]), 
custodial facilities (jails and other detention centers, long-term 
care facilities, hospitals, and other health care facilities), schools, 
emergency shelters, utilities (water supply, wastewater treatment 
facilities, and power), communications facilities, and any other assets 
determined by the community to be of critical importance for 
the protection of the health and safety of the population. The adverse 
effects of damaged critical facilities can extend far beyond 
direct physical damage. Disruption of health care, fire, and police 
services can impair search and rescue, emergency medical care, 
and even access to damaged areas. 

The number and nature of critical facilities in a community 
can differ greatly from one jurisdiction to another, and usually 
comprise both public and private facilities. In this sense, each 
community needs to determine the relative importance of the 
publicly and privately owned facilities that deliver vital services, 
provide important functions, and protect special populations. 

Minimum requirements for the design of new critical facilities 
and for improvements to existing facilities are found in the model 
building codes and the design and construction standards. ASCE 
7, Minimum Design Loads for Buildings and Other Structures, is the 
best known standard. Published by the American Society of Civil 
Engineers (ASCE), it classifies buildings and other structures into 
four categories based on occupancy. Most critical facilities fall into 
Category III or Category IV, described below: 

Category I includes buildings and other structures whose failure 
would represent a low hazard to human life, such as agricultural 
buildings and storage facilities.

Category II includes all buildings not specifically included in other 
categories.

Category III includes buildings and other structures that represent 
a substantial hazard to human life in the event of failure. They include 
buildings with higher concentrations of occupants (i.e., 
where more than 300 people congregate in one area). These are 
typically educational facilities with capacities greater than 250 for 
elementary and secondary facilities, 500 for colleges and adult education 
facilities, or 150 for daycare facilities. 

Category IV includes essential facilities such as hospitals, fire and 
police stations, rescue and other emergency service facilities, 
power stations, water supply facilities, aviation facilities, and other 
buildings critical for the national and civil defense. 

This manual concentrates on a number of critical or, as they are 
sometimes called, essential facilities, that deal with health and 
safety in emergencies, and include health care facilities, police and 
fire stations, EOCs, and schools. These facilities are chosen because 
of their vitally important role in protecting the health and safety of 
the community. Although limited in scope to several specific types 
of facilities, the information and recommendations in this manual 
are valuable and applicable to other types of critical facilities located 
in areas prone to flooding and exposed to high winds.

1.1.2 Hurricane Katrina

Although not the strongest storm to hit the coast of the United 
States, Hurricane Katrina caused the greatest disaster in the nation's 
history. The hurricane made its first landfall on August 25, 
2005, on the southeast coast of Florida as a Category 1 hurricane. 

It then crossed Florida into the Gulf of Mexico, where it gained 
strength to a Category 5 hurricane. Before making its second 
landfall near Buras in southeast Louisiana, Katrina weakened to 
a Category 3 hurricane. Moving across southeast Louisiana, Katrina 
continued northward, pushing storm surge into coastal areas 
of Alabama, Mississippi, and Louisiana. After crossing over Lake 
Borgne, it finally made a third landfall as a Category 3 hurricane 
near Pearlington, Mississippi, at the Louisiana/Mississippi border 
(see Figures 1-1 and 1-2). The hurricane caused extensive devastation 
along the gulf coast, with southeast Louisiana and the coast of 
Mississippi bearing the brunt of the catastrophic damage. 

Wind damage was widespread and severe in many areas; however, 
the greatest damage was caused by Hurricane Katrina's 
storm surge flooding. Although the storm weakened from 
a powerful Category 5 to a Category 3 hurricane just before 
making landfall in Louisiana and Mississippi, the storm surge 
appears to have maintained a level associated with a Category 
5 hurricane. The surge built by the stronger winds over open 
water could not dissipate as quickly as the wind speeds decreased, 
and the shallow depth of the off-shore shelf and the 
shape of the shoreline contributed to the high surge elevations. 
The Mississippi coastline experienced the highest storm surge 
on record. The storm surge also contributed to failures of a 
number of levees, notably the levee system that protects the City 
of New Orleans from Lake Borgne and Lake Pontchartrain. An 
estimated 80 percent of the city subsequently flooded. 

The disaster was further compounded by the poor performance 
of critical facilities during and after the storm. Critical facilities 
typically did not perform any better than ordinary commercial 
buildings, but the extent of the damage to these facilities and the 
subsequent disruption of their operations caused much greater 
hardship. Facilities such as hurricane evacuation shelters, police 
and fire stations, hospitals, and EOCs were severely damaged and 
many were completely destroyed. Some facilities experienced a 
loss of function when critical support equipment, such as vehicles 
and communication equipment, were damaged or destroyed. 
While most of the damage to critical facilities was caused by the 
storm surge, wind damage also was widespread and substantial. In 
several instances, critical facilities were destroyed completely or 
damaged so severely that all the occupants had to be evacuated 
after the hurricane had moved inland. The loss of so many critical 
facilities placed a severe strain on the emergency operations and 
recovery efforts.

Figure 1-1: Hurricane Katrinas path through Louisiana and Mississippi 
(based on hurricane storm track data from the National Hurricane Center)

The estimated death toll of Hurricane Katrina exceeded 1,800. More 
than 85 percent of casualties were recorded in Louisiana and about 
13 percent of victims lost their lives in Mississippi. Other deaths attributed 
both directly and indirectly to Katrina were reported in 
Florida, Alabama, Georgia, Kentucky, and Ohio. Hurricane Katrina 
ranks as the third deadliest hurricane in the United States, surpassed 
only by the Texas Hurricane at Galveston in 1900, where at 
least 6,000 and possibly as many as 10,000 lives were lost, and the 
Florida Hurricane at Lake Okeechobee in 1928, which claimed 
2,500 lives. Estimated total economic losses from Katrina are in 
excess of $150 billion, and insured losses are $40 billion, making 
Katrina the most expensive natural disaster in the nations history. 

Figure 1-2: Mississippi coast SLOSH NOAA data
SOURCE: National Oceanic and Atmospheric Administration (NOAA)

1.2 HAZARD MITIGATION

1.2.1 Hazard Mitigation for Critical 
Facilities

Mitigation can reduce the enormous cost of disasters to 
property owners, communities, and the government. 
Since the late 1980s, hazard mitigation has become 
well known in many parts of the country for 
initiatives in land use planning, adoption of 
building codes, elevation of homes, floodplain 
buyouts, and retrofitting buildings to resist 
damage in flooding, high winds, or seismic 
events. Incorporating mitigation measures 
in the planning and design of buildings is 
recommended because these measures reduce 
injuries and damage resulting from building 
failures during hazard events. Incorporating 
mitigation measures in the design of critical facilities, however, 
is crucial for minimizing the disruption of their operations and 
protecting the uninterrupted provision of critical services. 
The first Federal program to support State and local mitigation 
programs was established by the Stafford Act in 1988. Growing 
support and recognition of the need to improve disaster resistance 
led to passage of the Disaster Mitigation Act of 2000, which 
amended the Stafford Act. This statute reinforces the importance 
of comprehensive, multi-hazard mitigation planning, and emphasizes 
planning for disasters before they occur. As part of the 
planning process, States and communities 
are encouraged to identify existing critical facilities 
and to evaluate their vulnerability to 
natural hazards. To qualify for certain Federal 
mitigation grant programs, projects to rehabilitate 
critical facilities must be consistent with 
State and local mitigation plans. Appendix 
C provides an overview of conditions and requirements 
for obtaining funding assistance 
from major mitigation funding programs 
administered by the Federal Emergency Management 
Agency (FEMA). 

[text box]
Mitigation is defined as any sustained 
action taken to reduce or eliminate long-
term risk to life and property from hazard 
events. The goal is to save lives and 
reduce property damage in ways that are 
cost-effective and environmentally sound.
[end of text box]

There is no single procedure mandated for the 
planning, site selection, and design of critical 
facilities, because none can be assumed to be 
universally applicable. The decision to build a 
critical facility depends on many factors and requires 
a rigorous and comprehensive analysis of all the conditions 
that may affect the operation of a facility. This manual primarily addresses 
the design of new facilities and measures to improve the 
disaster resistance of existing facilities exposed to flooding and 
high winds, based on the assumption that all other alternatives to 
minimize or avoid such risks have been thoroughly evaluated and 
rejected as infeasible or impractical. It is outside the scope of this 
manual to try to depict in detail this evaluation process in its full 
range and complexity. Communities, as well as the owners and operators 
of critical facilities, must evaluate all alternatives, assess all 
risks, and consider all short-term and long-term effects of proposed 
projects, whenever construction or rehabilitation of these facilities 
is considered. Careful analysis of alternatives and the potential adverse 
effects of exposing critical facilities to natural hazards is also 
intended to help identify the most appropriate hazard-resistant 
measures when avoidance is not practical. 

1.2.2 Site Selection 

Site selection is a particularly significant step when planning new 
critical facilities or when planning substantial improvements to 
existing facilities in hazard-prone areas. The earliest steps in the 
planning process should be to identify hazards and assess the 
risks for the facility at the proposed site. In 
addition, alternative solutions should be 
considered in order to avoid site-specific hazards 
like floods. After decisions about the 
building location have been made, hazard 
mitigation involves acquiring a full understanding 
of the prevalent hazards and 
considering all appropriate hazard-resistance 
measures to ensure the uninterrupted operation 
of critical facilities. 

Since 1977, Federal agencies have been 
charged by Executive Order 11988 to 
provide leadership to reduce the risk of 
flood loss, to minimize the impact of floods 
on human safety, health and welfare, and 
to restore and preserve the natural and 
beneficial values served by floodplains in 
carrying out their responsibilities for (1) 
acquiring, managing, and disposing of 
Federal lands and facilities; (2) providing 
federally undertaken, financed, or assisted 
construction and improvements; and (3) 
conducting Federal activities and programs 
affecting land use, including but not limited to 
water and related land resources planning, 
regulating, and licensing activities.

Typically, the selection of a site for a critical facility is based on 
specific functions of a facility and the characteristics of its service 
area. In cases where critical facilities may be exposed to flooding 
and wind hazards, it is recommended that the final site decision 
be made only after all alternative sites have been evaluated for 
hazard exposure and the resulting effects of the hazard exposure 
on the design, construction, and operation of a facility. 

Considering that critical facilities should avoid hazard-prone areas, 
site selection may sometimes be a difficult and prolonged process. 
This is especially true in situations when the facility service requirements 
cannot be easily reconciled with requirements to minimize 
the exposure to hazards. Sometimes a facility, like a fire station for 
example, cannot fulfill its rapid response function if it is located 
outside the hazard zone, far from the area the facility is intended 
to serve. Additionally, site selection is not always controlled by the 
community. Many local jurisdictions report that the high cost and 
the scarcity of available land can severely limit the consideration of 
alternative locations. The consequences of accepting a flood-prone 
site include not only the potential physical damage, but also the 
loss of services provided by the critical facility. This loss of service 
can adversely affect the community as a whole, both in the immediate 
post-event period and during its long-term recovery. Section 
2.5.1 contains a discussion and a number of questions that can 
help guide determinations about whether the risks associated with 
building a critical facility in a floodplain are acceptable.

If the site selection process determines that no other practical 
and feasible alternatives are available and that a facility must be 
located in a hazard-prone area, the highest level of protection 
should be a design priority. 

All work on critical facilities must meet the 
minimum requirements of building codes and 
related regulations. However, the importance 
of uninterrupted operation of critical 
facilities frequently makes it necessary to go 
beyond the code requirements to provide 
acceptable levels of protection for the facilitys 
functionality during, and in the immediate 
aftermath of, a hazard event. 

1.2.3 Facility Design 

The nature of services provided by critical facilities requires 
that designers and decisionmakers define a design objective of 
achieving building performance levels beyond the minimum requirements 
prescribed by the building code. While compliance 
with the building code may satisfy the requirements to protect the 
facilitys occupants, it may be insufficient to ensure the continued 
operation of the facility. When designing or rehabilitating a critical 
facility located in an area subject to high-wind or flooding 
risks, this manual recommends a set of guidelines intended to 
minimize the interruption in operation of critical facilities, both 
during and in the aftermath of hazard events. 

-- Conduct an in-house assessment of the facility needs, with 
the assistance of decisionmakers and consultants. Public 
committees may contribute advice and guidance throughout 
the programming and design process. For large programs, 
committees may acquire specialists at different stages as 
necessary.
-- Determine the size and scope of the proposed program. In 
a smaller area, an architect may be employed to assist the 
decisionmakers with this task, possibly later becoming the 
design architect.
-- Assess the needs of the facility to determine the availability of 
suitable sites (and lease/purchase as necessary).
-- Develop occupant specifications, seeking advice from facility 
managers and both in-house and consulting professionals.
-- Assess financial needs.
-- Identify financial resources, including alternative sources of 
funding (e.g., Federal and State programs, local taxes, bond 
issues, and utility fees).
-- Ensure funding (e.g., bond issue, establishment of utility 
districts, etc.).
-- Appoint a building program management staff (appointed 
officials or a committee).
-- Determine the design and construction process (i.e., 
conventional design and bid, design/build, or construction 
management).
-- Select and hire architects and other special design consultants 
or design/build team members. The timing of this phase 
varies depending on the number of variables.
-- Develop building programs, including building size, room 
size, equipment, and environmental requirements. This may 
be done in-house, or architects and independent program 
consultants may assist.
-- Appoint a local representative to the staff and a public 
stakeholders committee for the design phase.
-- Develop designs with cost estimates. Hold public meetings, 
with the architects in attendance, and encourage public input 
into the design. Implement local area progress reviews.
-- Complete the design and solicit a local review of the contract 
documents.
-- Submit construction documents to the local jurisdiction and 
any permitting agencies for review and approval.
-- Submit documents to the building department.
-- Select the contractor (if bidding is used), or finalize design/
build or construction management contracts.
-- Undertake critical facility construction.
-- Administer the construction contract.
-- Monitor the construction progress and conduct inspections, as 
required.
-- Complete contracted tasks.
-- Conduct inspections and provide proof of the architects 
acceptance.
-- Inspect the critical facility and obtain concurrence/acceptance 
by the owner.
-- Commission the facility and occupy it.

The sequence of the above steps may vary, depending on the 
complexity of the program; some steps may be implemented simultaneously. 
Figure 1-3 shows a flow chart of this typical process. 
Also shown (in the five boxes to the right) are specific activities related 
to designing for multiple hazards and how these activities fit 
into the construction process. 

Figure 1-3: Process flow chart for decisionmakers

1.3 PERFORMANCE-BASED DESIGN

1.3.1 Background

The model building codes define the minimum design 
requirements to ensure occupants safety in critical facilities. 
Recent natural disasters have forced recognition 
that damage can occur even when buildings 
are compliant with the building code. 
The fact that a large number of critical 
facilities in communities affected by Hurricane 
Katrina were shut down (frequently 
as a result of minor building or equipment 
damage) suggests that satisfying the minimum 
code criteria may not be sufficient 
to ensure continued availability of critical 
services. Communities depend on the uninterrupted 
operation of critical facilities, 
especially during and immediately following 
natural disasters. In order to meet that need, 
critical facilities should be designed and constructed 
according to criteria that result in 
continued and uninterrupted provision of 
critical services. 
Building performance indicates how well 
a structure supports the defined needs of 
its users. The term performance, as it relates 
to critical facilities exposed to natural hazards, usually refers to a 
buildings condition 
after a disaster, i.e., it signifies a level of 
damage or a load. Acceptable performance 
indicates acceptable levels of damage or a 
building condition ,that allows uninterrupted 
facility operation. Consequently, performance-
based design for critical facilities is the 
process or methodology used by design professionals 
to create buildings that protect a 
facilitys functionality and the continued availability 
of services. This approach represents a 
major change in perception that gives performance-
based design considerations a greater 
importance in the decisionmaking process for 
design and construction of critical facilities. 

Performance-based codes define acceptable 
or tolerable levels of risk for a variety of 
health, safety, and public welfare issues. 
Currently available are the International 
Code Council Performance Code for 
Buildings and Facilities by the International 
Code Council (ICC, 2006), 101 Life Safety 
Code (NFPA, 2006a), and the NFPA 
5000 Building Construction and Safety 
Code (NFPA, 2006b) by the National Fire 
Protection Association (NFPA). The ICC 
performance code addresses all types of 
building issues, while the provisions of the 
101 Life Safety Code, Performance-Based 
Option, address only issues related to life 
safety systems. The NFPA 5000 Building 
Construction and Safety Code sets forth both 
performance and prescriptive options that 
apply to all traditional building code issues.

The performance-based design approach is 
not proposed as an immediate substitute for 
design to traditional codes. Rather, it is seen 
as an opportunity for enhancing and tailoring 
the design to match the objectives of the 
community.

1.3.2 Prescriptive Vs. Performance-Based Design

Design and construction in the United States is generally regulated 
by building codes and standards. Building codes typically 
seek to ensure the health, safety, and well-being of people in buildings. 
Toward this purpose, the building codes and standards set 
minimum design and construction requirements to address structural 
strength, adequate means of egress for facilities, sanitary 
equipment, light and ventilation, and fire safety. Building regulations 
may also promote other objectives, such as energy efficiency, 
serviceability, quality or value, and accessibility for persons with 
disabilities. These prescriptive standards are easy to understand and 
follow, and easy to monitor. This is their great strength. 

Historically, building codes were based on a prescriptive approach 
that limited the available solutions for compliance, which did not 
encourage creativity and innovation. Prescriptive or specification-based design 
emphasized the input, or the materials and 
methods required. In contrast, the focus of performance-based design 
is the output, or the expectations and requirements of the 
users of a building. 

FEMA recently funded the development 
of next-generation, performance-based 
seismic design guidelines for new and 
existing buildings. This process includes 
detailed modeling; simulation of building 
response to extreme loading; and 
estimation of potential casualties, loss of 
occupancy, and economic losses. The 
process allows the design of a building 
to be adjusted to balance the level of 
acceptable risks and the cost of achieving 
the required level of building performance. 
Currently the process focuses on seismic 
hazards, but it is general enough to be 
used with other hazards, as soon as the 
development of performance-based design 
criteria for wind and other extreme loads 
advances to the point that they can be 
incorporated into standardized models.

Performance-based design requirements define goals and objectives 
to be achieved and describe methods that can be used to demonstrate 
whether buildings meet these goals and objectives. This 
approach provides a systematic method for assessing the performance 
capabilities of a building, system, or component, which can 
then be used to verify the equivalent performance of alternatives, deliver 
standard performance at a reduced cost, or confirm the higher 
performance needed for critical facilities. 

1.3.3 The Process of Performance-Based Design of Critical Facilities

The performance-based design process explicitly evaluates how 
building systems are likely to perform under a variety of conditions 
associated with potential hazard events. The process takes into consideration 
the uncertainties inherent in quantifying potential risks 
and assessing the actual responses of building systems and the 
potential effects of the performance of these systems on the functionality 
of critical facilities. Identifying the performance capability 
of a facility is an integral part of the design process and guides the 
many design decisions that must be made. Figure 1-4 presents the 
key steps in this iterative performance-based design process. 

Performance-based design starts with selecting design criteria articulated 
through one or more performance objectives. Each 
performance objective is a statement of the acceptable risk of incurring 
different levels of damage and the consequential losses 
that occur as a result of this damage. Losses can be associated 
with structural or nonstructural damage, and can be expressed in 
the form of casualties, direct economic costs, and loss of service 
costs. Loss of service costs may be the most important loss component 
to consider for critical facilities. Acceptable risks are typically 
expressed as acceptable losses for specific levels of hazard intensity 
and frequency. They take into consideration all the potential 
hazards that could affect the building and the probability of their 
occurrence during a specified time period. The overall analysis 
must consider not only the intensity and frequency of occurrence 
of hazard events, but also the effectiveness and reliability of the 
building systems to survive the event without significant interruption in the 
operation of a facility. 

Figure 1-4: performance-based design flow diagram 
(ATC, 2003) 

1.3.4 ACCEPTABLE RISK AND PERFORMANCE LEvELS 
Performance-based design requires a quantitative measure of risk. 
It also establishes the basis for evaluating acceptable losses and selecting 
appropriate designs. While specific performance objectives 
can vary for each project, the notion of acceptable performance 
generally follows a trend corresponding to: 

-- Little or no damage for small, frequently occurring events 
-- Moderate damage for medium-sized, less frequent events 
-- Significant damage for very large, very rare events 

Performance objectives should be higher and the corresponding 
acceptable levels of damage lower for critical facilities and other 
important buildings than for non-critical facilities. This trend is illustrated 
in Figure 1-5, taken from the ICC Performance Code for 
Buildings and Facilities (ICC, 2006). This document defines acceptable 
performance for facilities in one of four performance 
groups (I, II, III, and IV), using four damage levels (mild, moderate, 
high, and severe), and given four hazard levels (small, 
medium, large, and very large). The relative return periods 
(length of time between occurrences) commonly associated with 
the hazard levels for each type of hazard event (seismic, flood, and 
wind) are indicated in Figure 1-6. 

Since losses can be associated with structural damage, 
nonstructural damage, or both, performance objectives must 
be expressed in terms of the potential performance of both 
structural and nonstructural systems. The ICC Performance Code 
for Buildings and Facilities has formalized the following four design 
performance levels, each of which addresses structural 
damage, nonstructural systems, occupant hazards, overall extent 
of damage, and release of hazardous materials. These 
definitions are general to all hazards and are related to tolerable 
limits of impact to the building, its contents, and its 
occupants.

Mild Impact: At the mild impact level, the building has no structural 
damage and is safe to occupy. The nonstructural systems 
needed for normal building or facility use and emergency 
operations are fully operational. The number of injured occupants 
is minimal, and the nature of the injuries minor. The 
overall extent of the damage is minimal. Minimal amounts of 
hazardous materials may be released into the environment.

Moderate Impact: At the moderate impact level, structural 
damage is repairable and some delay in re-occupancy can 
be expected. The nonstructural systems needed for normal 
building or facility use and emergency operations are fully operational, 
although some cleanup and repair may be needed. 
Injuries to occupants may be locally significant, but generally 
moderate in numbers and in nature. There is a low likelihood 
of a single life loss and very low likelihood of multiple 
life loss. The extent of the damage can be locally significant, 
but is moderate overall. Some hazardous materials may be released 
into the environment, but the risk to the community is 
minimal.

Figure 1-5: Maximum level of damage to be tolerated (Table 303.3, ICC, 2006b) 

Note: Performance Group I: Buildings that represent a low hazard to human life 
in the event of failure. Performance Group II: 
All buildings except those in Groups I, III, and IV. Performance Group III: 
Buildings with a substantial hazard to human life in the event of failure. Group 
IV: Buildings designed as essential facilities, including emergency operations 
centers and designated disaster shelters.

Figure 1-6: Relative magnitude and return period for seismic, flood, and wind 
events (ICC, 2006b)

High Impact: At the high impact level, there is significant damage 
to structural elements, but no falling debris. Significant delays 
in reoccupancy can be expected. The nonstructural systems 
needed for normal building use are significantly damaged and 
inoperable. Emergency systems may be damaged, but remain operational. 
Injuries to occupants may be locally significant with a 
high risk to life, but are generally moderate in numbers and nature. 
There is a moderate likelihood of a single life loss, with a 
low probability of multiple life loss. The extent of damage can be 
generally significant and at some locations total. Hazardous materials 
are released into the environment, with localized relocation 
required in the immediate vicinity.

Severe Impact: At the severe impact level, there is substantial structural 
damage. Repair may not be technically possible. The building 
is not safe for re-occupancy due to the potential for collapse. The 
nonstructural systems for normal use and emergency systems may 
be nonfunctional. Injuries to occupants may be high in number 
and significant in nature. Significant risk to life may exist. There 
is a high likelihood of single life loss and a moderate likelihood 
of multiple life loss. Overall damage is substantial. Significant 
amounts of hazardous materials may be released into the environment, 
with relocation needed beyond the immediate vicinity.

Once the preliminary design has been developed, a series of 
simulations (analyses of building response to loading) are 
performed to estimate the probable performance of the building 
under various design scenario events. Using fragility relationships 
(vulnerability functions defining the relationship between 
load and damage) developed through testing or calculation, 
building responses are equated to damage states expressed as 
levels of performance. If the simulated performance meets or 
exceeds the performance objectives, the design is completed. 
If not, the design must be revised in an iterative process until 
the performance objectives are met. In some cases it will not 
be possible to meet the stated objective at a reasonable cost, in 
which case the team of decisionmakers may elect to relax some of 
the original performance objectives. 

Continued and uninterrupted operation is the most important 
performance requirement of any critical facility, regardless of the 
level of structural and nonstructural building damage. In other 
words, the acceptable performance of a critical facility is achieved 
as long as the structural and nonstructural damage to the 
building does not disrupt or impair the continued operation of 
that facility. In recent hurricanes, however, undamaged structures 
were frequently rendered inoperable as a result of nonstructural 
damage resulting in unacceptable performance (FEMA, 2006).

In terms of affecting the ability of a facility to function, the failure 
of nonstructural systems (roofing; exterior envelope; heating, ventillating, 
and air conditioning [HVAC]; emergency systems) can be 
as significant as the failure of structural components. Performance-
based design provides a framework for considering the potential 
hazards that can affect a facility or site, and for explicitly evaluating 
the performance capability of the facility and its components. 

Consideration must also be given to the likely possibility that at 
least a portion of the distribution systems for critical infrastructure 
services (e.g., electrical power, communications, potable 
water, and sanitary sewer) could be interrupted. The impact of 
such an interruption in service should be assessed for the facility, 
along with an estimate of the time it would take until service 
could be restored or supplemented. For protecting the continued 
operation of critical facilities, the most reliable approach is to 
provide alternative onsite sources for critical infrastructure needs 
in the form of: (1) emergency power generation capabilities; (2) 
local wireless communications; (3) potable water supplies; and 
(4) temporary onsite storage for sanitary waste.

While the practice of performance-based design is currently 
more advanced in the field of seismic design than the fields of 
flood and high-wind design, the theory of performance-based 
design is completely transferable to all hazards. The practice of 
performance-based design will prompt designers and owners of 
buildings in flood- or high-wind-prone regions to begin thinking 
in terms of a few basic objectives:

-- Can the real probabilities and frequencies of high-wind and 
flood events during the useful life of the building be defined 
with an acceptable degree of accuracy?
-- Can the extent and kinds of damage that can be tolerated be 
defined?
-- Are there ways in which an acceptable level of performance 
can be achieved?
-- Are there alternative levels of performance that can be 
achieved, and how much do they cost over the lifetime/
ownership of the building compared to the benefits of 
reduced damage and improved performance?
-- How do these levels compare to the performance levels of 
designs using the minimum requirements of the applicable 
building code?

1.3.5 Performance-Based Flood Design 

The performance levels and objectives for flood hazards, first outlined 
in FEMA 424 (2004), have been expanded and generalized 
for performance-based flood design of critical facilities as follows:

Level 1 (Operational): The facility sustains no structural or 
nonstructural damage, emergency operations are fully functional, 
and the building can be immediately operational. The site is not 
affected by erosion, but may have minor debris and sediment 
deposits. 

Level 2 (Moderate Impact): The facility is affected by flooding above 
the lowest floor, but damage is minimal due to low depths and 
short duration of flooding. Cleanup, drying, and minor repairs are 
required, especially of surface materials and affected equipment, 
but the building can be back in service in a short period of time.

Level 3 (High Impact): The facility may sustain structural or 
nonstructural damage that requires repair or partial reconstruction, 
but the threat to life is minimal and occupant injuries should 
be few and minor. Water damage to the interior of the facility requires 
cleanup, drying, and repairs, and can prohibit occupancy of 
all or a portion of the facility for several weeks to several months.

Level 4 (Severe Impact): The facility is severely damaged and likely 
requires demolition or extensive structural repair. Threats to occupants 
are substantial, and warning plans should prompt evacuation 
prior to the onset of this level of flooding. Level 4 is applicable to 
facilities affected by all types of flooding, including those that result 
from failure of dams, levees, or floodwalls.

Planning and design to achieve an appropriate level of flood protection 
for critical facilities should include avoidance of flood 
hazard areas and adding a factor of safety (freeboard) to the 
anticipated flood elevation. Performance evaluation of a facility 
affected by flooding needs to include consideration of the 
building response to the following load conditions (fragility functions 
must be developed to relate calculated response to actual 
damage states): 

-- Lateral hydrostatic forcesm Vertical (buoyant) hydrostatic forces 
-- Hydrodynamic forcesm Surge forces 
-- Impact forces of flood-borne debris 
-- Breaking wave forces 
-- Localized scour 

1.3.6 Performance-Based High-Wind Design 

The performance objectives for wind hazards, outlined in FEMA 
424, have been expanded and generalized for performance-based 
flood design of critical facilities as follows:

Level 1 (Operational): The facility is essentially undamaged and can 
be immediately operational. 

Level 2 (Moderate Impact): The facility is damaged and needs some 
repairs, but can remain occupied and be functional after minor 
repairs to nonstructural components are complete. 

Level 3 (High Impact): The facility may be structurally damaged 
but the threat to life is minimal and occupant injuries should be 
few and minor. However, damage to nonstructural components 
(e.g., roofing, building envelope, exterior-mounted equipment) 
is great, and the cost to repair the damage is significant. If rain accompanies 
the windstorm, or if rain occurs prior to execution of 
emergency repairs, water damage to the interior of the facility can 
prohibit occupancy of all or a portion of the facility for several 
weeks to several months.

Level 4 (Severe Impact): The facility is severely damaged and will 
probably need to be demolished. Significant collapse may have 
occurred, and there is a great likelihood of occupant casualties 
unless the facility has a specially designed occupant shelter. Level 
4 is applicable to facilities struck by strong or violent hurricanes or 
tornadoes. For other types of windstorms, Level 4 should not be 
reached.

The challenge with respect to performance-based high-wind design 
is assessing the wind resistance of the building envelope and 
exterior-mounted equipment, and the corresponding damage susceptibility. 
This is challenging because of several factors:

-- Analytical tools (i.e., calculations) are currently not available 
for many envelope systems and components, and there is a 
lack of realistic long-term wind resistance data. 
-- Because of the complexity of their wind load response, many 
envelope systems and components require laboratory testing, 
rather than analytical evaluation, in order to determine their 
load-carrying capacity. 
-- It is likely that finite element analysis will eventually augment 
or replace laboratory testing, but substantial research is 
necessary before finite element analysis becomes available for 
the broad range of existing building envelope systems.
-- Before performance-based design for high winds can become 
a reality, a solid research base on the response of buildings and 
components to the effects of high winds must be established.


1.4 REFERENCES

American Society of Civil Engineers, Structural Engineering 
Institute, Minimum Design Loads for Buildings and Other Structures, 
ASCE/SEI 7-05, Reston, VA, 2006.

Applied Technology Council, Proceedings of FEMA-Sponsored 
Workshop on Performance-Based Seismic Design, ATC-58-3 Report, 
Redwood City, CA, 2003.

Applied Technology Council, prepared for the Building Seismic 
Safety Council, NEHRP Guidelines for the Seismic Rehabilitation of 
Buildings, funded and published by FEMA (FEMA 273 Report), 
Washington, DC, 1997.

Executive Order of the President, Floodplain Management, 
11988, 42 FR 26951, 3 CFR, p117, Washington, DC, 1977.

Federal Emergency Management Agency, Design Guide for 
Improving School Safety in Earthquakes, Floods, and High Winds, FEMA 
424, Washington, DC, 2004.

Federal Emergency Management Agency, Summary Report on 
Building Performance, Hurricane Katrina 2005, FEMA 549 Report, 
Washington, DC, 2006.

National Fire Protection Association, 101 Life Safety Code, Quincy, 
MA, 2006a.

National Fire Protection Association, NFPA 5000 Building 
Construction and Safety Code, Quincy, MA, 2006b.

International Code Council, Inc., International Code Council 
Performance Code for Buildings and Facilities, Falls Church, VA, 2006.

Structural Engineers Association of California, Performance-Based 
Seismic Engineering of Buildings, Vision 2000 Report, Sacramento, 
CA, 1995.


[End of Chapter 1]

MAKING CRITICAL FACILITIES SAFE FROM Flooding

2.1 GENERAL DESIGN CONSIDERATIONS

This chapter introduces the physical nature and mechanics 
of floods and explains how flood probabilities are 
determined and how flood hazard areas are identified. It 
describes the types of flood damage that can result when critical 
facilities are located in flood hazard areas or are affected by flooding. 
A series of requirements and best practices are introduced 
that facility owners, planners, and designers should consider for 
reducing the risks from flooding to new critical facilities and to 
existing facilities already located in areas prone to flooding.

This chapter demonstrates why avoidance of flood hazard areas 
is the most effective way to minimize the life-safety risk to the occupants 
and general public who rely on these facilities, as well as 
to minimize the potential for damage to buildings and other elements 
of critical facilities. When an existing facility is exposed 
to flooding, or if a new facility is proposed for a flood hazard area, 
steps need to be taken to minimize the risks. A well-planned, designed, 
constructed, and maintained critical facility 
should be able to withstand damage and remain functional after a flooding event, 
even one of low probability. 

2.1.1 NATURE AND CHARACTERISTICS OF FLOODING

Flooding is the most common natural hazard in the United States, 
affecting more than 20,000 local jurisdictions and representing 
more than 70 percent of Presidential disaster declarations. Several 
evaluations have estimated that 7 to 10 percent of the Nations 
land area is subject to flooding. Some communities have very little 
flood risk; others lie entirely within a floodplain.

Flooding is a natural process that may occur in a variety of forms: 
long-duration flooding along rivers that drain large watersheds; 
flash floods that send a devastating wall of water down a mountain 
canyon; and coastal flooding that accompanies high tides and 
onshore winds, hurricanes, and noreasters. When the natural 
process does not affect human activity, flooding is not a problem. 
In fact, many species of plants and animals that live adjacent to 
bodies of water are adapted to a regimen of periodic flooding. 

Flooding is only considered a problem when human development 
is located in flood-prone areas. Such development exposes people 
to potentially life threatening situations and makes property vulnerable 
to serious damage or destruction. It also can disrupt the 
natural surface flow, redirecting water onto lands not normally 
subject to flooding. 

Flooding along waterways normally occurs as a result of excessive 
rainfall or snowmelt that creates water flows exceeding the capacity 
of channels. Flooding along shorelines is usually a result of 
coastal storms that generate storm surges or waves above normal 
tidal fluctuations. Factors that can affect the frequency and severity 
of flooding and the resulting damage include:

-- Channel obstructions caused by fallen trees, accumulated 
debris, and ice jams
-- Channel obstructions caused by road and rail crossings where the bridge or 
culvert openings are insufficient to convey 
Floodwaters
-- Erosion of shorelines and stream banks, often with episodic 
collapse of large areas of land
-- Deposition of sediment that settles out of floodwaters or is 
carried inland by wave action
-- Increased upland development of impervious surfaces and 
manmade drainage improvements that increase runoff volumes
--Land subsidence, which increases flood depths
--Failure of dams (resulting from seismic activity, lack of maintenance, 
flows that exceed the design, or destructive acts), which 
may suddenly and unexpectedly release large volumes of water
--Failure of levees (associated with flows that exceed the 
design, weakening by seismic activity, lack of maintenance, or 
destructive acts), which may result in sudden flooding of areas 
behind levees

Each type of flooding has characteristics that represent important 
aspects of the hazard. These characteristics should be considered 
in the selection of critical facility sites, the design of new facilities, 
and the expansion or rehabilitation of existing flood-prone 
facilities.

Riverine flooding results from the accumulation of runoff from 
rainfall or snowmelt, such that the volume of flow exceeds the 
capacity of waterway channels and spreads out over the adjacent 
land. Riverine flooding flows downstream under the force 
of gravity. Its depth, duration, and velocity are functions of many 
factors, including watershed size and slope, degree of upstream 
development, soil types and nature of vegetation, topography, 
and characteristics of storms (or depth of snowpack and rate of 
melting). Figure 2-1 illustrates a cross-section of the generic riverine 
floodplain.

Figure 2-1: The riverine floodplain
* Floodway is defined in Section 2.1.1.2

Coastal flooding is experienced along the Atlantic, Gulf, and 
Pacific coasts, and many larger lakes, including the Great 
Lakes. Coastal flooding is influenced by storm surges associated 
with tropical cyclonic weather systems (hurricanes, tropical 
storms, tropical depressions, typhoons), extratropical systems 
(noreasters), and tsunamis (surge induced by seismic activity). 
Coastal flooding can also be characterized by wind-driven waves, 
which also affect reaches along the Great Lakes shorelines; winds 
blowing across the broad expanses of water generate waves that 
can rival those experienced along ocean shorelines. Some Great 
Lakes shorelines experience coastal erosion, in part because the 
erosion is associated with fluctuations in water levels. Figure 2-2 is 
a schematic of the generic coastal floodplain.

A number of factors associated with riverine and coastal flooding are 
important in the selection of sites for critical facilities, in site design, 
and in the architectural and engineering design of critical facilities. 

* Zones are defined in Section 2.1.1.2
Figure 2-2: The floodplain along an open coast 

Depth: The most obvious characteristic of any flood is the depth of 
the water. Depending on many factors, such as the shape of a river 
valley or the presence of obstructing bridges, riverine flooding 
may rise just a few feet or tens of feet above normal levels. The 
depth of coastal flooding is influenced by such factors as the tidal 
cycle, the duration of the storm, the elevation of the land, and 
the presence of waves. Depth is a critical factor in building design, 
because the hydrostatic forces on a vertical surface (such as 
a foundation wall) are directly related to depth, and because costs 
associated with protecting buildings from flooding increase with 
depth. Under certain conditions, hurricanes can produce storm 
surge flooding that is 20 to 30 feet above mean sea level or, in extreme 
cases such as reported during Hurricane Katrina, as much 
as 35 feet above mean sea level.

Duration: Duration is the measure of how long the water remains 
above normal levels. The duration of riverine flooding is primarily 
a function of watershed size and the longitudinal slope of 
the valley (which influences how fast water drains away). Small 
watersheds are more likely to be flashy, which refers to the rapidity 
with which floodwaters rise and fall. Areas adjacent to large 
rivers may be flooded for weeks or months. Most coastal flooding 
is influenced by the normal tidal cycle, as well as how fast coastal 
storms move through the region. Areas subject to coastal flooding 
can experience long duration flooding where drainage is poor 
or slow as a result of topography or the presence of flood control 
structures. For example, there may be depressions 
in the land that would hold water, 
or water may be trapped behind a floodwall 
or levee with inadequate drainage. More 
commonly, coastal flooding is of shorter 
duration, on the order of 12 to 24 hours, especially 
if storms move rapidly. Flooding 
along large lakes, including those behind 
dams, can be of very long duration because 
the large volume of water takes longer to 
drain. For building design, duration is important 
because it affects access, building 
usability, and saturation and stability of soils 
and building materials. Information about 
flood duration is sometimes available as part 
of a flood study, or could be developed by a 
qualified engineer. 

Local drainage problems create ponding 
and local flooding that often is not directly 
associated with a body of water such as 
a creek or river. Although such flooding is 
relatively shallow and not characterized 
by high velocity flows, considerable 
damage may result. Areas with poor 
drainage frequently experience repetitive 
damage. Some local drainage problems 
are exacerbated by old or undersized 
drainage system infrastructure. Flooding 
caused by drainage problems typically 
occurs as sheetflow or along waterways 
with small drainage areas. This type of 
flooding is often not mapped or regulated.

Velocity: The velocity of floodwaters ranges from extremely high 
(associated with flash floods or storm surge) to very low or nearly 
stagnant (in backwater areas and expansive floodplains). Velocity 
is important in site planning because of the potential for erosion. 
In structural design, velocity is a factor in determining the hydrodynamic 
loads and impact loads. Even shallow, high-velocity 
water can threaten the lives of pedestrians and motorists. Accurate 
estimates of velocities are difficult to make, although velocity information 
may be found in some floodplain studies.

Wave action: Waves contribute to erosion and scour (see Figure 
2-2), and also contribute significantly to design loads on buildings. 
The magnitude of wave forces can be 10 to more than 100 
times greater than wind and other design loads, and thus may control 
many design parameters. Waves must be accounted for in 
site planning along coastal shorelines, in flood hazard areas that 
are inland of open coasts, and other areas where waves occur, including 
areas with sufficient fetch that winds can generate waves 
(such as lakes and expansive riverine floodplains). Waves on top 
of storm surges may be as much as 50 percent higher than the 
depth of the surge.

Impacts from debris and ice: Floating debris and ice contribute to 
the loads that must be accounted for in structure design. The 
methods and models used to predict and delineate flood hazard 
areas do not specifically incorporate debris loads. Thus, there are 
few sources to determine the potential effects of debris impact, 
other than past observations and judgment. 

Erosion and scour: Erosion is the lowering of the ground surface as 
a result of a flood event, or the gradual recession of a shoreline as 
a result of long-term coastal processes. Scour refers to a localized 
lowering of the ground surface due to the interaction of currents 
and/or waves with structural elements, such as pilings. Soil characteristics 
influence an areas susceptibility to scour. Erosion and 
scour may affect the stability of foundations and filled areas, and 
may cause extensive site damage. 

2.1.1.1 Probability of Occurrence or Frequency

The probability of occurrence, or frequency, is a statement of the 
likelihood that an event of a certain magnitude will occur in a 
given period of time. For many decades, floodplain management 
has been based on the flood that has a 1 percent chance of occurring 
in any given year, commonly called the 100-year flood. 
For certain critical actions and decisions, 
such as planning or constructing a critical facility, 
the basis of risk decisions should be the 
flood that has a 0.2 percent probability of occurring 
in any given year, commonly called 
the 500-year flood. 

The term 100-year flood as an expression 
of probability or frequency is often misunderstood 
because it conveys the impression 
that a flood of that magnitude will occur only 
once every 100 years. Actually, the 1-percent-
annual-chance flood has one chance in 100 
of occurring in any given year. The fact that 
a 1-percent-annual-chance flood is experienced at a specific location 
does not alter the probability that a comparable flood could 
occur at the same location in the next year, or even multiple times 
in a single year. As the length of the period increases, so does the 
probability that a flood of a specific magnitude or greater will 
occur. For example, during a 30-year period (the usual lending period 
for a home mortgage), the probability that a 100-year flood 
will occur is 26 percent. And during a 70-year period (the potential 
useful life of many buildings), the probability increases to 50 
percent. Similarly, the 500-year flood has a 0.2-percent probability 
of being equaled or exceeded in any given year, and during a 70-
year period the probability of occurrence is 18 percent.

Regardless of the flood selected for design purposes (the 
design flood), the designer must determine specific characteristics 
associated with that flood. Determining a flood with a 
specific probability of occurrence is done in a multi-step process 
that typically involves using computer models that are in 
the public domain. If a sufficiently long record of flood information 
exists, the design flood may be determined by applying 
statistical tools to the data. Alternatively, water resource engineers sometimes 
apply computer models to 
simulate different rainfall events over watersheds, 
to predict how much water will run 
off and accumulate in channels. Other computer 
models are used to characterize the 
flow of water down the watershed and predict 
how high the floodwaters will rise. 

The assigned frequency of a flood (e.g., 
100-year) is independent of the number 
of years between actual occurrences. 
Hurricane Camille hit the Mississippi coast 
in 1969 with storm surge flooding that far 
exceeded previous events, and Hurricane 
Katrina affected much the same area. 
Although just 36 years apart, both storms 
produced flood levels significantly higher 
than the 100-year flood.

For coastal areas, both historical storms 
and simulated storm surge models can 
be used to predict the probability that 
floodwaters will rise to a certain level and be accompanied 
by waves of certain heights. Many coastal storms will produce 
storm surge flooding that, depending on local topography, 
may extend inland significantly farther than anticipated for 
the 1-percent-annual-chance flood. Statistically, such extreme 
storm surges occur less frequently than the 1-percent or 0.2-
percent-annual-chance floods, but their consequences can be 
catastrophic.

Planners and designers should research the relationship 
between the flood levels for different frequency events and extreme 
events, especially in hurricane-prone communities. The 
difference in flood levels may be extreme in some situations, 
depending on local conditions and the source of flooding. In 
other areas the lower probability flood depths might not be 
much higher than the 1-percent-annual-chance flood.

The National Flood Insurance Program (NFIP) is a Federal 
program that encourages communities to regulate flood 
hazard areas and, in return, offers property owners insurance 
protection against losses from flooding (see Sections 2.1.3.1 
and 2.1.3.2). The NFIP uses the 1-percent-
annual-chance flood as the basis for flood hazard maps, for setting insurance 
rates, and for application of regulations in order to minimize future 
flood damage. The 1-percent-annual-chance flood is also used 
as the standard for examination of older buildings to determine 
the measures to apply in order to reduce future damage.

Satisfying the minimum requirements of the NFIP does not 
provide adequate protection for critical facilities that need to 
be functional even after low probability events. Nearly every year, a very low 
probability flood occurs 
somewhere in the United States, often with 
catastrophic consequences. Therefore, for 
planning and design of critical facilities, 
use of a lower probability flood (at least 
the 500-year) is strongly recommended. 
As noted in Section 2.1.3.3, the 500-year 
level of protection is required if Federal 
funds are involved in constructing facilities 
that are vital for emergency response and 
rapid recovery, including hospitals, EOCs, 
emergency shelters, and other buildings that support vital services. 
This reinforces the importance of protecting both the 
functionality and financial investment in a critical facility with 
stricter standards than those applied to other buildings.

Flood frequency analyses are performed 
using historical records, and the results 
are influenced by the length of the 
record. Such analyses do not account 
for recent changes to the land (upland 
development or subsidence) or future 
changes (additional development, greater 
subsidence, or climatic variations).

2.1.1.2 Hazard Identification and Flood Data

Flood hazard maps identify areas of the landscape that are subject 
to flooding, usually flooding by the 1-percent-annual-chance 
flood. Maps prepared by the NFIP are the minimum basis of 
State and local floodplain regulatory programs. Some States 
and communities have prepared maps of a floodplain based on 
the assumption that the upper watershed area is fully developed 
according to existing zoning. Some communities base their regulations 
on a flood of record or a historically significant flood that 
exceeds the base flood shown on the NFIP maps.

The flood hazard maps used by the appropriate regulatory authority 
should be consulted during planning and site selection, 
site design, and architectural and engineering design (whether 
for the design of new buildings or rehabilitation of existing 
buildings). Regardless of the flood hazard data required for regulatory 
purposes, additional research should be conducted on 
past major floods and other factors that could lead to more severe 
flooding.

The NFIP produces Flood Insurance Rate Maps (FIRMs) for more 
than 20,000 communities nationwide. FIRMs are prepared for each 
local jurisdiction that has been determined to have some degree 
of flood risk. The current effective maps are typically available 
for viewing in community planning or permit 
offices. It is important to use the most recent 
flood hazard map when determining 
site-specific flood hazard characteristics. Although 
many FIRMs are more than 15 years 
old, often one or more panels or portions of 
a map panel have been revised and republished. 
Communities must adopt revised maps 
to continue participating in the NFIP. 

The Saffir-Simpson Hurricane Scale 
categorizes hurricanes based on sustained 
wind speeds (see Section 3.1.1). Storm 
surge is not always correlated with the 
category because other factors influence 
surge elevations, notably forward speed of 
the storm, tide cycle, offshore bathymetry, 
and land topography.

Some FIRMs do not show the 0.2-percent-
annual-chance flood hazard area (500-year 
floodplain), and many FIRMs do not provide 
detailed information about predicted 
flood elevations along every body of water, 
especially smaller streams and tributaries. Determining 
the 500-year flood is especially 
difficult when records of past flood events are 
limited. When existing data are insufficient, additional statistical 
methods and engineering analyses are necessary to determine the 
flood-prone areas and the appropriate characteristics of flooding 
required for site layout and building design. 

If a proposed facility site or existing facility is affected by 
flooding, a site-specific topographic survey is critical to delineate 
the land that is below the flood elevation used for planning purposes. 
If detailed flood elevation information is not available, a 
floodplain study may be required to identify the important flood 
characteristics and data required for sound design. Having flood 
hazard areas delineated on a map conveys a degree of precision 
that may be misleading. Flood maps have a number of limitations 
that should be taken into consideration, especially during site selection 
and design of critical facilities. Some of the well-known 
limitations are:

Flood hazard areas are approximations based on probabilities; 
the flood elevations shown and the areas delineated should 
not be taken as absolutes, in part because they are based on 
numerical approximations of the real world. 
It is important to note that the number of 
revised and updated FIRMs is increasing 
rapidly. During the last few years FEMA, 
in partnership with many States and 
communities, has been implementing 
an initiative to modernize and update 
all maps that are determined to be out 
of date. The modernization process 
may involve an examination of flood 
experience in the period since the original 
flood studies were prepared, use of more 
detailed topography and base maps, re-
computation of flood discharges and flood 
heights, and re-delineation of flood hazard 
area boundaries.

1. Flood maps may also be viewed at FEMAs Map Store at http://www.fema.gov. For 
a fee, copies may be ordered online or by calling 
(800) 358-9616. The Flood Insurance Study (FIS) and engineering analyses used to 
determine the flood hazard area may be ordered through 
the FEMA Web site.


FIRMs and Flood Insurance Studies 
(FISs) are prepared to meet the 
requirements of the NFIP. For the most 
part, floodplains along smaller streams 
and drainage areas (less than 1 square 
mile) are not shown.
Especially for older maps, the topography 
used to delineate the flood boundary may 
have had contour intervals of 5, 10, or 
even 20 feet, which significantly affects 
the precision with which the boundary 
is determined. The actual elevation of 
the ground relative to the flood elevation 
is critical, as opposed to whether an area 
is shown as being in or out of the mapped 
flood hazard area. 
 Maps are based on the data available at the time they were 
prepared, and therefore do not account for subsequent 
upland development (new development that increases rainfall-
runoff tends to increase flooding). 
 The scale of the maps may impede 
precise determinations (many older maps 
are 1 inch = 2,000 feet).
 Flooding characteristics may have been 
altered by development, sometimes by 
upland development that has increased 
runoff, and other times by local 
modifications that have altered the shape 
of the land surface of the floodplain 
(such as fills or levees).
 Local conditions are not reflected, 
especially conditions that change 
regularly, such as stream bank erosion 
and shoreline erosion.
 Areas exposed to very low probability 
flooding are not shown, such as flooding 
In communities along the Gulf and Atlantic 
coasts, facility owners, planners, and 
designers should check with emergency 
management offices for maps that estimate 
storm surge flooding from hurricanes. 
Local planning or engineering offices may 
have post-disaster advisory flood maps 
and documentation of past storm surge 
events. The FIRMs and regulatory design 
flood elevations (DFEs) do not reflect low 
probability/high magnitude flooding 
that may result from a hurricane making 
landfall at a specific location.

Designers and property owners in coastal 
regions should be aware that current FIRMs 
may not fully account for natural and 
manmade changes to beaches, wetlands, 
and other coastal environments (e.g., the 
erosion of protective dunes during the 
base flood). Since the original FIRMs 
were published in the early 1980s, FEMA 
has made significant improvements in 
the models and methods used to identify 
coastal flood hazards. Before any action 
is considered, the Flood Insurance Study 
report should be checked to verify that all 
pertinent hazards have been addressed. 
A coastal engineer or similar professional 
should be consulted if there are any 
questions concerning the coastal flood data.

from extreme hurricane storm surges, extreme riverine 
flooding, dam failures, or overtopping or failure of levees.
The flood hazard maps prepared by the NFIP show different flood 
zones to delineate different floodplain characteristics (see Figures 
2-3 and 2-4). The flood zones shown on the NFIP maps, and some 
other designations, are as described below. 

A Zones: (also called unnumbered A Zones or approximate A 
Zones). This designation is used for flood hazard areas where 
engineering analyses have not been performed to develop 
detailed flood elevations. Base flood elevations 
(BFEs) are not provided. Additional 
engineering analyses and site-specific assessments 
usually are required to determine the 
design flood elevation.

AE Zones or A1-A30 Zones: (also called numbered 
A Zones). These designations are 
used for flood hazard areas where engineering 
analyses have produced detailed flood elevations and 
boundaries for the base flood (1-percent-annual-chance flood). 
BFEs are provided. For riverine waterways with these zones, FISs 
include longitudinal profiles showing water surface elevations for 
different frequency flood events.

Floodways: The floodway includes the waterway channel and adjacent 
land areas that must be reserved in order to convey the 
discharge of the base flood without cumulatively increasing the 
water surface elevation above a designated height. Floodways 
are designated for most waterways that have AE Zones or numbered 
A Zones. FISs include data on floodway widths and mean 
floodway velocities. 

AO and AH Zones: These zones include areas of shallow flooding 
and are generally shown where the flood depth averages from 1 to 
3 feet, where a clearly defined channel does not exist, where the 
path of flooding is unpredictable, and where velocity flow may be 
evident. These zones are characterized by ponding or sheetflow. 
BFEs may be provided for AH Zones; flood depths may be specified 
in AO Zones.

Base flood elevation is the elevation 
above a datum to which floodwaters are 
predicted to rise during the 1-percent-
annual-chance flood (also called the base 
flood or the 100-year flood).

Figure 2-3: Riverine flood hazard zones

Figure 2-4: Coastal flood hazard areas

Shaded X (or B) Zones: This zone shows areas of the 500-year flood 
(0.2-percent-annual-chance flood), or areas protected by flood 
control levees. This zone is not shown on many NFIP maps; its absence 
does not imply that flooding of this frequency will not occur. 

Unshaded X (or C) Zones: These zones are all land areas not mapped 
as flood hazard areas that are outside of the floodplain and designated 
for the purposes of regulating development pursuant to 
the NFIP. These zones may still be subject to small stream flooding 
and flooding from local drainage problems.

V Zones (V, VE, and V1-V30): Also known as coastal high-hazard 
areas or special flood hazard areas subject to high-velocity wave action. 
V Zones are relatively narrow areas along open coastlines and 
some large lake shores that are subject to high-velocity wave action 
from storms or seismic sources. V Zones extend from offshore 
to the inland limit of a primary frontal dune, or to an inland limit 
where the height of breaking waves drops below 3 feet.

Coastal A Zone: This zone, which is not delineated on NFIP maps, 
is where the potential of breaking wave heights is between 1.5 
feet and 3 feet during base flood conditions. Coastal A Zones 
are landward of the mapped V Zone, or landward of open coasts 
that do not have a V Zone because breaking 
waves are predicted to be less than 3 feet 
high. In these areas, the principal sources of 
flooding are tides, storm surges, seiches, or 
tsunamis, not riverine flooding. 

Flood hazards and characteristics of flooding 
must be identified to evaluate appropriately 
the impact of site development, to calculate 
flood loads, to design floodproofing measures, 
and to identify and prioritize retrofit 
measures for existing critical facilities. Table 2-3 in Section 2.5 outlines 
a series of questions to facilitate this objective.

Many characteristics of flooding are not shown on the FIRMs but 
may be found in the FIS or the study or report prepared by the entity 
that produced the flood hazard map. Hurricane storm surge 
inundation maps based on the National Hurricane Center models have been prepared 
by the U.S. Army Corps 
of Engineers for most reaches of the Atlantic 
and Gulf coasts. The maps combine the results 
of many scenarios to show the maximum 
potential surge inundation associated with 
different categories of hurricanes. State and 
local emergency management offices use the maps for evacuation 
planning. 

Coastal A Zone: The current editions of the 
model building codes refer to ASCE 7 and 
ASCE 24, which are two design standards 
that include requirements for Coastal 
A Zones that account for the increased 
risk from the additional wave height (see 
Section 2.3.2). 

2.1.1.3 Design Flood Elevation 

The DFE establishes the minimum level of flood protection that 
must be provided. The DFE, as used in the model building codes, 
is defined as either the BFE determined by the NFIP and shown on 
FIRMs, or the elevation of a design flood designated by the community, 
whichever is higher. The DFE will always be at least as high 
as the BFE. Communities may use a design flood that is higher 
than the base flood for a number of reasons. 
For example, a design flood may be used to 
account for future upland development, to 
recognize a historic flood, or to incorporate a 
factor of safety, known as freeboard. 

Facility owners, planners, and designers 
should check with the appropriate regulatory 
authority to determine the minimum 
flood elevation to be used in site planning 
and design. Although the NFIP minimum 
is the BFE, State or local regulations commonly 
cite the 0.2-percent-annual-chance flood (500-year flood) 
as the design 
requirement for critical facilities, or the regulations 
may call for added freeboard above the minimum flood elevation. 
Even if there is no specific requirement to use the 0.2-percent-annual-
chance flood for siting and design purposes, it is strongly 
recommended that decisionmakers take into consideration the 
flood conditions associated with this lower probability event or 
from other floods of record.

Hurricanes can produce storm surge 
flooding and waves that rise much higher 
than the BFE shown on the FIRMs.

Freeboard is a factor of safety usually 
expressed in feet above a flood level. Freeboard 
compensates for the many unknown 
factors that could contribute to flood 
heights, such as wave action, constricting 
bridge openings, and the hydrological 
effect of urbanization of the watershed. A 
freeboard from 1 to 3 feet is often applied 
to critical facilities.

2.1.1.4 Advisory Base Flood Elevation 

The flood maps and flood hazard data described in Section 2.1.1.2 
are the minimum information required to be used for regulatory 
purposes. The updating of FIRMs is a continuous process and 
it relies heavily on examination of storm event data and physical 
changes to the landscape. If significant flood events have occurred 
since the effective date of the FIRM, these events may change the 
statistical analyses, which would then prompt an update of the 
flood maps and produce revised elevations for the 1-percent-annual-
chance flood. Critical facility owners, planners, and designers 
should contact community officials to determine whether there 
have been any significant flood events or other changes that may 
affect flood hazards since the effective date of the FIRM. The best 
available information should be used at all times. 

FEMA works closely with communities to develop new flood 
hazard data or revise existing data during the standard flood study 
process. Updating flood hazard data includes the analysis of historical 
data. If a major flood event significantly alters the physical 
environment or if it is determined to be statistically significant, 
FEMA may decide to release Advisory BFEs (ABFEs) and Flood 
Recovery Maps (see Figure 2-5).

Figure 2-5: Example of a flood recovery map showing ABFEs and other flood hazard 
information. 

ABFEs represent the best estimate of the 
expected 1-percent-annual-chance flood elevations. 
They are provided as interim flood 
hazard information until more detailed flood 
hazard data become available. Flood Recovery 
Maps depict the ABFEs, and in general, 
reflect additional information such as inundation 
limits and surveyed high water marks (but not the 500-year 
flood hazard area). For coastal areas, the Flood Recovery Maps may 
also show the inland debris line and the limit of the 1.5-foot wave 
(Coastal A Zone). 

When ABFEs and Flood Recovery Maps are produced and released, 
FEMA strongly encourages States and communities, as 
well as private property owners and critical facility owners, to use 
the information to make decisions about reconstruction until 
more definitive data become available. FEMA issues guidance to 
help the users apply the updated flood elevation information at 
specific locations. 

After Flood Recovery Maps are released, FEMA begins the formal 
process of updating the FIRMs. The community and property 
owners are notified through public notices and meetings when 
the preliminary revised maps are available and a formal comment 
period is opened. The final maps are prepared after consideration 
of comments. Communities are required to adopt and use the revised 
FIRMs in order to continue their participation in the NFIP. 

2.1.2 FLOOD LOADS

Floodwaters can impose a variety of loads on buildings and 
building elements. This section provides a brief overview of flood 
loads and factors that are important for calculating flood loads, 
including:

 Hydrostatic loads, including buoyancy, which increase as the 
depth of water increasesm Hydrodynamic loads, which result from moving water
After Hurricane Katrina, FEMA expedited 
development of Flood Recovery Maps and 
ABFEs for the Mississippi coastthe new 
maps were delivered just 3 months after 
the storm. 
 Breaking wave loads, which are most likely to occur in coastal 
areas 
 Impact loads resulting from floating debris striking a building 
or building elementm Long-term erosion and localized scour, which can increase 
the effects and magnitudes of other loads

2.1.2.1 Design Flood Depth 

Water depth associated with the design flood is computed by determining 
the DFE (see Section 2.1.1.3 or 2.1.1.4) and subtracting 
the elevation of the ground at the building site. Since these 
elevation data usually are obtained from different sources, it is important 
to determine whether they are based on the same datum. 
If not, standard corrections must be applied. 

Flood depth is the most important factor required to compute 
flood loads, because almost every other flood load calculation depends 
directly or indirectly on this factor. In riverine areas, the 
flood depth rarely accounts for waves. In coastal areas, the total 
flood depth is composed of a stillwater depth, plus the expected 
height of waves (see Figure 2-6).

Figure 2-6: Definition sketchwave height and stillwater depth

The following characteristics that may add to the flood depth 
should be taken into consideration.

Small waves: In Coastal A Zones (see Section 
2.3.2), the DFE shown on FEMAs maps does 
not include the wave height. Coastal A Zones 
are characterized by 1.5- to 3-foot high waves. 
The flood depth should be increased by 3 feet 
for sites close to the V Zone boundary or the 
shoreline. For sites farther inland, where the 
flood depth is at least 3 feet, it should be increased 
by 1.5 feet. Interpolation may be used 
to determine the amount that should be added 
to the flood depth to account for waves in the Coastal A Zone. 

Erosion and scour: Flood depths in areas with erodible soils should 
consider the effects of erosion where floodwaters lower the 
ground surface or cause local scour around foundation elements. 
In these areas, the flood depth determined using the design flood 
elevation should be increased to account for changes in conditions 
during a flood event. Not only does lowering the ground 
surface effectively result in deeper water against the foundation, it 
may also remove supporting soil from the foundation, which must 
be accounted for in the foundation design. 

2.1.2.2 Design Flood VelocityRiverine

There are few sources of information that are readily available for 
estimating design flood velocities at specific locations along riverine 
bodies of water. If a riverine source has been studied using 
detailed hydraulic methods, some information may be available 
in summary form in published studies. Studies prepared for the 
NFIP (see Section 2.1.1.2) contain tables of data for waterways 
for which floodways were delineated. For specified cross-sections 
along the waterway, the Floodway Data Table includes a mean 
velocity expressed in feet per second. This value is the average 
of all velocities across the floodway. Generally, velocities in the 
flood fringe (landward of the floodway) will be lower than in the 
floodway. 

Waves and storm-induced erosion are most 
common in coastal areas. However, wide 
rivers and lakes may experience wind-
driven waves and erodible soils are found 
throughout the United States. For more 
information about waves and erosion, refer 
to FEMA 55, Coastal Construction Manual. 

For waterways without detailed studies, methods that are commonly 
used in civil engineering for estimating open channel flow velocities 
can be applied. 

2.1.2.3 Design Flood VelocityCoastal

Estimating design flood velocities in coastal flood hazard areas is 
subject to considerable uncertainty, and there is little reliable historical 
information or measurements from actual coastal flood 
events. In this context, velocity does not refer to the motion associated 
with breaking waves, but the speed of the mass movement of 
floodwater over an area.

The direction and velocity of floodwaters can vary significantly 
throughout a coastal flood event. Floodwaters can approach a 
site from one direction as a storm approaches, then shift to another 
direction (or through several directions) as the storm 
moves through the area. Floodwaters can inundate some low-lying 
coastal sites from both the front (e.g., ocean) and the back (e.g., 
bay, sound, or river). In a similar manner, at any given site, flow 
velocities can vary from close to zero to very high. For these reasons, 
when determining flood loads for building design, velocities 
should be estimated conservatively and it should be assumed that 
floodwaters can approach from the most critical direction and 
that flow velocities can be high. 

Despite the uncertainties, there are methods to approximate 
coastal flood velocities. One common method is based on the 
stillwater depth (flood depth without waves). Designers should 
consider the topography, the distance from the source of flooding, 
and the proximity to other buildings and obstructions before selecting 
the flood velocity for design. Those factors can direct and 
confine floodwaters, with a resulting acceleration of velocities. 
This increase in velocities is described as the 
expected upper bound. The expected 
lower bound velocities are experienced in 
areas where those factors are not expected 
to influence the direction and velocity of 
floodwaters. 

Upper bound velocities caused by Hurricane 
Katrina along the Mississippi coast, 
where storm surge depths neared 35 feet 
deep, have been estimated at nearly 30 
feet per second (20 miles per hour).

Figure 2-7 shows the general relationship between velocity and 
stillwater depth. For design purposes, actual flood velocities are assumed 
to lie between the upper and lower bounds. Conservative 
designs will take into account the upper bound velocities.

2.1.2.4 Hydrostatic Loads

Hydrostatic loads occur when water comes into contact with 
a building or building component, both above and below the 
ground level. They act as lateral pressure or vertical pressure 
(buoyancy). Hydrostatic loads on inclined or irregular surfaces 
may be resolved into lateral and vertical loads based on the surface 
geometry and the distribution of hydrostatic pressure. 

Lateral hydrostatic loads are a direct function of water depth (see 
Figure 2-8). These loads can cause serious deflection or displacement 
of buildings or building components if there is a substantial 
difference in water levels on opposite sides of the component 
(or inside and outside of the building). Hydrostatic loads are balanced 
on foundation elements of elevated buildings, such as piers and columns, because 
the element is surrounded by water. If not oriented parallel to the flow of 
water, shearwalls may experience hydrostatic loads due to a difference of water 
depth on either side of the wall. To reduce excessive pressure from standing 
water, floodplain management requirements in A Zones call for 
openings in walls that enclose areas below the flood elevation 
(see description of continuous perimeter wall foundation in Section 
2.3.1.2).

Figure 2-7: Velocity as a function of stillwater flood depth 

Buoyant forces resulting from the displacement of water are 
also of concern, especially for dry floodproofed buildings and 
aboveground and underground tanks. Buoyancy force is resisted 
by the dead load of the building or the weight of the tank. 
When determining buoyancy force, the weight of occupants 
or other live loads (such as the contents of a tank) should not 
be considered. If the building or tank does not weigh enough 
empty, then additional stabilizing measures need to be taken 
to avoid flotation. This becomes a significant consideration for 
designs intended to dry floodproof a building. Buoyancy force 
is slightly larger in saltwater, because saltwater weighs slightly 
more than fresh water.

Figure 2-8: Hydrostatic loads on buildings 

2.1.2.5 Hydrodynamic Loads

Water flowing around a building or a structural element that extends 
below the flood level imposes hydrodynamic loads. The 
loads, which are a function of flow velocity and structure geometry, 
include frontal impact on the upstream face, drag along the 
sides, and suction on the downstream side (see Figure 2-9). Ways 
to determine or estimate flood velocities are described in Section 
2.1.2.2 and Section 2.1.2.3.

The most common computation methods for hydrodynamic 
loads are outlined in the design standard Minimum Design Loads 
for Buildings and Other Structures, produced by the American 
Society of Civil Engineers Structural Engineers Institute (ASCE/
SEI, 2005). Those methods assume that the flood velocity is constant 
(i.e., steady state flow) and that the dynamic load imposed 
by floodwaters moving at less than 10 feet per second can be 
converted to an equivalent hydrostatic 
load. This conversion is accomplished 
by adding an equivalent surcharge depth to the depth 
of water on the upstream side. The equivalent surcharge depth is 
a function of the velocity. Loads imposed by floodwaters with velocities greater 
than 10 feet per second cannot be converted to equivalent hydrostatic 
loads. Instead, they must be determined according to the principles of fluid 
mechanics or hydraulic models. 

Figure 2-9: Hydrodynamic loads on a building or building element

Hydrodynamic loads become important when flow reaches 
moderate velocities of 5 feet per second. The components of hydrodynamic 
loads are laterally imposed, caused by the impact of 
the mass of water against the building, and drag forces along the 
wetted surfaces. Drag coefficients for common building elements, 
such as columns and piers, can be found in a number of sources. 
ASCE 7 recommends values for a variety of conditions. 

Another component of hydrodynamic loads is wave loads. As described 
in ASCE 7, design and construction of buildings and 
other structures subject to wave loads shall account for the following 
loads: waves breaking on any portion of the building 
or structure; uplift forces caused by shoaling waves beneath a 
building or structure, or portion thereof; wave runup striking any 
portion of the building or structure; wave-induced drag and inertia 
forces; and wave-induced scour at the base of a building or 
structure, or its foundation. 

Wave forces striking buildings and building elements can be 10 
to 100 or more times higher than wind forces and other forces. 
Forces of this magnitude can be substantial, even when acting 
over the relatively small surface area of the supporting structure 
of elevated buildings. Post-storm damage inspections show that 
breaking wave loads overwhelm virtually all wood-frame and unreinforced 
masonry walls below the wave crest elevation. Only 
engineered and massive structural elements are capable of withstanding 
breaking wave loads. The magnitude of wave forces is 
the rationale behind the floodplain management requirement for 
the bottom of the lowest horizontal structural member to be at 
or above the design flood elevation in environments where waves 
are predicted to be 3 feet or higher (V Zones). Because waves as 
low as 1.5 feet can impose considerable loads, there is a growing 
awareness of the value of accounting for waves in areas that are referred 
to as Coastal A Zones. 

Computation of wave loads depends on the determination of wave 
height. Equations for wave height are based on the assumption 
that waves are depth-limited (on the order of 75 to 80 percent of 
stillwater depth) and that waves propagating into shallow water 
break when the wave height reaches a certain proportion of the 
underlying stillwater depth. These assumptions are used by FEMA 
to determine coastal high hazard areas (V Zones) where breaking 
waves are predicted to be 3 feet or higher. At any given site, wave 
heights may be moderated by other factors. Designers should refer 
to ASCE 7 for detailed discussion and computation procedures.

Breaking wave loads on vertical walls or supporting structural 
members reach a maximum when the direction of wave approach 
is perpendicular to the wall. The duration of individual loads is 
brief, with peak pressures probably occurring within 0.1 to 0.3 
seconds after the wave breaks. It is common to assume that the 
direction of approach will be perpendicular to the shoreline, in 
which case the orientation of the wall to the shoreline will influence 
the magnitude of the load placed on the wall. ASCE 7 
provides a method for reducing breaking wave loads on vertical 
walls for waves that approach a building from a direction other 
than straight on. Structures should be designed for repetitive impact 
loads that occur during a storm. Some storms may last for just 
a few hours, as hurricanes move through the area, or for several 
days, as during some winter coastal storms (noreasters) that affect 
the Mid-Atlantic and northeastern States. 

2.1.2.6 Debris Impact Loads

Debris impact loads are imposed on a building or building elements 
by objects carried by moving water. Objects commonly 
carried by floodwaters include trees, dislodged tanks, and remnants 
of manmade structures such as docks and buildings (see 
Figure 2-10). Extreme impact loads result from less common 
sources, such as shipping containers, boats, and barges. The 
magnitude of these loads is very difficult to predict, yet some reasonable 
allowance should be made during the design process. 

Impact loads are influenced by the location of the building in 
the potential debris stream. The potential for debris impacts is 
significant if a building is located immediately adjacent to, or 
downstream from, other buildings, among closely-spaced buildings, 
or downstream from large floatable objects. While these 
conditions may be observable in coastal areas, it is more diffi
cult to estimate the potential for debris in riverine flood hazard 
areas. Any riverine waterway, whether a large river or smaller 
urban stream, can carry large quantities of debris, especially 
uprooted trees. 

The basic equation for estimating the magnitude of impact loads 
depends on several variables that must be selected by the designer. 
These variables include several coefficients, building or building 
element stiffness, debris weight, debris velocity, and duration of 
impact. The latter three variables, described in more detail in 
ASCE 7, are briefly described below.

Debris weight: Debris weight is one of the more difficult variables 
to estimate. Unless otherwise indicated by field conditions, ASCE 
7 recommends using an average object weight of 1,000 pounds. 
This weight corresponds to a 30-foot long log only 1 foot in diameter, 
small in comparison to large trees that may be uprooted 
during a flood. In coastal areas, expected debris weights depend 
on the nature of the debris. In the Pacific Northwest, large trees 
and logs are common, with weights in excess of 4,000 pounds. In 
areas where piers and pilings are likely to become debris, 1,000 
pounds is reasonable. In areas where most debris is likely to result 
from building damage (failed decks, steps, failed walls, propane 
tanks), the average debris weight may be less than 500 pounds.

Figure 2-10: The South Cameron Memorial Hospital, Cameron, LA, was 
damaged by debris carried by Hurricane Katrinas storm surge 
(2005). Source: LSU AGCENTER

Debris velocity: The velocity of the debris depends on the nature 
of the debris and the velocity of floodwaters. For the impact load 
computation, the velocity of the water-borne object is assumed to 
be the same as the flood velocity. Although this assumption is reasonable 
for smaller objects, it is conservative for large objects.

Debris impact duration: Duration of impact is the elapsed time 
during which the impact load acts on the building or building element. 
The duration of impact is influenced primarily by the 
natural frequency2 of the building or element, which is a function 
of the buildings stiffness. Stiffness is determined by the 
properties of the material, the number of supporting members 
(columns or piles), the height of the building above the ground, 
and the height at which the element is struck. Despite all the variables 
that may influence duration of impact, early assumptions 
suggested a 1-second duration. A review of results from several 
laboratory tests that measured impacts yielded much briefer periods, 
and ASCE 7 currently recommends a duration of 0.03 
second. 

2.1.2.7 Erosion and Localized Scour

Erosion generally refers to a lowering of the ground surface as a 
result of a flood event. Erosion may occur in riverine and coastal 
flood hazard areas. In coastal areas, erosion may affect the general 
ground surface and may cause a short-term or long-term recession of 
the shoreline. Erosion should be considered during load calculations, 
because it increases the local flood depth, which in turn influences 
load calculations. In areas subject to gradual erosion of the ground surface, 
additional foundation embedment depth can mitigate the effects. 
However, where waterways are prone to changing channels and 
where shoreline erosion is significant, engineered solutions are 
unlikely to be effective. Avoidance of sites in areas subject to active 
erosion is the safest and most cost-effective course of action.

Localized scour results from turbulence at the ground level 
around foundation elements. Scour occurs in both riverine and 
coastal flood hazard areas, especially in areas with erodible soils. 

2. The frequency at which an object will vibrate freely when set in motion.

Determining potential scour is critical in the design of foundations 
to ensure that failure during and after flooding does not occur as 
a result of the loss in either bearing capacity or anchoring resistance 
around the posts, piles, piers, columns, footings, or walls (see 
Figure 2-11). Scour determinations require knowledge of the flood 
depth, flow conditions, soil characteristics, and foundation type. 

At some locations, soil at or below the ground surface can be resistant 
to localized scour, and calculated scour depths based on 
unconsolidated surface soils below will be excessive. In instances 
where the designer believes the underlying soil at a site will be 
scour-resistant, the assistance of a geotechnical engineer or geologist 
should be sought. 

2.1.3 FLOODPLAIN MANAGEMENT REQUIREMENTS AND BUILDING CODES 

The NFIP is the basis for the minimum requirements included in 
model building codes and standards for design and construction 
methods to resist flood damage. The original authorizing legislation 
for the NFIP is the National Flood Insurance Act of 1968 (42 
U.S.C. 4001 et seq.). In that act, Congress expressly found that a 
program of flood insurance can promote the public interest by 
encouraging sound land use by minimizing exposure of property 
to flood losses 

Figure 2-11: Local scour undermined this shallow foundation (also note that the 
building was not anchored to the foundation). 

The most convincing evidence of the effectiveness of the NFIP 
minimum requirements is found in flood insurance claim payment 
statistics. Buildings that pre-date the NFIP requirements 
are, by and large, not constructed to resist flood damage. Buildings 
that post-date the NFIP (i.e., those that were constructed 
after a community joined the program and began applying the 
minimum requirements) are designed to resist flood damage. 
The NFIP reports that aggregate loss data indicate that buildings 
that meet the minimum requirements experience 70 percent less 
damage than buildings that pre-date the NFIP. There is ample 
evidence that buildings designed to exceed the minimum requirements 
are even less likely to sustain damage. 

2.1.3.1 Overview of the NFIP

The NFIP is based on the premise that the Federal government 
will make flood insurance available in communities that agree to 
recognize and incorporate flood hazards in land use and development 
decisions. In some States and communities this is achieved 
by guiding development to areas with a lower risk. When decisions 
result in development within flood hazard areas, application 
of the criteria set forth in Federal regulation 44 CFR 60.3 are intended 
to minimize exposure and flood-related damage. State 
and local governments are responsible for applying the provisions 
of the NFIP through the regulatory permitting processes. At the 
Federal level, the NFIP is managed by FEMA and has three main 
elements:

 Hazard identification and mapping, under which engineering 
studies are conducted and flood maps are prepared in 
partnership with States and communities. These maps 
delineate areas that are predicted to be subject to flooding 
under certain conditions. 
 Floodplain management criteria for development, which 
establish the minimum requirements to be applied to 
development within mapped flood hazard areas. The intent is 
to recognize hazards in the entire land development process. 
 Flood insurance, which provides some financial protection for 
property owners to cover flood-related damage to buildings 
and contents.
Federal flood insurance is intended to shift 
some of the costs of flood disasters away 
from the taxpayer by providing property 
owners an alternative to disaster assistance 
and disaster loans. Disaster assistance provides 
limited funding for repair and cleanup, 
and is available only after the President 
signs a major disaster declaration for the 
area. NFIP flood insurance claims are paid 
any time damage from a qualifying flood 
event occurs, regardless of whether a major 
disaster is declared. Community officials 
should be aware that public buildings may 
be subject to a mandated reduction in disaster 
assistance payments if the building is 
in a mapped flood hazard area and is not 
covered by flood insurance. 

Another important objective of the NFIP is to break the cycle of 
flood damage. Many buildings have been flooded, repaired or rebuilt, 
and flooded again. Before the NFIP, in some parts of the 
country this cycle occurred every couple of years, with reconstruction 
taking place in the same flood-prone areas, using the 
same construction techniques that did not adequately resist flood 
damage. NFIP provisions guide development to lower risk areas 
by requiring compliance with performance measures to minimize 
exposure of new buildings and buildings that undergo major renovation 
or expansion (called substantial improvement or repair 
of substantial damage). This achieves the long-term objective of 
building disaster-resistant communities. 

Substantial damage is damage of any 
origin sustained by a structure whereby 
the cost of restoring the structure to its 
condition before the damage would 
equal or exceed 50 percent of the market 
value of the structure before the damage 
occurred. 

Substantial improvement is any repair, 
reconstruction, rehabilitation, addition, 
or improvement of a building, the cost 
of which exceeds 50 percent of the 
market value of the building before the 
improvement or repair is started (certain 
historic structures may be excluded).

3. For the purpose of adjusting claims for flood damage, the NFIP defines a 
flood as a general and temporary condition of partial or complete 
inundation of two or more acres of normally dry land area or of two or more 
properties (at least one of which is the policyholders property) 
from: overflow of inland or tidal waters; unusual and rapid accumulation or 
runoff of surface waters from any source; mudflow; or collapse or 
subsidence of land along the shore of a lake or similar body of water as a 
result of erosion or undermining caused by waves or currents of water 
exceeding anticipated cyclical levels that result in a flood as defined above.

2.1.3.2 Summary of the NFIP Minimum Requirements 

The performance requirements of the NFIP are set forth in Federal 
regulation 44 CFR Part 60. The requirements apply to all 
development, which the NFIP broadly defines to include buildings 
and structures, site work, roads and bridges, and other activities. 
Buildings must be designed and constructed to resist flood 
damage, which is primarily achieved through elevation (or floodproofing). 
Additional specific requirements apply to existing 
development, especially existing buildings. Existing buildings that 
are proposed for substantial improvement, including restoration 
following substantial damage, are subject to the regulations. 

Although the NFIP regulations primarily focus on how to build 
structures, one of the long-term objectives of the program is to 
guide development to less hazardous locations. Preparing flood 
hazard maps and making the information available to the public 
is fundamental in satisfying that objective. With that information, 
people can make informed decisions about where to build, how to 
use site design to minimize exposure to flooding, and how to design 
buildings that will resist flood damage.

The NFIPs broad performance requirements for site work in 
flood hazard areas are as follows:

 Building sites shall be reasonably safe from flooding.
 Adequate site drainage shall be provided to reduce exposure 
to flooding. 
 New and replacement sanitary sewage systems shall be 
designed to minimize or eliminate infiltration of floodwaters 
into the systems and discharges from the systems into 
floodwaters.
 Development in floodways shall be prohibited, unless 
engineering analyses show that there will be no increases in 
flood levels. 

The NFIPs broad performance requirements for new buildings 
proposed for flood hazard areas (and substantial improvement of 
existing flood-prone buildings) are as follows:

 Buildings shall be designed and adequately anchored to 
prevent flotation, collapse, or lateral movement resulting from 
hydrodynamic and hydrostatic loads, including the effects of 
buoyancy.
 Building materials used below the design flood elevation shall 
be resistant to flood damage.
 Buildings shall be constructed to minimize flood damage 
(primarily by elevating to or above the base flood level, or by 
specially designed and certified floodproofing measures).
 Buildings shall be constructed with electrical, heating, 
ventilation, plumbing, and air conditioning equipment and 
other service facilities designed to prevent water from entering 
or accumulating within the components.

Owners, planners and designers should 
determine if there are any applicable 
State-specific requirements for floodplain development. 
Some States require that local 
jurisdictions apply standards that exceed 
the minimum requirements of the NFIP. In 
particular, some States require that critical facilities 
be located outside of the floodplain 
(including the 500-year floodplain) or they 
are to be designed and constructed to resist 
conditions associated with the 500-year flood. 
Some States have regulations that impose 
other higher standards, while some States 
have direct permitting authority over certain 
types of construction or certain types of 
applicants. 

As participants in the NFIP, States are required to ensure that development 
that is not subject to local regulations, such as State 
construction, satisfies the same performance requirements. If 
critical facilities are exempt from local permits, this may be accomplished 
through a State permit, a governors executive order, 
or other mechanisms that apply to entities not subject to local 
authorities.

States often use governors executive 
orders to influence State-constructed and 
State-funded critical facilities, requiring 
location outside of the 500-year floodplain 
where feasible, or protection to the 
500-year flood level if avoiding the 
floodplain is not practical. In 2004, a 
review of State and local floodplain 
management programs determined that 
Alabama, Illinois, Michigan, New York, 
North Carolina, Ohio, and Virginia have 
requirements for critical facilities (ASFPM, 
2004). 


2.1.3.3 Executive Order 11988 and Critical Facilities 

When Federal funding is provided for the planning, design, 
and construction of new critical facilities, or for the repair of existing 
critical facilities located within the 500-year floodplain, the 
funding agency is required to address additional considerations. 
Executive Order 11988, Floodplain Management, requires Federal 
agencies to apply a decisionmaking process to avoid, to the extent 
possible, the long- and short-term adverse impacts associated with 
the occupancy and modification of floodplains, and to avoid the 
direct or indirect support of floodplain development whenever 
there is a practicable alternative. If there is no practicable alternative, 
the Federal agency must minimize any adverse impacts to life, 
property, and the natural and beneficial functions of floodplains. 

The executive order establishes the base flood elevation as the 
minimum standard for all Federal agencies. Implementation guidance 
specifically addresses critical actions, which are described 
as those actions for which even a slight chance of flooding would 
be too great. The construction or repair of critical facilities, such 
as fire stations, hospitals and clinics, EOCs, the storage of hazardous 
wastes, and the storage of critical records, are examples of 
critical actions.   

After determining that a site is in a mapped 
flood hazard area, and after giving public 
notice, the Federal funding agency is required 
to identify and evaluate practicable 
alternatives to locating a critical facility in a 
500-year floodplain. If the Federal agency 
has determined that the only practicable alternative 
is to proceed, then the impacts of 
the proposed action must be identified. If 
the identified impacts are harmful to people, property, and the 
natural and beneficial functions of the floodplain, the Federal 
agency is required to minimize the adverse effects on the floodplain 
and the funded activity.

FEMAs eight-step decisionmaking process 
for complying with Executive Order 11988 
must be applied before Federal disaster 
assistance is used to repair, rehabilitate, 
or reconstruct damaged existing critical 
facilities in the 500-year floodplain.

Having identified the impacts of the proposed action and the 
methods to minimize these impacts, the Federal agency is required 
to re-evaluate the proposed action. The re-evaluation must 
consider whether the action is still feasible, whether the action can 
be modified to relocate the facility or eliminate or reduce identified 
impacts, or if a no action alternative should be chosen. If 
the finding results in a determination that there is no practicable 
alternative to locating a critical facility in the floodplain, or otherwise 
affecting the floodplain, then a statement of findings and a 
public explanation must be provided. 

2.1.3.4 Scope of Model Building Codes and Standards 

The International Building Code (IBC, 2003) and the Building Construction 
and Safety Code (NFPA 5000, 2003) were the first model 
codes to include comprehensive provisions that address flood hazards. 
Both codes are consistent with the minimum provisions of 
the NFIP that pertain to the design 
and construction of buildings. 
The NFIP requirements that pertain to site development, 
floodways, coastal setback lines, erosion-
prone areas, and other environmental 
constraints are found in other local ordinances. The 
codes require designers to identify and design for anticipated environmental 
loads and load combinations, 
including wind, seismic, 
snow, and flood loads, as well as the soil conditions.

The IBC and NFPA 5000 incorporate by reference a number of standards 
that are developed through a rigorous consensus process. The 
best known is Minimum Design Loads for Buildings and Other Structures 
(ASCE 7-05). The model building codes require that applicable 
loads be accounted for in the design. The 1998 edition of ASCE 7 
was the first version of the standard to include flood loads explicitly, 
including hydrostatic loads, hydrodynamic loads (velocity and 
waves), and debris impact loads. 

The IBC and NFPA 5000 also incorporate by reference a standard 
that was first published by ASCE in 1998 and revised in 
2005, Flood Resistant Design and Construction (ASCE/SEI 24-05). 

Developed through a consensus process, 
ASCE 24 addresses specific topics pertinent 
to designing buildings in flood hazard areas, 
including floodways, coastal high hazard 
areas, and other high-risk flood hazard areas 
such as alluvial fans, flash flood areas, mudslide 
areas, erosion-prone areas, and high 
floodwater velocity areas. 

Section 1.2 describes the four categories used 
by ASCE 7 to classify structures based on occupancy; 
different requirements apply based on 
a structures category. The same categories are used in ASCE 24 
and different flood-resistant requirements apply to the different 
categories. Table 2-1 summarizes the elevation requirements of 
ASCE 24 that exceed the NFIP minimum requirements for the 
critical facilities addressed by this manual (Category III or Category 
IV structures). 

ASCE 7-05 outlines methods to determine 
design loads and load combinations in 
flood hazard areas, including hydrostatic 
loads, hydrodynamic loads, wave loads, 
and debris impact loads.

ASCE 24-05 addresses design requirements for structures in coastal high-
hazard areas (V Zones).

Table 2-1: ASCE/SEI 24-05 provisions related to the elevation of critical 
facilities 

Category III
Category IV
Elevation of Lowest Floor or Bottom 
of Lowest Horizontal Structural 



2.2 CRITICAL FACILITIES EXPOSED TO FLOODING 

2.2.1 EVALUATING RISK AND AVOIDING FLOOD HAZARDS

Flood hazards are very site-specific. 
When a flood hazard map is prepared, 
lines drawn on the map appear to precisely 
define the hazard area. Land that is on 
one side of the line is in the mapped flood 
hazard area, while the other side of the line 
is out. Although the delineation may be an 
approximation, having hazard areas shown 
on a map facilitates avoiding such areas to the maximum extent 
practical. Where it is unavoidable, facility owners should carefully 
evaluate all of the benefits and all of the costs in order to determine 
long-term acceptable risks, and to develop appropriate plans 
for design and construction of new facilities.

Section 2.2.2 describes the damage sustained by existing buildings 
exposed to flood hazards, including site damage, structural 
and nonstructural building damage, destruction or impairment of 
service equipment, and loss of contents. These types of damage, 
along with loss of function and community service, are avoided if 
critical facilities are located away from flood hazard areas. Damage 
is reduced when critical facilities that must be located in flood 
hazard areas are built to exceed the minimum requirements.

Even in communities with expansive 
floodplains, it should be possible to avoid 
locating new critical facilities in floodways 
and coastal areas subject to significant 
waves (V Zones).

2.2.1.1 Benefits/Costs: Determining Acceptable Risk

Many decisions that are made with respect to 
critical facilities are, in part, based on a determination 
of acceptable risk. Risk includes 
the potential losses associated with a hazard. 
Ideally, risk is defined in terms of expected 
probability and frequency of the hazard occurring, 
the people and property exposed, 
and the potential consequences. Choosing 
a site that is affected by flooding is a decision 
to accept some degree of risk. Although 
the flood-prone land may have a lower initial 
cost, the incremental costs of construction, 
plus the likely increased costs of maintenance, 
repair, and replacement, may be 
significant. Another cost of locating a critical 
facility in a flood-prone area is related to access problems if roads 
and driveways are impassable. Although the building may be elevated 
and protected, if access is restricted periodically, then the 
use of the facility is affected. 

The building owner and the design team can influence the degree 
of risk (e.g., the frequency with which flooding may affect the 
site). They control it through the selection of the site design and 
the building design measures. Fundamentally, this process is a balancing 
of the benefits of an acceptable level of disaster resistance 
with the costs of achieving that degree of protection. With respect 
to mitigation of future hazard events:

 Benefits are characterized and measured as future damages 
avoided if the mitigation measures (including avoiding flood 
hazard areas) are implemented.
 Costs are the costs associated with implementing measures to 
eliminate or reduce exposure to hazards. 
Section 2.2.2 describes damage and losses that are incurred by 
buildings exposed to flooding. Direct damage includes damage to 
physical property, including the site, the building, building materials, 
utilities, and building contents. Indirect damage that is not listed includes 
health hazards, loss of functionality, emergency response, evacuation, 
and expenses associated with occupying another building during repairs.

Extreme hurricane storm surge flooding 
may be a very low-probability event, but 
the flood water depths and waves may 
be much more severe than the conditions 
of the base flood shown on the FIRMs. 
The potential impacts on a critical facility 
must be carefully considered in order to 
make an informed decision regarding 
acceptable risk and potential damage. If 
possible, it is always best to avoid locating 
critical facilities in areas subject to extreme 
storm surge flooding. 

Benefits other than avoided physical damage 
are difficult to measure. They are associated 
with future damage that does not occur because 
of the mitigation activity, cleanup that 
is not required because of the mitigation activity, 
and service that is not interrupted 
because flooding does not affect normal 
operation of the facility. In addition, benefits 
accrue over long periods of time, thus 
making it more difficult to make a direct comparison of the benefits 
with the up-front costs of mitigation. Mitigation costs can be 
more readily expressed in terms of the higher costs of a flood-
free site, or the initial capital costs of work designed to resist flood 
damage. Thus, without a full accounting of both benefits and 
costs, decisionmakers may not be able to make fully informed decisions. 
Some questions that should be answered include:

 If the site is flood-prone and the building is out of the flood 
hazard area or is elevated on fill, what are the average annual 
cleanup costs associated with removal of sand, mud, and debris 
deposited by floods of varying frequencies?
 If the facility building is elevated by means other than fill, will 
periodic inundation of the exposed foundation elements cause 
higher average annual maintenance costs?
 If the facility is protected with floodproofing measures, what 
are the costs of annual inspections, periodic maintenance 
and replacement of materials, and staff training and periodic 
drills?
 If the critical facility meets only the minimum elevation 
requirements, what are the average annual damage and 
cleanup costs over the anticipated useful life of the building, 
including the occurrence of floods that exceed the design 
flood elevation?
Sometimes developers are required to 
set aside land to meet adequate facilities 
requirements, or land may be donated to 
support community or non-profit facilities, 
such as fire stations. If the donated land 
is affected by flood hazards, it may be 
difficult to avoid floodplain impacts entirely. 
Careful consideration should be made 
whether the benefits of accepting the land 
outweigh the costs and risks associated 
with mitigating the flood risk. 
 How do long-term costs associated with periodic inundation 
compare to up-front costs of selecting a different site or 
building to a higher level of protection?
 If the facility is located in a hurricane-prone community, how 
should the facility design account for low probability, but high 
impact, storm surge flooding?
 If access to the facility is periodically restricted due to flooding, 
especially long-duration flooding, what are the cost effects? 
How often should an alternate location be provided to 
continue normal operations?

2.2.1.2 Identifying Flood Hazards at Critical Facilities Sites

As part of site selection and to guide locating a new critical facility 
and other improvements on a site, facility owners, planners, and 
designers should investigate site-specific flood hazard characteristics. 
Similarly, when examining existing critical facilities and 
when planning improvements or rehabilitation work, an important 
step is to determine the site characteristics and flood hazards. 
The best available information should be examined, including 
flood hazard maps, records of historical flooding, storm surge 
maps, and advice from local experts and others who can evaluate 
flood risks. Table 2-3 in Section 2.5 outlines questions that should 
be answered prior to initiating site layout and design 
work.

2.2.1.3 Critical Facilities as Emergency Shelters 

Emergency managers regularly identify facilities (especially 
schools) to serve as short-term and long-term shelters. Schools 
are attractive sites for shelters because they have kitchen facilities 
designed to serve many people, restroom facilities likely to be 
adequate for many people, and plenty of space for cots in gymnasiums, 
cafeterias, and wide corridors.

New schools that will function as emergency shelters warrant a 
higher degree of protection than other schools and should be appropriately 
designed as critical facilities (see Section 1.3 for an 
overview on performance-based design). If located in, or adjacent 
to, flood hazard areas, it is appropriate to provide protection 
for the building and utility systems to at least the 0.2-percent-annual-
chance (500-year) flood level or, at a minimum, 2 to 3 feet 
above the DFE. Additional guidance on hazard-resistant shelters is 
found in FEMA 361, Design and Construction Guidance for Community 
Shelters.

Additional measures that may be appropriate for consideration 
when flood-prone critical facilities are used as shelters include the 
following:

 Wastewater service must be functional during conditions of the 
flooding.
 Emergency power service must be provided.
 Dry ground access is important, in the event flooding exceeds 
design levels.

2.2.2 VULNERABILITY: WHAT FLOODING CAN DO TO EXISTING CRITICAL FACILITIES

Existing flood-prone facilities are susceptible to damage, the nature 
and severity of which is a function of site-specific flood 
characteristics. As described below, damage may include: site 
damage, structural and nonstructural building damage, destruction 
or impairment of utility service equipment and loss of 
contents. 

Regardless of the nature and severity of damage, flooded facilities 
typically are not functional while cleanup and repairs are 
undertaken. The length of closure, and thus the impact on the 
ability of the facility to become operational, depends on the severity 
of the damage and lingering health hazards. Sometimes 
repairs are put on hold pending a decision on whether a facility 
should be rebuilt at the flood-prone site. When damage 
is substantial, rehabilitation or reconstruction is allowed only if 
compliance with flood-resistant design requirements is achieved 
(see Section 2.1.3.2).

2.2.2.1 Site Damage

The degree of site damage associated with flooding is a function 
of several variables related to the characteristics of the flood, as 
well as the site itself.

Erosion and scour: All parts of a site subject to flooding by fast 
moving water could experience erosion, and local scour could 
occur around any permanent obstructions to flow. Graded 
areas, filled areas, and cut or fill slopes are especially susceptible. 
Stream and channel bank erosion, and erosion of coastal shorelines, are natural 
phenomena that may, over time, threaten site improvements and buildings. 

Debris and sediment removal: Even when buildings are not subject 
to water damage, floods can produce large quantities of debris 
and sediment that can damage a site and be expensive to 
remove. 

Landscaping: Grass, trees, and plants suffer after floods, especially 
long-duration flooding that prevents oxygen uptake, and 
coastal flooding that stresses plants that are not salt-tolerant. 
Fast-moving floodwaters and waves also can uproot plants and 
trees.

Fences: Some types of fences that are relatively solid can significantly 
restrict the free flow of floodwaters and trap floating 
debris. Fences can be damaged by flowing water, and can be 
knocked down under pressure of flowing water or if the buildup 
of debris results in significant loads (see Figure 2-12). 

Accessory structures: Accessory structures can sustain both structural 
and nonstructural damage. In some locations, such 
structures can be designed and built using techniques that 
minimize damage potential, without requiring elevation above 
the DFE. 

Access roads: Access roads that extend across flood-prone areas 
may be damaged by erosion, washout of drainage culverts, 
failure of fill and bedding materials, and loss of surface (see 
Figure 2-13). Road damage could prevent uninterrupted access 
to a facility and thus impair its functionality. 

Parking lots and parking garages: Paved parking lots may be damaged 
by failure of bedding materials and loss of driving surface. 
Vehicles left in parking lots and parking garages could also be 
damaged. Most large parking garages are engineered structures 
that can be designed to allow for the flow of water.

Stormwater management facilities and site drainage: Site improvements 
such as swales and stormwater basins may be eroded, 
filled with sediments, or clogged by debris.

2.2.2.2 Structural Damage

Structural damage includes all damage to the load-bearing portions 
of a building. Structural damage can be caused by each 
of the characteristics of flooding described in Section 2.1.1. 

Figure 2-12: Katrinas storm surge flooding knocked down this 
fence adjacent to a fire station (2005).

Figure 2-13: Flooding caused the failure of this road bed. 
Source: U.S. Army Corps of Engineers





Damage to other components of buildings is described below, 
including saturation of materials (Section 2.2.2.3), utility service 
equipment (Section 2.2.2.4), and contents (Section 2.2.2.5).

Depth: The hydrostatic load or pressure against a wall or foundation 
is directly related to the depth of water (refer to Figure 
2-9). Standard stud and siding, or unreinforced brick veneer 
walls, may collapse under hydrostatic loads associated with relatively 
shallow water. Reinforced masonry walls perform better 
than unreinforced masonry walls (see Figure 2-14), although 
an engineering analysis is required to determine performance. 
Walls and floors of below-grade areas (basements) are particularly 
susceptible to damage by hydrostatic pressure. When soils 
are saturated, pressures against below-grade walls are a function 
of the total depth of water, including the depth below-grade and 
the weight of the saturated soils.

Figure 2-14: Interior unreinforced masonry walls of the Port 
Sulphur High School in Louisiana were damaged by hydrostatic loads associated 
with Hurricane Katrinas storm surge (2005).

Buoyancy and uplift: If below-grade areas are essentially watertight, 
buoyancy or uplift forces can float a building out of the ground or 
rupture concrete floors (see Figure 2-15). Buildings that are not 
adequately anchored can be floated or pushed off foundations. Although 
rare for large and heavy critical facility buildings, this is a 
concern for outbuildings and portable (temporary) units.

Duration: Long duration saturation can cause dimensional changes 
and contribute to deterioration of wood members. By itself, saturation 
is unlikely to result in significant structural damage to masonry 
construction. Saturation of soils, a consequence of long duration 
flooding, increases pressure on below-grade foundation walls. 

Velocity, wave action, and debris impacts: Each of these components 
of dynamic loads can result in structural damage if buildings are 
not designed to resist overturning, repetitive pounding by waves, 
or short-duration impact loads generated by floating debris.

Erosion and scour: Structural damage is associated with foundation 
failure when erosion or scour results in partial or complete 
removal of supporting soil (see Figure 2-16). Erosion of slopes, especially 
unprotected slopes, can lead to slope failures and loss of 
foundation supporting soil. 


Figure 2-15: Concrete floor ruptured by hydrostatic pressure 
(buoyancy). Hurricane Katrina (2005)

2.2.2.3 Nonstructural Damage 

Many flood-prone buildings are exposed to floodwaters that are 
not fast moving, or that may be relatively shallow and not result 
in structural damage. Simple inundation and saturation of the 
building and finish materials can result in significant and costly 
nonstructural damage, including long-term health complications 
associated with mold. Floodwaters often are contaminated 
with chemicals, petroleum products, or sewage. Under such circumstances, 
recovery generally involves removal of nonstructural 
materials and finishes because cleanup and decontamination is expensive 
and time-consuming. Damage to contents is discussed in 
Section 2.2.2.5. 

Nonstructural damage can vary as a function of the duration of 
water exposure. Some materials are not recoverable even after 
very brief inundation, while others remain serviceable if in contact 
with water for only a few hours. Use of water-resistant materials 
will help to minimize nonstructural damage caused by saturation 
and reduce the costs of cleanup and restoration to service (see 
Flood-Resistant Materials Requirements, FIA-TB-2).

Wall finishes: Painted concrete and concrete masonry walls usu-
ally resist water damage, provided the type of paint can be readily 
cleaned, such as high strength epoxy paints. Tiled walls may be 
acceptable, depending on the type of adhesive and foundation 
(gypsum board substrate and wood-framed walls with tile typically 
do not remain stable). 

Figure 2-16: Scour around the foundation of this building 
contributed to significant damage. 

Flooring: Many critical facilities have durable floors that resist 
water damage. Ground floors often are slab-on-grade and finished 
with tile or sheet goods. Flooring adhesives in use since 
the early 1990s likely are latex-based and tend to break down 
when saturated. Most carpeting, even the indoor-outdoor kind, 
is difficult to clean. Wood floors are particularly susceptible to 
saturation damage, although short duration inundation may 
not cause permanent de-formation of some wood floors. However, 
because of low tolerance for surface variations, gymnasium 
floors in schools are particu-larly sensitive and tend to warp after 
flooding of any duration (see Figure 2-17). 

Wall and wood components: When soaked for long periods of time, 
some building components change composition or shape. Most 
types of wood will swell when wetted and, if dried too quickly, will 
crack, split or warp. Plywood can delaminate and wood door and window frames may 
swell and become unstable. Gypsum wallboard, wood composition panels, other wall 
materials, and wood cabinetry not intended for wet locations can fall apart (see 
Figure 2-18). The longer these materials are wet, the more moisture, sediment, 
and pollutants they absorb. Some wall materials, such as the paper 
facing on gypsum wallboard, wick standing water, resulting in 
damage above the actual high-water line (see Figure 2-19). 

Figure 2-17: This parquet wood gymnasium floor was damaged by dimensional 
changes due to saturation. Hurricane Katrina (2005)

Figure 2-18: Damaged walls and cabinets 

Figure 2-19: Water damage and mold growth extend above the 
water line Source: Oak Ridge National Laboratory
Metal components: Metal structural components are unlikely to be 
permanently damaged by short-term inundation. However, hollow 
metal partitions are particularly susceptible when they come into 
contact with water because they cannot be thoroughly dried and 
cleaned. Depending on the degree of corrosion protection on the 
metal, repetitive flooding by saline coastal waters may contribute 
to long-term corrosion.

Metal connectors and fasteners: Depending on the composition of the 
metal, repetitive flooding, especially by saline coastal waters, may 
contribute to long-term corrosion. Connectors and fasteners are 
integral to the structural stability of buildings; therefore, failure 
caused by accelerated corrosion would jeopardize the building.

2.2.2.4 Utility System Damage

Utility system service equipment that is exposed to flooding is 
vulnerable to damage. Damage may result in a total loss, or may 
require substantial cleaning and restoration efforts. The degree 
of damage varies somewhat as a function of the characteristics of 
flooding. Certain types of equipment and installation measures 
will help minimize damage and reduce the costs of cleanup and 
restoration to service.

Displacement of equipment and appliances: Installation below the 
flood level exposes equipment and appliances to various flood 
forces, including drag resulting from flowing water and buoyancy. 
Gas-fired appliances are particularly dangerous: flotation can separate 
appliances from gas sources, resulting in fires and explosive 
situations. Displaced equipment may dislodge lines from fuel oil 
tanks, contributing to the threat of fires and causing water pollution 
and environmental damage.

Elevators: If located in areas subject to flooding, elevator 
component equipment and controls will be damaged, and 
communication between floors will be impaired. 

Corrosion: Corrosion related to inundation of equipment and appliances 
may not be apparent immediately, but can increase 
maintenance demand and shorten the useful life of some equipment 
and appliances. 

Electrical systems and components: Electrical systems and components, 
and electrical controls of heating, ventilation, and air 
conditioning systems, are subject to damage simply by getting wet, 
even for short durations. Unless specifically designed for wet locations, 
switches and other electrical components can short out due 
to deposits of sediment, or otherwise not function even when allowed 
to dry before operation. Wiring and components that have 
been submerged may be functional, although generally it is more 
cost-effective to discard flooded outlets, switches, and other less 
expensive components than to attempt thorough cleaning.

Communications infrastructure: Critical communications infrastructure, 
such as control panels and wiring for warning systems, 911 
systems, and regular telephone and wireless networks, are most 
susceptible to failure during emergencies if located in below-grade 
basements. 

Specialized piping: Unprotected piping for medical gas supply 
systems may be damaged and threaten care that depends on uninterrupted 
supply of oxygen and other gasses for the treatment of 
patients.

Ductwork damage: Ductwork is subject to two flood-related problems. 
Flood forces can displace ductwork, and saturated insulation 
can overload support straps, causing failure.

Mold and dust: Furnaces, air handlers, and ductwork that have been 
submerged must be thoroughly cleaned and sanitized. Otherwise, 
damp conditions contribute to the growth of mold and accumulated 
sediment can be circulated throughout the critical facility, 
causing respiratory problems. Fiberglass batt or cellulose insulation 
that has been submerged cannot be sanitized and must be 
replaced. In sensitive environments, ductwork should be replaced 
rather than cleaned.

Gas-fired systems: Water-borne sediment can impair safe functioning 
of jets and controls in gas-fired furnaces and water heaters, 
necessitating professional cleaning and inspection prior to restoration 
of service. Control equipment (valves, electrical switches, 
relays, temperature sensors, circuit breakers, and fuses) that have 
been submerged may pose an explosion and fire hazard and 
should be replaced.

Emergency power generators: Generators that are installed at-grade 
are susceptible to inundation and will be out of service after a 
flood (see Figure 2-20).

Tanks (underground): Underground storage tanks are subjected to 
significant buoyant forces and can be displaced, especially when 
long-duration flooding occurs. Computations of stability should 
be based on the assumption that the tank is empty in order to 
maximize safety. Tank inlets, fill openings, and vents should be 
above the DFE, or designed to prevent the inflow of floodwaters 
or outflow of tank contents during flood conditions.

Tanks (aboveground): Aboveground storage tanks are subject to 
buoyant forces and displacement caused by moving water. Standard 
strapping of propane tanks may be inadequate for the 
anticipated loads. Tank inlets, fill openings, and vents should be 
above the DFE, or designed to prevent the inflow of floodwaters 
or outflow of tank contents during flood conditions.

Public Utility Service: Damage to public utility service (potable 
water supply and wastewater collection) can affect operations and 
may cause damage to critical facilities:


Figure 2-20: Although it was anchored and not displaced by 
floodwaters, this generator was out of service after being submerged. 

 Potable water supply systems may become contaminated 
if public water distribution lines or treatment facilities are 
damaged, or if wellheads are submerged.
 During heavy rains, sewers back up from infiltration and 
inflow of stormwater into the sewer lines and manholes, 
cross connections between storm and sanitary sewers, and 
flooded wastewater treatment plants. Sewer backup into a 
critical facility poses a major health hazard. Even when the 
water has receded, exposed building components, finish 
materials, and contents are contaminated, and usually must 
be removed because adequate cleaning is difficult, if not 
impossible. 

2.2.2.5 Contents Damage

Critical facilities may contain high-value contents that can be damaged 
and become unrecoverable when subjected to flooding. For 
the purpose of this discussion, the term contents includes items 
such as furniture, appliances, computers, laboratory equipment 
and materials, records, and specialized machinery. The following 
types of contents are often considered a total loss.

Furniture: In long-duration flooding, porous woods become saturated 
and swollen, and joints may separate. Furniture with 
coverings or pads generally cannot be restored. Metal furniture is 
difficult to thoroughly dry and clean, is subject to corrosion, and 
typically is discarded. Some wood furniture may be recoverable 
after brief inundation.

Computers: Flood-damaged computers and peripheral equipment 
cannot be restored after inundation, although special recovery 
procedures may be able to recover information on hard drives.

Communications equipment: Even though some communications 
equipment may be able to be restored with appropriate 
cleaning, the loss of functionality would seriously impair the 
ability of the facility to provide critical services immediately after 
a flood. Equipment with printed circuit boards generally cannot 
be restored.

Office records and police files: When facilities are located in flood-
prone space, valuable records may be lost. Although expensive, 
some recovery of computerized and paper records may be possible 
with special procedures (see Figure 2-21).

Health care equipment and laboratory materials: Most medical and 
health care equipment cannot be cleaned and restored to safe 
functioning, and would need to be replaced. Depending on the 
nature of laboratory materials and chemicals, complete disposal 
or special cleanup procedures may be required.

Kitchen goods and equipment: Floodwaters can dislodge appliances 
that can float and damage other equipment (see Figure 2-22). 
Stainless steel equipment generally has cleanable surfaces that can 
be disinfected and restored to service. Because of contamination, 
all food stuffs must be discarded. 

Vehicles associated with critical facilities: If left in flood-prone areas, 
fire engines, police cars, ambulances, and other vehicles require 
replacement or cleaning to be serviceable and may not be functional 
and available for service immediately after a flood.

Figure 2-21: Medical records saturated by floodwaters 
Source: Hancock Medical Center 

Figure 2-22: Kitchen appliances and equipment from Port 
Sulphur High School were displaced and damaged 
by Hurricane Katrina floodwaters (2005). 

2.3 REQUIREMENTS AND BEST PRACTICES IN SPECIAL HAZARD AREAS

2.3.1 RISK REDUCTION IN A ZONES 

Flood hazard areas designated as A Zones on FIRMs are areas 
where significant wave action is not expected (see Section 
2.1.1.2). A Zones are found along riverine bodies of water 
(rivers, streams, creeks, etc.), landward of V Zones, and on some 
open coastlines that do not have mapped V Zones. When constructing 
a critical facility on a site affected by an A Zone flood hazard, site 
design is influenced by several constraints, such as the presence of 
flood hazard areas, wetlands, poor soils, steep slopes, sensitive habitats, 
mature tree stands, and the environmental requirements set by 
the various regulatory authorities and the agency that approves development 
plans.

Four aspects of the design of flood-resistant buildings and sites are 
described in this section: site modifications, 
elevation considerations, flood-resistant materials, and floodproofing 
considerations. Section 2.3.5 addresses related facilities, including access 
roads, utility installations, water and wastewater systems, storage tanks, 
and accessory structures.

2.3.1.1 Site Modifications

When sites being considered for critical facilities are affected by 
flood hazards, planners and designers may want to evaluate the 
feasibility of certain site modifications in order to provide an in
creased level of protection to buildings. The evaluations involve engineering 
analyses to determine whether the desired level of protection 
is cost-effective, and whether the proposed site modifications alter the 
floodplain in ways that could increase flooding. The effectiveness of typical 
site modifications and their ramifications must be examined for 
each specific site. 

Earthen fill: Fill can be placed in the flood hazard area for the purpose 
of elevating a site above the design flood elevation. If the fill 
is placed and compacted so as to be stable during the rise and fall 
of floodwaters, and if the fill is protected from erosion, then modifying 
a site with fill to elevate a facility is preferred over other 
methods of elevation. Not only will buildings be less exposed to 
flood forces, but, under some circumstances (such as long duration 
floods), critical facilities may be able to continue to function. 
Whether nonstructural fill is placed solely to modify the site, or 
structural fill is placed for the purpose of elevating buildings, 
placement of fill can change flooding characteristics, including 
increased flooding on other properties. Engineering analyses 
can be conducted to determine whether eliminating floodplain 
storage by filling will change the direction of the flow of water, 
create higher flow velocities, or increase the water surface elevation 
in other parts of the floodplain. Fill is a less effective elevation 
method in flood hazard areas exposed to wave action, such as the 
banks of wide rivers, back bays, or Coastal A Zones, because wave 
action may erode the fill and adequate armoring or other protection 
methods can be expensive.

Excavation: Excavation alone rarely results in significantly altering 
the floodplain on a given parcel of land. Excavation that modifies 
a site is more commonly used in conjunction with fill in order to 
offset or compensate for the adverse impacts of fill.

Earthen levee: A levee is a specially designed barrier that modifies 
the floodplain by keeping the water away from certain areas (see 
Figure 2-23). Levees are significant structures that require detailed, 
site-specific geotechnical investigations; engineering analyses to 
identify whether flooding will be made worse on other properties; 
structural and site design to suit existing constraints; design of in
terior drainage (on the land side); and long-term commitment for 
maintenance, inspection, and repairs. It is important to remember 
that areas behind levees are protected only up to a certain design 
flood levelonce overtopped or breeched, most levees fail 
and catastrophic flooding results. Levees that protect critical facilities 
usually are designed for at least the 0.2-percent-annual-chance 
flood (500-year) and have freeboard to increase the factor of safety.

Site modifications are not appropriate 
in floodways along riverine waterways, 
where obstructions to flows can increase 
flood elevations. Engineering analyses are 
required to determine the impact of such 
modifications. 

Floodwall: Floodwalls are similar to levees in that they provide protection 
to certain areas (see Figure 2-23). Failure or overtopping 
of a floodwall can result in catastrophic flooding. A floodwall is a 
significant structure that is designed to hold back water of a certain 
depth based on the design flood for the site. Generally, due to 
design factors, floodwalls are most effective in areas with relatively 
shallow flooding and minimal wave action. As with levees, designs 
must accommodate interior drainage on the land side, and maintenance 
and operations are critical for adequate performance. 

Figure 2-23: Schematic of typical earthen levee and permanent floodwall

Floodwalls that protect essential and critical facilities usually are 
designed for the 0.2-percent-annual-chance flood (500-year) and 
have freeboard to increase the factor of safety. 

2.3.1.2 Elevation Considerations

The selection of the appropriate method 
of elevating a critical facility in an A Zone 
flood hazard area depends on many factors, 
including cost, level of safety and property 
protection determined as acceptable risk, nature 
of the flood hazard area, and others. 
Methods of elevation are described below. 
The minimum elevation requirement is that 
the lowest floor (including the basement) 
must be at or above the DFE (plus freeboard, 
if desired or required). Table 2-1 in Section 
2.1.3.4 summarizes the elevation requirements in ASCE 24. Given 
the importance of critical facilities, elevation of the lowest floor to 
or above the 0.2 percent-annual-chance flood (500-year) elevation 
is crucial. 

For elevation methods other than fill, the 
area under elevated buildings in A Zones 
may be used only for limited purposes: 
parking, building access, and limited storage 
(crawlspaces are treated as enclosures, see 
below). Owners and designers are cautioned 
that enclosures below the design flood elevation 
are exposed to flooding and the 
contents will be damaged or destroyed by 
floodwaters. The walls surrounding an enclosure 
must have flood openings that are 
intended to equalize interior and exterior water levels during 
rising and falling flood conditions, to prevent differential hydrostatic 
pressures that could lead to structural damage. The 
enclosed area must not contain utilities and equipment (including 
ductwork) below the required elevation. 

Lowest floor is the floor of the lowest 
enclosed area (including the basement). 
An unfinished or flood-resistant enclosure, 
usable solely for parking of vehicles, 
building access, or storage in an area 
other than a basement, is not the lowest 
floor, provided the enclosure is built in 
compliance with applicable requirements. 

ASCE 7 outlines methods to determine 
design loads and load combinations in 
flood hazard areas, including hydrostatic 
loads, hydrodynamic loads, wave 
loads, and debris impact loads. ASCE 
24 addresses design requirements for 
structures in flood hazard areas. 

Slab-on-grade foundation on structural fill: This 
is considered to be the safest method to elevate 
a building in many flood hazard areas, 
except those where waves and high velocity 
flows may cause erosion. Structural 
fill can be placed so that, when water rises 
up to the DFE, it will not touch the building 
(see Figure 2-24) and building access is 
maintained. The fill must be designed to 
minimize adverse impacts, such as increasing flood elevations on 
adjacent properties, increasing erosive velocities, and causing local 
drainage problems. To ensure stability, especially as floodwaters recede 
and the soils drain, fill must be designed for the anticipated 
water depths and duration. A geotechnical engineer or soil scientist 
may need to examine underlying soils to determine if the 
bearing capacity is sufficient to carry the added weight of fill, or 
if consolidation over time may occur. In addition, the effects of 
long-term compaction of the fill should be considered, and may 
prompt additional elevation as a factor of safety. The horizontal 
extent of fill from the foundation should be designed to facilitate 
access by emergency and fire vehicles, with a minimum 25-foot 
width recommended. Designers are cautioned to avoid excavating 
a basement into fill without added structural protection (and 
certification that the design meets requirements for dry floodproofing), 
due to the potential for significant hydrostatic loads 
and uplift on basement floors.

Communities may require a registered 
design professional to certify that buildings 
elevated on fill are reasonably safe from 
flooding. FEMA NFIP Technical Bulletin 
10 (2001) discusses criteria for this 
certification.

Figure 2-24: Municipal building elevated on fill

Fill

Stem wall foundations: Stem wall foundations have a continuous 
perimeter grade beam, or perimeter foundation wall, that is backfilled 
with compacted earth to the underside of the concrete floor 
slab (see Figure 2-25). Because this foundation type is backfilled 
and has no crawlspace, hydrostatic pressures are minimized. Stem 
wall foundations are designed to come in contact with floodwaters 
on the exterior. They are more stable than perimeter wall foundations 
with crawlspaces, but could experience structural damage if 
undermined by local scour and erosion. Designs must account for 
anticipated debris and ice impacts, and incorporate methods and 
materials to minimize impact damage.

Columns or shear wall foundations (open foundations): Open foundations 
consist of vertical load bearing members (columns, piers, pilings, 
and shear walls) without solid walls connecting the vertical members. 
Open foundations minimize changes to the floodplain and 
local drainage patterns, and the area under the building can be 
used for parking or other uses (see Figure 2-26). The design of 
the vertical members must also account for hydrodynamic loads 
and debris and ice impact loads. Flood loads on shear walls are reduced 
if they are oriented parallel to the anticipated direction of 
flow. Erodible soils may be present and local scour may occur; both 
must be accounted for in designs by extending the load-bearing 
members and foundation elements well below the expected scour 
depth. Depending on the total height of the elevated facility, the 
design may need to take into consideration the increased exposure 
to wind and uplift, particularly where breaking waves are expected. 

Figure 2-25: Typical stem wall foundation

Continuous perimeter walls (enclosed foundations with crawlspace): 
Unlike stem wall foundations, continuous perimeter walls enclose 
an open area or crawlspace (see Figure 2-27). The perimeter walls 
must have flood openings that are intended to equalize interior 
and exterior water levels automatically during changing flood 
conditions to prevent differential hydrostatic pressures that could 
lead to structural damage. Flood openings may be engineered 
and certified for the required performance level, or must meet 
prescriptive requirements (notably, the opening must provide 
at least 1 square inch of net open area for each square foot of 
area enclosed). Perimeter wall design must also account for 
hydrodynamic loads, and debris and ice impact loads. Enclosed 
crawlspaces must not contain utilities or equipment (including 
ductwork) below the required elevation. Designers must provide 
adequate underfloor ventilation and subsurface drainage to 
minimize moisture problems after flooding. 

Figure 2-26: School elevated on columns 

Pier supports for manufactured and portable units: Manufactured 
buildings and portable units must be elevated above the DFE 
(plus freeboard, if required). Pier supports must account for hydrodynamic 
loads and debris and ice impact loads and units must 
be anchored to resist wind loads. Although written specifically 
for manufactured housing units, FEMA 85, Manufactured Home 
Installation in Flood Hazard Areas, has useful information that is applicable 
to portable units. 

2.3.1.3 Flood-Resistant Materials 

All structural materials, nonstructural (finish) materials, and connectors 
that are used below certain elevations (see Table 2-2) 
should be flood-resistant. Flood-resistant materials have sufficient 
strength, rigidity, and durability to adequately resist flood loads 
and damage due to saturation. They are building materials that 
are capable of withstanding direct and prolonged 
contact with floodwaters without 
sustaining any damage that requires more 
than cosmetic repair. As defined in ASCE 
24, the term prolonged contact means partial 
or total inundation by floodwaters for 72 
hours for non-coastal areas (fresh water) or 
12 hours for coastal areas.
 
Figure 2-27: Typical crawlspace with flood openings

In general, materials that are exposed to floodwaters are to be 
capable of resisting damage, deterioration, corrosion, or decay. 
Typical construction materials range from highly resistant to not 
at all resistant to water damage. FEMA NFIP Technical Bulletin 
FIA-TB-2 contains tables with building materials, classified based 
on flood resistance (Table 2-2).

In areas away from the coast, exposed structural steel should 
be primed, coated, plated, or otherwise protected against corrosion. 
Secondary components such as angles, bars, straps, and 
anchoring devices, as well as other metal components (plates, 
connectors, screws, bolts, nails angles, bars, straps, and the 
like) should be stainless steel or hot-dipped galvanized after 
fabrication. 

FEMA NFIP Technical Bulletin FIA-TB-2, 
Flood-Resistant Materials Requirements, 
provides some additional information. 
Many types of materials and application 
products are classified by degrees of 
resistance to flood damage. 

Table 2-2: Classes of Flood-Resistant Materials
NFIP Class
Class Description

Acceptable
5
Highly resistant to floodwater damage. Materials in this class are permitted for 
partially enclosed or outside uses with essentially unmitigated flood exposure.

4
Resistant to floodwater damage. Materials in this class may be exposed to 
and/or submerged in floodwaters in interior spaces and do not require special 
waterproofing protection.

Unacceptable
3
Resistant to clean water damage. Materials in this class may be submerged in 
clean water during periods of intentional flooding.

2
Not resistant to water damage. Materials in this class require essentially dry 
spaces that may be subject to water vapor and slight seepage.

1
Not resistant to water damage. Materials in this class require dry conditions.

Source: From U.S. Army Corps of Engineers, FloodProofing Regulations (1995).

Concrete and masonry that are designed and constructed in compliance 
with applicable standards are generally considered to be 
flood-resistant. However, masonry facings are undesirable finishes 
unless extra anchoring is added to prevent separation (see Figure 
2-28). Wood and timber members exposed to flood waters should 
be naturally decay resistant species or pressure treated with appropriate 
preservatives. 

Structural steel and other metal components exposed to corrosion 
should be stainless steel or hot-dipped galvanized after fabrication. 

2.3.1.4 Dry Floodproofing Considerations 

Dry floodproofing involves a combination of design and special 
features that are intended to prevent the entry of water into a 
building and its utilities while also resisting flood forces. It involves 
structural reinforcement so that exterior walls are sufficiently robust 
to withstand the loads described in Section 2.1.2 (hydrostatic 
pressure, hydrodynamic loads, wave loads, 
and debris impact loads). Exterior walls must 
also be designed to prevent infiltration and 
seepage of water, whether through the wall 
itself or through any openings, including 
where utility lines penetrate the envelope. 
Floodproofed buildings constructed on 
permeable soils require additional design 
attention, because they are susceptible to hydrostatic 
pressure from below.

Figure 2-28: Brick facing separated from the masonry wall at 
Port Sulpher High School, LA. 

According to the NFIP regulations, nonresidential 
buildings and nonresidential 
portions of mixed-use buildings may be dry 
floodproofed. Areas used for living and 
sleeping purposes in health care facilities 
and dormitory rooms at fire stations may 
not be dry floodproofed. Although floodproofing 
of the nonresidential spaces is 
allowed, careful consideration must be given to the possible risk 
to occupants and additional physical damage.

All flood protection measures are designed for certain flood conditions. 
Therefore, there is some probability that the design will 
be exceeded (i.e., water will rise higher than accounted for in the 
design). When this happens to a dry floodproofed building, the 
consequences can be catastrophic. As a general rule, dry floodproofing 
is a poor choice for new critical facilities when avoidance 
of the floodplain or elevation methods to raise the building above 
the flood level can be applied. Floodproofing may be acceptable 
for retrofitting existing buildings under certain circumstances (see 
Section 2.4.4). 

A number of dry floodproofing limitations and requirements are 
specified in ASCE 24:

 Dry floodproofing is limited to areas where flood velocities at 
the site are less than or equal to 5 feet per second.
 If human intervention is proposed, such as measures to 
protect doors and windows, the flood warning time shall be a 
minimum of 12 hours unless the community operates a flood 
Communities that participate in the NFIP 
will require that a registered professional 
engineer or architect develop or review the 
structural design, specifications, and plans, 
and certify that the dry floodproofing 
design and methods of construction to be 
used are in accordance with accepted 
standards of practice. The standards of 
practice require that the building, together 
with attendant utility and sanitary facilities, 
be designed so that it is watertight, with 
walls substantially impermeable to the 
passage of water and with structural 
components having the capability of 
resisting hydrostatic and hydrodynamic 
loads and effects of buoyancy associated 
with the design flood event.


warning system and implements a notification procedure that 
provides sufficient time to undertake the measures requiring 
intervention.
 At least one door satisfying building code requirements for an 
exit door or primary means of escape must be provided above 
the level of protection.
 An emergency plan, approved by the community and 
posted in at least two conspicuous locations, is required in 
floodproofed buildings; the plan is to specify the location 
of panels and hardware, methods of installation, conditions 
that activate deployment, a schedule for routine maintenance 
of any aspect that may deteriorate over time, and periodic 
practices and drills. 

Windows and doors that are below the flood level used for dry 
floodproofing design present significant potential failure points. 
They must be specially designed units (see Figure 2-29) or be 
fitted with gasketed, mountable panels that are designed for 
the anticipated flood conditions and loads. Generally speaking, 
it is difficult to protect window and door openings from water 
more than a few feet deep. The framing and connections must 
be specifically designed for these protective measures, or water 
pressure may cause window and door frames to separate from 
the building. 

Dry floodproofing is required to extend to 1 
or 2 feet above the BFE (see Table 2-1). For 
the purpose of obtaining NFIP flood insurance, 
the floodproofing must extend at least 
1 foot above the BFE, or the premiums will 
be very high. Therefore, a higher level of 
protection is recommended. 

The documents Flood Resistant 
Design and Construction (ASCE 24-
05), Flood Proofing: How to Evaluate 
Your Options (USACE, 1993), Flood 
Proofing Regulations (USACE, 1995), 
Floodproofing Non-Residential Structures 
(FEMA 102, 1986), Non-Residential 
Floodproofing  Requirements and 
Certification (FIA-TB-3 [FEMA NFIP, 1993]), 
Flood Proofing Systems & Techniques 
(USACE, 1984) provide additional 
information about floodproofing. 


Floodproofing techniques are considered 
to be permanent measures if they are always 
in place and do not require any specific 
human intervening action to be effective. 
Use of contingent floodproofing measures 
that require installation or activation, such 
as window shields or inflatable barriers, 
may significantly reduce the certainty that 
floodproofing will be effective. Rigorous adherence 
to a periodic maintenance plan 
is critical to ensure proper functioning. 
The facility must have a formal, written 
plan, and people responsible for implementing 
the measures must be informed 
and trained. These measures also depend 
on the timeliness and credibility of the warning. In addition, 
floodproofing devices often rely on flexible seals that require 
periodic maintenance and that, over time, may deteriorate and 
become ineffective. Therefore, a maintenance plan must be developed 
and a rigorous annual inspection and training must be 
conducted. 

Dry floodproofed critical facilities must never be considered safe for occupancy 
during periods of high water; floodproofing measures are intended only to reduce 
physical damage. 

Figure 2-29: Permanent watertight doors for deep water 
SOURCE: PRESRAY CORPORATION 

Safety of occupants is a significant concern with dry floodproofed 
buildings. Regardless of the degree of protection 
provided, dry floodproofed buildings should not be occupied 
during flood events, because failure or overtopping of the floodproofing 
measures is likely to cause catastrophic structural 
damage. When human intervention is required, the people responsible 
for implementing those measures remain at risk while 
at the building, even if a credible warning system is in place, because 
of the many uncertainties associated with predicting the 
onset of flood conditions. 

2.3.2 RISK REDUCTION IN V ZONES 

Flood hazard areas designated as V Zones on FIRMs are relatively 
narrow areas along open coasts and lake shores where the 
base flood conditions are expected to produce 3-foot or higher 
waves. V Zones, sometimes called coastal high hazard areas or special 
flood hazard areas subject to high-velocity wave action, are 
found on the Pacific, Gulf, and Atlantic coasts, and around the 
Great Lakes. 

Every effort should be made to locate critical facilities outside of 
V Zones, because the destructive nature of waves makes it difficult 
to design a building to be fully functional during and after a flood 
event. This is particularly true in coastal areas subject to hurricane 
surge flooding (see Section 2.3.4). However, when a decision is 
made to build a critical facility in a V Zone or Coastal A Zone, the 
characteristics of the site and the nature of the flood hazards must 
be examined prior to making important design decisions.

Beach front areas with sand dunes pose special problems. Man-
made alterations of sand dunes are not allowed unless analyses 
indicate that such modifications will not increase potential flood 
damage. The site modifications described in Section 2.3.1.1 that 
may be used in some A Zones to reduce flood hazards generally 
are not feasible in V Zones because of wave forces and potential 
erosion and scour. In particular, structural fill is not allowed as a 
means to raise a building site above the flood level.

The NFIP and ASCE 24 do not allow use of dry floodproofing 
measures to protect nonresidential structures in V Zones.

2.3.2.1 Elevation Considerations

The selection of the appropriate method of 
elevating a critical facility in a V Zone flood 
hazard area depends on many factors, including 
cost, desired level of safety and 
property protection, and the nature of the 
flood hazard area. The NFIP regulations and 
the building codes require the elevation of 
the bottom of the lowest horizontal structural 
member of the lowest floor (including 
basement) to be at or above the DFE (plus 
freeboard, where required). Given the importance 
of critical facilities, elevation to or 
above the 0.2-percent-annual-chance flood 
(500-year) elevation is appropriate and 
strongly recommended. 

Buildings in V Zones must be elevated using 
open foundations, which consist of vertical 
load bearing members (columns, piers, pilings, 
and shear walls) without solid walls connecting the vertical 
members. The design of the vertical members must also account 
for hydrodynamic loads and debris impact loads. Flood loads on 
shear walls are reduced if the walls are oriented parallel to the anticipated 
direction of flow. Since erodible soils may be present and 
local scour may occur, both conditions must be accounted for in 
designs of load-bearing members and foundations. 

The area under elevated buildings in V Zones may be used only 
for limited purposes: parking, building access, and limited storage. 
Owners and designers are cautioned that enclosures below the 
DFE are exposed to flooding. Areas under elevated buildings may 
be open or enclosed by lattice walls or screening. However, if areas 
are enclosed by solid walls, the walls must be specifically designed 
to break away under certain flood loads to allow the free passage 
of floodwaters under the building. Breakaway walls are non-load 
bearing walls, i.e., they do not provide structural support for the 
building. They must be designed and constructed to collapse 
under the impact of floodwaters in such a way that the supporting 
foundation system and the structure are not affected. 

Communities that participate in the NFIP 
will require that a registered professional 
engineer or architect develop or review 
the structural design, specifications, and 
plans, and certify that the design and 
methods of construction to be used are 
in accordance with accepted standards 
of practice. The standards of practice 
require that the foundation and structure 
attached thereto is anchored to resist 
flotation, collapse, and lateral movement 
due to the effects of wind and water loads 
acting simultaneously on all building 
components. Water loading values shall 
be those associated with the base flood 
conditions, and wind loading values shall 
be those required by applicable State or 
local building codes and standards. 

2.3.2.2 Flood-Resistant Materials 

Section 2.3.1.3 addresses the general requirement that all structural 
materials, nonstructural (finish) materials, and connectors 
that are used below certain elevations are to be flood-resistant materials. 
In coastal areas, airborne salt aerosols and inundation with 
saline water increase the potential for corrosion of some metals. 
Structural steel and other metal components that are exposed to 
corrosive environments should be stainless steel or hot-dipped galvanized 
after fabrication. 

2.3.3 RISK REDUCTION IN COASTAL A ZONES 

Coastal A Zones are areas of the mapped floodplain where 
breaking waves that are between 1.5 to 3 feet high are expected 
under base flood conditions. Coastal A Zones are part of the area 
shown as the A Zone on a FIRM, landward of the mapped V Zone 
or landward of open coasts that do not have a V Zone. FIRMs do 
not distinguish between Coastal A Zones and A Zones. Designers 
should determine whether Coastal A Zone conditions are likely to 
occur at a critical facility site because of the anticipated wave action 
and loads. This determination is based on an examination of 
the site and its surroundings, the actual surveyed ground elevations, 
and the predicted stillwater elevations found in the Flood 
Insurance Study. 

Coastal A Zones are present where two conditions exist: where the 
expected floodwater depth is sufficient to support waves 1.5 to 3 
feet high, and where such waves can actually occur (see Figure 2-
30). The first condition occurs where stillwater depths (vertical 
distance between the stillwater elevation and the ground) are 
more than 2 feet deep. The second condition occurs where there 
are few obstructions between the shoreline and the site. The stillwater 
depth requirement is necessary, but is not sufficient by itself 
to warrant designation as a Coastal A Zone, because obstructions 
in the area may block wind and dampen waves. Obstructions that 
may dampen waves include buildings, locally high ground, and 
dense tree stands. 

Field observations and laboratory research 
have determined that flooding with breaking waves between 1.5 and 3 
feet high produces more damage than
flooding of similar depths without waves. 
Therefore, ASCE 24 specifically requires 
application of the NFIPs V Zone design 
requirements in Coastal A Zones. Section 
2.3.2.1 addresses elevation requirements 
and foundation types, and Section 2.3.2.2 
addresses flood-resistant materials, used 
in V Zones and Coastal A Zones. The 
designers are advised to pay special attention to two additional 
considerations:

 Debris loads may be significant in Coastal A Zones landward of 
V Zones where damaged buildings, piers, and boardwalks can 
produce battering debris. Foundations designed to account for 
debris loads will minimize damage.
 Especially in high wind regions, designers must pay special 
attention to the entire roof-to-foundation load path when 
designing and specifying connections. If designed to meet 
V Zone requirements, designs for buildings in Coastal A 
Zones will account for simultaneous wind and flood forces. 
Corrosion-resistant connections are especially important for 
the long-term integrity of the structure.

Figure 2-30: Flood hazard zones in coastal areas 

Although the NFIP regulations and the model 
building codes allow dry floodproofing of 
nonresidential buildings in flood hazard areas 
where waves are predicted to be between 
1.5 and 3 feet during the base flood (called 
Coastal A Zones), designers are cautioned to 
fully consider the additional forces associated 
with wave impacts, which may make dry 
floodproofing a less feasible alternative. 

2.3.4 RISK REDUCTION IN HURRICANE STORM SURGE AREAS 

Coastal communities along the Atlantic and Gulf coasts are subject 
to storm surge flooding generated by hurricanes and tropical 
storms. Depending on a number of variables, storm surge flood 
depths may significantly exceed the BFE. In addition, waves are 
likely to be larger than predicted for the base flood, and will occur 
in areas where significant wave action during the base flood is not 
expected. Application of the minimum requirements related to 
elevation of the lowest floor and foundation design does not result 
in flood resistance for such extreme conditions. The following 
special considerations will provide a greater degree of protection 
for critical facilities located in areas subject to storm surges.

Higher foundations: Foundations should be designed to elevate 
the building so that the lowest horizontal structural members are 
higher than the minimum required elevation. Additional elevation 
not only reduces damage that results from lower probability 
events, but the cost of Federal flood insurance is usually lower. 
However, accessibility may be affected and there will be some additional 
construction costs that must be balanced against avoided 
future damage and a higher likelihood that a facility can be more 
rapidly restored to full function.

Scour and erosion: Storm surge flooding and waves can cause scour 
and erosion, even at locations that are some distance from the 
shoreline. Foundation designs for critical facilities in coastal communities 
should account for some erosion and local scour of 
supporting soil during low probability surge events.

Water-borne debris: Storm surge flooding can produce large quantities 
of floating debris, even at locations that are some distance 
from the shoreline. Debris damages nonstructural building components 
and, in some cases, prolonged battering can lead to 
structural failure. Foundation designs for critical facilities in 
coastal communities should account for debris loads. This is especially 
important where damage to other buildings in the area may 
generate additional debris, thereby increasing the loads. 

Continuous load path: Especially in high wind regions, designers 
should pay special attention to the entire roof-to-foundation load 
path when designing and specifying connections. Connections 
must be capable of withstanding simultaneous wind and flood 
forces. Poorly connected buildings may fail or float off of foundations 
when floodwaters and waves are higher than the design 
flood elevation. Corrosion-resistant connections are critical for the 
long-term integrity of the structure, and should be inspected and 
maintained periodically. 

Emergency equipment: Equipment that is required for emergency 
functioning during or immediately after a storm surge event, 
such as emergency generators and fuel tanks, is best installed well 
above the design flood elevation. 

Occupancy of surge-prone areas: Designers and owners should plan 
to use the lowest elevated floor for non-critical uses that, even if 
exposed to flooding more severe than the design flood, will not 
impair critical functioning during post-flood recovery. 

2.3.5 RISK REDUCTION FOR RELATED FACILITIES

Critical facilities do not exist as purely independent buildings. 
They usually are accompanied by a variety of related facilities, 
such as utility installations both inside and outside of buildings, 
gas and electric services, water and wastewater services, above-
ground or underground storage tanks, accessory structures and 
outbuildings, and access roads and parking lots.

2.3.5.1 Access Roads 

Access roads to critical facilities should be designed to provide safe 
access at all times, to minimize impacts on flood hazard areas, to 
minimize damage to the road itself, and to minimize exposing vehicles 
to dangerous situations. Depending on the site and specific 
flood characteristics, balancing those elements can be difficult. 
Designers should take the following into consideration.

Safety factors: Although a critical facilitys access road may not be 
required to carry regular traffic like other surface streets, a flood-
prone road always presents a degree of risk to public safety. To 
minimize those risks, some State or local regulatory authorities require 
that access roads be designed so that the driving surface is 
no more than 1 to 2 feet below the DFE. To maximize evacuation 
safety, two separate accesses to different feeder roads are recommended. 
In some circumstances, especially long-duration flooding 
where a critical facility is built on fill, dry access may allow continued 
operations. 

Floodplain impacts: Engineering analyses may be required to document 
the effects on flood elevations and flow patterns if large 
volumes of fill are required to elevate a road to minimize or eliminate 
flooding above the driving surface.

Drainage structure and road surface design: The placement of multiple 
drainage culverts, even if not needed for local drainage, can facilitate 
the passage of floodwaters and minimize the potential for 
a road embankment to act as a dam. Alternatively, an access road 
can be designed with a low section over which high water can flow 
without causing damage. Embankments should be designed to remain 
stable during high water and as waters recede. They should be 
sloped and protected to resist erosion and scour. Similarly, the surface 
and shoulders of roads that are intended to flood should be 
designed to resist erosion. The increased resistance to erosion may 
be accomplished by increasing the thickness of the road base.

2.3.5.2 Utility Installations 

Utilities associated with new critical facilities in flood hazard areas 
must be protected either by elevation or special design and installation 
measures. Utilities subject to this provision include all 
systems, equipment, and fixtures, including mechanical, electrical, 
plumbing, heating, ventilating, and air conditioning. Potable 
water systems (wellheads and distribution lines) and wastewater 
collection lines are addressed in Section 2.3.5.3. 

Utility systems and equipment are best protected when elevated 
above the DFE (plus freeboard, if required). In some 
cases, equipment can be located inside protective floodproofed 
enclosures, although it must be recognized that flooding that exceeds 
the design level of such an enclosure will adversely affect 
the equipment (see Figure 2-31). Designers should pay partic
ular attention to underfloor utilities and 
ductwork to ensure that they are properly 
elevated. Plumbing conduits, water supply 
lines, gas lines and electric cables that must 
extend below the DFE should be located, anchored, 
and protected to resist the effects of 
flooding. Equipment that is outside of elevated 
building also must be elevated:

 In A Zones, equipment may be affixed to raised support 
structures or mounted on platforms that are attached to or 
cantilevered from the primary structure. 
 In V Zones and Coastal A Zones, equipment may be affixed 
to raised support structures designed for the flood conditions 
(waves, debris impact, erosion, and scour) or mounted on 
platforms that are attached to or cantilevered from the 
primary structure. If an enclosure is constructed under the 
elevated building, the designer must take care that utilities 
and attendant equipment are not mounted on or pass through 
walls that are intended to break away. 
For more information on utility installations, 
see Protecting Building Utilities from Flood 
Damage: Principles and Practices for 
the Design and Construction of Resistant 
Building Utility Systems (FEMA 348, 1999).

Figure 2-31: Equipment room with watertight door 
SOURCE: PRESRAY CORPORATION 

Although it is difficult to achieve, the model building codes and 
NFIP regulations provide an alternative that allows utility systems 
and equipment to be located below the DFE. This alternative requires 
that such systems and equipment be designed, constructed, 
and installed to prevent floodwaters from entering or accumulating 
within the components during flood events.

2.3.5.3 Potable Water and Wastewater Systems

New installations of potable water systems and wastewater collection 
systems are required to resist flood damage, including 
damage associated with infiltration of floodwaters and discharge 
of effluent. Health concerns arise when water supply systems are 
exposed to floodwaters. Contamination from flooded sewage systems 
poses additional health and environmental risks. Onsite 
water supply wellheads should be located on land elevated from 
the surrounding landscape to allow contaminated surface water 
and runoff to drain away. Well casings should extend above the 
design flood elevation, and casings should be sealed with a tight-
fitting, floodproof, and vermin-proof well cap. The space between 
the well casing and the side of the well must be sealed to minimize 
infiltration and contamination by surface waters. 

Sewer collection lines should be located and designed to avoid infiltration 
and backup due to rising floodwaters. Devices designed to prevent backup are 
available and are recommended to provide an added measure of protection. 

Onsite sewage systems usually are not used as the primary sewage 
disposal system for new critical facilities. However, it would be prudent 
for owners, planners, and designers to consider a backup 
onsite sewage system if a facilitys functionality will be impaired 
if the public system is affected by flooding. Designers are advised 
that local or State health departments may impose constraints that 
limit or prevent locating septic fields in floodplain soils or within 
a mapped flood hazard area. If allowed, septic fields should be located 
on the highest available ground to minimize inundation and 
impairment by floodwaters. An alternative to a septic field is installation 
of a holding tank that is sized to contain wastewater for 
a period of time, perhaps a few days if the municipal system is expected 
to be out of service.

2.3.5.4 Storage Tank Installations 

Aboveground and underground storage tanks located in flood 
hazard areas must be designed to resist flotation, collapse, and 
lateral movement. ASCE 24 specifies that aboveground tanks are 
to be elevated or constructed, installed and anchored to resist 
at least 1.5 times the potential buoyant and other flood forces 
under design flood conditions, assuming the tanks are empty. 
Similarly, underground tanks are to be anchored to resist at 
least 1.5 times the potential buoyant forces under design flood 
conditions, assuming the tanks are empty. In all cases, designers 
are cautioned to address hydrodynamic loads and debris impact 
loads that may affect tanks that are exposed to floodwaters. 
Vents and fill openings or cleanouts should be elevated above 
the DFE or designed to prevent the inflow of floodwaters or outflow 
of the contents of tanks. 

2.3.5.5 Accessory Structures 

Depending on the type of accessory structures, full compliance 
with floodplain management regulations is appropriate and may 
be required. For example, buildings or portable classrooms that 
serve educational purposes (e.g., offices, classrooms), even if detached 
from the primary school building, are not considered to 
be accessory in nature and must be elevated and protected to the 
same standards as other buildings. 

Some minor accessory structures need not fully comply, but may 
be wet floodproofed using techniques that allow them to flood 
while minimizing damage. Examples include small storage sheds, 
garages, and restrooms. Accessory structures must be anchored 
to resist flotation, collapse, and lateral movement. Flood-resistant 
materials must be used and utilities must be elevated above 
the DFE (plus freeboard, if required). Openings in walls must be 
provided to allow the free inflow and outflow of floodwaters to 
minimize the hydrostatic loads that can cause structural damage. 
Because wet floodproofed accessory buildings are designed to 
flood, critical facility staff must be aware that contents will be 
damaged. 





2.4 RISK REDUCTION FOR EXISTING CRITICAL FACILITIES

2.4.1 Introduction

Section 2.2.2 describes the type of damage that can be 
sustained by critical facilities that already are located in 
flood hazard areas. The vulnerability of these facilities 
can be reduced if they can be made more resistant to flood damage. 
Decisionmakers may take such action when flood hazards 
are identified and there is a desire to undertake 
risk reduction measures proactively. 
Interest may be prompted by a flood or by 
the requirement to address flood resistance 
as part of proposed substantial improvement 
or an addition. Some questions and 
guidance intended to help identify building 
characteristics of importance when considering 
risk reduction measures for existing 
facilities are included in the checklist in 
Section 2.5. 

Work on existing buildings and sites is subject 
to codes and regulations, and the 
appropriate regulatory authority with jurisdiction 
should be consulted. With respect 
to reducing flood risks, work generally falls 
into the categories described in the following 
subsections.

Owners and operators of public and not-
for-profit critical facilities should be aware 
of the importance of flood insurance 
coverage for facilities that are located in 
the flood hazard areas shown on NFIP 
maps. If not insured for flood peril, the 
amount of flood insurance that should 
have been in place will be deducted from 
any Federal disaster assistance payment 
that would otherwise have been made 
available. A particular facility may have to 
absorb up to $1 million in unreimbursed 
flood damage per building, because 
the NFIP offers $500,000 in building 
coverage and $500,000 in contents 
coverage for nonresidential buildings 
(coverage limits as of early 2006).

2.4.2 SITE MODIFICATIONS 

A plan to modify the site of an existing facility that is subject to 
flooding requires careful examination by an experienced professional 
engineer. Determining the suitability of a specific measure 
requires a complex evaluation of many factors, including the nature 
of flooding and the nature of the site. The first part of Table 
2-3 in Section 2.5 identifies elements that influence the choice 
of mitigation measures applicable to existing sites. Some flood 
characteristics may make it infeasible to apply site modification 
measures to existing facilities (e.g., depths greater than 3 to 4 feet, 
very high velocities, insufficient warning because of flash flooding 
or rapid rate of rise, and very long duration). 

A common problem with all site modifications is the matter of 
site access. Depending on the topography of the site, construction 
of barriers to floodwaters may require special access points. 
Access points may be protected with manually installed stop-logs 
or designed gates that drop in, slide, or float into place. Whether 
activated by automatic systems or manually operated, access protection 
requires sufficient warning time.

Other significant constraining factors include poor soils and insufficient 
land area which can make site modifications either 
infeasible or very costly. A critical facility may be among several 
buildings and properties that can be protected, increasing the 
benefits. For any type of barrier, rainfall that collects on the land 
side must be accounted for in the design, whether through adequately 
sized stormwater storage basins constructed on land set 
aside for this purpose, or by providing large-capacity pumps to 
move collected water to the water side of the barrier.

Each of these site modification measures described below has limitations, 
including the fact that floods larger than the design flood 
will exceed the level of protection.

Regrading the site (berm): Where a facility is exposed to relatively 
shallow flooding and sufficient land area is available, regrading 
the site or constructing an earthen berm may provide adequate 
protection.

Earthen levee: Earthen levees are engineered structures that are designed 
to keep water away from land area and buildings. Hydraulic 
analyses and geotechnical investigations are required to determine 
their feasibility and effectiveness. For existing sites, constraints include 
the availability of land (levees have a large footprint and 
require large land areas), cost (including availability of suitable fill 
material and long-term maintenance), and difficulties with site access. 
Levees are rarely used to protect a single site, although they 
may offer a reasonable solution for a group of buildings. Locating 
levees and floodwalls within a designated floodway is generally 
not allowed. Rapid onset flooding makes it impractical to design a 
flood levee with access points that require installation of a closure 
system. Earthen levees may also be subject to high velocity flows 
that cause erosion and affect their stability.

Permanent floodwall: Floodwalls are freestanding, permanent engineered 
structures that are designed to prevent encroachment of 
floodwaters. Typically, a floodwall is located some distance from a 
building, so that structural modification of the existing building 
is not required. Floodwalls may protect only the low side of a site 
(in which case they must tie into high ground) or completely 
surround a site (which may affect access because special closure 
structures are required and must be installed before the onset of 
flooding, see Figure 2-32).

Figure 2-32: A masonry floodwall with multiple engineered openings protected the 
Oak Grove Lutheran School in Fargo, ND from flooding in 2001.
SOURCE: Flood Central America, LLC

Mobilized floodwall: This category of flood protection measures 
includes fully engineered flood protection structures that have 
permanent features (foundation and vertical supports) and features 
that require human intervention when a flood is predicted 
(horizontal components called planks or stop-logs). Mobilized 
floodwalls have been used to protect entire sites, or to tie into permanent 
floodwalls or high ground. Because of the manpower and 
time required for proper placement, these measures are better 
suited to conditions that allow long warning times.

2.4.3 ADDITIONS 

All model building codes generally treat additions as new construction 
and require additions to critical facilities in flood hazard 
areas to be elevated or dry floodproofed to minimize exposure 
to flooding. However, full compliance with the code and NFIP 
requirements is only required if an addition is a substantial improvement 
(i.e., the cost of the addition plus all other work equals 
or exceeds 50 percent of the market value of 
the building). Designers are cautioned that 
existing buildings as well may be required to 
be brought into compliance with the flood-
resistant provisions of the code or local 
ordinances if the addition is structurally connected 
to the existing building. 

Section 2.3.1.2 outlines elevation options that are applicable 
to additions in A Zones (see Section 2.3.2.1 for elevation considerations 
applicable to additions in V Zones). Elevation of an 
addition on fill may not be feasible unless structural fill can be 
placed adjacent to the existing building. Utility service equipment 
for additions must meet the requirements for new installations 
(see Section 2.3.5.2).

With respect to code compliance and designing additions to resist 
flood damage, one of the more significant issues that may 
come up is ease of access. If the lowest floor of the existing facility 
is below the DFE, steps, ramps, or elevators will be required for 
the transition to the new addition. Some jurisdictions may wish 
to allow variances to the requirement for elevation, because alternative 
means of access are available, such as ramps and elevators. 

For more information on additions and 
substantial improvements, see Answers to 
Questions About Substantially Damaged 
Buildings (FEMA 213, 1991).

Under the regulations of the NFIP and FEMA guidance, it is not 
considered appropriate to grant such a variance. 

2.4.4 REPAIRS, RENOVATIONS, AND UPGRADES

Every critical facility that is considered for upgrades and renovations, 
or that is being repaired after substantial damage from any 
cause, must be examined for structural integrity and stability to 
determine compatibility with structural modifications that may be 
required to achieve acceptable performance. When an existing facility 
is located in a flood hazard area, that examination should 
include consideration of measures to resist flood damage and reduce 
risks. 

The model building codes and the regulations of the NFIP require 
that work constituting substantial improvement of an 
existing building be in compliance with the flood-resistant provisions 
of the code. Non-substantial improvements should take into 
account measures to reduce future flood damage, such as those 
described in Section 2.4.8, and wet floodproofing measures that 
allow water to enter the building to avoid structural damage, as 
well as emergency measures (see Section 2.4.9).

Compliance with flood-resistant provisions 
means the existing building must be elevated 
or dry floodproofed. Both options can be difficult 
for existing critical facilities, given the 
typical use, size, and complexity of some of 
these buildings. Retrofit dry floodproofing 
(described in Section 2.4.5) is generally limited 
to water depths of 3 feet or less, unless 
the structural capacity of the buildings have 
been assessed by a qualified design professional 
and found to be capable of resisting 
the anticipated loads. 

Elevating an existing building presents an 
entirely different set of challenges and also 
requires detailed structural engineering 
analyses. It involves the same equipment and 
methods used to move other types of buildings; expert building 
movers have successfully moved large, heavy, and complex 
buildings, sometimes by segmenting them. A critical facility that is 
elevated in-place must meet the same performance standards set 
for new construction.

Additional information on rehabilitation 
of existing buildings is provided in 
Flood Proofing: How to Evaluate Your 
Options (USACE, 1993), Floodproofing 
Non-Residential Structures (FEMA 102), 
FloodproofingRequirements and 
Certification (FIA-TB-3), and Engineering 
Principles and Practices for Retrofitting 
Flood-prone Buildings (FEMA 259, 
1995). Although written primarily for 
homes, this last reference contains very 
detailed checklists and worksheets that 
can be modified. They also provide some 
guidance for evaluating the costs and 
benefits of various measures.

2.4.5 RETROFIT DRY FLOODPROOFING 

Modification of an existing building may 
be required or desired in order to address 
exposure to design flood conditions. Modifications 
that may be considered include 
construction of a reinforced supplementary 
wall, measures to counter buoyancy 
(especially if there is below-grade space), installation 
of special watertight door and window barriers (see Figure 2-33), and providing 
watertight seals around the points of entry of utility lines. 
The details of structural investigations and structural design of 
such protection measures are beyond the scope of this manual. 

Dry floodproofing refers to measures and 
methods to render a building envelope 
substantially impermeable to floodwater.

Figure 2-33: Boulder Community Hospital, Boulder, CO installed this permanently 
mounted floodgate in a low floodwall; the floodgate swings to the left 
to close off the door that leads to the mechanical equipment room.

Because of the tremendous flood loads that may be exerted on 
a building not originally designed for such conditions, detailed 
structural engineering evaluations are required to determine 
whether an existing building can be dry floodproofed. The following 
elements must be examined: 

 The strength of the structural system
 Whether non-load bearing walls can resist anticipated loads; secondary 
walls can be constructed immediately adjacent to existing 
walls, with a waterproof membrane, to provide adequate strength
 The effects of buoyancy on the walls and floors of below-grade 
Areas
 Effective means to install watertight doors and windows, or 
mountable panels
 Protection where utilities enter the building
 Methods to address seepage, especially where long-duration 
flooding is anticipated
 Whether there is sufficient time for human intervention 
measures, given the availability of official warnings of 
predicted flood conditions
Application of waterproofing products or membranes directly to 
exterior walls may minimize 
infiltration of water, although there 
are concerns with durability and limitations on use (this measure 
is most effective for shallow, short-duration flooding). Retrofit 
measures that require human intervention are considered emergency 
measures and are discussed in Section 2.4.9. 

2.4.6 UTILITY INSTALLATIONS 

Some aspects of an existing flood-prone critical facilitys utility systems 
may be modified to reduce damage. The effectiveness of 
such measures depends not only on the nature of the flooding, 
but the type of utility and the degree of exposure. Table 2-3 in Section 
2.5 lists some questions that will help facility planners and designers 
to examine risk reduction measures. 

Even if a facility is unlikely to sustain extensive 
structural damage from flooding, high 
costs and delayed reoccupancy may result 
from flood-damaged utility systems. The risk 
reduction design measures described below 
can be applied, whether undertaken as part of 
large-scale retrofits of existing buildings, or as 
separate projects.

Relocate from below-grade areas: The most vulnerable utility installations 
are those located below grade, and the most effective 
protection measure is to relocate them to properly elevated floors 
or platforms that are at least 2 feet above the DFE. The complexity 
of rerouting pipes, conduits, ductwork, electrical service, lines, 
and connections will depend on site-specific factors.

Elevate components: Whether located inside or outside of the 
building, some components of utility systems can be elevated-
in-place on platforms, including electric transformers, 
communications switch boxes, water heaters, air conditioning 
compressors, furnaces, boilers, and heat pumps (see Figure 2-34). 

Additional guidance on improving the 
flood resistance of utility installations in 
existing buildings is found in FEMA 348, 
Protecting Building Utilities From Flood 
Damage: Principles and Practices for the 
Design and Construction of Flood Resistant 
Building Utility Systems.

Figure 2-34: Elevated utility box

Anchor tanks and raise openings: Existing tanks can be elevated or 
anchored, as described in Section 2.3.5.4. If anchored below the 
DFE, tank inlets, vents, fill pipes, and openings should be elevated 
above the DFE, or fitted with covers designed to prevent the inflow 
of floodwaters or outflow of the contents of the tanks.

Protect components: If utility components cannot be elevated, it may 
be feasible to construct watertight enclosures, or enclosures with 
watertight seals that require human intervention to install when 
flooding is predicted.

Elevate control equipment: Control panels, gas meters, and electrical 
panels can be elevated, even if the equipment they service cannot 
be protected.

Separate electrical controls: Where areas within an existing facility 
are flood-prone, separation of control panels and electrical 
feeders will facilitate shutdown before floodwaters arrive, and help 
protect workers during cleanup.

Protect against electrical surges: Current fluctuations and service 
interruptions are common in areas affected by flooding. Equipment 
and sensitive electrical components can be protected by installing 
surge protection and uninterruptible power supplies.

Connections for portable generators: Pre-wired portable generator 
connections allow for quick, failure-free connection and 
disconnection of the generators when needed for continued 
functionality.

2.4.7 POTABLE WATER AND WASTEWATER SYSTEMS

All plumbing fixtures that are connected to the potable water 
system may become weak points in the system if they allow floodwaters 
to contaminate the system. Relocating the uses that require 
plumbing to elevated floors and removing the fixtures that are 
below the DFE provides protection. Wellheads can be sealed with 
watertight casings or protected within sealed enclosures.

Wastewater system components become sources of contamination 
during floods. Rising floodwaters may force untreated sewage to 
backup through toilets. Specially designed back-flow devices can 
be installed, or restrooms below the DFE can be provided with 
overhead piping that may require specially designed pumps to operate 
properly. Septic tanks can be sealed and anchored. 

2.4.8 OTHER DAMAGE REDUCTION MEASURES 

A number of steps can be taken to make existing facilities in flood 
hazard areas more resistant to flood damage, which also facilitates 
rapid recovery, cleanup, and reoccupancy. Whether these measures 
are applicable to a specific facility depends, in part, on the 
characteristics of the flood hazard and the characteristics of the 
building itself. Facility planners and designers should consider the 
following:

 Rehabilitate and retrofit the building envelope with openings 
specifically designed to allow floodwaters to flow in and 
out to minimize hydrostatic pressure on walls (called wet 
floodproofing, see Figure 2-35). Although it allows water to 
enter the building, this measure minimizes the likelihood of 
major structural damage. Walls that enclose interior spaces 
would also be retrofitted with openings.

Figure 2-35: The enclosed entry and storage area to the right 
of the fire truck bays were retrofitted with flood 
openings.   
SOURCE:   SMART VENT, LLC

 Replace interior walls that have cavities with flood-resistant 
construction or removable panels to facilitate cleanup and 
drying.
 Abandon the use of below-grade areas (basements) by filling 
them in to prevent structural damage.
 Permanently relocate high-value or sensitive functions that 
are often found on the ground floor of critical facilities (e.g., 
offices, records, libraries, and computer laboratories) to 
higher floors or elevated additions.
 Install backflow devices in sewer lines.
 Pre-plan actions to move high-value contents from the lower 
floors to higher floors when a flood warning is issued.
 Replace wall, flooring, and finish materials with flood-resistant 
materials. 
 Use epoxy or other impervious paints on concrete and other 
permeable surfaces to minimize contamination. 
 Install separate electric circuits and ground fault interrupter 
circuit breakers in areas that will flood. Emergency measures 
should be provided so that electrical service can be shut down 
to avoid electrocution hazards.
 Relocate chemicals to storage areas not subject to flooding.

2.4.9 EMERGENCY MEASURES

Emergency response to flooding is outside the scope of this 
manual. However, it is appropriate to examine feasible emergency 
measures that may provide some protection. The following discussion 
pertains only to emergency measures that have been used to 
reduce flood damage to older buildings that are already located 
in flood hazard areas. These measures do not achieve compliance 
with building and life safety codes, they may not provide protection 
to occupants, and they can experience a high frequency of 
failure depending on human factors related to deployment. 

Emergency barriers are measures of last resort, and should be 
used only when a credible flood warning with adequate lead-time 
is available and dependable. These measures have varying degrees 
of success, depending on the available manpower, skill 
required, long-term maintenance of materials and equipment, 
suitability for site-specific flood conditions, and having enough 
advanced warning. Complete evacuation of protected buildings 
is required, as these measures should not be considered 
adequate protection for occupants. Furthermore, emergency 
barriers are not acceptable in lieu of designed flood resistant 
protection for new buildings. 

Sandbag walls: Unless emergency placement is planned well 
in advance or under the direction of trained personnel, most 
sandbag barriers are not constructed in accordance with proper 
practices, leading to leakage and failures. Because of the intensive 
work effort and length of time required for protection from 
even relatively shallow water, sandbag walls are not a reliable 
protection measure. To be effective, sandbags and sand should 
be stockpiled and checked regularly to ensure that sandbags 
have not deteriorated. Sandbags have some other drawbacks, 
including high disposal costs and their tendency to absorb pollutants 
from contaminated floodwaters, which necessitates 
disposal as hazardous waste.

Water-filled barriers: A number of vendors make water-filled barriers 
that can be assembled with relative ease, depending on the 
source of water for filling. The barriers must be specifically sized 
for the site. Training and annual drills are important so that 
personnel know how to place and deploy the barriers. Proper 
storage, including cleaning after deployment, is necessary to 
protect the materials over long periods of time.

Panels for doors: For shallow and short-duration flooding, panels 
of sturdy material can be made to fit doorways to minimize the 
entry of floodwaters. Effectiveness is increased significantly if a 
flexible gasket or sealant is provided, and the mounting hardware 
is designed to apply even pressure. Personnel must know 
where the materials are stored and be trained in their deployment. 
A number of vendors make special doors for permanent 
installation and drop-in panels or barriers that are designed to 
be watertight (see Figure 2-36).

Figure 2-36: Example of an aluminum flood barrier used for flooding less than 3 
feet deep. 
SOURCE: SAVANNAH TRIMS 


2.5 CHECKLIST FOR BUILDING VULNERABILITY OF FLOOD-PRONE CRITICAL FACILITIES

The Checklist for Building Vulnerability of Flood-Prone 
Critical Facilities (Table 2-3) is a tool that can be used to 
help assess site-specific flood hazards and building vulnerability. 
The checklist is useful during site selection, preliminary 
design of a new building, or when considering rehabilitation of an 
existing facility. In addition to examining building design issues 
that affect vulnerability, the checklist also helps users to examine 
the functionality of the critical 
and emergency systems upon which 
most critical facilities depend. The checklist is organized into 
separate sections, so that each section can be assigned to a subject 
expert for greater accuracy 
of the examination. The results should 
be integrated into a master vulnerability assessment to guide the 
design process and the choice of appropriate mitigation measures.

Vulnerability Sections Guidance Observations
Site Conditions

Is the site located near 
a body of water (with or 
without a mapped flood 
hazard area)? Is the site in a 
flood hazard area shown on 
the communitys map (FIRM 
or other adopted map)? If so, 
what is the flood zone?

All bodies of water are subject to flooding, but 
not all have been designated as a floodplain on 
FIRMs. 

Flood hazard maps usually are available for 
review in local planning and permit offices. 
Electronic versions of the FIRMs may be available 
online at www.fema.gov. Paper maps may be 
ordered by calling (800) 358-9616.

Is the site affected by a 
regulatory floodway ?

Is the site located in a storm 
surge inundation zone (or 
tsunami inundation area)?

Development in floodways, where floodwaters 
typically are fast and deep, must be supported 
by engineering analyses.

In coastal communities, even sites at some 
distance inland from the shoreline may be 
exposed to extreme storm surge flooding. Storm 
surge maps may be available at State or local 
emergency management offices.

What is the DFE (or does an 
analysis have to be done to 
determine the DFE)? What 
is the minimum protection 
level required by regulatory 
authorities?

Does the FIS or other study 
have information about the 
500-year flood hazard area?

Has FEMA issued post-
disaster advisory flood 
elevations and maps?

What are the expected 
depths of flooding at the 
site (determined using flood 
elevations and ground 
elevations)?

Reference the FIS for flood profiles and 
data tables. Site-specific analyses should be 
performed by qualified engineers. 

Check with regulatory authorities to determine 
the required level of protection.

If a major flood event has affected the 
community, FEMA may have issued new 
flood hazard information, especially if areas 
not shown on the FIRMs have been affected. 
Sometimes these maps are adopted and replace 
the FIRMs; sometimes the new data are advisory 
only.

Has the site been affected by 
past flood events? What is 
the flood of record? 

Records of actual flooding augment studies 
that predict flooding, especially if historic 
events resulted in deeper or more widespread 
flooding. Information may be available from 
local planning, emergency management, and 
public works agencies, or State agencies, the 
U.S. Army Corps of Engineers, or the Natural 
Resources Conservation Service.

The flood of record is often a lower probability 
event (with higher flood elevations) than the 100-
year flood.

What is the expected 
velocity of floodwaters on the 
site?

Are waves expected to affect 
the site?

Velocity is a factor in computing loads associated 
with hydrodynamic forces, including drag on 
building surfaces. Approximations of velocity 
may be interpolated from data in the FIS 
Floodway Data Table if the waterway was 
studied using detailed methods, application of 
approximation methods based on continuity, 
local observations and sources, or site-specific 
studies. 

Waves can exert considerable dynamic forces 
on buildings and contribute to erosion and scour. 
Wind-driven waves occur in areas subject to 
coastal flooding and where unobstructed winds 
affect wide floodplains (large lakes and major 
rivers). Standing waves may occur in riverine 
floodplains where high velocities are present.

Is there information on how 
quickly floodwaters may 
affect the site?

What is the expected 
duration of flooding?

Warning time is a key factor in the safe and 
orderly evacuation of critical facilities. Certain 
protective measures may require adequate 
warning so that actions can be taken by skilled 
personnel.

Duration has bearing on the stability of earthen 
fills, access to a site and emergency response, 
and durability of materials that come into contact 
with water. Records of actual flooding are the 
best indicator of duration as most floodplain 
analyses do not examine duration. 

Is there a history of flood-
related debris problems or 
erosion on the site?

Site design should account for deposition of 
debris and sediment, as well as the potential 
for erosion-related movement of the shoreline or 
waterway. Buildings exposed to debris impact 
or undermining by scour and erosion should be 
designed to account for these conditions. 

Is the site within an area 
predicted to flood if a 
levee or floodwall fails or is 
overtopped? 

Is the site in an area 
predicted to be inundated 
if an upstream dam were to 
fail?

Flood protection works may be distant from sites 
and not readily observable. Although a low 
probability event, failure or overtopping can 
cause unexpected and catastrophic damage 
because the protected lands are not regulated as 
flood hazard areas.

The effects of an upstream dam failure are 
not shown on the FIRMs or most flood hazard 
maps prepared locally. Although dam failure 
generally is considered an unlikely event, the 
potential threat should be evaluated due to the 
catastrophic consequences. (Note: owners of 
certain dams should have emergency action 
plans geared toward notification and evacuation 
of vulnerable populations and critical facilities.)

Does the surrounding 
topography contribute to the 
flooding at the site? Is there 
a history of local surface 
drainage problems due to 
inadequate site drainage?

If areas with poor local drainage and frequent 
flooding cannot be avoided, filling, regrading, 
and installation of storm drainage facilities may 
be required.

Given the nature of 
anticipated flooding and 
soils, is scour around and 
under the foundation likely?

Scour-prone sites should be avoided, in part due 
to likely long-term maintenance requirements. 
Flooding that is high velocity or accompanied by 
waves is more likely to cause scour, especially on 
fills, or where local soils are unconsolidated and 
subject to erosion.

Has water from other 
sources entered the building 
(i.e., high groundwater, 
water main breaks, sewer 
backup, etc.)? Is there a 
history of water intrusion 
through floor slabs or well-
floor connections? Are 
there underground utility 
systems or areaways that 
can contribute to basement 
flooding? Are there 
stormwater sewer manholes 
upslope of window areas 
or openings that allow 
local drainage to enter the 
basement/lower floor areas? 

These questions pertain to existing facilities that 
may be impaired by water from sources other 
than the primary source of flooding. The entire 
building envelope, including below-grade areas, 
should be examined to identify potential water 
damage.

Is at least one access road 
to the site/building passable 
during flood events? 

Are at-grade parking lots 
located in flood-prone areas?

Are below-grade parking 
areas susceptible to 
flooding?

Access is increasingly important as the 
duration of flooding increases. For the safety of 
occupants, most critical facilities should not be 
occupied during flood events.

Areas where vehicles could be affected 
should have signage to warn users of the risk. 
Emergency response plans should include 
notification of car owners.

Are any portions of the 
building below the Design 
Flood Elevation?

Has the building been 
damaged in previous floods?

For existing buildings, it is important to 
determine which portions are vulnerable in 
order to evaluate floodproofing options. If flood 
depths are expected to exceed 2 or 3 feet, dry 
floodproofing may not be feasible. Alternatives 
include modifying the use of flood-prone areas.

Are any building spaces 
below-grade (basements)? 

Below-grade spaces and their contents are 
most vulnerable to flooding and local drainage 
problems. Rapid pump out of below-grade 
spaces can unbalance forces if the surrounding 
soil is saturated, leading to structural failure. 
If below-grade spaces are intended to be dry 
floodproofed, the design must account for 
buoyant forces.

Are any critical building 
functions occupying space 
that is below the elevation 
of the 500-year flood or the 
Design Flood Elevation?

Can critical functions be 
relocated to upper levels that 
are above predicted flood 
elevations?

If critical functions cannot be 
relocated, is floodproofing 
feasible?

If critical functions must 
continue during a flood 
event, have power, supplies, 
and access issues been 
addressed?

New critical facilities built in flood hazard areas 
should not have any functions occupying flood-
prone spaces (other than parking, building 
access and limited storage). 

Existing facilities in floodplains should be 
examined carefully to identify the best options for 
protecting functionality and the structure itself.

Have critical contents 
(files, computers, servers, 
equipment, research, and 
data) been located on levels 
of the facility above the flood 
elevations? 

Are critical records 
maintained off-site?

For existing facilities that are already located 
in flood hazard areas, the nature of the facility 
may require continued use of flood-prone space. 
However, the potential for flooding should be 
recognized and steps taken to minimize loss of 
expensive equipment and irreplaceable data. If 
critical contents cannot be permanently located 
on higher floors, a flood response plan should 
take into account the time and attention needed 
to move such contents safely.

Building Envelope

Are there existing 
floodproofing measures in 
place below the expected 
flood elevation? What is the 
nature of these measures and 
what condition are they in? 
Is there an annual inspection 
and maintenance plan?

Is there an action plan 
to implement floodproofing 
measures when flooding is 
predicted? Do the building 
operators/occupants know 
what to do when a flood 
warning is issued?

Floodproofing measures are only as good 
as the design and their condition, especially 
if many years have passed since initial 
installation. Floodproofing measures that require 
human intervention are entirely dependent on 
the adequacy of advance warning, and the 
availability and ability of personnel to properly 
install the measures. 

For existing buildings, what 
types of openings penetrate 
the building envelope below 
the 500-year flood elevation 
or the DFE (doors, windows, 
cracks, vent openings, 
plumbing fixtures, floor 
drains, etc.)?

For dry floodproofing to be effective, every 
opening must be identified and measures taken 
to permanently seal or to prepare special 
barriers to resist infiltration. Sewage backflow 
can enter through unprotected plumbing 
fixtures.

Are flood-resistant materials 
used for structural and 
nonstructural components 
and finishes below the 500-
year elevation or the DFE?

Flood-resistant materials are capable of 
withstanding direct and prolonged contact with 
floodwaters without sustaining damage that 
requires more than cosmetic repair. Contact 
is considered to be prolonged if it is 72 hours 
or longer in freshwater flooding areas, or 12 
hours or longer in areas subject to coastal 
flooding.

Is the potable water supply 
for the facility protected 
from flooding? If served 
by a well, is the wellhead 
protected? 

Operators of critical facilities that depend on 
fresh water for continued functionality should 
learn about the vulnerability of the local water 
supply system and the systems plans for 
recovery of service in the event of a flood.

Is the wastewater service 
for the building protected 
from flooding? Are any 
manholes below the DFE? 
Is infiltration of floodwaters 
into sewer lines a problem? 
If the site is served by an 
onsite system that is located 
in a flood-prone area, 
have backflow valves been 
installed?

Most waste lines exit buildings at the lowest 
elevation. Even buildings that are outside of the 
floodplain can be affected by sewage backups 
during floods. 

Are there any aboveground 
or underground tanks on 
the site in flood hazard 
areas? Are they installed 
and anchored to resist 
flotation during the design 
flood? Are tank openings 
and vents elevated above 
the 500-year elevation 
or the DFE, or otherwise 
protected to prevent entry 
of floodwater or exit of 
product during a flood 
event?

Dislodged tanks become floating debris 
that pose special hazards during recovery. 
Lost product causes environmental damage. 
Functionality may be impaired if tanks for 
heating fuel, propane, or fuel for emergency 
generators are lost or damaged. 

Mechanical Systems

Are air handlers, HVAC 
systems, ductwork, and 
other mechanical equipment 
and systems located above 
the 500-year elevation or 
the DFE? Are the vents and 
inlets located above flood 
level, or sealed to prevent 
entry of floodwater?

In existing buildings, utility equipment that is 
critical for functionality should be relocated to 
higher floors or into elevated additions. 

Plumbing and Gas Systems

Are plumbing fixtures and 
gas-fired equipment (meters, 
pilot light devices/burners, 
etc.) located above the 500-
year elevation or the DFE?

In existing buildings, utility equipment that is 
critical for functionality should be relocated to 
higher floors or into elevated additions.

Is plumbing and gas piping 
that extends below flood 
levels installed to minimize 
damage?

Piping that is exposed could be impacted by 
debris.

Electrical Systems

Are electrical systems, 
including backup power 
generators, panels, and 
primary service equipment, 
located above the 500-year 
elevation or the DFE? 

Are pieces of electrical 
stand-by equipment and 
generators equipped with 
circuits to turn off power?

Are the switches and wiring 
required for safety (minimal 
lighting, door openers) 
located below the flood level 
designed for use in damp 
locations?

In existing buildings, utility equipment that is 
critical for functionality should be relocated to 
higher floors or into elevated additions.

Fire Alarm Systems

Is the fire alarm system 
located above the 500-year 
elevation or the DFE?

In existing buildings, utility equipment that is 
critical for functionality should be relocated to 
higher floors or into elevated additions.

Communications and IT Systems

Are the communication/IT 
systems located above the 
500-year elevation or the 
DFE? 

Structural

What is the construction 
type and the foundation 
type and what is the load 
bearing capacity?

Has the foundation 
been designed to 
resist hydrostatic and 
hydrodynamic flood loads?

If the building has below-
grade areas, are the 
lower floor slabs subject to 
cracking and uplift?

If siting in a floodplain is unavoidable, new 
facilities are to be designed to account for all 
loads and load combinations, including flood 
loads. 

Building spaces below the design flood level 
can be dry floodproofed, although it must be 
recognized that higher flood levels will overtop 
the protection measures and may result in 
severe damage. Dry floodproofing creates large 
unbalanced forces that can jeopardize walls 
and foundations that are not designed to resist 
the hydrostatic and hydrodynamic loads.

If the building is elevated 
on a crawlspace an open 
foundation, are there any 
enclosed areas?

New buildings may have enclosures below 
the flood elevation provided the use of the 
enclosures is limited (crawlspace, parking, 
building access, limited storage). In addition, 
the enclosures must have flood openings to 
automatically allow for inflow and outflow of 
floodwaters to minimize differential hydrostatic 
pressure. 

Existing buildings that are elevated and have 
enclosures below the flood elevation can be 
retrofit with flood openings.

For an existing building 
with high value uses below 
the flood elevation, is 
the building suitable for 
elevation-in-place or can 
it be relocated to higher 
ground? 

Elevating a building provides better protection 
than dry floodproofing. Depending on the type 
and soundness of the foundation, even large 
buildings can be elevated on a new foundation 
or moved to a site outside of the floodplain.


2.6 REFERENCES AND SOURCES OF ADDITIONAL INFORMATION

American Society of Civil Engineers, Structural Engineering Institute, 
Flood Resistant Design and Construction, ASCE/SEI 24-05, 
Reston, VA, 2005.

American Society of Civil Engineers, Structural Engineering Institute, 
Minimum Design Loads for Buildings and Other Structures, 
ASCE/SEI 7-05, Reston, VA, 2005.

Association of State Floodplain Managers, Inc., Floodplain Management 
2003: State and Local Programs, Madison, WI, 2004.

FEMA, Answers to Questions about Substantially Damaged Buildings, 
FEMA 213, Washington, DC, May 1991.

FEMA, Answers to Questions about the National Flood Insurance Program, 
FEMA 387, Washington, DC, August 2001. 

FEMA, Coastal Construction Manual, FEMA 55 (3rd Edition), 
Washington, DC, 2000.

FEMA, Design and Construction Guidance for Community Shelters, 
FEMA 361, Washington, DC, July 2000.

FEMA, Engineering Principles and Practices for Retrofitting Flood-prone 
Residential Buildings, FEMA 259, Washington, DC, January 1995.

FEMA, Floodproofing Non-Residential Structures, FEMA 102, Washington, 
DC, May 1986.

FEMA, Protecting Building Utilities From Flood Damage: Principles and 
Practices for the Design and Construction of Flood Resistant Building 
Utility Systems, FEMA 348, Washington, DC, November 1999. 

FEMA, NFIP Technical Bulletins:
 Users Guide to Technical Bulletins, FIA-TB-0, April 1993. 
 Openings in Foundation Walls, FIA-TB-1, April 1993.
 Flood-Resistant Materials Requirements, FIA-TB-2, April 1993.
 Non-Residential FloodproofingRequirements and Certification, 
FIA-TB-3, April 1993. 
 Elevator Installation, FIA-TB-4, April 1993. 
 Free-of-Obstruction Requirements, FIA-TB-5, April 1993. 
 Below-Grade Parking Requirements, FIA-TB-6, April 1993.
 Wet Floodproofing Requirements, FIA-TB-7, December 1993.
 Corrosion Protection for Metal Connections in Coastal Areas, FIA-
TB-8, 1996.
 Design and Construction Guidance for Breakaway Walls Below 
Elevated Coastal Buildings, FIA-TB-9, 1999.
 Ensuring That Structures Built on Fill In or Near Special Flood 
Hazard Areas Are Reasonably Safe From Flooding, FIA-TB-10, 
2001. 
 Crawlspace Construction for Buildings Located in Special Flood 
Hazard Areas, FIA-TB-11, 2001.
International Code Council, Inc., ICC Performance Code for Buildings 
and Facilities, Country Club Hills, IL, 2003.

International Code Council, Inc., International Building Code, 
Country Club Hills, IL, 2003.

International Code Council, Inc. and FEMA, Reducing Flood Losses 
Through the International Codes, Meeting the Requirements of the National 
Flood Insurance Program (2nd Edition), Country Club Hills, 
IL, 2005.

National Fire Protection Association, Building Construction and 
Safety Code (NFPA 5000), Quincy, MA, 2003. 

U.S. Army Corps of Engineers, Flood Proofing Regulations, EP 1165-
2-314, Washington, DC, 1995. 

U.S. Army Corps of Engineers, National Flood Proofing Committee, 
Flood Proofing  How To Evaluate Your Options, Washington, 
DC, July 1993.

U.S. Army Corps of Engineers, Flood Proofing Programs, Techniques 
and References, Washington, DC, 1996.

U.S. Army Corps of Engineers, Flood Proofing PerformanceSuccesses 
& Failures, Washington, DC, 1998.

Organizations and Agencies:

FEMA: FEMAs regional offices (www.fema.gov) can be contacted 
for advice and guidance on NFIP mapping and regulations. 

NFIP State Coordinating offices help local governments to meet 
their floodplain management obligations, and may provide technical 
advice to others; the offices are listed by the Association of 
State Floodplain Managers, Inc. (www.floods.org/stcoor.htm). 

State departments of education or agencies that coordinate State 
funding and guidelines for critical facilities may have State-specific 
requirements.

U.S. Army Corps of Engineers: District offices offer Flood Plain 
Management Services (www.usace.army.mil/inet/functions/cw/). 

FEMA publications may be obtained at no cost by calling (800) 
480-2520, faxing a request to (301) 497-6378, or downloaded from 
the library/publications section online at http://www.fema.gov. 

[End of Chapter 2]



3.1 GENERAL DESIGN CONSIDERATIONS

Wind with sufficient speed to cause damage to weak critical 
facilities can occur anywhere in the United States 
and its territories. Even a well-designed, constructed, 
and maintained critical facility may be damaged in a wind event 
much stronger than one the building was designed for. However, 
except for tornado damage, this scenario is a rare occurrence. 
Rather, most damage occurs because various building elements 
have limited wind resistance due to inadequate design, poor installation, 
or material deterioration. Although the magnitude and 
frequency of strong windstorms vary by locale, all critical facilities 
should be designed, constructed, and maintained to minimize 
wind damage (other than that associated with tornadoessee 
Section 3.5).

This chapter discusses structural, building envelope, and 
nonstructural building systems, and illustrates various types of 
wind-induced damage that affect them. Numerous examples of 
best practices pertaining to new and existing critical facilities are 
presented as recommended design guidelines. Incorporating 
those practices applicable to specific projects will result in greater 
wind resistance reliability and will, therefore, decrease expenditures 
for repair of wind-damaged facilities, provide enhanced 
protection for occupants, and avoid disruption of critical services.

1. The U.S. territories include American Samoa, Guam, Northern Mariana Islands, 
Puerto Rico, and the U.S. Virgin Islands. ASCE provides basic 
wind speed criteria for all but Northern Mariana Islands.

3.1.1 Nature of High Winds

A variety of windstorm types occur in different areas of the United 
States. The characteristics of the types of storms that can affect the 
site should be considered by the design team. The primary storm 
types are listed below.

Straight-line wind: This type of wind generally blows in a straight 
line and is the most common. Straight-line wind speeds range 
from very low to very high. High winds associated with intense 
low pressure can last for approximately a day at a given location. 
Straight-line winds occur throughout the United States and its 
territories.

Down-slope wind: Wind blowing down the slope of mountains is referred 
to as down-slope wind. Down-slope winds with very high 
speeds frequently occur in Alaska and Colorado. In the continental 
United States, mountainous areas are referred to as special wind regions 
(see Figure 3-1). Neither ASCE 7 nor model building codes provide specific wind 
speeds 
in special wind regions. ASCE 7 does provide 
guidance on how to determine design wind 
speeds in these regions. If the local building 
department has not established the basic 
speed, use of regional climatic data and consultation 
with a wind engineer or meteorologist is advised. 

Thunderstorm: This type of storm can form rapidly and produce 
high wind speeds. Approximately 10,000 severe thunderstorms 
occur in the United States each year, typically in the spring and 
summer. They are most common in the Southeast and Midwest. 
Besides producing high winds, they often create heavy rain and 
sometimes spawn tornadoes and hail storms. Thunderstorms commonly 
move through an area quite rapidly, causing high winds for 
only a few minutes at a given location. However, thunderstorms 
can also stall and become virtually stationary.

Downburst: Also known as a microburst, this is a powerful downdraft 
associated with a thunderstorm. When the downdraft 
reaches the ground, it spreads out horizontally, and may form one 
or more horizontal vortex rings around the downdraft. The out flow is typically 
6,000 to 12,000 feet across, and the vortex ring 
may rise 2,000 feet above the ground. The lifecycle of a downburst 
is usually 15 to 20 minutes. Observations suggest that approximately 
5 percent of all thunderstorms produce a downburst, 
which can result in significant damage in a localized area.

ASCE 7, Minimum Design Loads for 
Buildings and Other Structures, provides 
guidance for determining wind loads on 
buildings. The IBC and NFPA 5000 refer 
to ASCE 7 for wind load determination.

Northeaster (noreaster): A northeaster is a cyclonic storm occurring 
off the east coast of North America. These winter weather 
events are notorious for producing heavy snow, rain, and high 
waves and wind. A noreaster gets its name from the continuously 
strong northeasterly winds blowing in from the ocean ahead of 
the storm and over the coastal areas. These storms may last for several 
days. 

Figure 3-1: Hurricane-prone regions and special wind regions
SOURCE: adapted from asce 7-05

Hurricane: This is a system of spiraling winds converging with 
increasing speed toward the storms center (the eye of the hurricane). 
Hurricanes form over warm ocean waters. The diameter 
of the storm varies and can be between 50 and 600 miles. A hurricanes 
forward movement (translational speed) can vary between 
approximately 5 miles per hour (mph) to 
more than 25 mph. Besides being capable 
of delivering extremely strong winds for several 
hours and moderately strong winds for a 
day or more, many hurricanes also bring very 
heavy rainfall. Hurricanes also occasionally 
spawn tornadoes. The Saffir-Simpson Hurricane 
Scale (see Table 3-1) categorizes the 
intensity of hurricanes. The five-step scale 
ranges from Category 1 (the weakest) to Category 
5 (the strongest). Hurricane-prone 
regions are defined in Section 3.1.3.

Of all the storm types, hurricanes have the 
greatest potential for devastating a large geographical area and, 
hence, affect the greatest number of people. The terms hurricane, 
cyclone, and typhoon describe the same type of storm. 
The term used depends on the region of the world where the 
storm occurs. See Figure 3-1 for hurricane-prone regions.

The Saffir-Simpson Hurricane Scale is based 
on measurements of sustained wind speeds 
in hurricanes; these measurements are 
taken over open water. The wind speeds 
described in the Saffir-Simpson Hurricane 
Scale are used to prepare storm response 
actions and are not intended to be used 
for building design. Design wind loads on 
buildings should be determined using the 
basic wind speeds given in ASCE 7.

Table 3-1: Saffir-Simpson Hurricane Scale

Tornado: This is a violently rotating column 
of air extending from the base of a 
thunderstorm to the ground. The Fujita 
scale categorizes tornado severity based on 
observed damage. The six-step scale ranges 
from F0 (light damage) to F5 (incredible 
damage). Weak tornadoes (F0 and F1) are 
most common, but strong tornadoes (F2 and F3) frequently occur. 
Violent tornadoes (F4 and F5) are rare. Tornado path widths are 
typically less than 1,000 feet; however, widths of approximately 
2.5 miles have been reported. Wind speed rapidly decreases with 
increased distance from the center of a tornado. A critical facility 
on the periphery of a strong or violent tornado could be subjected 
to moderate to high wind speeds, depending upon the distance 
from the core of the tornado. However, even 
though the wind speed at a given facility 
might not be great, a facility on the periphery 
could still be impacted by many large 
pieces of wind-borne debris. Tornadoes are 
responsible for the greatest number of wind-
related deaths each year in the United States. 
Figure 3-2 shows the frequency of tornado 
occurrence for a period between 1950 and 
1998, and Figure 3-3 shows the design wind 
speeds recommended by FEMA for designing 
community shelters.

3.1.2 Probability of Occurrence

Via the importance factor,2 ASCE 7 requires Category III and IV 
buildings to be designed for higher wind loads than Category I 
and II buildings (see Section 1.1.1). Hence, critical facilities designed 
in accordance with ASCE 7 have greater resistance to 
stronger, rarer storms. When designing a critical facility, design 
professionals should consider the following types of winds.

Routine winds: In many locations, winds with low to moderate 
speeds occur daily. Damage is not expected to occur during 
these events.

The majority of the tornadoes spawned 
during hurricanes are classified as F2 or 
weaker. However, a few F3 and at least 
two F4 tornadoes have been reported. 

Beginning in February 2007, the National 
Weather Service will use the Enhanced 
Fujita Scale (EF-Scale) to categorize 
tornado severity. This new scale has 
six steps, ranging from EF0 to EF5. The 
new scale was developed by Texas Tech 
Universitys Wind Science and Engineering 
Center. See www.spc.noaa.gov/efscale/ 
for further information on the EF-Scale.

2. The importance factor accounts for the degree of hazard to human life and 
damage to property. Importance factors are given in ASCE 7.

Stronger winds: At a given site, stronger winds (i.e., winds with a 
speed in the range of 70 to 80 mph peak gust, measured at 33 
feet in Exposure C --- refer to Section 3.1.3) may occur from several 
times a year to only once a year or even less frequently. This 
is the threshold at which damage normally begins to occur to 
building elements that have limited wind resistance due to problems 
associated with inadequate design, insufficient strength, poor 
installation, or material deterioration.

Design level winds: Critical facilities exposed to design level events 
and events that are somewhat in excess of design level should experience 
little, if any damage. Actual storm history, however, 
has shown that design level storms frequently cause extensive 
building envelope damage. Structural damage also occurs, but less 
frequently. Damage incurred in design level events is typically associated 
with inadequate design, poor installation, or material 
deterioration. The exceptions are wind-driven water infiltration 
and wind-borne debris (missiles) damage. Water infiltration is discussed 
in Sections 3.3.3.1, 3.3.3.2, and 3.3.3.3. 

Figure 3-2: Frequency of recorded F3, F4, and F5 tornadoes (1950-1998)

Tornadoes: Although more than 1,200 tornadoes typically occur 
each year in the United States, the probability of a tornado occurring 
at any given location is quite small. The probability of 
occurrence is a function of location. As shown in Figure 3-2, only 
a few areas of the country frequently experience tornadoes, and 
tornadoes are very rare in the west. The Oklahoma City area is the 
most active location, with 112 recorded tornadoes between 1890 
and 2003 (www.spc.noaa.gov/faq/tornado/#History). 

Figure 3-3: Design wind speeds for community shelters 

Well designed, constructed, and maintained 
critical facilities should experience little if 
any damage from weak tornadoes, except 
for window breakage. However, weak tornadoes 
often cause building envelope damage 
because many critical facilities have wind resistance 
deficiencies. Most critical facilities 
experience significant damage if they are in 
the path of a strong or violent tornado because 
they typically are not designed for this 
type of storm. 

3.1.3 Wind/Building Interactions

When wind interacts with a building, both 
positive and negative (i.e., suction) pressures 
occur simultaneously (see Figure 3-4). Critical facilities must 
have sufficient strength to resist the applied loads from these 
pressures to prevent wind-induced building failure. Loads exerted 
on the building envelope are transferred to the structural 
system, where in turn they must be transferred through the 
foundation into the ground. The magnitude of the pressures is 
a function of the following primary factors.

Missile damage is very common during 
hurricanes and tornadoes. Missiles can 
puncture roof coverings, many types of 
exterior walls, and glazing. The IBC does 
not address missile-induced damage 
except for glazing in wind-borne debris 
regions. (Wind-borne debris regions are 
limited to portions of hurricane-prone 
regions.) In hurricane-prone regions, 
significant missile-induced building 
damage should be expected, even during 
design level hurricane events, unless 
special enhancements are incorporated 
into the buildings design (discussed in 
Section 3.4).

Figure 3-4: Schematic of wind-induced pressures on a building

Exposure: The characteristics of the terrain 
(i.e., ground roughness and surface irregularities 
in the vicinity of a building) influence 
the wind loading. ASCE 7 defines three exposure 
categories, Exposures B, C, and D. 
Exposure B is the roughest terrain category 
and Exposure D is the smoothest. Exposure 
B includes urban, suburban, and wooded 
areas. Exposure C includes flat open terrain with scattered obstructions 
and areas adjacent to water surfaces in hurricane-prone 
regions (which are defined below under basic wind speed). 
Exposure D includes areas adjacent to water surfaces outside hurricane-
prone regions, mud flats, salt flats, and unbroken ice. 
Because of the wave conditions generated by hurricanes, areas 
adjacent to water surfaces in hurricane-prone regions are considered 
to be Exposure C rather than the smoother Exposure D. The 
smoother the terrain, the greater the wind pressure; therefore, 
critical buildings located in Exposure C would receive higher wind 
loads than those located in Exposure B, even at the same basic 
wind speed. 

Basic wind speed: ASCE 7 specifies the basic wind speed for determining 
design wind loads. The basic wind speed is measured at 33 
feet above grade in Exposure C (flat open terrain). If the building 
is located in Exposure B or D, rather than C, an adjustment for 
the actual exposure is made in the ASCE 7 calculation procedure.

Since the 1995 edition of ASCE 7, the basic wind speed measurement 
has been a 3-second peak gust speed. Prior to that time, 
the basic wind speed was a fastest-mile speed (i.e., the speed averaged 
over the time required for a mile-long column of air to pass 
a fixed point).3 Most of the United States has a basic wind speed 
(peak gust) of 90 mph, but much higher speeds occur in Alaska 
and in hurricane-prone regions. The highest speed, 170 mph, occurs 
in Guam. 

Hurricane-prone regions include Atlantic and Gulf coastal areas 
(where the basic wind speed is greater than 90 mph), Hawaii, and the 
U.S. territories in the Caribbean and South Pacific (see Figure 3-1).

For additional exposure information, 
see the Commentary of ASCE 7, which 
includes several aerial photographs that 
illustrate the different terrain conditions 
associated with Exposures B, C, and D. 

3. Peak gust speeds are about 15 to 20 mph higher than fastest-mile speeds 
(e.g., a 90-mph peak basic wind speed is equivalent to a 76-mph 
fastest-mile wind speed). IBC Chapter 16 provides a table of equivalent basic 
wind speeds.

In the formula for determining wind pressures, 
the basic wind speed is squared. 
Therefore, as the wind speed increases, the 
pressures are exponentially increased, as 
illustrated in Figure 3-5. This figure also illustrates 
the relative difference in pressures 
exerted on the main wind-force resisting 
system (MWFRS) and the components and 
cladding (C&C) elements.

Topography: Abrupt changes in topography, such as isolated hills, 
ridges, and escarpments, cause wind to speed up. Therefore, a 
building located near a ridge would receive higher wind pressures 
than a building located on relatively flat land. ASCE 7 provides a 
procedure to account for topographic influences.

Building height: Wind speed increases with height above the 
ground. Taller buildings are exposed to higher wind speeds and 
greater wind pressures. ASCE 7 provides a procedure to account 
for building height.

The MWFRS is an assemblage of structural 
elements assigned to provide support and 
stability for the overall structure. The system 
generally receives wind loading from more 
than one surface. The C&C are elements of 
the building envelope that do not qualify as 
part of the main wind-force resisting system. 

Figure 3-5: Wind pressure as a function of wind speed

Internal pressure (building pressurization/depressurization): Openings 
through the building envelope, in combination with wind interacting 
with a building, can cause either an increase in the 
pressure within the building (i.e., positive internal pressure), 
or it can cause a decrease in the pressure (i.e., negative internal 
pressure). Building envelope openings occur around doors and 
window frames, and by air infiltration through walls that are not 
absolutely airtight. A door or window left open, or glazing that is 
broken during a storm, can greatly influence the magnitude of 
the internal pressure. 

Wind striking an exterior wall exerts a positive pressure on the 
wall, which forces air through openings and into the interior of 
the building (this is analogous to blowing up a balloon). At the 
same time that the windward wall is receiving positive pressure, 
the side and rear walls are experiencing negative (suction) pressure 
from winds going around the building. As this occurs, air 
within the building is pulled out at openings in these walls. As 
a result, if the porosity of the windward wall is greater than the 
combined porosity of the side and rear walls, the interior of the 
building is pressurized. But if the porosity of the windward wall is 
lower than the combined porosity of the side and rear walls, the 
interior of the building is depressurized (this is analogous to letting 
air out of a balloon). 

When a building is pressurized, the internal pressure pushes up 
on the roof. This push from below the roof is combined with suction 
on the roof above, resulting in an increased upward wind 
pressure on the roof. The internal pressure also pushes on the 
side and rear walls. This outward push is combined with the suction 
on the exterior side of these walls (see Figure 3-6). When a 
building becomes fully pressurized (e.g., due to window breakage 
or soffit failure), the loads applied to the exterior walls and roof 
are significantly increased. The rapid build-up of internal pressure 
can also blow down interior partitions and blow suspended 
ceiling boards out of their support grid. The breaching of a small 
window can be sufficient to cause full pressurization of the facilitys 
interior.

When a building is depressurized, the internal pressure pulls the 
roof down, which reduces the amount of uplift exerted on the 
roof. The decreased internal pressure also pulls inward on the 
windward wall, which increases the wind load on that wall (see 
Figure 3-7).

The ASCE 7 wind pressure design procedure accounts for the influence 
of internal pressure on the wall and roof loads, and it 
provides positive and negative internal pressure coefficients for 
use in load calculations. Buildings that are designed to accommodate 
full pressurization are referred to as partially enclosed 
buildings. Buildings that are only intended to experience limited 
internal pressurization are referred to as enclosed buildings. 
Buildings that do not experience internal pressurization are referred 
to as open buildings (such as covered walkways and most 
parking garages).

Figure 3-6: Schematic of internal pressure condition when the 
dominant opening is in the windward wall

Figure 3-7: Schematic of internal pressure condition when the 
dominant opening is in the leeward wall

Building shape: The highest uplift pressures occur at roof corners 
because of building aerodynamics (i.e., the interaction 
between the wind and the building). The roof perimeter has a 
somewhat lower load compared to the corners, and the field of 
the roof has still lower loads. Exterior walls typically have lower 
loads than the roof. The ends (edges) of walls have higher suction 
loads than the portion of wall between the ends. However, 
when the wall is loaded with positive pressure, the entire wall is 
uniformly loaded. Figure 3-8 illustrates these aerodynamic influences. 
The negative values shown in Figure 3-8 indicate suction 
pressure acting upward from the roof surface and outward from 
the wall surface. Positive values indicate positive pressure acting 
inward on the wall surface.

Aerodynamic influences are accounted for by using external pressure 
coefficients in load calculations. The value of the coefficient 
is a function of the location on the building (e.g., roof corner or 
field of roof) and building shape as discussed below. Positive coefficients 
represent a positive (inward-acting) pressure, and negative 
coefficients represent negative (outward-acting [suction]) pressure. 
External pressure coefficients for MWFRS and C&C are 
listed in ASCE 7.

Building shape affects the value of pressure coefficients and, 
therefore, the loads applied to the various building surfaces. For 
example, the uplift loads on a low-slope roof are larger than the 
loads on a gable or hip roof. The steeper the slope, the lower the 
uplift load. Pressure coefficients for monoslope (shed) roofs, sawtooth 
roofs, and domes are all different from those for low-slope 
and gable/hip roofs.

Building irregularities, such as re-entrant corners, bay window projections, 
a stair tower projecting out from the main wall, dormers, 
and chimneys can cause localized turbulence. Turbulence causes 
wind speed-up, which increases the wind loads in the vicinity of 
the building irregularity, as shown in Figures 3-9 and 3-10. Figure 
3-9 shows the aggregate ballast on a hospitals single-ply membrane 
roof blown away at the re-entrant corner and in the vicinity 
of the corners of the wall projections at the window bays. The 
irregular wall surface created turbulence, which led to wind speed-
up and loss of aggregate in the turbulent flow areas. 

Figure 3-8: Relative roof uplift pressures as a function of roof geometry, roof 
slope, and location on roof, and relative positive and negative wall pressures 
as a function of location along the wall

Figure 3-10 shows a stair tower at a hospital 
that caused turbulence resulting in wind 
speed-up. The speed-up increased the suction 
pressure on the base flashing along the 
parapet behind the stair tower. The built-
up roofs base flashing was pulled out from 
underneath the coping because its attachment 
was insufficient to resist the suction 
pressure. The base flashing failure propagated 
and caused a large area of the roof 
membrane to lift and peel. Some of the wall covering on the 
stair tower was also blown away. Had the stair tower not existed, 
the built-up roof would likely not have been damaged. To avoid 
damage in the vicinity of building irregularities, attention needs 
to be given to the attachment of building elements located in 
turbulent flow areas. 

To avoid the roof membrane damage shown in Figure 3-10, it 
would be prudent to use corner uplift loads in lieu of perimeter 
uplift loads in the vicinity of the stair tower, as illustrated in 
Figure 3-11. Wind load increases due to building irregularities 
can be identified by wind tunnel studies; however, wind tunnel 
studies are rarely performed for critical facilities. Therefore, 
identification of wind load increases due to building irregularities will 
normally be based on the designers professional 
judgment. Usually load increases will only need to be applied to 
the building envelope, and not to the MWFRS. 

Figure 3-9: Aggregate blow-off associated with building 
irregularities. Hurricane Hugo (South Carolina, 1989)

Information pertaining to load calculations 
is presented in Section 3.3.1.2. For further 
general information on the nature of 
wind and wind-building interactions, see 
Buildings at Risk: Wind Design Basics for 
Practicing Architects, American Institute of 
Architects, 1997.

Figure 3-10: The irregularity created by the stair tower (covered with a metal 
roof) caused turbulence resulting in wind speed-up and roof 
damage. Hurricane Andrew (Florida, 1992) 

Figure 3-11: Plan view of a portion of 
the building in Figure 310 showing the use of a 
corner uplift zone in lieu of a perimeter uplift zone 
on the low-slope roof in the vicinity of the stair tower 

3.1.4 Building Codes

The IBC is the most extensively used model code. However, in 
some jurisdictions NFPA 5000 may be used. In other jurisdictions, 
one of the earlier model building codes, or a specially written 
State or local building code, may be used. The specific scope and/
or effectiveness and limitations of these other building codes will 
be somewhat different than those of the IBC. It is incumbent 
upon the design professionals to be aware of the specific code (including 
the edition of the code and local amendments) that has 
been adopted by the authority having jurisdiction over the location 
of the critical facility.

3.1.4.1 Scope of Building Codes

With respect to wind performance, the scope of the model 
building codes has greatly expanded since the mid-1980s. Some of 
the most significant improvements are discussed below.

Recognition of increased uplift loads at the roof perimeter and corners: 
Prior to the 1982 edition of the Standard Building Code (SBC), 
Uniform Building Code (UBC), and the 1987 edition of the National 
Building Code (NBC), these model codes did not account 
for the increased uplift at the roof perimeter and corners. Therefore, 
critical facilities designed in accordance with earlier editions 
of these codes are very susceptible to blow-off of the roof deck 
and/or roof covering.

Adoption of ASCE 7 for design wind loads: Although the SBC, UBC, 
and NBC permitted use of ASCE 7, the 2000 edition of the IBC 
was the first model code to require ASCE 7 for determining 
wind design loads. ASCE 7 has been more reflective of the current 
state of the knowledge than the earlier model codes, and 
use of this procedure typically has resulted in higher design 
loads. 

Roof coverings: Several performance and prescriptive requirements 
pertaining to wind resistance of roof coverings have been 
incorporated into the model codes. The majority of these additional 
provisions were added after Hurricanes Hugo (1989) and 
Andrew (1992). Poor performance of roof coverings was wide
spread in both of those storms. Prior to the 
1991 edition of the SBC and UBC, and the 
1990 edition of the NBC, these model codes 
were essentially silent on roof covering wind 
loads and test methods for determining 
uplift resistance. Code improvements continued 
to be made through the 2006 edition 
of the IBC, which added a provision that 
prohibits aggregate roof surfaces in hurricane-
prone regions.

Glazing protection: The 2000 edition of the 
IBC was the first model code to address 
wind-borne debris requirements for glazing 
in buildings located in hurricane-prone regions 
(via reference to the 1998 edition of 
ASCE 7). The 1995 edition of ASCE 7 was 
the first edition to address wind-borne debris 
requirements.

Parapets and rooftop equipment: The 2003 edition of the IBC was 
the first model code to address wind loads on parapets and 
rooftop equipment (via reference to the 2002 edition of ASCE 7, 
which was the first edition of ASCE 7 to address these elements).

3.1.4.2 Effectiveness and Limitations of Building 
Codes

A key element of an effective building code is for a community to 
have an effective building department. Building safety depends on 
more than the codes and the standards they reference. Building 
safety results when trained professionals have the resources and 
ongoing support they need to stay on top of the latest advancements 
in building safety. An effective building safety system 
provides uniform code interpretations, product evaluations, and 
professional development and certification for inspectors and 
plan reviewers. Local building departments play an important role 
in helping to ensure buildings are designed and constructed in 
accordance with the applicable building codes. Meaningful plan 
review and inspection by the building department are particularly 
important for critical facilities.

ASCE 7 requires impact-resistant glazing in 
wind-borne debris regions within hurricane-
prone regions. Impact-resistant glazing can 
either be laminated glass, polycarbonate, 
or shutters tested in accordance with 
standards specified in ASCE 7. The 
wind-borne debris load criteria were 
developed to minimize property damage 
and to improve building performance. The 
criteria were not developed for occupant 
protection. Where occupant protection is 
a specific criterion, the more conservative 
wind-borne debris criteria given in FEMA 
361, Design and Construction Guidance 
for Community Shelters is recommended.

General limitations to building codes include the following:

 Because codes are adopted and enforced on the local or 
State level, the authority having jurisdiction has the power to 
eliminate or modify wind-related provisions of a model code, 
or write its own code instead. In places where important 
wind-related provisions of the current model code are not 
adopted and enforced, critical facilities are more susceptible 
to wind damage. Additionally, a significant time lag often exists 
between the time a model code is updated and the time 
it is implemented by the authority having jurisdiction. Buildings 
designed to the minimum requirements of an outdated 
code are, therefore, not taking advantage of the current 
state of the knowledge. These buildings are prone to poorer 
wind performance compared to buildings designed according 
to the current model code.

 Adopting the current model code alone does not ensure good 
wind performance. The code is a minimum tool that should 
be used by knowledgeable design professionals in conjunction 
with their training, skills, professional judgment, and the best 
practices presented in this manual. To achieve good wind 
performance, in addition to good design, the construction 
work must be effectively executed, and the building must be 
adequately maintained and repaired.

 Critical facilities need to perform at a higher level than 
required by codes and standards. See Section 1.3 on 
performance based design.

IBC 2006: The 2006 edition of the IBC is believed to be a relatively 
effective code, provided that it is properly followed and 
enforced. Some limitations of the 2006 IBC have, however, been 
identified:

 With respect to hurricanes, the IBC provisions pertaining 
to building envelopes and rooftop equipment do not 
adequately address the special needs of critical facilities. 
For example: (1) they do not account for water infiltration 
due to puncture of the roof membrane by missiles; (2) 
they do not adequately address the vulnerabilities of brittle 
roof coverings (such as tile) to missile-induced damage 
and subsequent progressive failure; 
(3) they do not adequately address 
occupant protection with respect to 
missiles; (4) they do not adequately 
address protection of equipment in 
elevator penthouses; (5) they do not 
account for interruption of water service 
or prolonged interruption of electrical 
power; and (6) the current requirements 
for shelters are limited. All of these 
elements are of extreme importance for 
critical facilities, which need to remain 
operational before, during, and after a 
disaster. Guidance to overcome these 
shortcomings is given in Section 3.4.
m The 2006 IBC does not account for 
tornadoes; therefore, except for weak 
tornadoes, it is ineffective for this type 
of storm.4 Guidance to overcome this 
shortcoming is given in Section 3.5.
The 2000, 2003, and 2006 IBC rely on several 
referenced standards and test methods 
developed or updated in the 1990s. Prior 
to adoption, most of these standards and 
test methods had not been validated by actual building performance 
during design level wind events. The hurricanes of 2004 
and 2005 provided an opportunity to evaluate the actual performance 
of buildings designed and constructed to the minimum 
provisions of the IBC. Building performance evaluations conducted 
by FEMA revealed the need for further enhancements:

 A limitation of the 2006 IBC pertains to some of the test 
methods used to assess wind and wind-driven rain resistance 
of building envelope components. However, before this code 
limitation can be overcome, research needs to be conducted 
and new test methods need to be developed. 
The International Code Council (ICC) 
is developing a consensus standard, 
ICC/NSSA Standard for the Design and 
Construction of Storm Shelters, to provide 
basic requirements for the design and 
construction of emergency shelters in areas 
affected by hurricanes and tornadoes. If 
it is adopted by a community when it 
becomes available in early 2007, it will 
provide design and construction standards 
for buildings intended to resist the impact 
of high winds and wind-borne debris. This 
stand-alone standard will be linked to the 
IBC and IRC. It is the intent of the ICC 
that the shelter standard be incorporated 
by reference into the IBC and IRC in 
2009. FEMA should be consulted prior to 
designing or constructing shelters to the 
ICC/NSSA standard with FEMA funds 
to ensure all program requirements are 
met, as some components may need to 
be designed to stricter criteria than those 
included in the consensus standard. 

4. Except for glass breakage, code-compliant buildings should not experience 
significant damage during weak tornadoes.

 Except to the extent covered by reference to ASCE 7, the 2006 
IBC does not address the need for continuity, redundancy, 
or energy-dissipating capability (ductility) to limit the effects 
of local collapse, and to prevent or minimize progressive 
collapse after the loss of one or two primary structural 
members, such as a column. Chapter 1 of ASCE 7 addresses 
general structural integrity, and the Chapter 1 Commentary 
provides some guidance on this issue. 

3.2 CRITICAL FACILITIES EXPOSED TO HIGH WINDS

3.2.1 Vulnerability: What High Winds Can Do to Critical Facilities

This section provides an overview of the common types of wind 
damage and their ramifications. 

3.2.1.1 Types of Building Damage

When damaged by wind, critical facilities typically experience 
a variety of building component damage. The most common 
types of damage are discussed below in descending order of 
frequency. 

Roof: Roof covering damage (including rooftop mechanical, 
electrical, and communications equipment) is the most 
common type of wind damage. The school, illustrated in Figure 
3-12, was being used as a hurricane shelter at the time a portion 
of the roof membrane blew off. In addition to the membrane 
damage, several pieces of rooftop equipment were damaged, 
and virtually all of the loose aggregate blew off and broke many 
windows in nearby houses. The cast-in-place concrete deck kept 
most of the water from entering the building. 

Glazing: Exterior glazing damage is very common during hurricanes 
and tornadoes, but is less common during other storms. 
The glass shown in Figure 3-13 was broken by the aggregate 
from a built-up roof. The inner panes had several impact craters. 
In several of the adjacent windows, both the outer and 
inner panes were broken. The aggregate flew more than 245 
feet (the estimated wind speed was 104 mph, measured at 33 
feet in Exposure C).

Figure 3-12: A portion of the built-up 
membrane lifted and peeled after the metal 
edge flashing lifted. Hurricane Andrew (Florida, 1992)

Figure 3-13: The outer window panes were broken by aggregate 
from a built-up roof. Hurricane Hugo (South Carolina, 1989)

Wall coverings, soffits, and large doors: Exterior wall covering, soffit, 
and large door damage is common during hurricanes and tornadoes, 
but is less common during other storms. At the building 
shown in Figure 3-14, metal wall covering was attached to plywood 
over metal studs. The CMU wall behind the studs did not appear 
to be damaged. The building was located on the periphery of a violent 
tornado. 

Wall collapse: Collapse of non-load-bearing exterior walls is 
common during hurricanes and tornadoes, but is less common 
during other storms (see Figure 3-15).

Figure 3-14: Collapsed metal stud wallthe wall was 
blown completely away in another part of the 
building. (Oklahoma, 1999)

Figure 3-15: The unreinforced CMU wall collapsed at a school 
during Hurricane Marilyn. (U.S. Virgin Islands, 1995)

Structural system: Structural damage (e.g., roof deck blow-off, blow-
off or collapse of the roof structure, collapse of exterior bearing 
walls, or collapse of the entire building or major portions thereof) 
is the principal type of damage that occurs during strong and violent 
tornadoes (see Figure 3-16).

3.2.1.2 Ramifications of Damage

The ramifications of building component damage on critical facilities 
are described below.

Property damage: Property damage requires repairing/replacing 
the damaged components (or replacing the entire facility), and 
may require repairing/replacing interior building components, 
furniture, and other equipment, and mold remediation. Even 
when damage to the building envelope is 
limited, such as blow-off of a portion of the 
roof covering or broken glazing, substantial 
water damage frequently occurs because 
heavy rains often accompany strong winds 
(particularly in the case of thunderstorms, 
tropical storms, hurricanes, and tornadoes). 
At the newly constructed gymnasium 
shown in Figure 3-17, the structural metal 
roof panels were applied over metal purlins. The panels with 3-
inch-high trapezoidal ribs at 24 inches on center detached from 
their concealed clips. A massive quantity of water entered the 
building and buckled the wood floor. 

Figure 3-16: The school wing was destroyed by a violent 
tornado. (Oklahoma, 1999)

Modest wind speeds can drive rain into 
exterior walls. Unless adequate provisions 
are taken to account for water infiltration 
(see Sections 3.3.3.1 to 3.3.3.3), 
damaging corrosion, dry rot, and mold 
can occur within walls.

Wind-borne debris such as roof aggregate, gutters, rooftop 
equipment, and siding blown from buildings can damage vehicles 
and other buildings in the vicinity. Debris can travel well 
over 300 feet in high-wind events.

Portable classrooms on school campuses are often particularly 
vulnerable to significant damage because they are seldom designed 
to the same wind pressures as permanent buildings. 
Portable classrooms are frequently blown over during high-wind 
events, because the anchoring techniques typically used are inadequate 
to secure the units to the ground. Wind-borne debris 
from portable classrooms, or an entire portable classroom, may 
strike the permanent school building and cause serious damage.

Ancillary buildings (such as storage buildings) adjacent to critical 
facilities are also vulnerable to damage. Although loss of 
these buildings may not be detrimental to the operation of the 
critical facility, debris from ancillary buildings may strike and 
damage the critical facility. The damaged building shown in 


Figure 3-17: A massive quantity of water entered the building 
after the roof blew off. Typhoon Paka (Guam, 1997) 

Figure 3-18 contained the hospitals supplies and maintenance 
shop. With the loss of this building, tents had to be set up to provide 
supply storage. Almost all of the tools and stock materials for 
repairs were lost.

Injury or death: Although infrequent, critical 
facility occupants or people outside the 
facility have been injured and killed when 
struck by collapsed building components 
(such as exterior masonry walls or the roof 
structure) or wind-borne debris. The greatest 
risk of injury or death is during strong hurricanes 
and strong/violent tornadoes.

Interrupted use: Depending on the magnitude 
of wind and water damage, it can 
take days, months, or more than a year to repair the damage 
or replace a facility. In addition to the costs associated with repairing/
replacing the damage, other social and financial costs 
can be even more significant. The repercussions related to interrupted 
use of the critical facility can include the loss of emergency 
and first-responder services, lack of medical care, and the costs 
to rent temporary facilities. These additional costs can be quite 
substantial.

Figure 3-18: A hurricane-damaged, pre-engineered storage 
building adjacent to a hospital. Hurricane Charley (Florida, 2004)

Although people are not usually outside 
during hurricanes, it is not uncommon for 
people to seek shelter or assistance in 
critical facilities during a storm. Missiles, 
such as roof aggregate or tile shedding 
from a critical facility, could injure or kill 
late arrivals before they have a chance to 
enter the building. 

3.2.2 Evaluating Critical Facilities for Risk from High Winds

This section describes the process of hazard risk assessment. Although 
no formal methodology for risk assessment has been 
adopted, prior experience provides a sufficient knowledge base 
upon which a set of guidelines can be structured into a recommended 
procedure for risk assessment of critical facilities. The 
procedures presented below establish guidelines for evaluating 
the risk to new and existing buildings from wind storms other 
than tornadoes. These evaluations will allow development of a 
vulnerability assessment that can be used along with the sites 
wind regime to assess the risk to critical facilities.

In the case of tornadoes, neither the IBC nor ASCE 7 requires 
buildings (including critical facilities) to be designed to resist 
tornado forces, nor are occupant shelters required in buildings 
located in tornado-prone regions. Constructing tornado-resistant 
critical facilities is extremely expensive because of the 
extremely high pressures and missile impact loads that tornadoes 
can generate. Therefore, when consideration is voluntarily 
given to tornado design, the emphasis is 
typically on occupant protection, which is 
achieved by hardening portions of a critical 
facility for use as safe havens. FEMA 361 
includes a comprehensive risk assessment 
procedure that designers can use to assist 
building owners in determining whether a 
tornado shelter should be included as part 
of a new critical facility. See Section 3.5 for 
the design of tornado shelters and other 
recommendations pertaining to critical facilities 
in tornado-prone regions.

3.2.2.1 New Buildings

When designing new critical facilities, a 
two-step procedure is recommended for 
evaluating the risk from wind storms (other 
than tornadoes).

In this manual, the term tornado-prone 
regions refers to those areas of the United 
States where the number of recorded 
F3, F4, and F5 tornadoes per 3,700 
square miles is 6 or greater per year 
(see Figure 3-2). However, an owner of 
a critical facility may decide to use other 
frequency values (e.g., 1 or greater, 16 
or greater, or greater than 25) in defining 
whether the building is in a tornado-prone 
area. In this manual, tornado shelters are 
recommended for all critical facilities in 
tornado-prone regions.

Where the frequency value is 1 or greater, 
and the facility does not have a tornado 
shelter, the best available refuge areas 
should be identified, as discussed in 
Section 3.5.

Step 1: Determine the basic wind speed from ASCE 7. As the 
basic wind speed increases beyond 90 mph, the risk of damage increases. 
Design, construction, and maintenance enhancements 
are recommended to compensate for the increased risk of damage 
(see Section 3.3).

Step 2: For critical facilities in hurricane-prone regions, refer to 
the design, construction, and maintenance enhancements recommended 
in Section 3.4. 

For particularly important critical facilities (such as hospitals) 
in remote areas outside of hurricane-prone regions, it is recommended 
that robust design measures be considered to minimize 
the potential for disruption resulting from wind damage. Because 
of their remote location, disruption of such facilities could 
severely affect the occupants or community. Some of the recommendations 
in Section 3.4 may therefore be prudent.

3.2.2.2 Existing Buildings

The resistance of existing buildings is a function of their original 
design and construction, various additions or modifications, and 
the condition of building components (which may have weakened 
due to deterioration or fatigue). For existing buildings, a two-step 
procedure is also recommended.

Step 1: Calculate the wind loads on the building using the current 
edition of ASCE 7, and compare these loads with the 
loads for which the building was originally designed. The original 
design loads may be noted on the contract drawings. If 
not, determine what building code or standard was used to develop 
the original design loads, and calculate the loads using 
that code or standard. If the original design loads are significantly 
lower than current loads, upgrading the load resistance 
of the building envelope and/or structure should be considered. 
An alternative to comparing current loads with original 
design loads is to evaluate the resistance of the existing facility 
as a function of the current loads to determine what elements 
are highly overstressed.

Step 2: Perform a field investigation to evaluate the primary 
building envelope elements, rooftop equipment, and structural 
system elements, to determine if the facility was generally 
constructed as indicated on the original contract drawings. 
As part of the investigation, the primary elements should be 
checked for deterioration. Load path continuity should also be 
checked.

If the results of either step indicate the need for remedial work, 
see Section 3.6.

3.3 CRITICAL FACILITY DESIGN CONSIDERATIONS

3.3.1 General Design Considerations

The performance of critical facilities in past wind storms indicates 
that the most frequent and the most significant factor in 
the disruption of the operations of these facilities has been the 
failure of nonstructural building components. While acknowledging 
the importance of the structural systems, Chapter 3 emphasizes 
the building envelope components and the nonstructural systems. 
According to the National Institute of Building Science (NIBS), 
the building envelope includes the below-grade basement walls 
and foundation and floor slab (although these are generally considered 
part of the buildings structural system). The envelope includes 
everything that separates the interior of a building from the outdoor 
environment, including the connection of all the nonstructural 
elements to the building structure. The nonstructural systems include 
all mechanical, electrical, electronic, communications, and 
lightning protection systems. Historically, damage to roof coverings 
and rooftop equipment has been the leading cause of 
building performance problems during wind storms. Special consideration 
should be given to the problem of water infiltration 
through failed building envelope components, which can cause 
severe disruptions in the functioning of critical facilities. 
The key to enhanced wind performance is paying sufficient attention 
to all phases of the construction process (including site 
selection, design, and construction) and to post-occupancy maintenance 
and repair. 

3.3.1.1 Site 

When selecting land for a critical facility, sites located in Exposure 
D (see Section 3.1.3 for exposure definitions) should be avoided if 
possible. Selecting a site in Exposure C or preferably in Exposure 
B would decrease the wind loads. Also, where possible, avoid selecting 
sites located on an escarpment or the upper half of a hill, 
where the abrupt change in the topography would result in increased 
wind loads.6 

Trees with trunks larger than 6 inches in diameter, poles (e.g., 
light fixture poles, flag poles, and power poles), or towers (e.g., 
electrical transmission and large communication towers) should 
not be placed near the building. Falling trees, poles, and towers 
can severely damage a critical facility and injure the occupants 
(see Figure 3-19). Large trees can crash through pre-engineered 
metal buildings (which often house fire stations) and 
wood frame construction (which is commonly used for nursing 
homes). Falling trees can also rupture roof membranes and 
break windows.

Figure 3-19: Had this tree fallen in the opposite direction, it 
would have landed on the school. Hurricane Ivan (Florida, 2004)

6. When selecting a site on an escarpment or the upper half of a hill is 
necessary, the ASCE 7 design procedure accounts for wind speed-up 
associated with this abrupt change in topography.

Providing at least two means of site egress is 
prudent for all critical facilities, but is particularly 
important for facilities in hurricane-prone 
regions. If one route becomes blocked by trees 
or other debris, or by floodwaters, the other access 
route may still be available.

3.3.1.2 Building Design 

Good wind performance depends on good 
design (including details and specifications), 
materials, installation, maintenance, 
and repair. A significant shortcoming in 
any of these five elements could jeopardize 
the performance of a critical facility against 
wind. Design, however, is the key element to 
achieving good performance of a building against wind damage. 
Design inadequacies frequently cannot be compensated for with 
other elements. Good design, however, can compensate for other 
inadequacies to some extent. The following steps should be included 
in the design process for critical facilities.

Step 1: Calculate Loads 

Calculate loads on the MWFRS, the building envelope, and 
rooftop equipment in accordance with ASCE 7 or the local 
building code, whichever procedure results in the highest loads. 
In calculating wind loads, design professionals 
should consider the following items.

Importance factor: The effect of using a 1.15 
importance factor versus 1 is that the design 
loads for the MWFRS and C&C are increased 
by 15 percent. The importance factor for 
most critical facilities is required to be 1.15. 
However, ASCE 7 permits a factor of 1 for 
some critical facilities. For example, schools 
with an occupant load of less than 250 
people are permitted to be designed with an 
importance factor of only 1 (provided they 
are not used as a shelterif used as a shelter, 
schools are required to be designed with an importance factor of 
1.15, regardless of occupant load). Other facilities where occupant 
load controls the importance factor include certain health 
care facilities, such as nursing homes with 50 or more residents, 
for which a factor of 1.15 is required. For nursing homes with less 
than 50 residents, a factor of 1 can be used. Some critical facilities 
are not specifically addressed in ASCE 7. For example, various 
buildings on a hospital campus, such as medical office buildings 
that are integrally connected to the hospital and various types of 
non-emergency treatment facilities (such as storage, cancer treatment, 
physical therapy, and dialysis) are not specifically required 
by ASCE 7 to be designed with a 1.15 factor. This manual recommends 
a value of 1.15 for all critical facilities.

In the past, design professionals seldom 
performed load calculations on the 
building envelope (i.e., roof and wall 
coverings, doors, windows, and skylights) 
and rooftop equipment. These building 
components are the ones that have failed 
the most during past wind events. In 
large part they failed because of the 
lack of proper load determination and 
inappropriate design of these elements. 
It is imperative that design professionals 
determine the loads for the building 
envelope and rooftop equipment, and 
design them to accommodate such loads.

Uplift loads on roof assemblies can also 
be determined from FM Global (FMG) 
Data Sheets. If the critical facility is FMG 
insured, and the FMG-derived loads are 
higher than those derived from ASCE 7 or 
the building code, the FMG loads should 
govern. However, if the ASCE 7 or code-
derived loads are higher than those from 
FMG, the ASCE 7 or code-derived loads 
should govern (whichever procedure 
results in the highest loads). 

Wind directionality factor: The ASCE 7 wind load calculation procedure 
incorporates a wind directionality factor (kd). The 
directionality factor accounts for the reduced probability of maximum 
winds coming from any given direction. By applying the 
prescribed value of 0.85, the loads are reduced by 15 percent. Because 
hurricane winds can come from any direction, and because 
of the historically poor performance of building envelopes and 
rooftop equipment, this manual recommends a more conservative 
approach for critical facilities in hurricane-prone regions. A directionality 
factor of 1.0 is recommended for the building envelope 
and rooftop equipment (a load increase over what is required by 
ASCE 7). For the MWFRS, a directionality factor of 0.85 is recommended 
(hence, no change for MWFRS).

Step 2: Determine Load Resistance

When using allowable stress design, after loads have been determined, 
it is necessary to select a reasonable safety factor in 
order to determine the minimum required load resistance. 
For building envelope systems, a minimum safety factor of 2 is 
recommended. For anchoring exterior-mounted mechanical, 
electrical, and communications equipment (such as satellite 
dishes), a minimum safety factor of 3 is recommended. When 
using strength design, load combinations and load factors specified 
in ASCE 7 are used.

ASCE 7 provides criteria for combining wind loads with other types 
of loads (such as dead and flood loads) using allowable stress design.

For structural members and cladding elements 
where strength design can be used, 
load resistance can be determined by calculations. 
For other elements where allowable 
stress design is used (such as most types of 
roof coverings), load resistance is primarily 
obtained from system testing.

The load resistance criteria need to be provided 
in contract documents. For structural 
elements, the designer of record typically accounts 
for load resistance by indicating the 
material, size, spacing, and connection of the 
elements. For nonstructural elements, such 
as roof coverings or windows, the load and 
safety factor can be specified. In this case, the 
specifications should require the contractors 
submittals to demonstrate that the system will 
meet the load resistance criteria. This performance 
specification approach is necessary if, 
at the time of the design, it is unknown who 
will manufacture the system.

Regardless of which approach is used, it is important that the 
designer of record ensure that it can be demonstrated, via calculations 
or tests, that the structure, building envelope, and 
nonstructural systems (exterior-mounted mechanical, electrical, 
and communications equipment) have sufficient 
strength to resist design wind loads.

Step 3: Detailed Design

It is vital to design, detail, and specify the 
structural system, building envelope, and 
exterior-mounted mechanical, electrical, 
and communications equipment to meet 
the factored design loads (based on appropriate 
analytical or test methods). It 
is also vital to respond to the risk assessment 
criteria discussed in Section 3.2.2, as 
appropriate.

When using allowable stress design, a 
safety factor is applied to account for 
reasonable variations in material strengths, 
construction workmanship, and conditions 
when the actual wind speed somewhat 
exceeds the design wind speed. For 
design purposes, the ultimate resistance 
an assembly achieves in testing is reduced 
by the safety factor. For example, if a 
roof assembly resisted an uplift pressure 
of 100 pounds per square foot (psf), after 
applying a safety factor of 2, the assembly 
would be suitable where the design load 
was 50 psf or less. Conversely, if the 
design load is known, multiplying it by the 
safety factor equals the minimum required 
test pressure (e.g., 50 psf design load 
multiplied by a safety factor of 2 equals a 
minimum required test pressure of 100 psf). 

Connections are a key aspect of load 
path continuity between various structural 
and nonstructural building elements. In a 
window, for example, the glass must be 
strong enough to resist the wind pressure 
and must be adequately anchored to the 
window frame, the frame adequately 
anchored to the wall, the wall to the 
foundation, and the foundation to the 
ground. As loads increase, greater 
load capacity must be developed in the 
connections.

As part of the detailed design effort, load path continuity 
should be clearly indicated in the contract documents via illustration 
of connection details. Load paths need to accommodate 
design uplift, racking, and overturning loads. Load path continuity 
obviously applies to MWFRS elements, but it also applies 
to building envelope elements. Figure 3-20 shows a load path 
discontinuity between a piece of HVAC equipment and its 
equipment stand. The equipment on this new Federal courthouse 
blew away because it was resting on vibration isolators 
that provided lateral resistance, but no uplift resistance (also see 
Figure 3-75).

Figure 3-21 illustrates the load path concept. Members are sized 
to accommodate the design loads. Connections are designed to 
transfer uplift loads applied to the roof, and the positive and negative 
loads applied to the exterior bearing walls, down to the 
foundation and into the ground. The roof covering (and wall 
covering, if there is one) is also part of the load path. To avoid 
blow-off, the nonstructural elements must also be adequately attached 
to the structure.

Figure 3-20: Temporary coverings placed over two large 
openings in the roof that were left after the ductwork 
blew away. Hurricane Katrina (Mississippi, 2005)

As part of the detailed design process, special consideration 
should be given to the durability of materials and water 
infiltration.

Figure 3-21: Illustration of load path continuity 

Durability: Because some locales have very aggressive atmospheric 
corrosion (such as areas near oceans), special attention needs 
to be given to the specification of adequate protection for ferrous 
metals, or to specify alternative metals such as stainless 
steel. FEMA Technical Bulletin, Corrosion 
Protection for Metal Connectors in Coastal Areas 
(FIA-TB-8, 1996) contains information on 
corrosion protection. Attention also needs 
to be given to dry rot avoidance, for example, 
by specifying preservative-treated 
wood or developing details that avoid excessive 
moisture accumulation. Appendix J 
of the Coastal Construction Manual, (FEMA 
55, 2000) presents information on wood 
durability.

Durable materials are particularly important 
for components that are inaccessible 
and cannot be inspected regularly (such as 
fasteners used to attach roof insulation). 
Special attention also needs to be given to 
details. For example, details that do not 
allow water to stand at connections or sills 
are preferred. Without special attention to 
material selection and details, the demands 
on maintenance and repair will be increased, 
along with the likelihood of failure 
of components during high winds.

Water infiltration (rain): Although prevention 
of building collapse and major building 
damage is the primary goal of wind-resistant 
design, consideration should also be 
given to minimizing water damage and subsequent 
development of mold from the 
penetration of wind-driven rain. To the extent 
possible, non-load-bearing walls and 
door and window frames should be designed 
in accordance with rain-screen 
principles. With this approach, it is assumed 
that some water will penetrate past the face 
of the building envelope. The water is intercepted 
in an air-pressure equalized cavity 
that provides drainage from the cavity to the outer surface of 
the building. See Sections 3.3.3.2 and 3.3.3.3, and Figure 3-40 
for further discussion and an example. 

Coastal environments are conducive to 
metal corrosion, especially in buildings 
within 3,000 feet of the ocean. Most 
jurisdictions require metal building 
hardware to be hot-dipped galvanized 
or stainless steel. Some local codes 
require protective coatings that are thicker 
than typical off-the-shelf products. For 
example, a G90 zinc coating (0.75 mil 
on each face) may be required. Other 
recommendations include the following:

 Use hot-dipped galvanized or stainless 
steel hardware. Reinforcing steel should 
be fully protected from corrosion by the 
surrounding material (masonry, mortar, 
grout, or concrete). Use galvanized 
or epoxy-coated reinforcing steel 
in situations where the potential for 
corrosion is high.

 Avoid joining dissimilar metals, 
especially those with high galvanic 
potential.

 Avoid using certain wood preservatives 
in direct contact with galvanized metal. 
Verify that wood treatment is suitable 
for use with galvanized metal, or use 
stainless steel.

 Metal-plate-connected trusses should 
not be exposed to the elements. Truss 
joints near vent openings are more 
susceptible to corrosion and may 
require increased corrosion protection.

Note: Although more resistant than other 
metals, stainless steel is still subject to 
corrosion. 

In conjunction with the rain-screen principle, 
it is desirable to avoid using sealant 
as the first or only line of defense against 
water infiltration. When sealant joints are 
exposed, obtaining long-lasting watertight 
performance is difficult because of the 
complexities of sealant joint design and installation 
(see Figure 3-40, which shows the sealant protected by a 
removable stop).

Step 4: Peer Review

If the design teams wind expertise and experience is limited, 
wind design input and/or peer review should be sought from a 
qualified individual. The design input or peer review could be arranged 
for the entire building, or for specific components such as 
the roof or glazing systems, that are critical and beyond the design 
teams expertise. 

Regardless of the design teams expertise and experience, peer review 
should be considered when a critical facility:

m Is located in an area where the basic wind speed is greater 
than 90 mph (peak gust)particularly if the facility is a 
hospital, or will be used as an EOC or hurricane shelter.
m Will incorporate a tornado shelter.
3.3.1.3 Construction Contract Administration

After a suitable design is complete, the design team should endeavor 
to ensure that the design intent is achieved during 
construction. The key elements of construction contract administration 
are submittal reviews and field observations, as 
discussed below.

Further information on the rain-screen 
principle can be found in the National 
Institute of Building Sciences Building 
Envelope Design Guide (www.wbdg.org/
design/envelope.php).

Submittal reviews: The specifications need to stipulate the submittal 
requirements. This includes specifying what systems require 
submittals (e.g., windows) and test data (where appropriate). Each 
submittal should demonstrate the development of a load path 
through the system and into its supporting element. For example, 
a window submittal should show that the glazing has sufficient 
strength, its attachment to the frame is adequate, and the attachment 
of the frame to the wall is adequate.

During submittal review, it is important for the designer of record 
to be diligent in ensuring that all required documents are 
submitted and that they include the necessary information. The 
submittal information needs to be thoroughly checked to ensure 
its validity. For example, if an approved method used to 
demonstrate compliance with the design load has been altered 
or incorrectly applied, the test data should be rejected, unless 
the contractor can demonstrate the test method was suitable. 
Similarly, if a new test method has been developed by a manufacturer 
or the contractor, the contractor should demonstrate 
its suitability.

Field observations: It is recommended that the design team analyze 
the design to determine which elements are critical to ensuring 
high-wind performance. The analysis should include the structural 
system and exterior-mounted electrical equipment, but it 
should focus on the building envelope and exterior-mounted 
mechanical and communications equipment. After determining 
the list of critical elements to be observed, observation frequency 
and the need for special inspections by an inspection firm 
should be determined. Observation frequency and the need for 
special inspections will depend on the results of the risk assessment 
described in Section 3.2.2, complexity of the facility, and 
the competency of the general contractor, subcontractors, and 
suppliers.

See Section 3.4 for additional information pertaining to critical facilities 
located in hurricane-prone regions.

3.3.1.4 Post-Occupancy Inspections, Periodic Maintenance, Repair, and 
Replacement

The design team should advise the building owner of the importance 
of periodic inspections, maintenance, and timely repair. It 
is important for the building owner to understand that a facilitys 
wind resistance will degrade over time due to exposure to weather 
unless it is regularly maintained and repaired. The goal should 
be to repair or replace items before they fail in a storm. This 
approach is less expensive than waiting for failure and then repairing 
the failed components and consequential damage. 

The building envelope and exterior-mounted equipment should 
be inspected once a year by persons knowledgeable of the 
systems/materials they are inspecting. Items that require maintenance, 
repair, or replacement should be documented and 
scheduled for work. For example, the deterioration of glazing is 
often overlooked. After several years of exposure, scratches and 
chips can become extensive enough to weaken the glazing. Also, if 
an engineered film was surface-applied to glazing for wind-borne 
debris protection, the film should be periodically inspected and 
replaced before it is no longer effective.

A special inspection is recommended following unusually high 
winds. The purpose of the inspection is to assess whether the 
strong storm caused damage that needs to be repaired to maintain 
building strength and integrity. In addition to inspecting 
for obvious signs of damage, the inspector should determine if 
cracks or other openings have developed that may allow water infiltration, 
which could lead to corrosion or dry rot of concealed 
components.

See Section 3.4 for additional information pertaining to buildings 
located in hurricane-prone regions.

3.3.2 Structural Systems

Based on post-storm damage evaluations, with the exception of 
strong and violent tornado events, the structural systems (i.e., 
MWFRS and structural components such as roof decking) of critical 
facilities have typically performed quite well during design 
wind events. There have, however, been notable exceptions; in 
these cases, the most common problem has been blow-off of the 
roof deck, but instances of collapse have also been documented 
(see Figure 3-22). The structural problems have primarily been 
caused by lack of an adequate load path, with connection failure 
being a common occurrence. Problems have also been caused by 
reduced structural capacity due to termites, workmanship errors 
(commonly associated with steel decks attached by puddle welds), 
and limited uplift resistance of deck connections in roof perimeters 
and corners (due to lack of code-required enhancement in 
older editions of the model codes).

With the exception of strong and violent tornado events, structural 
systems designed and constructed in accordance with the 
IBC should typically offer adequate wind resistance, provided attention 
was given to load path continuity and to the durability 
of building materials (with respect to corrosion and termites). 
However, the greatest reliability is offered by cast-in-place concrete. 
There are no known reports of any cast-in-place concrete 
buildings experiencing a significant structural problem during 
wind events, including the strongest hurricanes (Category 5) 
and tornadoes (F5). 

Figure 3-22: Collapse of a large portion of a new pre-engineered 
metal building used as a shelter for approximately 
1,400 people. Hurricane Charley (Florida, 2004)

The following design parameters are recommended for structural 
systems (see Section 3.4.2 for critical facilities located in hurricane-
prone regions):

 If a pre-engineered metal building is being contemplated, 
special steps should be taken to ensure the structure has more 
redundancy than is typically the case with pre-engineered buildings.
7 Steps should be taken to ensure the structure is not vulnerable 
to progressive collapse in the event a primary bent (steel 
moment frame) is compromised or bracing components fail.
 Exterior load-bearing walls of masonry or precast concrete 
should be designed to have sufficient strength to resist external 
and internal loading when analyzed as C&C. CMU walls should 
have vertical and horizontal reinforcing and grout to resist wind 
loads. The connections of precast concrete wall panels should 
be designed to have sufficient strength to resist wind loads.
 For roof decks, concrete, steel, plywood, or oriented strand 
board (OSB) is recommended. 
m For steel roof decks, it is recommended that a screw 
attachment be specified, rather than puddle welds or 
powder-driven pins. Screws are more reliable and much less 
susceptible to workmanship problems. Figure 3-23 shows 
decking that was attached with puddle welds. At most of the 
welds, there was only superficial bonding of the metal deck to 
the joist, as illustrated by this example. Only a small portion of 
the deck near the center of the weld area (as delineated by the 
circle) was well fused to the joist. Figures 3-24 and 3-25 show 
problems with acoustical decking attached with powder-driven 
pins. The pin shown on the left of Figure 3-25 is properly 
seated. However, the pin at the right did not penetrate far 
enough into the steel joist below. 
 For attaching wood sheathed roof decks, screws, ring-shank, 
or screw-shank nails are recommended in the corner regions 
of the roof. Where the basic wind speed is greater than 90 
mph, these types of fasteners are also recommended for the 
perimeter regions of the roof.

7. The structural system of pre-engineered metal buildings is composed of rigid 
steel frames, secondary members (including roof purlins and wall 
girts made of Z- or C-shaped members) and bracing.

 For precast concrete decks it is recommended that the deck 
connections be designed to resist the design uplift loads 
because the deck dead load itself is often insufficient to resist 
the uplift. The deck in Figure 3-26 had bolts to provide uplift 
resistance; however, anchor plates and nuts had not been 
installed. Without the anchor plates, the dead load of the deck 
was insufficient to resist the wind uplift load.

Figure 3-23: View looking down at the top of a steel joist after the metal 
decking blew away. Only a small portion of 
the deck was well fused to the joist (circled area). 
Tornado (Oklahoma, 1999)

Figure 3-25: View looking along a sidelap of a deck attached 
with powder-driven pins. The right pin does not provide adequate uplift and 
shear resistance.

Figure 3-24: Looking down at a sidelap of a deck attached 
with powder-driven pins. The washer at the top pin 
blew through the deck.

 For precast Tee decks, it is recommended that the reinforcing 
be designed to accommodate the uplift loads in addition 
to the gravity loads. Otherwise, large uplift forces can cause 
member failure due to the Tees own pre-stress forces after 
the uplift load exceeds the dead load of the Tee. This type 
of failure occurred at one of the roof panels shown in Figure 
3-27, where a panel lifted because of the combined effects of 
wind uplift and pre-tension. Also, because the connections 
between the roof and wall panels provided very little uplift 
load resistance, several other roof and wall panels collapsed.

Figure 3-26: Portions of this waffled 
precast concrete roof deck were blown off. Typhoon 
Paka (Guam, 1997)

Figure 3-27: Twin-Tee roof panel lifted as a result of the combined 
effects of wind uplift and pre-tension. Tornado 
(Missouri, May 2003)

 For buildings that have mechanically attached single-ply or 
modified bitumen membranes, designers should refer to 
the decking recommendations presented in the Wind Design 
Guide for Mechanically Attached Flexible Membrane Roofs, B1049 
(National Research Council of Canada, 2005).
 If an FMG-rated roof assembly is specified, the roof deck also 
needs to comply with the FMG criteria.
 Walkway and entrance canopies are often damaged during 
high winds (see Figure 3-28). Wind-borne debris from 
damaged canopies can damage nearby buildings and injure 
people, hence these elements should also receive design and 
construction attention. 

Figure 3-28: The destroyed walkway canopy in front of a school 
became wind-borne debris. Hurricane Ivan (Florida, 2004)

ASCE 7-05 provides pressure coefficients for open canopies of various slopes 
(referred to as free roofs in ASCE 7). The free roof figures for MWFRS in ASCE 
7-05 (Figures 6-18A to 6-18D) include two load cases, Case A and Case B. While 
there is no discussion describing the two load cases, they pertain to 
fluctuating loads and are intended to represent upper and lower limits of 
instantaneous wind pressures. Loads for both cases must be calculated to 
determine the critical loads. Figures 6-18A to 6-18C are for a wind direction 
normal to the ridge. For wind direction parallel to the ridge, use Figure 6-18D 
in ASCE 7-05.

3.3.3 Building Envelope 

The following section highlights the design considerations for 
building envelope components that have historically sustained the 
greatest and most frequent damage in high winds.

3.3.3.1 Exterior Doors

This section addresses primary and secondary 
egress doors, sectional (garage) doors, and 
rolling doors. Although blow-off of personnel 
doors is uncommon, it can cause serious 
problems (see Figure 3-29). Blown-off doors 
allow entrance of rain and tumbling doors 
can damage buildings and cause injuries. 

Blown off sectional and rolling doors are quite common. These 
failures are typically caused by the use of door and track assemblies 
that have insufficient wind resistance, or by inadequate 
attachment of the tracks or nailers to the wall. At the relatively 
new fire station shown in Figure 3-30, two 
of the windward doors were pushed out of 
their tracks. At the third door, the track was 
pushed out from the nailer. With the collapse 
of these doors, the apparatus bay was 
fully pressurized. Because the connections 
between the trusses and the beam were too 
weak to accommodate the uplift load, the 
entire roof structure over the apparatus bay 
blew off. 

See Section 3.4.3.1 for critical facilities located in hurricane-
prone regions.

Loads and Resistance

The IBC requires that the door assembly (i.e., door, hardware, 
frame, and frame attachment to the wall) be of sufficient strength 
to resist the positive and negative design wind pressure. Design 
professionals should require that doors comply with wind 
load testing in accordance with ASTM E 1233. Design professionals should also 
specify the attachment 
of the door frame to the wall (e.g., type, 
size, spacing, and edge distance of frame 
fasteners). For sectional and rolling doors attached 
to wood nailers, design professionals 
should also specify the attachment of the 
nailer to the wall.

For further general information on doors, 
see Fenestration Systems in the National 
Institute of Building Sciences Building 
Envelope Design Guide (www.wbdg.org/
design/envelope.php)

Particular attention should be given to 
the design and installation of fire station 
apparatus bay doors which have been 
blown-in or blown-out frequently (see 
Figure 3-30). If doors blow inward, they 
can damage fire engines and ambulances 
and impair emergency response. 

For design guidance on attachment of door 
frames, see Technical Data Sheet #161, 
Connecting Garage Door Jambs to Building 
Framing, published by the Door & Access 
Systems Manufacturers Association, 2003 
(available at www.dasma.com).

Figure 3-29: Door on a hospital penthouse blown off its 
hinges during Hurricane Katrina (Mississippi, 2005)


Figure 3-30: The roof structure over the apparatus bay blew 
off following the failure of sectional doors. Hurricane 
Charley (Florida, 2004)

Water Infiltration

Heavy rain that accompanies high winds (e.g., thunderstorms, 
tropical storms, and hurricanes) can cause significant wind-
driven water infiltration problems. The magnitude of the 
problem increases with the wind speed. Leakage can occur between 
the door and its frame, the frame 
and the wall, and between the threshold 
and the door. When wind speeds approach 
120 mph, some leakage should be anticipated 
because of the very high wind 
pressures and numerous opportunities for 
leakage path development. 

The following recommendations should be considered to minimize 
infiltration around exterior doors. 

Vestibule: Adding a vestibule allows both the inner and outer doors 
to be equipped with weatherstripping. The vestibule can be designed 
with water-resistant finishes (e.g., concrete or tile) and the 
floor can be equipped with a drain. In addition, installing exterior 
threshold trench drains can be helpful (openings must be small 
enough to avoid trapping high-heeled shoes). Note that trench 
drains do not eliminate the problem, since water can still penetrate 
at door edges.

Door swing: Out-swinging doors have weatherstripping on the interior 
side of the door, where it is less susceptible to degradation, 
which is an advantage when compared to 
in-swinging doors. Some interlocking weatherstripping 
assemblies are available for 
out-swinging doors.

The successful integration of the door frame 
and the wall is a special challenge when 
designing doors. See Section 3.3.3.2 for discussion 
of this juncture. 

ASTM E 2112 provides information pertaining to the installation 
of doors, including the use of sill pan flashings with end dams and 
rear legs (see Figure 3-31). It is recommended that designers use 
ASTM E 2112 as a design resource.

Where corrosion is problematic, anodized 
aluminum or galvanized doors and frames, 
and stainless steel frame anchors and 
hardware are recommended. 

For primary swinging entry/exit doors, 
exit door hardware is recommended to 
minimize the possibility of the doors being 
pulled open by wind suction. Exit hardware 
with top and bottom rods is more secure 
than exit hardware that latches at the jamb.

Weatherstripping

A variety of pre-manufactured weatherstripping components is 
available, including drips, door shoes and bottoms, thresholds, 
and jamb/head weatherstripping. 

Drips: These are intended to shed water away from the opening between 
the frame and the door head, and the opening between the 
door bottom and the threshold (see Figures 3-32 and 3-33). Alternatively, 
a door sweep can be specified (see Figure 3-33). For 
high-traffic doors, periodic replacement of the neoprene components 
will be necessary.

Figure 3-31: Door sill pan flashing with end dams, rear leg, 
and turned-down front leg 

Figure 3-33: Door shoe with drip and vinyl seal (left). 
Neoprene door bottom sweep (right)

Figure 3-32: Drip at door head and drip with hook at head

Door shoes and bottoms: These are intended to minimize the gap 
between the door and the threshold. Figure 3-33 illustrates a door 
shoe that incorporates a drip. Figure 3-34 illustrates an automatic 
door bottom. Door bottoms can be surface-mounted or mortised. 
For high-traffic doors, periodic replacement of the neoprene components 
will be necessary.

Thresholds: These are available to suit a variety of conditions. 
Thresholds with high (e.g., 1-inch) vertical offsets offer enhanced 
resistance to wind-driven water infiltration. However, 
the offset is limited where the thresholds are required to comply 
with the Americans with Disabilities Act (ADA), or at high-traffic 
doors. At other doors, high offsets are preferred. 

Thresholds can be interlocked with the door (see Figure 3-
35), or thresholds can have a stop and seal (see Figure 3-36). In 
some instances, the threshold is set directly on the floor. Where 
this is appropriate, setting the threshold in butyl sealant is recommended 
to avoid water infiltration between the threshold 
and the floor. In other instances, the threshold is set on a pan 
flashing, as previously discussed in this section. If the threshold 
has weep holes, specify that the weep holes not be obstructed 
(see Figure 3-35). 

Figure 3-34: Automatic door bottom

Figure 3-36: Threshold with stop and seal

Figure 3-35: Interlocking threshold with drain pan

Adjustable jamb/head weatherstripping: This type of weatherstripping 
is recommended because the wide sponge neoprene offers 
good contact with the door (see Figure 3-37). The adjustment 
feature also helps to ensure good contact, provided the proper adjustment 
is maintained.

Meeting stile: At the meeting stile of pairs of doors, an overlapping 
astragal weatherstripping offers greater protection than weatherstripping 
that does not overlap. 

3.3.3.2 Windows and Skylights

This section addresses general design considerations for exterior 
windows and skylights in critical facilities. For additional information 
on windows and skylights in critical facilities located in 
hurricane-prone regions, see Section 3.4.3.2, and for those in tornado-
prone regions, see Section 3.5.

Loads and Resistance

The IBC requires that windows, curtain walls, 
and skylight assemblies (i.e., the glazing, 
frame, and frame attachment to the wall 
or roof) have sufficient strength to resist 
the positive and negative design wind pressure 
(see Figure 3-38). Design professionals 
should specify that these assemblies comply 
with wind load testing in accordance with ASTM E 1233. It is 
important to specify an adequate load path and to check its continuity 
during submittal review.

Water Infiltration 

Heavy rain accompanied by high winds can cause wind-driven 
water infiltration problems. The magnitude of the problem 
increases with the wind speed. Leakage can occur at the glazing/
frame interface, the frame itself, or between the frame and wall. 
When the basic wind speed is greater than 120 mph, because of 
the very high design wind pressures and numerous opportunities 
for leakage path development, some leakage should be anticipated 
when the design wind speed conditions are approached.

Figure 3-37: Adjustable jamb/head weatherstripping

For further general information on windows, 
see the National Institute of Building 
Sciences Building Envelope Design Guide 
(www.wbdg.org/design/envelope.php).

The successful integration of windows and curtain walls into exterior 
walls is a challenge in protecting against water infiltration. 
To the extent possible when detailing the interface between 
the wall and the window or curtain wall units, designers should 
rely on sealants as the secondary line of defense 
against water infiltration, rather than 
making the sealant the primary protection. 
If a sealant joint is the first line of defense, a 
second line of defense should be designed to 
intercept and drain water that drives past the 
sealant joint.

When designing joints between walls and windows and curtain wall 
units, consider the shape of the sealant joint (i.e., a square joint 
is typically preferred) and the type of sealant 
to be specified. The sealant joint should be 
designed to enable the sealant to bond on 
only two opposing surfaces (i.e., a backer rod 
or bond-breaker tape should be specified). 
Butyl is recommended as a sealant for concealed 
joints, and polyurethane for exposed 
joints. During installation, cleanliness of the 
sealant substrate is important (particularly if 
polyurethane or silicone sealants are specified), 
as is the tooling of the sealant. ASTM 

Figure 3-38: Two complete windows, including frames, blew out as a result of an 
inadequate number of fasteners. Typhoon Paka (Guam, 1997)

Where corrosion is a problem, use of 
anodized aluminum or stainless steel 
frames and stainless steel frame anchors 
and screws are recommended.

The maximum test pressure used in the 
current ASTM test standard for evaluating 
resistance of window units to wind-driven 
rain is well below design wind pressures. 
Therefore, units that demonstrate adequate 
wind-driven rain resistance during testing 
may experience leakage during actual 
wind events.

E 2112 provides guidance on the design of 
sealant joints, as well as other information 
pertaining to the installation of windows, including 
the use of sill pan flashings with end 
dams and rear legs (see Figure 3-39). Windows 
that do not have nailing flanges should 
typically be installed over a pan flashing. It 
is recommended that designers use ASTM E 
2112 as a design resource. 

Sealant joints can be protected with a removable 
stop, as illustrated in Figure 3-40. 
The stop protects the sealant from direct 
exposure to the weather and reduces the 
possibility of wind-driven rain penetration. 

Where water infiltration protection is particularly 
demanding and important, it is recommended that onsite 
water infiltration testing in accordance with ASTM E 1105 be 
specified.


Figure 3-39: View of a typical window sill pan flashing with 
end dams and rear legs 
Source: ASTM E 2112

Figure 3-40: Protecting sealant with a stop retards weathering 
and reduces the exposure to wind-driven rain.

3.3.3.3 Non-Load-Bearing Walls, Wall Coverings, and Soffits

This section addresses exterior non-load-bearing walls, exterior 
wall coverings, and soffits, as well as the underside of elevated 
floors, and provides guidance for interior 
non-load-bearing masonry walls. See Section 
3.4.3.3 for additional information pertaining 
to critical facilities located in hurricane-
prone regions, and Section 3.5 for additional 
information pertaining to critical facilities located 
in tornado-prone regions. 

Loads and Resistance

The IBC requires that soffits, exterior non-load-bearing walls, and 
wall coverings have sufficient strength to resist the positive and 
negative design wind pressures.

For further general information on non-
load-bearing walls and wall coverings, see 
the National Institute of Building Sciences 
Building Envelope Design Guide 
(www.wbdg.org/design/envelope.php).

To ensure the continuity of elevator service, elevator penthouse walls must 
possess adequate 
wind and water resistance. If the walls blow away or water leaks through the 
wall system, the 
elevator controls and/or motors can be destroyed. Loss of elevators may 
critically affect facility 
operations because the restoration can take weeks even with expedited work (see 
Figure 3-41).

Figure 3-41: The wall covering blew off the penthouse at this 
hospital complex allowing rainwater to destroy 
the elevator controls. Hurricane Ivan (Florida, 2004)

Soffits: Depending on the wind direction, 
soffits can experience either positive or negative 
pressure. Besides the cost of repairing 
the damaged soffits, wind-borne soffit debris 
can cause property damage and injuries 
(see Figure 3-42). Failed soffits may also provide 
a convenient path for wind-driven rain 
to enter the building. Storm-damage research 
has shown that water blown into attic 
spaces after the loss of soffits caused significant 
damage and the collapse of ceilings. 
At the relatively new fire station shown in 
Figure 3-43, essentially all of the perforated 
aluminum soffit was blown away. Wind-
driven water entered the attic and saturated the batt insulation, 
which caused the ceiling boards to collapse. After the storm, the 
fire station was evacuated solely because of this damage. Even 
in instances where soffits remain in place, water can penetrate 
through soffit vents and cause damage. At this time, there are no 
known specific test standards or design guidelines to help design 
wind- and water-resistant soffits and soffit vents.

Where corrosion is a problem, stainless 
steel fasteners are recommended for wall 
and soffit systems. For other components 
(e.g., furring, blocking, struts, and hangers), 
nonferrous components (such as wood), 
stainless steel, or steel with a minimum of 
G-90 hot-dipped galvanized coating are 
recommended. Additionally, access panels 
are recommended so components within 
soffit cavities can be periodically inspected 
for corrosion or dry rot.

Figure 3-42: This suspended metal 
soffit was not designed for upward-acting wind 
pressure. Typhoon Paka (Guam, 1997)

Exterior non-load-bearing masonry walls: Particular care 
should be given to the design and construction of 
exterior non-load-bearing masonry walls. Although 
these walls are not intended to carry gravity loads, 
they should be designed to resist the external and 
internal loading for components and cladding in order to avoid 
collapse. When these types of walls collapse, they represent a severe 
risk to life because of their great weight (see Figure 3-15). 

Interior non-load-bearing masonry walls: Special consideration 
should also be given to interior non-load-bearing masonry walls. 
Although these walls are not required by building codes to be designed 
to resist wind loads, if the exterior glazing is broken, or 
the exterior doors are blown away, the interior walls could be subjected 
to significant load as the building rapidly becomes fully 
pressurized. To avoid casualties, it is recommended that interior 
non-load-bearing masonry walls adjacent to occupied areas be designed 
to accommodate loads exerted by a design wind event, 
using the partially enclosed pressure coefficient (see Figure 3-44). 
By doing so, wall collapse may be prevented if the building envelope 
is breached. This recommendation is applicable to critical 
facilities located in areas with a basic wind speed greater than 120 
mph, those used for hurricane shelters, and to critical facilities in 
tornado-prone regions that do not have shelter space designed in 
accordance with FEMA 361.

Figure 3-43: This fire station was 
abandoned after Hurricane Charley 
because of soffit failure. (Florida, 2004)
Wall Coverings

There are a variety of exterior wall coverings. Brick veneer, exterior 
insulation finish systems (EIFS), stucco, metal wall panels, and 
aluminum and vinyl siding have often exhibited poor wind performance. 
Veneers (such as ceramic tile and stucco) over concrete, 
stone veneer, and cement-fiber panels and siding have also blown 
off. Wood siding and panels rarely blow off. Although tilt-up precast 
walls have failed during wind storms, precast wall panels 
attached to steel or concrete framed buildings typically offer excellent 
wind performance.

Brick veneer:8 Brick veneer is frequently blown off walls during 
high winds. When brick veneer fails, wind-driven water can enter 
and damage buildings, and building occupants can be vulnerable 
to injury from wind-borne debris (particularly if the walls are 
sheathed with plastic foam insulation or wood fiberboard in lieu 
of wood panels). Pedestrians in the vicinity of damaged walls can 
also be vulnerable to injury from falling bricks (see Figure 3-45). 
Common failure modes include tie (anchor) fastener pull-out 
(see Figure 3-46), failure of masons to embed ties into the mortar 
(Figure 3-47), poor bonding between ties and mortar, a mortar of 
poor quality, and tie corrosion.

Figure 3-44: The red arrows show the original location of 
a CMU wall that nearly collapsed following a 
rolling door failure. Hurricane Charley (Florida, 
2004)

8. The brick veneer discussion is from Attachment of Brick Veneer in High-Wind 
Regions - Hurricane Katrina Recovery Advisory (FEMA, 
December 2005). 

Figure 3-45: The brick veneer failure 
on this building was attributed to tie corrosion. 
Hurricane Ivan (Florida, 2004)

Figure 3-46: This tie remained embedded in the mortar 
joint while the smooth-shank nail pulled from the stud.

Ties are often installed before brick laying begins. When this is 
done, ties are often improperly placed above or below the mortar 
joints. When misaligned, the ties must be angled up or down to 
be embedded into the mortar joints (Figure 3-48). Misalignment 
not only reduces the embedment depth, but also reduces the 
effectiveness of the ties, because wind forces do not act in parallel 
direction to the ties.

Corrugated ties typically used in residential and nursing home veneer 
construction provide little resistance to compressive loads. 
The use of compression struts would likely be beneficial, but off-
the-shelf devices do not currently exist. Two-piece adjustable ties 
(Figure 3-49) provide significantly greater compressive strength 
than corrugated ties.

Figure 3-47: These four ties were never embedded into the 
mortar joint. 

Figure 3-48: Misalignment of the tie reduces the embedment 
and promotes veneer failure.

The following Brick Industry Association (BIA) technical notes 
provide guidance on brick veneer: Technical Notes 28: Anchored 
Brick Veneer, Wood Frame Construction (2002); Technical Notes 
28B: Brick Veneer/Steel Stud Walls (2005); and Technical Notes 44B: 
Wall Ties (2003) (available online at www.bia.org). These technical 
notes provide attachment recommendations; however, they are 
not specific for high-wind regions. To enhance wind performance 
of brick veneer, the following are recommended: 

m Calculate wind loads and determine tie spacing in accordance 
with the latest edition of the Building Code Requirements for 
Masonry Structures, ACI 530/ASCE 5/TMS 402 (ACI 530, 
1996)). A stud spacing of 16 inches on center is recommended 
so that ties can be anchored at this spacing.
m Ring-shank nails are recommended in lieu of smooth-shank nails 
for wood studs. A minimum embedment of 2 inches is suggested.
m For use with wood studs, two-piece adjustable ties are 
recommended. However, where corrugated steel ties are 
used, they should be 22-gauge minimum, 7/8-inch wide by 6-
inch long, and comply with ASTM A 1008, with a zinc coating 
complying with ASTM A 153 Class B2. For ties used with steel 
studs, see BIA Technical Notes 28B, Brick Veneer/Steel Stud Walls. 
Stainless steel ties should be used for both wood and steel 
studs in areas within 3,000 feet of the coast.

Figure 3-49: Examples of two-piece adjustable ties

 Install ties as the brick is laid so that the ties are properly 
aligned with the mortar joints.
 Locate ties within 8 inches of door and window openings, and 
within 12 inches of the top of veneer sections.
 Although corrugated ties are not recommended, if used, bend 
the ties at a 90-degree angle at the nail head to minimize tie 
flexing when the ties are loaded in tension or compression 
(Figure 3-50).
 Embed ties in joints so that the mortar completely 
encapsulates the ties. Embed a minimum of 1 inches into 
the bed joint, with a minimum mortar cover of 5/8-inch to the 
outside face of the wall (see Figure 3-51). 

Figure 3-50: Bend ties at nail heads

Figure 3-51: Tie embedment 

To avoid water leaking into the building, it is important that weep 
holes be adequately spaced and not be blocked during brick installation, 
and that through-wall flashings be properly designed 
and installed. At the hospital shown in Figure 3-52, water leaked 
into the building along the base of many of the brick veneer walls. 
When high winds accompany heavy rain, a substantial amount of 
water can be blown into the wall cavity. 

EIFS: Figure 3-53 shows typical EIFS assemblies. Figures 3-41, 3-54, 
and 4-6 show EIFS blow-off. In these cases, the molded expanded 
polystyrene (MEPS) was attached to gypsum board, which in turn 
was attached to metal studs. The gypsum board detached from 
the studs, which is a common EIFS failure. When the gypsum 
board on the exterior side of the studs is blown away, it is common 
for gypsum board on the interior side to also be blown off. The 
opening allows the building to become fully pressurized and allows 
the entrance of wind-driven rain. Other common types of failure 
include wall framing failure, separation of the MEPS from its substrate, 
and separation of the synthetic stucco from the MEPS. 

Figure 3-52: Water leaked inside along 
the base of the brick veneer walls. Hurricane 
Katrina (Louisiana, 2005) 

At the hospital shown in Figure 3-55, the EIFS was applied over a 
concrete wall. The MEPS debonded from the concrete. In general, 
a concrete substrate prevents wind and water from entering a 
building, but if the EIFS debonds from the concrete, EIFS debris 
can break unprotected glazing. 

Figure 3-53: Typical EIFS assemblies

Wind-borne EIFS debris can be devastating to unprotected 
glazing. At the hospital shown in Figure 3-56, the hospitals original 
concrete wall panels had been furred with metal hat channels 
and covered with EIFS. In a large corner area, the EIFS and 
gypsum board substrate blew off the hat channels and broke a 
large number of windows in the multi-story connecting walkway 
between the hospital and the medical office building (MOB). The 
EIFS debris also broke a large number of windows in the MOB 
(see Figure 3-56). Glass shards from the MOB punctured the roof 
membrane over the dialysis unit. The costly damage resulted in 
loss of several rooms in the MOB and hampered functioning of 
the hospital complex.

Figure 3-54: EIFS blow-off at building 
corner. In places, metal fascia was also blown in. 
Tornado (Oklahoma, 1999)

Figure 3-55: EIFS blown off a cast-in-
place concrete wall. Note the damaged rooftop 
ductwork. Hurricane Ivan (Florida, 2004)

Reliable wind performance of EIFS is very demanding 
on the designer and installer, as well 
as the maintenance of EIFS and associated 
sealant joints in order to minimize the reduction 
of EIFS wind resistance due to water 
infiltration. It is strongly recommended that 
EIFS be designed with a drainage system that 
allows the dissipation of water leaks. For further 
information on EIFS performance during 
high winds and design guidance see FEMA 489 
and 549.

Another issue associated with EIFS is the potential for judgment errors. 
EIFS applied over studs is sometimes mistaken for a concrete 
wall, which may lead people to seek shelter behind it. However, instead 
of being protected by several inches of concrete, only two 
layers of gypsum board (i.e., one layer on each side of the studs) 
and a layer of MEPS separate the occupants from the impact of 
wind-borne debris that can easily penetrate such a wall and cause 
injury.

Figure 3-56:EIFS debris blown off 
the hospital building in the background (red 
square) broke numerous windows in the MOB in 
the foreground. Hurricane Ivan (Florida, 2004) 

Stucco: Wind performance of traditional stucco walls is similar to 
the performance of EIFS, as shown in Figure 3-57. In several areas 
the metal stud system failed; in other areas the gypsum sheathing 
blew off the studs; and in other areas, the metal lath blew off the 
gypsum sheathing. The failure shown in Figure 3-57 illustrates the 
importance of designing and constructing wall framing (including 
attachment of stud tracks to the building and attachment of the 
studs to the tracks) to resist the design wind loads.

Metal wall panels: Wind performance of metal wall panels is highly 
variable. Performance depends on the strength of the specified 
panel (which is a function of material and thickness, panel profile, 
panel width, and whether the panel is a composite) and the adequacy 
of the attachment (which can either be by concealed clips 
or exposed fasteners). Excessive spacing between clips/fasteners 
is the most common problem. Clip/fastener spacing should be 
specified, along with the specific type and size of fastener. Figures 
3-14 and 3-58 illustrate metal wall panel problems. At the school 
shown in Figure 3-58 (which was being used as a shelter), the 
metal panels were attached with concealed fasteners. The panels 
unlatched at the standing seams. In addition to generating wind-
borne debris, loss of panels allowed wind-driven rain to enter the 
building.

Figure 3-57: The stucco wall failure was 
caused by inadequate attachment between 
the stud tracks and the buildings structure. 
Hurricane Ivan (Florida, 2004)

To minimize water infiltration at metal wall panel joints, it is recommended 
that sealant tape be specified at sidelaps when the 
basic wind speed is in excess of 90 mph. However, endlaps should 
be left unsealed so that moisture behind the panels can be wicked 
away. Endlaps should be a minimum of 3 inches (4 inches where 
the basic wind speed is greater than 120 mph) to avoid wind-
driven rain infiltration. At the base of the 
wall, a 3-inch (4-inch) flashing should also be 
detailed, or the panels should be detailed to 
overlap with the slab or other components by 
a minimum of 3 inches (4 inches).

Vinyl siding: Vinyl siding blow-off is typically 
caused by nails spaced too far apart and/or 
the use of vinyl siding that has inadequate 
wind resistance. Vinyl siding is available 
with enhanced wind resistance features, 
such as an enhanced nailing hem, greater 
interlocking area, and greater thickness. 

Figure 3-58: The loss of metal wall 
panels allowed a substantial amount of wind-
driven rain to penetrate this building. Hurricane 
Ivan (Florida, 2004) 

The Vinyl Siding Institute (VSI) sponsors 
a Certified Installer Program that 
recognizes individuals with at least 1 
year of experience who can demonstrate 
proper vinyl siding application. If vinyl 
siding is specified, design professionals 
should consider specifying that the siding 
contractor be a VSI-certified installer. For 
further information on this program, see 
www.vinylsiding.org.

Secondary line of protection: Almost all wall coverings permit the 
passage of some water past the exterior surface of the covering, 
particularly when the rain is wind-driven. For this reason, most 
wall coverings should be considered water-shedding, rather than 
waterproofing coverings. To avoid moisture-related problems, 
it is recommended that a secondary line of protection with a 
moisture barrier (such as housewrap or asphalt-saturated felt) 
and flashings around door and window openings be provided. 
Designers should specify that horizontal laps of the moisture 
barrier be installed so that water is allowed to drain from the 
wall (i.e., the top sheet should lap over the bottom sheet so that 
water running down the sheets remains on their outer surface). 
The bottom of the moisture barrier needs to be designed to 
allow drainage. Had the metal wall panels shown in Figure 3-58 
been applied over a moisture barrier and sheathing, the amount 
of water entering the building would have likely been eliminated 
or greatly reduced. 

In areas that experience frequent wind-driven rain, incorporating 
a rain screen design, by installing vertical furring strips 
between the moisture barrier and siding materials, will facilitate 
drainage of water from the space between the moisture barrier 
and backside of the siding. In areas that frequently experience 
strong winds, enhanced flashing is recommended. Enhancements 
include use of flashings that have extra-long flanges, 
and the use of sealant and tapes. Flashing design should recognize 
that wind-driven water could be pushed up vertically. 
The height to which water can be pushed increases with wind 
speed. Water can also migrate vertically and horizontally by capillary 
action between layers of materials (e.g., between a flashing 
flange and housewrap). Use of a rain screen design, in conjunction 
with enhanced flashing design, is recommended in areas 
that frequently experience wind-driven rain or strong winds. It 
is recommended that designers attempt to determine what type 
of flashing details have successfully been used in the area where 
the facility will be constructed.

Underside of Elevated Floors

If sheathing is applied to the underside of joists or trusses elevated 
on piles (e.g., to protect insulation installed between the 
joists/trusses), its attachment should be specified in order to 
avoid blow-off. Stainless steel or hot-dip galvanized nails or screws 
are recommended. Since ASCE 7 does not provide guidance for 
load determination, professional judgment in specifying attachment 
is needed.

3.3.3.4 Roof Systems

Because roof covering damage has historically 
been the most frequent and the costliest 
type of wind damage, special attention needs 
to be given to roof system design. See Section 
3.4.3.4 for additional information pertaining 
to critical facilities located in hurricane-
prone regions, and Section 3.5 for critical 
facilities located in tornado-prone regions.

Code Requirements 

The IBC requires the load resistance of the roof assembly to 
be evaluated by one of the test methods listed in IBCs Chapter 
15. Design professionals are cautioned that designs that deviate 
from the tested assembly (either with material substitutions or 
change in thickness or arrangement) may adversely affect the 
wind performance of the assembly. The IBC does not specify a 
minimum safety factor. However, for the roof system, a safety 
factor of 2 is recommended. To apply the safety factor, divide 
the test load by 2 to determine the allowable design load. 
Conversely, multiply the design load by 2 to determine the minimum 
required test resistance.

For structural metal panel systems, the IBC requires test methods 
UL 580 or ASTM E 1592. It is recommended 
that design professionals specify use of E 
1592, because it gives a better representation 
of the systems uplift performance capability. 

For further general information on roof 
systems, see the National Institute of 
Building Sciences Building Envelope 
Design Guide (www.wbdg.org/design/
envelope.php).

The roof of the elevator penthouse must 
possess adequate wind and water 
resistance to ensure continuity of elevator 
service. It is recommended that a 
secondary roof membrane, as discussed 
in Section 3.3.3.3, be specified over the 
elevator penthouse roof deck. 

Load Resistance 

Specifying the load resistance is commonly done by specifying a 
Factory Mutual Research (FMR) rating, such as FM 1-75. The first 
number (1) indicates that the roof assembly passed the FMR tests 
for a Class 1 fire rating. The second number (75) indicates the uplift 
resistance in pounds per square foot (psf) that the assembly 
achieved during testing. With a safety factor of two this assembly 
would be suitable for a maximum design uplift load of 37.5 psf.

The highest uplift load occurs at the roof corners because of 
building aerodynamics as discussed in Section 3.1.3. The perimeter 
has a somewhat lower load, while the field of the roof has the 
lowest load. FMG Property Loss Prevention Data Sheets are formatted 
so that a roof assembly can be selected for the field of the 
roof. For the perimeter and corner areas, FMG 
Data Sheet 1-29 provides three options: 1) use 
the FMG Approval Guide listing if it includes 
a perimeter and corner fastening method; 2) 
use a roof system with the appropriate FMG Approval 
rating in the field, perimeter, and corner, 
in accordance with Table 1 in FMG Data Sheet 
1-29; or 3) use prescriptive recommendations 
given in FMG Data Sheet 1-29. 

When perimeter and corner uplift resistance 
values are based on a prescriptive method rather 
than testing, the field assembly is adjusted to 
meet the higher loads in the perimeter and corners 
by increasing the number of fasteners or 
decreasing the spacing of adhesive ribbons by 
a required amount. However, this assumes that 
the failure is the result of the fastener pulling 
out from the deck, or that the failure is in the vicinity 
of the fastener plate, which may not be the case. Also, the 
increased number of fasteners required by FMG may not be sufficient 
to comply with the perimeter and corner loads derived from 
the building code. Therefore, if FMG resistance data are specified, 
it is prudent for the design professional to specify the resistance for 
each zone of the roof separately. Using the example cited above, 
if the field of the roof is specified as 1-75, the perimeter would be 
specified as 1-130 and the corner would be specified as 1-190. 

FM Global (FMG) is the name of the 
Factory Mutual Insurance Company and its 
affiliates. One of FMGs affiliates, Factory 
Mutual Research (FMR) provides testing 
services, produces documents that can be 
used by designers and contractors, and 
develops test standards for construction 
products and systems. FMR evaluates 
roofing materials and systems for resistance 
to fire, wind, hail, water, foot traffic and 
corrosion. Roof assemblies and components 
are evaluated to establish acceptable levels 
of performance. Some documents and 
activities are under the auspices of FMG 
and others are under FMR. 

If the roof system is fully adhered, it is not possible to increase 
the uplift resistance in the perimeter and corners. Therefore, for 
fully adhered systems, the uplift resistance requirement should be 
based on the corner load rather than the field load.

Roof System Performance 

Storm-damage research has shown that sprayed polyurethane 
foam (SPF) and liquid-applied roof systems are very reliable 
high-wind performers. If the substrate to which the SPF or liquid-
applied membrane is applied does not lift, it is highly unlikely 
that these systems will blow off. Both systems are also more resistant 
to leakage after missile impact damage than most other 
systems. Built-up roofs (BURs) and modified bitumen systems 
have also demonstrated good wind performance provided the 
edge flashing/coping does not fail (which happens frequently). 
The exception is aggregate surfacing, which is prone to blow-off 
(see Figures 3-12 and 3-13). Modified bitumen applied to a concrete 
deck has demonstrated excellent resistance to progressive 
peeling after blow-off of the metal edge flashing. Metal panel performance 
is highly variable. Some systems are very wind-resistant, 
while others are quite vulnerable. 

Of the single-ply attachment methods, the paver-ballasted and 
fully adhered methods are the least problematic. Systems with 
aggregate ballast are prone to blow-off, unless care is taken in 
specifying the size of aggregate and the parapet height (see Figure 
3-9). The performance of protected membrane roofs (PMRs) with 
a factory-applied cementitious coating over insulation boards is 
highly variable. When these boards are installed over a loose-laid 
membrane, it is critical that an air retarder be incorporated to prevent 
the membrane from ballooning and disengaging the boards. 
ANSI/SPRI RP-4 (which is referenced in the IBC) provides wind 
guidance for ballasted systems using aggregate, pavers, and cementitious-
coated boards. 

The National Research Council of Canada, Institute for Research 
in Constructions Wind Design Guide for Mechanically Attached 
Flexible Membrane Roofs (B1049, 2005) provides recommendations 
related to mechanically attached single-ply and modified 
bituminous systems. B1049 is a comprehensive wind design guide 
that includes discussion on air retarders. Air retarders can be 
effective in reducing membrane flutter, in addition to being beneficial 
for use in ballasted single-ply systems. When a mechanically 
attached system is specified, careful coordination with the structural 
engineer in selecting deck type and thickness is important. 

If a steel deck is selected, it is critical to specify that the membrane 
fasteners be attached in rows perpendicular to the steel flanges 
to avoid overstressing the attachment of the deck to the deck support 
structure. At the school shown in Figure 3-59, the fastener 
rows of the mechanically attached single-ply membrane ran parallel 
to the top flange of the steel deck. The deck fasteners were 
overstressed and a portion of the deck blew off and the membrane 
progressively tore. At another building, shown in Figure 3-60, the 
membrane fastener rows also ran parallel to the top flange of the 
steel deck. When membrane fasteners run parallel to the flange, 
the flange with membrane fasteners essentially carries all the uplift 
load because of the decks inability to transfer any significant 
load to adjacent flanges. Hence, at the joists shown in Figure 3-60, 
the deck fasteners on either side of the flange with the membrane 
fasteners are the only connections to the joist that are carrying 
substantial uplift load.

Figure 3-59: The orientation of the 
membrane fastener rows led to blow-off of the steel 
deck. Hurricane Marilyn (U.S. Virgin Islands, 1995)

For metal panel roof systems, the following are recommended:

 When clip or panel fasteners are attached to nailers, detail the 
connection of the nailer to the nailer support (including the 
detail of where nailers are spliced over a support). 
 When clip or panel fasteners are loaded in withdrawal 
(tension), screws are recommended in lieu of nails. 
 For concealed clips over a solid substrate, it is recommended 
that chalk lines be specified so that the clips are correctly 
spaced.
 When the basic wind speed is 110 mph or greater, it is 
recommended that two clips be used along the eaves, ridges, 
and hips.
 For copper panel roofs in areas with a basic wind speed greater 
than 90 mph, it is recommended that Type 316 stainless steel 
clips and stainless steel screws be used in lieu of copper clips.
 Close spacing of fasteners is recommended at hip and ridge 
flashings (e.g., spacing in the range of 3 to 6 inches on center, 
commensurate with the design wind loads.)

Figure 3-60: View of the underside of 
a steel deck showing the mechanically attached 
single-ply membrane fastener rows running 
parallel to, instead of across, the top flange of 
the deck. 

Edge Flashings and Copings

Roof membrane blow-off is almost always a result of lifting and 
peeling of the metal edge flashing or coping, which serves to 
clamp down the membrane at the roof edge. Therefore, it is important 
for the design professional to carefully consider the 
design of metal edge flashings, copings, and the nailers to which 
they are attached. The metal edge flashing on the modified 
bitumen membrane roof shown in Figure 3-61 was installed underneath 
the membrane, rather than on top of it, and then stripped 
in. In this location, the edge flashing was unable to clamp the 
membrane down. At one area, the membrane was not sealed to 
the flashing. An ink pen was inserted into the opening prior to 
photographing to demonstrate how wind could catch the opening 
and lift and peel the membrane. 

ANSI/SPRI ES-1, Wind Design Standard for Edge Systems Used in Low 
Slope Roofing Systems (2003) provides general design guidance including 
a methodology for determining the outward-acting load 
on the vertical flange of the flashing/coping (ASCE 7 does not 
provide this guidance). ANSI/SPRI ES-1 is referenced in the IBC. 
ANSI/SPRI ES-1 also includes test methods for assessing flashing/
coping resistance. This manual recommends a minimum safety 
factor of 3 for edge flashings, copings, and nailers for critical facil
ities. For FMG-insured facilities, FMR-approved flashing should be 
used and FM Data Sheet 1-49 should also be consulted. 

Figure 3-61: The ink pen shows an 
opening that the wind can catch, and cause 
lifting and peeling of the membrane. 

The traditional edge flashing/coping attachment method relies 
on concealed cleats that can deform under wind load and lead to 
disengagement of the flashing/coping (see Figure 3-62) and subsequent 
lifting and peeling of the roof membrane (as shown in 
Figure 3-12). When a vertical flange disengages and lifts up, the 
edge flashing and membrane are very susceptible to failure. Normally, 
when a flange lifts such as shown in Figure 3-62, the failure 
continues to propagate and the metal edge flashing and roof 
membrane blows off.

Storm-damage research has revealed that, in lieu of cleat attachment, 
the use of exposed fasteners to attach the vertical flanges 
of copings and edge flashings has been found to be a very effective 
and reliable attachment method. The coping shown in 
Figure 3-63 was attached with -inch diameter stainless steel concrete 
spikes at 12 inches on center. When the fastener is placed 
in wood, #12 stainless steel screws with stainless steel washers are 
recommended. The fasteners should be more closely spaced in 
the corner areas (the spacing will depend upon the design wind 
loads). ANSI/SPRI ES-1 provides guidance on fastener spacing 
and thickness of the coping and edge flashing.

Figure 3-62: The metal edge flashing 
disengaged from the continuous cleat and 
the vertical flange lifted. Hurricane Hugo (South 
Carolina, 1989)

Gutters 

Storm-damage research has shown that gutters are seldom constructed 
to resist wind loads (see Figure 3-64). When a gutter lifts, 
it typically causes the edge flashing that laps into the gutter to lift 
as well. Frequently, this results in a progressive lifting and peeling 
of the roof membrane. The membrane blow-off shown in Figure 
3-65 was initiated by gutter uplift. The gutter was similar to that 
shown in Figure 3-64. The building, housing the county Sheriffs 
office, suffered water leakage that shut down the county 911 call 
center, destroyed the crime lab equipment, and caused significant 
interior water damage.

Figure 3-63: Both vertical faces of the 
coping were attached with exposed fasteners instead 
of concealed cleats. Typhoon Paka (Guam, 1997)

Figure 3-64: This gutter, supported by a type of bracket that 
provides no significant uplift resistance, failed 
when wind lifted it together with the metal 
edge flashing that lapped into the gutter. Hurricane 
Francis (Florida, 2004)

Special design attention needs to be given to attaching gutters 
to prevent uplift, particularly for those in excess of 6 inches in 
width. Currently, there are no standards pertaining to gutter 
wind resistance. It is recommended that the designer calculate 
the uplift load on gutters using the overhang coefficient from 
ASCE 7. There are two approaches to resist gutter uplift.

 Gravity-support brackets can be designed to resist uplift 
loads. In these cases, in addition to being attached at its 
top, the bracket should also be attached at its low end to the 
wall. The gutter also needs to be designed so it is attached 
securely to the bracket in a way that will effectively transfer 
the gutter uplift load to the bracket. Bracket spacing will 
depend on the gravity and uplift load, the brackets strength, 
and the strength of connections between the gutter/bracket 
and the bracket/wall. With this option, the brackets top will 
typically be attached to a wood nailer, and that fastener will 
be designed to carry the gravity load. The brackets lower 
connection will resist the rotational force induced by gutter 
uplift. Because brackets are usually spaced close together 
to carry the gravity load, developing adequate connection 
strength at the lower fastener is generally not difficult. 
 The other option is to use gravity-support brackets only to 
resist gravity loads, and use separate sheet-metal straps at 45-
degree angles to the wall to resist uplift loads. Strap spacing 
will depend on the gutter uplift load and strength of the 
connections between the gutter/strap and the strap/wall. 
Note that FMG Data Sheet 1-49 recommends placing straps 
10 feet apart. However, at that spacing with wide gutters, 
fastener loads induced by uplift are quite high. When straps 
are spaced at 10 feet, it can be difficult to achieve sufficiently 
strong uplift connections. 

Figure 3-65: The original modified 
bitumen membrane was blown away after the 
gutter lifted in the area shown by the red arrow 
(the black membrane is a temporary roof). Hurricane 
Francis (Florida, 2004)

When designing a brackets lower connection to a 
wall or a straps connection to a wall, designers should 
determine appropriate screw pull-out values. With this 
option, a minimum of two screws at each end of a strap is 
recommended. At a wall, screws should be placed side by 
side, rather than vertically aligned, so the strap load is carried 
equally by the two fasteners. When fasteners are vertically 
aligned, most of the load is carried by the top fastener.
Since the uplift load in the corners is much higher than the load 
between the corners, enhanced attachment is needed in corner 
areas regardless of the option chosen. ASCE 7 provides guidance 
about determining a corner areas length.

Parapet Base Flashings 

Information on loads for parapet base flashings was first introduced 
in the 2002 edition of ASCE 7. The loads on base flashings 
are greater than the loads on the roof covering if the parapets exterior 
side is air-permeable. When base flashing is fully adhered, 
it has sufficient wind resistance in most cases. However, when base 
flashing is mechanically fastened, typical fastening patterns may 
be inadequate, depending on design wind conditions (see Figure 
3-66). Therefore, it is imperative that the base flashing loads be 
calculated, and attachments be designed to accommodate these 
loads. It is also important for designers to specify the attachment 
spacing in parapet corner regions to differentiate them from the 
regions between corners.

Steep-Slope Roof Coverings 

For a discussion of wind performance of asphalt shingle and tile 
roof coverings, see FEMA 488 (2005), 489 (2005), and 549 (2006). 
For recommendations pertaining to asphalt shingles and tiles, see 
Fact Sheets 19, 20, and 21 in FEMA 499 (2005).

3.3.4 Nonstructural Systems and Equipment

Nonstructural systems and equipment include all components 
that are not part of the structural system or building envelope. Exterior-
mounted mechanical equipment (e.g., exhaust fans, HVAC 
units, relief air hoods, rooftop ductwork, and boiler stacks), electrical 
equipment (e.g., light fixtures and lightning protection 
systems), and communications equipment (e.g., antennae and 
satellite dishes) are often damaged during high winds. Damaged 
equipment can impair the operation of the facility, the equipment 
can detach and become wind-borne missiles, and water can enter 
the facility where equipment was displaced (see Figures 3-20, 3-67, 
3-68, 3-72, 3-76, and 3-78). The most common problems typically 
relate to inadequate equipment anchorage, inadequate strength 
of the equipment itself, and corrosion.

Figure 3-66: If mechanically attached 
base flashings have an insufficient number 
of fasteners, the base flashing can be blown 
away. Hurricane Andrew (Florida, 1992) 

See Section 3.4.4 for additional information pertaining to critical 
facilities located in hurricane-prone regions.

3.3.4.1 Exterior-Mounted Mechanical Equipment

This section discusses loads and attachment methods, as well as 
the problems of corrosion and water infiltration.

Figure 3-67: Toppled rooftop mechanical equipment. 
Hurricane Andrew (Florida, 1992)

Figure 3-68: This gooseneck was attached with only two 
small screws. A substantial amount of water was 
able to enter the building during Hurricane Francis. 
(Florida, 2004)

Loads and Attachment Methods 

Information on loads on rooftop equipment was first introduced 
in the 2002 edition of ASCE 7. For guidance on load calculations, 
see Calculating Wind Loads and Anchorage Requirements for 
Rooftop Equipment (ASHRAE, 2006). A minimum safety factor 
of 3 is recommended for critical facilities. Loads and resistance 
should also be calculated for heavy pieces of equipment since the 
dead load of the equipment is often inadequate to resist the design 
wind load. The 30 x 10 x 8 18,000-pound HVAC unit shown 
in Figure 3-69 was attached to its curb with 16 straps (one screw 
per strap). Although the wind speeds were estimated 
to be only 85 to 95 miles per hour 
(peak gust), the HVAC unit blew off the medical 
office building. 

To anchor fans, small HVAC units, and relief 
air hoods, the minimum attachment 
schedule provided in Table 3-2 is recommended. 
The attachment of the curb to the 
roof deck also needs to be designed and constructed 
to resist the design loads. 

Mechanical penetrations through the 
elevator penthouse roof and walls must 
possess adequate wind and water 
resistance to ensure continuity of elevator 
service (see Section 3.3.3.3). In addition 
to paying special attention to equipment 
attachment, air intakes and exhausts 
should be designed and constructed to 
prevent wind-driven water from entering 
the penthouse. 

Figure 3-69: Although this 18,000-
pound HVAC unit was attached to its curb with 
16 straps, it blew off during Hurricane Ivan. 
(Florida, 2004)

9. Discussion is based on: Attachment of Rooftop Equipment in High-wind Regions
Hurricane Katrina Recovery Advisory (May 2006, 
revised July 2006)
Table 3-2: Number of #12 Screws for Base Case Attachment of Rooftop Equipment

Fan cowling attachment: Fans are frequently 
blown off their curbs because they are poorly 
attached. When fans are well attached, the 
cowlings frequently blow off (see Figure 
3-70). Blown off cowlings can tear roof membranes 
and break glazing. Unless the fan 
manufacturer specifically engineered the 
cowling attachment to resist the design wind 
load, cable tie-downs (see Figure 3-71) are 
recommended to avoid cowling blow-off. 
For fan cowlings less than 4 feet in diameter, 
1/8-inch diameter stainless steel cables 
are recommended. For larger cowlings, use 
3/16-inch diameter cables. When the basic 
wind speed is 120 mph or less, specify two cables. 
Where the basic wind speed is greater 
than 120 mph, specify four cables. To minimize 
leakage potential at the anchor point, 
it is recommended that the cables be adequately anchored to 
the equipment curb (rather than anchored to the roof deck). 
The attachment of the curb itself also needs to be designed and 
specified. 

To avoid corrosion-induced failure (see 
Figure 3-78), it is recommended that 
exterior-mounted mechanical, electrical, 
and communications equipment be 
made of nonferrous metals, stainless 
steel, or steel with minimum G-90 hot-dip 
galvanized coating for the equipment 
body, stands, anchors, and fasteners. 
When equipment with enhanced corrosion 
protection is not available, the designer 
should advise the building owner that 
periodic equipment maintenance and 
inspection is particularly important to 
avoid advanced corrosion and subsequent 
equipment damage during a windstorm.

Figure 3-70: Cowlings blew off two of the fans on a police 
building that housed the countys EOC. Hurricane 
Ivan (Florida, 2004) 

Ductwork: To avoid wind and wind-borne debris damage to rooftop 
ductwork, it is recommended that ductwork not be installed on 
the roof (see Figure 3-72). If ductwork is installed on the roof, it 
is recommended that the ducts gauge and the method of attachment 
be able to resist the design wind loads.

Figure 3-71: Cables were attached to prevent the cowling from blowing off. 
Typhoon Paka (Guam, 1997)

Figure 3-72: Two large openings remained (circled area 
and inset to the left) after the ductwork on this roof 
blew away. Hurricane Katrina (Mississippi, 2005)

Condenser attachment: In lieu of placing 
rooftop-mounted condensers on wood 
sleepers resting on the roof (see Figure 3-
73), it is recommended that condensers 
be anchored to equipment stands. The attachment 
of the stand to the roof deck also 
needs to be designed to resist the design 
loads. In addition to anchoring the base of 
the condenser to the stand, two metal straps 
with two side-by-side #12 screws or bolts 
with proper end and edge distances at each 
strap end are recommended when the basic 
wind speed is greater than 90 mph (see 
Figure 3-74).

Vibration isolators: If vibration isolators are used to mount equipment, 
only those able to resist design uplift loads should be 
specified and installed, or an alternative means to accommodate 
uplift resistance should be provided (see Figure 3-75). 

Three publications pertaining to seismic 
restraint of equipment provide general information 
on fasteners and edge distances: 

 Installing Seismic Restraints for 
Mechanical Equipment (FEMA 412, 
2002) 

 Installing Seismic Restraints for 
Electrical Equipment (FEMA 413, 
2004)

 Installing Seismic Restraints for Duct 
and Pipe (FEMA 414, 2004) 

Figure 3-73: Sleeper-mounted condensers displaced by 
high winds. Hurricane Katrina (Mississippi, 2005) 

Figure 3-74: This condenser had supplemental attachment 
straps (see red arrows). Typhoon Paka (Guam, 1997)

Figure 3-75: Failure of vibration isolators that provided lateral resistance but 
no uplift resistance caused equipment damage. 
A damaged vibration isolator is shown in the 
inset. Hurricane Katrina (Mississippi, 2005)

Boiler and exhaust stack attachment: To avoid wind damage to boiler 
and exhaust stacks, wind loads on stacks should be calculated and 
guy-wires should be designed and constructed to resist the loads. 
Toppled stacks, as shown at the hospital in Figure 3-76, can allow 
water to enter the building at the stack penetration, damage the 
roof membrane, and become wind-borne debris. The designer 
should advise the building owner that guy-wires should be inspected 
annually to ensure they are taut.

Access panel attachment: Equipment access panels frequently blow 
off. To minimize this, job-site modifications, such as attaching 
hasps and locking devices like carabiners, are recommended. 
The modification details need to be customized. Detailed design 
may be needed after the equipment has been delivered to the job 
site. Modification details should be approved by the equipment 
manufacturer.

Equipment screens: Screens around rooftop equipment are frequently 
blown away (see Figure 3-77). Screens should be designed 
to resist the wind load derived from ASCE 7. Since the effect of 
screens on equipment wind loads is unknown, the equipment attachment 
behind the screens should be designed to resist the 
design load. 

Figure 3-76: Three of the five stacks that did not have guy-
wires were blown down. Hurricane Marilyn (U.S. 
Virgin Islands, 1995) 

Water Infiltration

During high winds, wind-driven rain can be driven through air 
intakes and exhausts unless special measures are taken. Louvers 
should be designed and constructed to prevent leakage between 
the louver and wall. The louver itself should be designed to avoid 
water being driven past the louver. However, it is difficult to prevent 
infiltration during very high winds. Designing sumps with 
drains that will intercept water driving past louvers or air intakes 
should be considered. ASHRAE 62.1 (2004) provides some information 
on rain and snow intrusion. The Standard 62.1 Users 
Manual provides additional information, including examples and 
illustrations of various designs.

3.3.4.2 Exterior-Mounted Electrical and Communications Equipment

Damage to exterior-mounted electrical equipment is infrequent, 
mostly because of its small size (e.g., disconnect switches). Exceptions 
include communication towers, surveillance cameras, 
electrical service masts, satellite dishes, and lightning protection 
systems. The damage is typically caused by inadequate mounting 
as a result of failure to perform wind load calculations and anchorage 
design. Damage is also sometimes caused by corrosion 
(see Figure 3-78 and the text box on corrosion in Section 3.3.4.1).

Figure 3-77: Equipment screen panels, such as these blown away 
at a hospital, can break glazing, puncture roof 
membranes, and cause injury. Hurricane Ivan 
(Florida, 2004)

Communication towers and poles: ANSI/C2 provides guidance for 
determining wind loads on power distribution and transmission 
poles and towers. AASHTO LTS-4-M (amended by LTS-4-12, 
2001 and 2003, respectively) provides guidance for determining 
wind loads on light fixture poles (standards).

Both ASCE 7 and ANSI/TIA-222-G contain wind load provisions 
for communication towers (structures). The IBC allows the use 
of either approach. The ASCE wind load provisions are generally 
consistent with those contained in ANSI/TIA-222-G. ASCE 7, 
however, contains provisions for dynamically sensitive towers that 
are not present in the ANSI/TIA standard. ANSI/TIA classifies 
towers according to their use (Class I, Class II, and Class III). This 
manual recommends that towers (including antennae) that are 
mounted on, located near, or serve critical facilities be designed as 
Class III structures.

Figure 3-78: Collapsed hospital light fixtures caused by severe 
corrosion (see inset). Hurricane Ivan (Florida, 2004)

Collapse of both large and small communication towers at emergency 
operation centers, fire and police stations, and hospitals 
is quite common during high-wind events (see Figures 3-79 and 
3-80). These failures often result in complete loss of communication 
capabilities. In addition to the disruption of communications, 
collapsed towers can puncture roof membranes and allow water 
leakage into the facilities, unless the roof system incorporated 
a secondary membrane (as discussed in Section 3.4.3.4). At the 
tower shown in Figure 3-79 the anchor bolts were pulled out of 
the deck, which resulted in a progressive peeling of the fully adhered 
single-ply roof membrane. Tower collapse can also injure or 
kill people. 

See Section 3.3.1.1 regarding site considerations for light fixture 
poles, power poles, and electrical and communications towers.

Figure 3-79: The collapse of the antenna 
tower caused progressive peeling of the roof 
membrane. Also note that the exhaust fan blew off the 
curb, but the high parapet kept it from blowing off the 
roof. Hurricane Andrew (Florida, 1992) 

Electrical service masts: Service mast failure is typically caused by 
collapse of overhead power lines, which can be avoided by using 
underground service. Where overhead service is provided, it is 
recommended that the service mast not penetrate the roof. Otherwise, 
a downed service line could pull on the mast and rupture the 
roof membrane. 

Satellite dishes: For the satellite dish shown in Figure 3-81, the 
dish mast was anchored to a large metal pan that rested on the 
roof membrane. CMU was placed on the pan to provide overturning 
resistance. This anchorage method should only be used 
where calculations demonstrate that it provides sufficient resistance. 
In this case the wind approached the satellite dish in 
such a way that it experienced very little wind pressure. In hurricane-
prone regions, use of this anchorage method is not 
recommended (see Figure 3-82). 

Lightning protection systems: For attachment of lightning protection 
systems on buildings higher than 100 feet above grade, and 
for buildings located where the basic wind speed is in excess of 90 
mph, see Section 3.4.4.3.

Figure 3-80: The antenna tower at this fire station buckled. 
Hurricane Katrina (Mississippi, 2005) 

The recommendations given in Section 3.3 are summarized in 
Table 3-3.

Figure 3-81: Common anchoring method for satellite dish. 
Hurricane Ivan (Florida, 2004)

Figure 3-82: A satellite dish anchored 
similarly to that shown in Figure 3-81 was 
blown off of this five-story building. Hurricane 
Charley (Florida, 2004) 

Table 3-3: Risk Reduction Design Methods

3.4 BEST PRACTICES IN HURRICANE-
PRONE REGIONS

This section presents the general design and construction 
practice recommendations for critical facilities located in 
hurricane-prone regions. These recommendations are additional 
to the ones presented in Section 3.3 and in many cases 
supersede those recommendations. Critical facilities located in 
hurricane-prone regions require special design and construction 
attention because of the unique characteristics of this type 
of windstorm. Hurricanes can bring very high winds that last for 
many hours, which can lead to material fatigue failures. The variability 
of wind direction increases the probability that the wind will 
approach the building at the most critical angle. Hurricanes also 
generate a large amount of wind-borne debris, which can damage 
various building components and cause injury and death. 
Although all critical facilities in hurricane-prone regions require 
special attention, three types of facilities are particularly important 
because of their function or occupancy: EOCs, healthcare 
facilities, and shelters. EOCs serve as centralized management 
hubs for emergency operations. The loss of an EOC can severely 
affect the overall response and recovery in the area. Healthcare 
facilities normally have vulnerable occupants (patients) at the 
time of a hurricane, and afterwards, many injured people seek 
medical care. Significant damage to a facility can put patients at 
risk and jeopardize delivery of care to those seeking treatment. 
Shelters often have a large number of occupants. The collapse 
of a shelter building or entrance of wind-borne debris into 
a shelter has the potential to injure or kill many people. See 
Chapter 4 for information on the performance of some EOCs, 
healthcare facilities, shelters, and other types of critical facilities 
that were affected by Hurricane Katrina.

In order to ensure continuity of service during and after hurricanes, 
the design, construction, and maintenance of the following 
critical facilities should be very robust to provide sufficient resiliency 
to withstand the effects of hurricanes.

EOCs: Communications are important for most types of critical 
facilities, but for EOCs they are vital. To inhibit disruption of operations, 
water infiltration that could damage electrical equipment 
must be prevented, antenna towers need to be strong enough 
to resist the wind, and the emergency and standby power system 
needs to remain operational.

Healthcare facilities: Full or partial evacuation of a hospital prior 
to, during, or after a hurricane, is time consuming, expensive, 
and for some patients, potentially life-threatening. Water infiltration 
that could damage electrical equipment 
or medical supplies, or inhibit the use of 
critical areas (such as operating rooms and 
nursing floors) needs to be prevented. The 
emergency and standby power systems need 
to remain operational and be adequately 
sized to power all needed circuits, including 
the HVAC system. Provisions are needed for 
water and sewer service in the event of loss of 
municipal services, and antenna towers need 
to be strong enough to resist the wind.

Shelters: During and after hurricanes, these facilities are often 
occupied by more than 1,000 people. The primary purpose of 
shelters is to protect occupants from injury or death as a result 
of building collapse or entrance of wind-borne debris. However, 
beyond meeting this basic requirement, providing a degree of 
occupant comfort during a stressful time is important. The buildings 
design and construction should avoid significant water 
infiltration and provide at least a minimum level of lighting and 
mechanical ventilation using emergency generators. Shelters 
should also have provisions for sewage service (such as portable 
toilets) in the event of loss of municipal water or sewer service. 

Nursing homes are often no more 
hurricane-resistant than residential buildings. 
Evacuating these facilities (particularly 
skilled nursing homes and facilities caring 
for patients with Alzheimers disease) can 
be difficult. Except for antenna towers, the 
issues identified for hospitals are applicable 
to nursing homes.

FEMA recommends that shelters be designed in accordance with 
FEMA 361, Design and Construction Guidance for Community Shelters 
(2000).

3.4.1 Site and General Design Considerations

Via ASCE 7, the 2006 edition of the IBC has only one special wind-
related provision pertaining to Category III and IV buildings in 
hurricane-prone regions. It pertains to glazing protection within 
wind-borne debris regions (as defined in ASCE 7). This single additional 
requirement does not provide adequate protection for 
occupants of a facility during a hurricane, nor does it ensure a 
critical facility will remain functional during and after a hurricane. 
A critical facility may comply with IBC but still remain vulnerable 
to water and missile penetration through the roof or walls. To provide 
occupant protection, the exterior walls and the roof must be 
designed and constructed to resist wind-borne debris as discussed 
in Sections 3.4.2 and 3.4.3. 

The following recommendations are made regarding siting:

 Locate poles, towers, and trees with trunks larger than 6 inches 
in diameter away from primary site access roads so that they do 
not block access to, or hit, the facility if toppled.
 Determine if existing buildings within 1,500 feet of the new 
facility have aggregate surfaced roofs. If roofs with aggregate 
surfacing are present, it is recommended that the aggregate be 
removed to prevent it from impacting the new facility. Aggregate 
removal may necessitate reroofing or other remedial work 
in order to maintain the roofs fire or wind resistance.
 In cases where multiple buildings, such as hospitals or school 
campuses, are occupied during a storm, it is recommended 
that enclosed walkways be designed to connect the buildings. 
The enclosed walkways (above- or below-grade) are particularly 
important for protecting people moving between buildings 
during a hurricane (e.g., to retrieve equipment or supplies) or 
for situations when it is necessary to evacuate occupants from 
one building to another during a hurricane.

3.4.2 Structural Systems 

Because of the exceptionally good wind performance and wind-
borne debris resistance that reinforced cast-in-place concrete 
structures offer, a reinforced concrete roof deck and reinforced 
concrete or reinforced and fully grouted CMU exterior walls are 
recommended as follows: 

Roof deck: A minimum 4-inch thick cast-in-place reinforced concrete 
deck is the preferred deck. Other recommended decks 
are minimum 4-inch thick structural concrete topping over steel 
decking, and precast concrete with an additional minimum 4-inch 
structural concrete topping.

If these recommendations are not followed 
for critical facilities located in areas where 
the basic wind speed is 100 mph or greater, 
it is recommended that the roof assembly 
be able to resist complete penetration of the 
deck by the D missile specified in ASTM E 
1996 (2005, see text box in Section 3.4.3.1).

Figure 3-83: Open walkways do not provide protection 
from wind-borne debris. Hurricane Katrina 
(Mississippi, 2005)

If precast concrete is used for the roof or 
wall structure, the connections should be 
carefully designed, detailed, and 
constructed. 

Exterior load-bearing walls: A minimum 6-inch thick cast-in-place 
concrete wall reinforced with #4 rebars at 12 inches on center 
each way is the preferred wall. Other recommended walls are a 
minimum 8-inch thick fully grouted CMU reinforced with #4 rebars 
in each cell, and precast concrete that is a minimum 6 inches 
thick and reinforced equivalent to the recommendations for cast-
in-place walls.

3.4.3 Building Envelope 

The design considerations for building envelope components of 
critical facilities in hurricane-prone regions include a number of 
additional recommendations. The principal concern that must be 
addressed is the additional risk from wind-borne debris and water 
leakage, as discussed below.

3.4.3.1 Exterior Doors 

Although the ASCE-7 wind-borne debris provisions only apply 
to glazing within a portion of hurricane-prone regions, it is recommended 
that all critical facilities located where the basic 
wind speed is 100 mph or greater comply with the following 
recommendations: 

 To minimize the potential for missiles penetrating exterior 
doors and striking people inside the facility, it is recommended 
that doors (with and without glazing) be designed to resist the 
E missile load specified in ASTM E 1996. The doors should 
be tested in accordance with ASTM E 1886 (2005). The test 
assembly should include the door, door frame, and hardware. 
 It is recommended that the doors on shelters meet the wind 
pressure and missile resistance criteria found in FEMA 361. 
Information on door assemblies that meet these criteria is 
included in FEMA 361. 

3.4.3.2 Windows and Skylights 

Exterior glazing that is not impact-resistant (such as laminated 
glass or polycarbonate) or protected by shutters is extremely susceptible 
to breaking if struck by wind-borne debris. Even small, 
low-momentum missiles can easily break glazing that is not protected 
(see Figures 3-84 and 3-85). At the hospital shown in 
Figure 3-84, approximately 400 windows were broken. Most of 
the breakage was caused by wind-blown aggregate from the hospitals 
aggregate ballasted single-ply membrane roofs, and aggregate 
from built-up roofs. With broken windows, a substantial amount of 
water can be blown into a building, and the internal air pressure 
can be greatly increased (as discussed in Section 3.1.3) which may 
damage the interior partitions and ceilings. 

ASTM E 1996 specifies five missile categories, A through E. The missiles are of 
various weights and fired at various velocities during testing. Building type 
(critical or non-critical) and basic wind speed determine the missiles required 
for testing. Of the five missiles, the E missile has the greatest momentum. 
Missile E is required for critical facilities located where the basic wind 
speed is greater than or equal to 130 mph. Missile D is permitted where the 
basic wind speed is less than130 mph. FEMA 361 also specifies a missile for 
shelters. The shelter missile has much greater momentum than the D and E 
missiles, as shown below:

Missile
Missile Weight
Impact Speed
Momentum
ASTM E 1996D
9 pound 2x4 lumber
50 feet per second 
(34 mph)
14 lbf -s*
ASTM E 1996E
9 pound 2x4 lumber
80 feet per second
(55 mph)
22 lbf -s*
FEMA 361 (Shelter Missile)
15 pound 2x4 lumber
147 feet per second 
(100 mph)
68 lbf -s*
*lbf -s = pounds force per second

In order to minimize interior damage, the IBC, through ASCE 7, 
prescribes that exterior glazing in wind-borne debris regions be 
impact-resistant, or be protected with an impact-resistant covering 
(shutters). For Category III and IV buildings in areas with a basic 
wind speed of 130 mph or greater, the glazing is required to resist 
a larger momentum test missile than would Category II buildings 
and Category III and IV buildings in areas with wind speeds of less 
than 130 mph.

Figure 3-84: Plywood panels (black continuous bands) installed 
after the glass spandrel panels were broken by 
roof aggregate. Hurricane Katrina (Mississippi, 2005) 

Figure 3-85: A small piece of asphalt 
shingle (red arrow) broke the window at this nursing 
home. Hurricane Katrina (Mississippi, 2005)

ASCE 7 refers to ASTM E 1996 for missile loads and to ASTM E 
1886 for the test method to be used to demonstrate compliance 
with the E 1996 load criteria. In addition to testing impact resistance, 
the window unit is subjected to pressure cycling after test 
missile impact to evaluate whether the window can still resist 
wind loads. If wind-borne debris glazing protection is provided 
by shutters, the glazing is still required by ASCE 7 to meet the 
positive and negative design air pressures.

Although the ASCE 7 wind-borne debris provisions only apply 
to glazing within a portion of hurricane-prone regions, it is recommended 
that all critical facilities located where the basic 
wind speed is 100 mph or greater comply with the following 
recommendations: 

 To minimize the potential for missiles penetrating exterior 
glazing and injuring people, it is recommended that exterior 
glazing up to 60 feet above grade be designed to resist the 
test Missile E load specified in ASTM E 1996 (see text box 
in Section 3.4.3.1). In addition, if roofs with aggregate 
surfacing are present within 1,500 feet of the facility, glazing 
above 60 feet should be designed to resist the test Missile A 
load specified in ASTM E 1996. The height of the protected 
glazing should extend a minimum of 30 feet above the 
aggregate surfaced roof per ASCE 7. 
Because large missiles are generally flying at lower 
elevations, glazing that is more than 60 feet above grade and 
meets the test Missile A load should be sufficient. However, 
if the facility is within a few hundred feet of another 
building that may create debris such as EIFS, tiles, or rooftop 
equipment, it is recommended that the test Missile E load be 
specified instead of the Missile A for the upper-level glazing. 
 For those facilities where glazing resistant to bomb blasts 
is desired, the windows and glazed doors can be designed 
to accommodate wind pressure, missile loads, and blast 
pressure. However, the window and door units need to be 
tested for missile loads and cyclic air pressure, as well as for 
blast. A unit that meets blast criteria will not necessarily meet 
the E 1996 and E 1886 criteria, and vice versa. 

With the advent of building codes requiring 
glazing protection in wind-borne debris 
regions, a variety of shutter designs have entered 
the market. Shutters typically have a 
lower initial cost than laminated glass. However, 
unless the shutter is permanently 
anchored to the building (e.g., an accordion 
shutter), storage space will be needed. Also, 
when a hurricane is forecast, costs will be incurred each time shutters 
are installed and removed. The cost and difficulty of shutter 
deployment and demobilization on upper-level glazing may be 
avoided by using motorized shutters, although laminated glass 
may be a more economical solution. For further information on 
shutters, see Section 3.6.2.2.

3.4.3.3 Non-Load-Bearing Walls, Wall Coverings, and Soffits 

In order to achieve enhanced missile resistance 
of non-load-bearing exterior walls, the 
wall types discussed in Section 3.4.2 (i.e., reinforced 
concrete, or reinforced and fully 
grouted CMU) are recommended. 

To minimize long-term problems with exterior 
wall coverings and soffits, it is recommended 
that they be avoided to the maximum extent 
possible. Exposed or painted reinforced concrete 
or CMU offers greater reliability (i.e., 
they have no coverings that can blow off and 
become wind-borne debris). 

For all critical facilities located where the 
basic wind speed is 100 mph or greater that 
are not constructed using reinforced concrete 
or reinforced and fully grouted CMU 
(as is recommended in this manual), it is recommended 
that the wall system selected be 
sufficient to resist complete penetration of 
the wall by the E missile specified in ASTM 
E 1996. 

For further information on designing 
glazing to resist blast, see the Blast 
Safety resource pages of the National 
Institute of Building Sciences' Building 
Envelope Design Guide (www.wbdg.org/
design/enve-lope.php).

For buildings not constructed using concrete 
roof decks and concrete or CMU walls (as 
recommended), shelters can be constructed 
within buildings for occupant protection. 
FEMA 320Taking Shelter From the 
Storm: Building a Safe Room Inside Your 
Home (2004) describes how restrooms 
and storage rooms can be designed for 
sheltering inside new and existing buildings.

It is recommended that wood-framed and 
pre-engineered metal buildings in areas 
with a basic wind speed of 100 mph or 
greater, that will be occupied during a 
hurricane, have a designated storage 
room(s), office(s), or small conference 
room(s) designed in accordance with FEMA 
320 to protect the occupants. Although 
FEMA 320 is intended for residential 
construction, the guidance is suitable for 
small shelters inside critical facilities such as 
fire and police stations. For large shelters, 
FEMA 361 criteria are recommended.

For interior non-load-bearing masonry walls in critical facilities located 
where the basic wind speed is greater than 120 mph, see the 
recommendations given in Section 3.3.3.3. 

3.4.3.4 Roof Systems 

The following types of roof systems are recommended for critical 
facilities in hurricane-prone regions, because they are more likely 
to avoid water infiltration if the roof is hit by wind-borne debris, 
and also because these systems are less likely to become sources of 
wind-borne debris:

 In tropical climates where insulation is not needed above the 
roof deck, specify either liquid-applied membrane over cast-in-
place concrete deck, or modified bitumen membrane torched 
directly to primed cast-in-place concrete deck.
 Install a secondary membrane over a concrete deck (if 
another type of deck is specified, a cover board may be 
needed over the deck). Seal the secondary membrane at 
perimeters and penetrations. Specify rigid insulation over 
the secondary membrane. Where the basic wind speed is 
up to 110 mph, a minimum 2-inch thick layer of insulation 
is recommended. Where the speed is between 110 and 130 
mph, a total minimum thickness of 3 inches is recommended 
(installed in two layers). Where the speed is greater than 130 
mph, a total minimum thickness of 4 inches is recommended 
(installed in two layers). A layer of 5/8-inch thick glass mat 
gypsum roof board is recommended over the insulation, 
followed by a modified bitumen membrane. A modified 
bitumen membrane is recommended for the primary 
membrane because of its somewhat enhanced resistance to 
puncture by small missiles compared with other types of roof 
membranes. 

The purpose of the insulation and gypsum roof board is to 
absorb missile energy. If the primary membrane is punctured 
or blown off during a storm, the secondary membrane should 
provide watertight protection unless the roof is hit with 
missiles of very high momentum that penetrate the insulation 
and secondary membrane. Figure 3-86 illustrates the merit of 
specifying a secondary membrane. The copper roof blew off 
the hospitals intensive care unit (ICU). Patients and staff were 
frightened by the loud noise generated by the metal panels as 
they banged around during the hurricane. Fortunately there 
was a very robust underlayment (a built-up membrane) that 
remained in place. Since only minor leakage occurred, the 
ICU continued to function. 
 For an SPF roof system over a concrete deck, where the basic 
wind speed is less than 130 mph, it is recommended that 
the foam be a minimum of 3 inches thick to avoid missile 
penetration through the entire layer of foam. Where the 
speed is greater than 130 mph, a 4-inch minimum thickness is 
recommended. It is also recommended that the SPF be coated, 
rather than protected with an aggregate surfacing.
 For a PMR, it is recommended that pavers weighing a minimum 
of 22 psf be specified. In addition, base flashings should 
be protected with metal (such as shown in Figure 3-93) to 
provide debris protection. Parapets with a 3 foot minimum 
height (or higher if so indicated by ANSI/SPRI RP-4, 2002) 
are recommended at roof edges. This manual recommends 
that PMRs not be used for critical facilities in hurricane-prone 
regions where the basic wind speed exceeds 130 mph. 

Figure 3-86: Because this roof system 
incorporated a secondary membrane, the ICU 
was not evacuated after the copper roof blew 
off. Hurricane Andrew (Florida, 1992) 

 For structural metal roofs, it is recommended 
that a roof deck be specified, 
rather than attaching the panels directly to 
purlins as is commonly done with pre-engineered 
metal buildings. If panels blow off 
buildings without roof decking, as shown 
in Figure 3-17, wind-borne debris and rain 
are free to enter the building. 

Structural standing seam metal roof panels with concealed 
clips and mechanically seamed ribs spaced at 12 inches on 
center are recommended. If the panels are installed over a 
concrete deck, a modified bitumen secondary membrane is 
recommended if the deck has a slope less than :12. If the 
panels are installed over a steel deck or wood sheathing, a 
modified bitumen secondary membrane (over a suitable cover 
board when over steel decking) is recommend, followed by 
rigid insulation and metal panels. Where the basic wind speed 
is up to 110 mph, a minimum 2-inch thick layer of insulation 
is recommended. Where the speed is between 110 and 130 
mph, a total minimum thickness of 3 inches is recommended. 
Where the speed is greater than 130 mph, a total minimum 
thickness of 4 inches is recommended. Although some clips 
are designed to bear on insulation, it is recommended that 
the panels be attached to wood nailers attached to the deck, 
because nailers provide a more stable foundation for the clips. 
If the metal panels are blown off or punctured during a 
hurricane, the secondary membrane should provide watertight 
protection unless the roof is hit with missiles of very high 
momentum. At the roof shown in Figure 3-87, the structural 
standing seam panel clips bore on rigid insulation over a steel 
deck. Had a secondary membrane been installed over the steel 
deck, the membrane would have likely prevented significant 
interior water damage and facility disruption.
 Based on field performance of architectural metal panels in 
hurricane-prone regions, exposed fastener panels are recommended 
in lieu of architectural panels with concealed clips. 
For panel fasteners, stainless steel screws are recommended. A 
secondary membrane protected with insulation is recommended, 
as discussed above for structural standing seam systems. 
Roofs over rooms used to store important 
records (such as police station evidence 
rooms) should incorporate secondary 
membranes to avoid water leakage damage. 
To preclude water infiltration damage from 
exterior walls, avoid locating important 
storage rooms adjacent to exterior walls. 

In order to avoid the possibility of roofing components blowing 
off and striking people arriving at a critical facility during a storm, 
the following roof systems are not recommended: aggregate surfacings 
either on BUR (shown in Figure 3-12), single-plies (shown 
in Figure 3-9), or SPF; lightweight concrete pavers; cementitious-
coated insulation boards; slate; and tile (see Figure 3-88). Even 
when slates and tiles are properly attached to resist wind loads, 
their brittleness makes them vulnerable to breakage as a result 
of wind-borne debris impact. The tile and slate fragments can be 
blown off the roof, and fragments can damage other parts of the 
roof causing a cascading failure. 

Figure 3-87: Significant interior water 
damage and facility interruption occurred 
after the standing seam roof blew off. Hurricane 
Marilyn (U.S. Virgin Islands, 1995)

Figure 3-88: Brittle roof coverings, 
like slate and tile, can be broken by missiles, and 
tile debris can break other tiles. Hurricane Charley 
(Florida, 2004)

Mechanically attached and air-pressure equalized single-ply membrane 
systems are susceptible to massive progressive failure after 
missile impact, and are therefore not recommended for critical 
facilities in hurricane-prone regions. At the building shown in 
Figure 3-89, a missile struck the fully adhered low-sloped roof and 
slid into the steep-sloped reinforced mechanically attached single-
ply membrane in the vicinity of the red arrow. A large area of the 
mechanically attached membrane was blown away as a result of 
progressive membrane tearing. Fully adhered single-ply membranes 
are very vulnerable to missiles (see Figure 3-90) and are 
not recommended unless they are ballasted with pavers. 

Figure 3-89: Mechanically attached 
single-ply membrane progressively tore after 
being cut by wind-borne debris. Hurricane 
Andrew (Florida, 1992)

Figure 3-90: Fully adhered single-ply 
roof membrane struck by a large number of missiles. 
Hurricane Marilyn (U.S. Virgin Islands, 1995)

Edge flashings and copings: If cleats are used for attachment, it is 
recommended that a peel-stop bar be placed over the roof membrane 
near the edge flashing/coping, as illustrated in Figure 3-91. 
The purpose of the bar is to provide secondary protection against 
membrane lifting and peeling in the event that edge flashing/
coping fails. A robust bar specifically made for bar-over mechanically 
attached single-ply systems is recommended. The bar needs 
to be very well anchored to the parapet or the deck. Depending 
on design wind loads, spacing between 4 and 12 inches on center 
is recommended. A gap of a few inches should be left between 
each bar to allow for water flow across the membrane. After the 
bar is attached, it is stripped over with a stripping ply.

Walkway pads: Roof walkway pads are frequently blown off during 
hurricanes (Figure 3-92). Pad blow-off does not usually damage 
the roof membrane. However, wind-borne pad debris can damage 
other building components and injure people. Walkway pads are 
therefore not recommended in hurricane-prone regions.

Figure 3-91: A continuous peel-stop bar 
over the membrane may prevent a catastrophic 
progressive failure if the edge flashing or coping is 
blown off. (Modified from FEMA 55, 2000)

Parapets: For low-sloped roofs, minimum 3-foot high parapets are 
recommended. With parapets of this height or greater, the uplift 
load in the corner region is substantially reduced (ASCE 7 permits 
treating the corner zone as a perimeter zone). Also, a high 
parapet (as shown in Figures 3-78 and 3-118) may intercept wind-
borne debris and keep it from blowing off the roof and damaging 
other building components or injuring people. To protect base 
flashings from wind-borne debris damage and subsequent water 
leakage, it is recommended that metal panels on furring strips be 
installed over the base flashing (Figure 3-93). Exposed stainless 
steel screws are recommended for attaching the panels to the furring 
strips because using exposed fasteners is more reliable than 
using concealed fasteners or clips (as were used for the failed 
panels shown in Figure 3-58). 

Figure 3-92: To avoid walkway pad 
blow off, as occurred on this hospital roof, 
walkway pads are not recommended. Hurricane 
Charley (Florida, 2004)

3.4.4 Nonstructural Systems and Equipment

Nonstructural systems and equipment include all components 
that are not part of the structural system or building envelope. 
Exterior-mounted equipment is especially vulnerable to hurricane-
induced damage, and special attention should be paid to 
positioning and mounting of these components in hurricane-
prone regions. 

3.4.4.1 Elevators 

Where interruption of elevator service would significantly disrupt 
facility operations, it is recommended that elevators be placed in 
separate locations within the building and be served by separate 
elevator penthouses. This is recommended, irrespective of the 
elevator penthouse enhancements recommended in Sections 3.3.3 
and 3.3.4, because of the greater likelihood that at least one of the 
elevators will remain operational and therefore allow the facility to 
function as intended. 

Figure 3-93: Base flashing protected by 
metal panels attached with exposed screws. Hurricane 
Katrina (Mississippi, 2005)

3.4.4.2 Mechanical Penthouses

By placing equipment in mechanical penthouses rather than 
leaving them exposed on the roof, equipment can be shielded 
from high-wind loads and wind-borne debris. Although screens 
(such as shown in Figure 3-77) could be designed and constructed 
to protect equipment from horizontally-flying debris, they are not 
effective in protecting equipment from missiles that have an angular 
trajectory. It is therefore recommended that mechanical 
equipment be placed inside mechanical penthouses. The penthouse 
itself should be designed and constructed in accordance 
with the recommendations given in Sections 3.4.2 and 3.4.3.

3.4.4.3 Lightning Protection Systems (LPS)

Lightning protection systems frequently become disconnected 
from rooftops during hurricanes. Displaced LPS components can 
puncture and tear roof coverings, thus allowing water to leak into 
buildings (see Figures 3-94 and 3-95). Prolonged and repeated 
slashing of the roof membrane by loose conductors (cables) and 
puncturing by air terminals (lightning rods) can result in lifting 
and peeling of the membrane. Also, when displaced, the LPS is no 
longer capable of providing lightning protection in the vicinity of 
the displaced conductors and air terminals. 

Figure 3-94: A displaced air terminal 
that punctured the membrane in several 
locations. Hurricane Marilyn (U.S. Virgin 
Islands, 1995) 

Lightning protection standards such as NFPA 780 and UL 96A 
provide inadequate guidance for attaching LPS to rooftops in 
hurricane-prone regions, as are those recommendations typically 
provided by LPS and roofing material manufacturers. LPS conductors 
are typically attached to the roof at 3-foot intervals. The 
conductors are flexible, and when they are exposed to high winds, 
the conductors exert dynamic loads on the conductor connectors 
(clips). Guidance for calculating the dynamic loads does not 
exist. LPS conductor connectors typically have prongs to anchor 
the conductor. When the connector is well-attached to the roof 
surface, during high winds the conductor frequently bends back 
the malleable connector prongs (see Figure 3-96). Conductor connectors 
have also debonded from roof surfaces during high winds. 
Based on observations after Hurricane Katrina and other hurricanes, 
it is apparent that pronged conductor connectors typically 
have not provided reliable attachment.

Figure 3-95: View of an end of a conductor that became 
disconnected. Hurricane Katrina (Mississippi, 2005) 

Figure 3-96: The conductor deformed 
the prongs under wind pressure, and pulled 
away from the connector. Hurricane Katrina 
(Mississippi, 2005)

To enhance the wind performance of LPS, the following are 
recommended: 

Parapet attachment: When the parapet is 12 inches high or greater, 
it is recommended that the air terminal base plates and conductor 
connectors be mechanically attached with #12 screws 
that have minimum 1-inch embedment into the inside face of 
the parapet nailer and are properly sealed for watertight protection. 
Instead of conductor connectors that have prongs, it is 
recommended that mechanically attached looped connectors be 
installed (see Figure 3-97). 

Attachment to built-up, modified bitumen, and single-ply membranes: 
For built-up and modified bitumen membranes, attach the air 
terminal base plates with asphalt roof cement. For single-ply membranes, 
attach the air terminal base plates with pourable sealer (of 
the type recommended by the membrane manufacturer). 

In lieu of attaching conductors with conductor connectors, it is 
recommended that conductors be attached with strips of membrane 
installed by the roofing contractor. For built-up and 
modified bitumen membranes, use strips of modified bitumen 
cap sheet, approximately 9 inches wide at a minimum. If strips 
are torch-applied, avoid overheating the conductors. For single-
ply membranes, use self-adhering flashing strips, approximately 9 
inches wide at a minimum. Start the strips approximately 3 inches 
from either side of the air terminal base plates. Use strips that are 
approximately 3 feet long, separated by a gap of approximately 3 
inches (see Figure 3-98).

Figure 3-97: This conductor was attached to 
the coping with a looped connector. Hurricane 
Katrina (Mississippi, 2005)

10. Discussion is based on Rooftop Attachment of Lightning Protection Systems in 
High-Wind RegionsHurricane Katrina Recover Advisory 
(May 2006, Revised July 2006).

As an option to securing the conductors with stripping plies, 
conductor connectors that do not rely on prongs could be used 
(such as the one shown in Figure 3-99). However, the magnitude 
of the dynamic loads induced by the conductor is unknown, 
and there is a lack of data on the resistance 
provided by adhesively-attached connectors. For this 
reason, attachment with stripping plies is the preferred 
option, because the plies shield the conductor from 
the wind. If adhesive-applied conductor connectors 
are used, it is recommended that they be spaced more 
closely than the 3-foot spacing required by NFPA 780 
and UL 96A. Depending on wind loads, a spacing of 6 
to 12 inches on center may be needed in the corner regions 
of the roof, with a spacing of 12 to 18 inches on 
center at roof perimeters (see ASCE 7 for the size of 
corner regions).

Figure 3-98: Plan showing conductor attachment 

Figure 3-99: Adhesively-attached conductor connector that does not use prongs 

Mechanically attached single-ply membranes: It is recommended that 
conductors be placed parallel to, and within 8 inches of, membrane 
fastener rows. Where the conductor falls between or is 
perpendicular to membrane fastener rows, install an additional 
row of membrane fasteners where the conductor will be located, 
and install a membrane cover-strip over the membrane fasteners. 
Place the conductor over the cover-strip and secure the conductor 
as recommended above.

By following the above recommendations, additional rows of 
membrane fasteners (beyond those needed to attach the membrane) 
may be needed to accommodate the layout of the 
conductors. The additional membrane fasteners and cover-
strip should be coordinated with, and installed by, the roofing 
contractor.

Standing seam metal roofs: It is recommended that pre-manufactured, 
mechanically attached clips that are commonly used to 
attach various items to roof panels be used. After anchoring 
the clips to the panel ribs, the air terminal base plates and conductor 
connectors are anchored to the panel clips. In lieu of 
conductor connectors that have prongs, it is recommended 
that mechanically attached looped connectors be installed (see 
Figure 3-97). 

Conductor splice connectors: In lieu of pronged splice connectors 
(see Figure 3-100), bolted splice connectors are recommended 
because they provide a more reliable connection (see Figure 3-
101). It is recommended that strips of flashing membrane (as 
recommended above) be placed approximately 3 inches from 
either side of the splice connector to minimize conductor movement 
and to avoid the possibility of the 
conductors becoming disconnected. To 
allow for observation during maintenance inspections, 
do not cover the connectors.

It is recommended that the building 
designer advise the building owner to 
have the LPS inspected each spring, to 
verify that connectors are still attached to 
the roof surface, that they still engage the 
conductors, and that the splice connectors 
are still secure. Inspections are also 
recommended after high-wind events.

3.4.5 Municipal Utilities 

Hurricanes typically disrupt municipal electrical service, and often 
they disrupt telephone (both cellular and land-line), water, and 
sewer services. These disruptions may last from several days to several 
weeks. Electrical power disruptions can be caused by damage 
to power generation stations and by damaged lines, such as major 
transmission lines and secondary feeders. Water disruptions can 
be caused by damage to water treatment or well facilities, lack of 
power for pumps or treatment facilities, or by broken water lines 
caused by uprooted trees. Sewer disruptions can be caused by 
damage to treatment facilities, lack of power for treatment facilities 
or lift stations, or broken sewer lines. Phone disruptions can 
be caused by damage at switching facilities and collapse of towers. 
Critical facilities should be designed to prevent the disruption of 
operations arising from prolonged loss of municipal services. 

Figure 3-100: If conductors detach from 
the roof, they are likely to pull out from pronged 
splice connectors. Hurricane Charley (Florida, 2004) 

Figure 3-101: Bolted splice connectors 
are recommended to prevent free ends of 
connectors from being whipped around by 
wind. Hurricane Katrina (Mississippi, 2005)

3.4.5.1 Electrical Power 

It is recommended that critical facilities that will be occupied 
during a hurricane, or will be needed within the first few weeks afterwards, 
be equipped with one or more emergency generators. In 
addition to providing emergency generators, it is recommended 
that one or more additional standby generators be considered, 
particularly for facilities such as EOCs, hospitals and nursing 
homes, shelters, and fire and police stations, where continued 
availability of electrical power is vital. The purpose of providing 
the standby generators is to power those circuits that are not powered 
by the emergency generators. With both emergency and 
standby generators, the entire facility will be completely backed 
up. It is recommended that the emergency generator and standby 
generator systems be electrically connected via manual transfer 
switches to allow for interconnectivity in the event of emergency 
generator failure. The standby circuits can be disconnected from 
the standby generators, and the emergency circuits can be manually 
added. The emergency generators should be rated for prime 
power (continuous operation). 

Running generators for extended time periods frequently results 
in equipment failure. Thus, provisions for back-up generation capacity 
are important, because the municipal power system may 
be out of service for many days or even weeks. Therefore, it is recommended 
that an exterior box for single pole cable cam locking 
connectors be provided so that a portable generator can be connected 
to the facility. With a cam locking box, if one or more of 
the emergency or standby generators malfunction, a portable 
generator can be brought to the facility and quickly connected. 

Back-up portable generators should be 
viewed as a third source of power (i.e., they 
should not replace standby generators), because 
it may take several days to get a back-up 
portable generator to the site. 

Generators should be placed inside wind-
borne debris resistant buildings (see 
recommendations in Sections 3.4.2 and 
3.4.3) so that they are not susceptible to 
damage from debris or tree fall. Locating 
generators outdoors (see Figure 4-44) or inside 
weak enclosures is not recommended. 
It is recommended that wall louvers for generators be capable 
of resisting the test Missile E load specified in ASTM E 1996. Alternatively, 
wall louvers can be protected with a debris-resistant 
screen wall so that wind-borne debris is unable to penetrate the 
louvers and damage the generators.

It is recommended that sufficient onsite fuel storage be provided 
to allow all of the facilitys emergency and standby generators to 
operate at full capacity for a minimum of 96 hours (4 days).11 If 
at any time it appears that refueling wont occur within 96 hours, 
provision should be made to shut off part or all the standby circuits 
in order to provide longer operation of the emergency 
circuits. For remote facilities or situations where it is believed 
that refueling may not occur within 96 hours, the onsite fuel 
storage capacity should be increased as deemed appropriate. It 
is recommended that fuel storage tanks, piping, and pumps be 
placed inside wind-borne debris resistant buildings, or underground. 
If the site is susceptible to flooding, refer to Chapter 2 
recommendations.

3.4.5.2 Water Service 

It is recommended that critical facilities that rely on water for 
continuity of service (especially hospitals and nursing homes) 
be provided with an independent water supplya well or onsite 
water storage. Facilities that only need drinking water for 
occupants can have bottled water provided 
instead.

It is recommended that shelters be 
provided with an emergency generator to 
supply power for lighting, exit signs, fire 
alarm system, public address system, and 
for mechanical ventilation. A standby 
generator is also recommended in the 
event that the emergency generator 
malfunctions. A cam locking box is also 
recommended to facilitate connection of a 
back-up portable generator. 

11. The 96-hour fuel supply is based in part on the Department of Veterans 
Affairs criteria.

If water is needed for cooling towers, the independent 
water supply should be sized to 
accommodate the system. It is recommended 
that the well or onsite storage be capable of 
providing an adequate water supply for fire 
sprinklers. Alternatively, it is recommended 
that the building designer should advise the 
building owner to implement a continual fire-watch and provide 
additional fire extinguishers until the municipal water service is 
restored. For hospitals, it is recommended that the well or onsite 
water storage be capable of providing a minimum of 100 gallons 
of potable water per day per patient bed for four days (the 100 gallons 
includes water for cooling towers).12 

It is recommended that pumps for wells or 
onsite storage be connected to an emergency 
power circuit, that a valve be provided 
on the municipal service line, and that onsite 
water treatment capability be provided 
where appropriate.

3.4.5.3 Sewer Service 

It is recommended that critical facilities that rely on sewer service 
for continuity of operations (especially hospitals and 
nursing homes) be provided with an alternative means of waste 
disposal, such as a temporary storage tank which can be pumped 
out by a local contractor. For facilities such as EOCs, fire and police 
stations, and shelters, portable toilets can be placed inside 
the facility before the onset of a hurricane. It is recommended 
that all critical facilities be provided with back-flow preventors.

For critical facilities with boilers, it is 
recommended to store fuel onsite for a 
minimum of 96 hours (4 days). Storage 
tanks, piping, and pumps should be inside 
wind-borne debris resistant buildings or be 
placed underground (if site is susceptible 
to flooding, refer to Chapter 2). 

For hospitals and nursing homes, it is 
recommended that onsite storage of 
medical gases be sized to provide a 
minimum of 96 hours (4 days) of service. 

12. This recommendation is based on the Department of Veterans Affairs criteria.

3.4.6 Post-Design Considerations 

In addition to adequate design, proper attention must be given to 
construction, post-occupancy inspection, and maintenance.

3.4.6.1 Construction Contract Administration 

It is important for owners of critical facilities in hurricane-prone 
regions to obtain the services of a professional contractor who 
will execute the work described in the contract documents in 
a diligent and technically proficient manner. The frequency of 
field observations and extent of special inspections and testing 
should be greater than those employed on critical facilities that 
are not in hurricane-prone regions.

3.4.6.2 Periodic Inspections, Maintenance, and 
Repair 

The recommendations given in Section 3.3.1.4 for post-occupancy 
and post-storm inspections, maintenance, and repair are 
crucial for critical facilities in hurricane-prone regions. Failure 
of a building component that was not maintained properly, repaired 
or replaced, can present a considerable risk of injury or 
death to occupants, and the continued operation of the facility 
can be jeopardized. 

The recommendations given in Section 3.4 are summarized in 
Table 3-4. 

Table 3-4: Recommendations for Design of Critical Facilities 
EOCs, healthcare facilities, and shelters

Design very robustly.

Shelters

Refer to FEMA 361, Design and Construction Guidance for Community 
Shelters.

Walkways between campus buildings

If buildings will be occupied during a hurricane, provide enclosed 
walkways.

Structural systems

Use reinforced cast-in-place concrete. If the roof deck is not cast-in-
place, use precast concrete or concrete topping over steel decking. 

Exterior walls

Use reinforced concrete or fully grouted and reinforced CMU without 
wall coverings, other than paint.

Exterior doors

Use doors designed and tested to resist test missiles.

Exterior windows and skylights

Use laminated glass or shutters designed and tested to resist test 
missiles. If equipped with shutters, glazing is still required to resist wind 
pressure loads.

Roof covering

Design a roof system that can accommodate missiles as recommended 
in Section 3.4.3.4. Avoid aggregate surfacings, lightweight concrete 
pavers, cementitious-coated insulation boards, slate, and tile. Avoid 
single-ply membranes unless ballasted with heavy pavers. 

Parapets 

Use minimum 3-foot high parapets for low-sloped roofs.

Elevators

Place elevators in separate locations served by separate penthouses.

Mechanical penthouses

Place rooftop equipment in penthouses rather than exposed on the 
roof.

Lightning protection systems

Attach LPS to the roof as recommended in Section 3.4.4.3.

Emergency power

Provide emergency power as recommended in Section 3.4.5.1. 

Water service

Provide a water supply independent of municipal supplies. 

Sewer service

Provide a means of waste disposal independent of municipal service.

Construction contract administration

Construction executed by a professional contractor and subcontractors. 
Conduct more frequent field observations, special inspections and 
testing.

Periodic inspections, maintenance, 
and repair

After construction, conduct diligent periodic inspections and special 
inspections after storms. Ensure diligent maintenance and prompt 
repairs. 

3.5 BEST PRACTICES IN TORNADO-PRONE REGIONS

Strong and violent tornadoes may reach wind speeds substantially 
greater than those recorded in the strongest 
hurricanes. The wind pressures that these tornadoes can 
exert on a building are tremendous, and far exceed the minimum 
pressures derived from building codes. Figure 3-102 shows a 
classroom wing in a school in Illinois. All of the exterior windows 
were broken, and virtually all of the cementitious wood-fiber deck 
panels were blown away. Much of the metal roof decking over the 
band and chorus area also blew off. The gymnasium collapsed, as 
did a portion of the multi-purpose room. The school was not in 
session at the time the tornado struck. 

Figure 3-102: A Northern Illinois school 
heavily damaged by a strong tornado in 1990

Strong and violent tornadoes can generate very powerful missiles. 
Experience shows that large and heavy objects, including vehicles, 
can be hurled into buildings at high speeds. The missile sticking 
out of the roof in the foreground of Figure 3-103 is a double 2-
inch by 6-inch wood member. The portion sticking out of the roof 
is 13 feet long. It penetrated a ballasted ethylene propylene diene 
monomer (EPDM) membrane, approximately 3 inches of polyisocyanurate 
roof insulation, and the steel roof deck. The missile 
lying on the roof just beyond is a 2-inch by 10-inch by 16-foot long 
wood member. 

There is little documentation regarding tornado-induced damage 
to critical facilities. Most of the damage reports available pertain 
to schools because schools are the most prevalent type of critical 
facilities and, therefore, are more likely to be struck. A 1978 report 
prepared for the Veterans Administration13 identified four 
hospitals that were struck by tornadoes between 1973 and 1976. 
Table 3-5 (taken from that report) further illustrates the effects 
tornados can have on critical facilities.

Figure 3-103: A violent tornado 
showered the roof of this school with missiles. 
(Oklahoma, 1999)

13. A Study of Building Damage Caused by Wind Forces, McDonald, J.R. and Lea, 
P.A, Institute for Disaster Research, Texas Tech University, 1978. 

Table 3-5: Examples of Ramifications of Tornado Damage at Four Hospitals

For critical facilities located in tornado-prone regions (as defined 
in Section 3.2.2), the following are recommended:

 Incorporate a shelter within the facility to provide occupant 
protection. For shelter design, FEMA 361 criteria are 
recommended. 
 For interior non-load-bearing masonry walls, see the 
recommendations given in Section 3.3.3.3.
 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.
 For hospitals, nursing homes, and other critical facilities 
where it is desired to minimize disruption of operations from 
nearby weak tornadoes and from strong and violent tornados 
that are on the periphery of the facility, the following are 
recommended: 
1) For the roof deck, exterior walls, and doors, follow the 
recommendations given in Sections 3.4.2 and 3.4.3. 
2) For exterior glazing, specify laminated glass window 
assemblies that are designed to resist the test Missile E load 
specified in ASTM E 1996, and are tested in accordance with 
ASTM E 1886. Note that missile loads used for designing 
tornado shelters significantly exceed the missile loads used 
for designing glazing protection in hurricane-prone regions. 
Missiles from a strong or violent tornado passing near the 
facility could penetrate the laminated glazing and result in 
injury or interior damage. Therefore, to increase occupant 
safety, even when laminated glass is specified, the facility 
should also incorporate a shelter as recommended above.



Existing Facilities without Tornado Shelters 

Where the number of recorded F3, F4, and F5 tornadoes per 
3,700 square miles is one or greater (see Figure 3-2 and discussion 
of Fujita Scale in Section 3.1.1), the best available refuge areas 
should be identified if the facility does not have a tornado shelter. 
FEMA 431, Tornado Protection, Selecting Refuge Areas in Buildings 
provides useful information for building owners, architects, and 
engineers who perform evaluations of existing facilities.

To minimize casualties in critical facilities, it is very important that 
the best available refuge areas be identified by a qualified architect 
or engineer.14 Once identified, those areas need to be clearly 
marked so that occupants can reach the refuge areas without 
delay. Building occupants should not wait for the arrival of a tornado 
to try to find the best available refuge area in a particular 
facility; by that time, it will be too late. If refuge areas have not 
been identified beforehand, occupants will take cover wherever 
they can, frequently in very dangerous places. Corridors, as shown 
in Figure 3-104, sometimes provide protection, but they can also 
be death traps. 

Figure 3-104: View of school corridor 
after passage of a violent tornado (Oklahoma, 1999) 

14. It should be understood that the occupants of a best available refuge area 
are still vulnerable to death and injury if the refuge area was not 
specifically designed as a tornado shelter.

Retrofitting a shelter space inside an existing 
building can be very expensive. An economical 
alternative is an addition that can function 
as a shelter as well as serve another purpose. 
This approach works well for smaller facilities. 
For very large facilities, constructing two or 
more shelter additions should be considered 
in order to reduce the time it takes to reach 
the shelter (often there is ample warning 
time, but sometimes an approaching tornado 
is not noticed until a few minutes before it 
strikes). This is particularly important for hospitals and nursing 
homes because of the difficulty of accommodating patients with 
different medical needs. 

The recommendations given in Section 3.5 are summarized in 
Table 3-6.

Table 3-6: Critical Facilities Located in Tornado-Prone Regions
Proposed FacilityOccupant protection 

Refer to FEMA 361 for design guidance.

Interior non-load-bearing masonry walls

See recommendations in Section 3.3.3.3.

Wind-borne missiles

Avoid use of brick veneer, aggregate surfacing, roof 
pavers, slate, and tile.

Healthcare and other critical facilities where it is desired 
to minimize disruption of operations from nearby weak 
tornadoes

See recommendations in Section 3.5.

Existing facilities without specifically designed tornado shelters
If one or more F3-F5 tornadoes per 3,700 square miles 

Identify best available refuge areas. See Figure 3-2 for 
historical data on frequency, and refer to FEMA 431 
(2003) for identification guidance.

If six or more F3-F5 tornadoes per 3,700 square miles 

Consider incorporating a shelter within the building or 
inside a new building addition. Refer to FEMA 320 and 
FEMA 361 for design guidance.

For small shelters within facilities such 
as fire and police stations, a designated 
storage room(s), office(s), or small 
conference room(s) can be economically 
retrofitted in accordance with FEMA 320 
to protect the occupants. Where it is 
desired to provide a large shelter area, 
FEMA 361 criteria are recommended.

3.6 REMEDIAL WORK ON EXISTING FACILITIES

Many existing critical facilities need to strengthen their 
structural or building envelope components. The reasons 
for this are the deterioration that has occurred 
over time, or inadequate facility strength to resist current design 
level winds. It is recommended that building owners have 
a vulnerability assessment performed by a qualified architectural 
and engineering team. A vulnerability assessment should be 
performed for all facilities older than 5 years. However, as illustrated 
by Figure 3-30 and the case of Garden Park Medical Center 
discussed in Section 4.2, an assessment is recommended for all facilities 
located in areas where the basic wind 
speed is greater than 90 mph (even if the 
facility is younger than five years). It is particularly 
important to perform vulnerability 
assessments on critical facilities located in 
hurricane-prone and tornado-prone regions.
Components that typically make buildings 
constructed before the early 1990s vulnerable 
to high winds are weak non-load-bearing 
masonry walls, poorly connected precast concrete 
panels, long-span roof structures with 
limited uplift resistance (e.g., at gyms), inadequately 
connected roof decks, weak glass 
curtain walls, building envelope, and exterior-mounted equipment. 
Although the technical solutions to these problems are not 
difficult, the cost of the remedial work is typically quite high. If 
funds are not available for strengthening or 
replacement, it is important to minimize the 
risk of injury and death by evacuating areas 
adjacent to weak non-load-bearing walls, 
weak glass curtain walls, and areas below 
long-span roof structures when winds above 
60 mph are forecast. 

American Red Cross (ARC) Publication 
4496, Standards for Hurricane Evacuation 
Shelter Selection (2002) provides 
information regarding assessing existing 
buildings for use as hurricane shelters. 
Unless a facility has been specifically 
designed for use as a shelter, it should 
only be used as a shelter of last resort, and 
even then, only if it meets the criteria given 
in ARC 4496. 

As a result of building code changes and 
heightened awareness, some of the common 
building vulnerabilities have generally been 
eliminated for facilities constructed in the 
mid-1990s or later. Components that typically 
remain vulnerable to high winds are the 
building envelope and exterior-mounted mechanical, 
electrical, and communications 
equipment. Many failures can be averted by 
identifying weaknesses and correcting them. 

By performing a vulnerability assessment, items that need to be 
strengthened or replaced can be identified and prioritized. A proactive 
approach in mitigating weaknesses can save significant sums 
of money and decrease disruption or total breakdown in critical 
facility operations after a storm. For example, 
a vulnerability assessment on a school such as 
that shown in Figure 3-105 can identify weakness 
of exterior classroom walls. Replacing 
walls before a hurricane is much cheaper 
than replacing the walls and repairing consequential 
damages after a storm, and proactive 
work avoids the loss of use while repairs are 
made.

A comprehensive guide for remedial work 
on existing facilities is beyond the scope of 
this manual. However, the following are examples 
of mitigation measures that are often 
applicable.

Critical facilities sometimes occupy 
buildings that have changed their original 
use (see the case of Hancock County EOC, 
discussed in Section 4.4). Buildings that 
were not designed for a critical occupancy 
were likely designed with a 1.0 rather 
than a 1.15 importance factor, and hence 
are not as wind-resistant as needed. It 
is particularly important to perform a 
vulnerability assessment if a facility 
is located in a building not originally 
designed for a critical occupancy, 
especially if the facility is located in a 
hurricane- or tornado-prone region. 

Before beginning remedial work, it is 
necessary to understand all significant 
aspects of the vulnerability of a facility 
with respect to wind and wind-driven rain. 
If funds are not available to correct all 
identified deficiencies, the work should be 
systematically prioritized so that the items 
of greatest need are first corrected. For 
example, at a building such as that shown 
in Figure 3-105, had the windows been 
retrofitted with shutters, that effort would 
have been ineffective, because the walls 
themselves collapsed. Mitigation efforts 
can be very ineffective if they do not 
address all items that are likely to fail.

3.6.1 Structural Systems

As discussed in Section 3.1.4.1, roof decks on many facilities designed 
prior to the 1982 edition of the SBC and UBC and the 
1987 edition of the NBC are very susceptible to failure. Poorly attached 
decks that are not upgraded are susceptible to blow-off, as 
shown in Figure 3-106. Decks constructed of cementitious wood-
fiber, gypsum, and lightweight insulating concrete over form 
boards were commonly used on buildings built in the 1950s and 
1960s. In that era, these types of decks typically had very limited 
uplift resistance due to weak connections to the support structure. 
Steel deck attachment is frequently not adequate because of 
an inadequate number of welds, or welds of poor quality. Older 
buildings with overhangs are particularly susceptible to blow-off, as 
shown in Figure 3-107, because older codes provided inadequate 
uplift criteria.

Figure 3-105:Several walls at this school 
collapsed. Windows were located above a non-
load-bearing masonry wall. Hurricane Katrina 
(Mississippi, 2005)

Figure 3-106: The schools built-up roof 
blew off after one of the cementitious wood-fiber 
deck panels detached from the joists. Hurricane 
Katrina (Mississippi, 2005) 

Figure 3-107: The cementitious wood-
fiber deck panels detached from the joists along the 
overhangs and caused the schools built-up 
membranes to lift and peel. Hurricane Katrina 
(Mississippi, 2005)

A vulnerability assessment of the roof deck should include evaluating 
the existing deck attachment, spot checking the structural 
integrity of the deck (including the underside, if possible), and 
evaluating the integrity of the beams/joists. If the deck attachment 
is significantly overstressed under current design wind 
conditions or the deck integrity is compromised, the deck should 
be replaced or strengthened as needed. The evaluation should be 
conducted by an investigator experienced with the type of deck 
used on the building. 

If a low-slope roof is converted to a steep-slope roof, the new 
support structure should be engineered and constructed to resist 
the wind loads and avoid the kind of damage shown in 
Figure 3-108.

Figure 3-108: The schools wood superstructure installed 
as part of a steep-slope conversion blew away 
because of inadequate attachment. Hurricane 
Katrina (Louisiana, 2005)

3.6.2 Building Envelope 

The following recommendations apply to building envelope components 
of existing critical facilities.

3.6.2.1 Sectional and Rolling Doors

Sectional and rolling doors (e.g., at fire station apparatus bays and 
hospital loading docks), installed in older buildings before attention 
was given to the wind resistance of these elements, are very 
susceptible to being blown away. Although weak doors can be retrofitted, 
it is difficult to ensure that the door, door tracks, and 
connections between the door and tracks are sufficient. It is therefore 
recommended that weak doors and tracks be replaced with 
new assemblies that have been tested to meet the factored design 
wind loads. As part of the replacement work, nailers between the 
tracks and building structure should either be replaced, or their 
attachment should also be strengthened.

If a facility has more than one sectional or rolling door, all doors 
should be replaced, rather than just replacing one of the doors. 
The fire station shown in Figure 3-109 had six sectional doors. 
One door had been replaced before a hurricane. It performed 
very well, but three of the older doors were blown away and two of 
the older doors remained in place but had some wind damage.

Figure 3-109: The new door in the center performed very 
well, but the older doors on either side of it were 
blown away. Hurricane Charley (Florida, 2004)

3.6.2.2 Windows and Skylights

Windows in older facilities may possess inadequate resistance 
to wind pressure. Window failures are typically caused by wind-
borne debris, however, glazing or window frames may fail as a 
result of wind pressure (see Figure 3-110). Failure can be caused 
by inadequate resistance of the glazing, inadequate anchorage 
of the glazing to the frame, failure of the frame itself, or inadequate 
attachment of the frame to the wall. For older windows 
that are too weak to resist the current design pressures, window 
assembly replacement is recommended. Some older window assemblies 
have sufficient strength to resist the design pressure, but 
are inadequate to resist wind-driven rain. If the lack of water resistance 
is due to worn glazing gaskets or sealants, replacing the 
gaskets or sealant may be viable. In other situations, replacing the 
existing assemblies with new, higher-performance assemblies may 
be necessary.

It is recommended that all non-impact-resistant, exterior glazing 
located in hurricane-prone regions (with a basic wind speed of 
100 mph or greater) be replaced with impact-resistant glazing 
or be protected with shutters, as discussed in Section 3.4.3.2. 

Figure 3-110: Wind pressure caused 
the window frames on the upper floor to fail (red 
arrow). Hurricane Katrina (Mississippi, 2005)

Shutters are typically a more economical approach for existing 
facilities. There are a variety of shutter types, all illustrated by 
Figures 3-111 to 3-113. Accordion shutters are permanently 
attached to the wall (Figure 3-111). When a hurricane is forecast, 
the shutters are pulled together and latched into place. Panel 
shutters (Figure 3-112) are made of metal or polycarbonate. When 
a hurricane is forecast, the shutters are taken from storage and 
inserted into metal tracks that are permanently mounted to the 
wall above and below the window frame. The panels are locked 
into the frame with wing nuts or clips. Track designs that have 
permanently mounted studs for the nuts have been shown to be 
more reliable than track designs using studs that slide into the 
track. A disadvantage of panel shutters is the need for storage 
space. Roll-down shutters (Figure 3-113) can be motorized or 
pulled down manually. Figure 3-113 illustrates the benefits of 
shuttering. Two of the unprotected window units experienced 
glass breakage and the third window unit blew in. 

Figure 3-111: This school has accordion 
shutters. Hurricane Ivan (Florida, 2004)

Deploying accordion or panel shutters a few stories above grade is 
expensive. Although motorized shutters have greater initial cost, 
their operational cost should be lower. Other options for providing 
missile protection on upper levels include replacing the existing assemblies 
with laminated glass assemblies, or installing permanent 
impact resistant screens. Engineered films are also available for application 
to the interior of the glass. The film needs to be anchored 
to the frame, and the frame needs to be adequately anchored to 
the wall. The film degrades over time and requires replacement 
(approximately every decade). Use of laminated glass or shutters is 
recommended in lieu of engineered films.

Figure 3-112: Illustrates a metal panel 
shutter. Hurricane Georges (Puerto Rico, 1998) 

Figure 3-113: The lower window 
assembly was protected with a motorized shutter. 
Hurricane Ivan (Florida, 2004)

3.6.2.3 Roof Coverings

For roofs with weak metal edge flashing or coping attachment, 
face-attachment of the edge flashing/coping (as shown in Figure 
3-63) is a cost-effective approach to greatly improve the wind resistance 
of the roof system. 

The vulnerability assessment of roofs ballasted with aggregate, 
pavers, or cementitious-coated insulation boards, should determine 
whether the ballast complies with ASNI/SPRI RP-4. 
Corrective action is recommended for non-compliant, roof coverings. 
It is recommended that roof coverings with aggregate 
surfacing, lightweight pavers, or cementitious-coated insulation 
boards on buildings located in hurricane-prone regions be replaced 
to avoid blow off (see Figure 3-114). 

Figure 3-114: Aggregate from the hospitals built-up roofs 
broke several windows in the intensive care unit, 
which had to be evacuated during the hurricane. 
Hurricane Charley (Florida, 2004)

When planning the replacement of a roof covering, it is recommended 
that all existing roof covering be removed down to the 
deck rather than simply re-covering the roof. Tearing off the covering 
provides an opportunity to evaluate the structural integrity 
of the deck and correct deck attachment and other problems. For 
example, if a roof deck was deteriorated due to roof leakage (see 
Figure 3-115), the deterioration would likely not be identified if 
the roof was simply re-covered. By tearing off down to the deck, 
deteriorated decking like that shown in Figure 3-115 can be found 
and replaced. In addition, it is recommended that the attachment 
of the wood nailers at the top of parapets and roof edges be 
evaluated and strengthened where needed, to avoid blow-off and 
progressive lifting and peeling of the new roof membrane (see 
Figure 3-116). 

Figure 3-115: The built-up roof on this 
school was blown off after a few of the rotted wood 
planks detached from the joists. Hurricane Katrina 
(Mississippi, 2005)

If the roof has a parapet, it is recommended that the inside of the 
parapet be properly prepared to receive the new base flashing. In 
many instances, it is prudent to re-skin the parapet with sheathing 
to provide a suitable substrate. Base flashing should not be applied 
directly to brick parapets because they have irregular surfaces that 
inhibit good bonding of the base flashing to the brick (see Figure 
3-117). Also, if moisture drives into the wall from the exterior 
side of the parapet with base flashing attached directly to brick, 
the base flashing can inhibit drying of the wall. Therefore, rather 
than totally sealing the parapet with membrane base flashing, the 
upper portion of the brick can be protected by metal panels (as 
shown in Figure 3-93), which permit drying of the brick.

Figure 3-116: The edge nailer on top 
of an old brick wall at a hospital blew off because it 
was inadequately attached. Hurricane Ivan (Florida, 
2004)

3.6.3 Exterior-Mounted Equipment

Exterior-mounted equipment on existing 
critical facilities should be carefully examined 
and evaluated.

3.6.3.1 Antenna (Communications Mast)

Antenna collapse is very common. Besides loss of communications, 
collapsed masts can puncture roof membranes or cause 
other building damage as shown in Figure 3-118. This case also 
demonstrates the benefits of a high parapet. Although the roof 
still experienced high winds that blew off this penthouse door, the 
parapet prevented the door from blowing off the roof.

In hurricane-prone regions, it is recommended that antennae 
strength be evaluated as part of the vulnerability assessment. 
Chapter 15 of ANSI/TIA-222-G provides guidance on the structural 
evaluation of existing towers. Appendix J of that standard 
contains checklists for maintenance and condition assessments. 
Additional bracing, guy-wires, or tower strengthening or replacement 
may be needed.

Figure 3-117: Failed base flashing 
adhered directly to the brick parapet. Hurricane 
Katrina (Louisiana, 2005) 

Fastening rooftop equipment to curbs, 
as discussed in Section 3.3.4.1, is a 
cost-effective approach to minimize wind-
induced problems.

3.6.3.2 Lightning Protection Systems

Adhesively-attached conductor connectors and pronged splice 
connectors typically have not provided reliable attachment during 
hurricanes. To provide more reliable attachment for LPS located 
in hurricane-prone regions where the basic wind speed is 100 mph 
or greater, or on critical facilities in excess of 100 feet above grade, 
it is recommended that attachment modifications based on the 
guidance given in Section 3.3.4.3 be used. 

The recommendations given in Section 3.6 are summarized in 
Table 3-7.

Figure 3-118: The antenna at this hospital collapsed and 
was whipped back and forth across the roof 
membrane. Hurricane Andrew (Florida, 1992) 

Table 3-7: Recommendations for Remedial Work on Existing Critical Facilities
Weakness Recommended remedy
Critical facilities older than 5 years, or any age if 
located in an area with basic wind speed greater than 
90 mph. 

Perform vulnerability assessment with life-safety issues as 
the first priority, and property damage and interruption of 
service as the second priority. 

A building with weak non-load-bearing masonry or 
curtain walls, poorly connected precast concrete panels, 
or weak long-span roof structures.

Implement remedial work on elements with insufficient 
strength to resist wind loads if the facility will be occupied 
during high wind events (e.g., strong thunderstorms). 

Sectional and rolling doors.

Replace weak doors and tracks. 

Worn window gaskets and sealants. 

Replace with new gaskets and sealants, or replace window 
assembly. 

Buildings in a hurricane-prone region where the basic 
wind speed is 100 mph or greater, with non-impact-
resistant exterior glazing. 

Replace with impact-resistant glazing or protect with 
shutters.

Inadequately attached edge flashings or copings.

Face-attach the vertical flanges. See Figure 3-63.

Ballasted single-ply roof membranes.

Take corrective action if non-compliant with ANSI/SPRI RP-4. 

Buildings in a hurricane-prone region with aggregate 
roof surfacing, lightweight pavers, or cementitious-
coated insulation boards. 

Replace roof covering to avoid blow-off.

Rooftop equipment unanchored or poorly anchored.

Add screws or bolts to anchor equipment to curbs. Add 
cables to secure fan cowlings. Add latches to secure 
equipment access panels. See Section 3.3.4.1.

Weak roof deck connections or weak roof structure.

When planning replacement of roof covering, remove roof 
covering and strengthen attachment of deck and/or roof 
structure. See Section 3.6.2.3.

Emergency generators in a hurricane-prone region not 
adequately protected from wind-borne debris. 

Build an enclosure to provide debris protection. See 
Section 3.4.5.1.

Antennae (communication masts) in hurricane-prone 
regions.

Evaluate wind resistance and strengthen as needed. See 
Chapter 15 and Appendix J of ANSI/TIA-222-G.

Lightning protection systems with adhesively-attached 
conductor connectors or pronged splice connectors 
located in hurricane-prone regions where the basic wind 
speed is 100 mph or greater, or on critical facilities in 
excess of 100 feet above grade.

Modify attachment according to recommendations in 
Section 3.4.4.3.

3.7 Checklist for Building Vulnerability of Critical 
Facilities Exposed to High Winds

The Building Vulnerability Assessment Checklist (Table 3-8) 
is a tool that can help in assessing the vulnerability of various 
building components during the preliminary design 
of a new building, or the rehabilitation of an existing building. 
In addition to examining design issues that affect vulnerability to 
high winds, the checklist also examines the potential adverse effects 
on the functionality of the critical and emergency systems 
upon which most critical facilities depend. The checklist is organized 
into separate sections, so that each section can be assigned 
to a subject expert for greater accuracy of the examination. The 
results should be integrated into a master vulnerability assessment 
to guide the design process and the choice of appropriate mitigation 
measures.

Table 3-8: Checklist for Building Vulnerability of Critical Facilities Exposed 
to High Winds
Vulnerability Sections Guidance Observations General

What is the age of the facility, and 
what building code and edition was 
used for the design of the building?

Substantial wind load improvements were made 
to the model building codes in the 1980s. Many 
buildings constructed prior to these improvements 
have structural vulnerabilities. Since the 1990s, 
several additional changes have been made, the 
majority of which pertain to the building envelope. 

Older buildings, not designed and constructed in 
accordance with the practices developed since 
the early 1990s, are generally more susceptible to 
damage than newer buildings.


Is the critical facility older than 5 
years, or is it located in a zone with 
basic wind speed greater than 90 
mph?

In either case, perform a vulnerability 
assessment with life-safety issues as the first 
priority, and property damage and interruption 
of service as the second priority.

Site

What is the design wind speed at the 
site? Are there topographic features 
that will result in wind speed-up?

ASCE 7 and Section 3.1.3.

What is the wind exposure on site?

Avoid selecting sites in Exposure D, and avoid 
escarpments and hills (Section 3.1.3).

Are there trees or towers on site?

Avoid trees and towers near the facility (Section 
3.3.1.1). If the site is in a hurricane-prone 
region, avoid trees and towers near primary 
access roads (Section 3.4.1).

Road access

Provide two separate means of access (Section 
3.3.1.1).

Is the site in a hurricane-prone 
region?

ASCE 7. If yes, follow hurricane-resistant design 
guidance (Section 3.4).

If in a hurricane-prone region, are 
there aggregate surfaced roofs within 
1,500 feet of the facility?

Remove aggregate from existing roofs (Section 
3.6.2.3). If the buildings with aggregate are 
owned by other parties, attempt to negotiate 
the removal of the aggregate (e.g., consider 
offering to pay the reroofing costs).

Architectural 

Will the facility be used as a shelter?

If yes, refer to FEMA 361.

Are there interior non-load-bearing 
walls?

Design for wind load according to Section 
3.3.3.3. 

Are there multiple buildings on site in 
a hurricane-prone region?

Provide enclosed walkways between buildings 
that will be occupied during a hurricane 
(Section 3.4.1).

Are multiple elevators needed for the 
building?

Place elevators in separate locations served by 
separate penthouses (Section 3.4.4.1).

Structural Systems Section 3.3.2

Is a pre-engineered building being 
considered?

If yes, ensure the structure is not vulnerable 
to progressive collapse. If a pre-engineered 
building exists, evaluate to determine if it is 
vulnerable to progressive collapse.

Is precast concrete being considered?

If yes, design the connections to resist wind 
loads. If precast concrete elements exist, verify 
that the connections are adequate to resist the 
wind loads.

Are exterior load-bearing walls being 
considered?

If yes, design as MWFRS and C&C. 

Is an FM Global-rated roof assembly 
specified?

If yes, comply with FM Global deck criteria.

Is there a covered walkway or 
canopy?

If yes, use free roof pressure coefficients 
from ASCE 7.Canopy decks and canopy 
framing members on older buildings often have 
inadequate wind resistance. Wind-borne debris 
from canopies can damage adjacent buildings 
and cause injury. 

Is the site in a hurricane-prone 
region?

A reinforced cast-in-place concrete structural 
system, and reinforced concrete or fully grouted 
and reinforced CMU walls, are recommended 
(Section 3.4.2).

Is the site in a tornado-prone region?

If yes, provide occupant protection. See FEMA 
361.

Do portions of the existing facility 
have long-span roof structures (e.g., 
a gymnasium)?

Evaluate structural strength, since older 
long-span structures often have limited uplift 
resistance.

Is there adequate uplift resistance 
of the existing roof deck and deck 
support structure?

The 1979 (and earlier) SBC and UBC, 
and 1984 (and earlier) BOCA/NBC, did 
not prescribe increased wind loads at roof 
perimeters and corners. Decks (except cast-in-
place concrete) and deck support structures 
designed in accordance with these older codes 
are quite vulnerable.The strengthening of the 
deck attachment and deck support structure is 
recommended for older buildings.

Structural Systems Section 3.3.2 (continued)

Are there existing roof overhangs 
that cantilever more than 2 feet?

Overhangs on older buildings often have 
inadequate uplift resistance.

Building Envelope Section 3.3.3

Exterior doors, walls, roof systems, 
windows, and skylights.

Select materials and systems, and detail to resist 
wind and wind-driven rain (Sections 3.3.3.1 to 
3.3.3.4).

Are soffits considered for the 
building?

Design to resist wind and wind-driven water 
infiltration (Section 3.3.3.3). If there are existing 
soffits, evaluate their wind and wind-driven rain 
resistance. If the soffit is the only element preventing 
wind-driven rain from being blown into 
an attic space, consider strengthening the soffit.

Are there elevator penthouses on 
the roof?

Design to prevent water infiltration at walls, 
roof, and mechanical penetrations (Sections 
3.3.3.3, 3.3.3.4, 3.3.4.1, and 3.4.4.1).

Is a low-slope roof considered on a 
site in a hurricane-prone region?

A minimum 3-foot parapet is recommended on 
low-slope roofs (Section 3.4.3.4). 

Is an EOC, healthcare facility, shelter, 
or other particularly important critical 
facility in a hurricane-prone region?

If yes, a very robust building envelope, resistant 
to missile impact, is recommended 
(Section 3.4). 

Is the site in a tornado-prone region?

To minimize generation of wind-borne missiles, 
avoid the use of brick veneer, aggregate roof 
surfacing, roof pavers, slate, and tile 
(Section 3.5). 

Are there existing sectional or rolling 
doors?

Older doors often lack sufficient wind 
resistance. Either strengthen or replace. This is 
particularly important for fire station apparatus 
bay doors.

Does the existing building have large 
windows or curtain walls?

If an older building, evaluate their wind 
resistance.

Does the existing building have 
exterior glazing (windows, glazed 
doors, or skylights)?

If the building is in a hurricane-prone region, 
replace with impact-resistant glazing, or protect 
with shutters.

Building Envelope Section 3.3.3 (continued)

Does the existing building have 
operable windows?

If an older building, evaluate its wind-driven 
rain resistance.

Are there existing exterior non-load-
bearing masonry walls?

If the building is in a hurricane- or tornado-
prone region, strengthen or replace.

Are there existing brick veneer, EIFS, 
or stucco exterior coverings?

If the building is in a hurricane-prone region, 
evaluate attachments. To evaluate wind 
resistance of EIFS, see ASTM E 2359 (2006).

Are existing exterior walls resistant to 
wind-borne debris?

If the building is in a hurricane-prone region, 
consider enhancing debris resistance, particularly 
if dealing with an important critical facility.

Are there existing ballasted single-ply 
roof membranes?

Determine if they are in compliance with ANSI/
SPRI RP-4. If non-compliant, take corrective action.

Does the existing roof have 
aggregate surfacing, lightweight 
pavers, or cementitious-coated 
insulation boards?

If the building is in a hurricane- prone region, 
replace the roof covering to avoid blow-off.

Does the existing roof have edge 
flashing or coping?

Evaluate the adequacy of the attachment. 

Does the existing roof system 
incorporate a secondary membrane?

If not, and if the building is in a hurricane-prone 
region, reroof and incorporate a secondary 
membrane into the new system. 

Does the existing building have a brittle 
roof covering, such as slate or tile?

If the building is in a hurricane-prone region, 
consider replacing with a non-brittle covering, 
particularly if it is an important critical facility.

Exterior-Mounted Mechanical Equipment

Is there mechanical equipment 
mounted outside at grade or the 
roof?

Anchor the equipment to resist wind loads (Section 
3.3.4.1). If there is existing equipment, 
evaluate the adequacy of the attachment, including 
attachment of cowlings and access panels.

Are there penetrations through the 
roof?

Design intakes and exhausts to avoid water 
leakage (Section 3.3.4.1).

Is the site in a hurricane-prone 
region?

If yes, place the equipment in a penthouse, rather 
than exposed on the roof (Section 3.4.4.2).

Exterior-mounted Electrical and Communications Equipment 

Are there antennae (communication 
masts) or satellite dishes?

See Section 3.3.4.2. If there are existing 
antennae or satellite dishes and the building is 
located in a hurricane-prone region, evaluate 
wind resistance. For antennae evaluation, see 
Chapter 15 of ANSI/TIA-222-G-2005.

Does the building have a lightning 
protection system?

See Sections 3.3.4.2 and 3.4.4.3 for lightning 
protection system attachment. For existing 
lightning protection systems, evaluate wind 
resistance (Section 3.6.3.1)

Municipal Utilities

Is the site in a hurricane-prone 
region?

See Section 3.4.5.1 for emergency and standby 
power recommendations.

Is the emergency generator(s) 
housed in a wind- and debris-
resistant enclosure?

If not, build an enclosure to provide debris 
protection in a hurricane-prone region (Section 
3.4.5.1).

Is the emergency generators wall 
louver protected from wind-borne 
debris?

If the building is in a hurricane-prone region, 
install louver debris impact protection (Section 
3.4.5.1).

Is the site in a hurricane-prone 
region?

If yes, an independent water supply and 
alternative means of sewer service are 
recommended, independent of municipal 
services (Sections 3.4.5.2 and 3.4.5.3). 

3.8 References and Sources of Additional Information 

NOTE: FEMA publications may be obtained at no cost by 
calling (800) 480-2520, faxing a request to (301) 497-
6378, or downloading from the library/publications 
section online at http://www.fema.gov.

American Association of State Highway and Transportation 
Officials, Standard Specifications for Structural Supports for 
Highway Signs, Luminaires and Traffic Signals, LTS-4-M and LTS-
4-12, January 2001 and October 2003.

American Concrete Institute, Building Code Requirements for Ma-
sonry Structures, ACI 530/ASCE 5/TMS 402, November 1996.

American Institute of Architects, Buildings at Risk: Wind Design 
Basics for Practicing Architects, 1997. 

American National Standards Institute/SPRI RP-4, Wind Design 
Standard for Ballasted Single-Ply Roofing Systems, 2002.

American National Standards Institute/SPRI ES-1, Wind Design 
Standard for Edge Systems Used in Low Slope Roofing Systems, 2003.

American National Standards Institute/Telecommunications 
Industry Association, Structural Standards for Antenna Supporting 
Structures and Antennas, ANSI/TIA-222-G, August 2005.

American Red Cross, Standards for Hurricane Evacuation Shelter 
Selection, Publication 4496, July 1992, rev. January 2002.

American Society of Civil Engineers, Structural Engineering In-
stitute, Minimum Design Loads for Buildings and Other Structures, 
ASCE/SEI 7-05, Reston, VA, 2005.

American Society for Testing and Materials, Standard Test 
Method for Field Determination of Water Penetration of Installed 
Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform or 
Cyclic Static Air Pressure Difference, ASTM E1105, 2000.

American Society for Testing and Materials, Standard Test 
Method for Structural Performance of Sheet Metal Roof and Siding 
Systems by Uniform Static Air Pressure Difference, ASTM E1592, 
2000.

American Society for Testing and Materials, Standard Test 
Method for Structural Performance of Exterior Windows, Curtain 
Walls, and Doors by Cyclic Static Air Pressure Differential, ASTM 
E1233, December 2000.

American Society for Testing and Materials, Standard Practice 
for Installation of Exterior Windows, Doors and Skylights, ASTM 
E2112, 2001.

American Society for Testing and Materials, 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, 2005.

American Society for Testing and Materials, Standard 
Specification for Performance of Exterior Windows, Curtain Walls, 
Doors and Impact Protective Systems Impacted by Windborne Debris in 
Hurricanes, ASTM E1996, 2005.

American Society for Testing and Materials, Standard 
Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware, 
ASTM A153, April 2005.

American Society for Testing and Materials, Standard 
Specification for Steel, Sheet, Cold-Rolled, Carbon, Structural, 
High-Strength Low-Alloy, High-Strength Low-Alloy with Improved 
Formability, Solution Hardened, and Bake Hardenable, ASTM 
A1008/A1008M, 2006.

American Society for Testing and Materials, Test Method for Field 
Pull Testing of an In-Place Exterior Insulation and Finish System 
Clad Wall Assembly, ASTM E 2359, 2006.

American Society for Testing and Materials, Standard Test 
Method for Structural Performance of Exterior Windows, Doors, 
Skylights, and Curtain Walls by Cyclic Air Pressure Differential, 
ASTM E1233, 2006.

American Society of Heating, Refrigeration and Air-
Conditioning Engineers, Inc. (ASHRAE), Ventilation for 
Acceptable Indoor Air Quality, Standard 62.1, 2004.

American Society of Heating, Refrigeration and Air-
Conditioning Engineers, Inc. (ASHRAE), Standard 62.1 Users 
Manual, 2006.

Brick Industry Association, Anchored Brick Veneer-Wood Frame 
Construction, Technical Notes 28, Revised August 2002.

Brick Industry Association, Wall Ties for Brick Masonry, 
Technical Notes 44B, Revised May 2003.

Brick Industry Association, Brick Veneer/Steel Stud Walls, 
Technical Notes 28B, December 2005.

Door & Access Systems Manufacturers Association, Connecting 
Garage Door Jambs to Building Framing, Technical Data Sheet 
#161, December 2003.

FM Global, Loss Prevention Data for Roofing Contractors, 
Norwood, MA, dates vary.

Factory Mutual Research, Approval Guide, Norwood, MA, 
updated quarterly.

FEMA, Building Performance: Hurricane Andrew in Florida, FEMA 
FIA-22, Washington, DC, December 1992.

FEMA, Building Performance: Hurricane Iniki in Hawaii, FEMA 
FIA-23, Washington, DC, January 1993.

FEMA, Corrosion Protection for Metal Connectors in Coastal Areas, 
FEMA Technical Bulletin 8-96, Washington, DC, August 1996. 

FEMA, Typhoon Paka: Observations and Recommendations on 
Building Performance and Electrical Power Distribution System, 
FEMA-1193-DR-GU, Washington, DC, March 1998.

FEMA, Hurricane Georges in Puerto Rico, FEMA 339, Washington, 
DC, March 1999.

FEMA, Oklahoma and Kansas Midwest Tornadoes of May 3, 1999, 
FEMA 342, Washington, DC, October 1999.

FEMA, Coastal Construction Manual, Third Edition, FEMA 55, 
Washington, DC, 2000.

FEMA, Design and Construction Guidance for Community Shelters, 
FEMA 361, Washington, DC, July 2000.

FEMA, Installing Seismic Restraints for Mechanical Equipment, 
FEMA 412, Washington, DC, December 2002.

FEMA, Tornado Protection, Selecting Safe Areas in Buildings, 
FEMA 431, Washington, DC, October 2003.

FEMA, Installing Seismic Restraints for Electrical Equipment, 
FEMA 413, Washington, DC, January 2004. 

FEMA, Installing Seismic Restraints for Duct and Pipe, FEMA 414, 
Washington, DC, January 2004.

FEMA, Taking Shelter From the Storm: Building a Safe Room Inside 
Your House, FEMA 320, Washington, DC, March 2004.

FEMA, MAT Report: Hurricane Charley in Florida, FEMA 488, 
Washington, DC, April 2005.

FEMA, MAT Report: Hurricane Ivan in Alabama and Florida, 
FEMA 489, Washington, DC, August 2005.

FEMA, Home Builders Guide to Coastal Construction Technical Fact 
Sheet Series, FEMA 499, August 2005.

FEMA, Attachment of Brick Veneer in High-Wind Regions
Hurricane Katrina Recovery Advisory, Washington, DC, December 
2005. 

FEMA, MAT Report: Hurricane Katrina in the Gulf Coast, FEMA 
549, Washington, DC, July 2006. 

FEMA, Attachment of Rooftop Equipment in High-Wind Regions
Hurricane Katrina Recovery Advisory, Washington, DC, May 2006, 
rev. July 2006.

FEMA, Rooftop Attachment of Lighting Protection Systems in High-
Wind RegionsHurricane Katrina Recovery Advisory, Washington, 
DC, May 2006, rev. July 2006. 

Institute of Electrical and Electronics Engineers, Inc., National 
Electrical Safety Code, ANSI/IEE/C2, 2006.

International Code Council, 2006 International Building Code, 
ICC IBC-2006, March 2006.

McDonald, J.R. and Lea, P.A, A Study of Building Damage Caused 
by Wind Forces, Institute for Disaster Research, Texas Tech 
University, 1978. 

National Institute of Building Sciences, Building Envelope Design 
Guide, Available online at www.wbdg.org/design/envelope.php. 

National Research Council of Canada, Institute for Research 
in Construction, Wind Design Guide for Mechanically Attached 
Flexible Membrane Roofs, B1049, 2005.

Reinhold, Timothy A. Calculating Wind Loads and Anchorage 
Requirements for Rooftop Equipment, American Society of 
Heating, Refrigerating and Air-Conditioning Engineers Journal, 
Volume 48, Number 3, March 2006. 

[End of Chapter 3]



4.1 INTRODUCTION

This chapter presents some observations on the performance 
of critical facilities during Hurricane Katrina that identify 
the various ways in which building and equipment damage, 
as well as loss of municipal services, can disrupt facility operations. 
These observations are intended to help people who own, operate, 
design, and build critical facilities to adjust their building 
designs, construction, and facility management practices to reflect 
the needs of comprehensive risk reduction.

During Hurricane Katrina, surging floodwaters and high winds 
caused considerable and often catastrophic building damage, 
forcing many critical facilities to cease operations and evacuate 
their premises even before the storm had passed. In many instances 
the continued operation of hospitals, police and fire 
stations, schools, and EOCs was severely compromised by relatively 
minor damage to the building or building-mounted equipment. 
Although the structural components of most critical facilities survived 
the hurricane, other building components performed less 
well, causing serious disruptions. 

The observations highlighted in this chapter, made by a team of 
building professionals (architects and engineers) experienced 
in hazard mitigation, document the variety and severity of the 
building damage, and the corresponding effects on facility operations. 
Field inspections and discussions with facility managers and 
other personnel served as the basis for analysis of the experiences 
of individual facilities. The descriptions of these experiences are 
accompanied with suggestions on possible mitigation measures 
that would improve hazard-resistance and protect the facilitys 
functionality in the future. A comprehensive risk assessment of the 
facilitys operation and building components and systems would 
be required before any specific mitigation measures were implemented. 
This chapter emphasizes the experiences and lessons 
learned from facility operation disruptions in particular circumstances, 
and may not be applicable to all situations. 

4.2 HEALTH CARE FACILITIES

4.2.1 BACKGROUND

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 natural disaster safety program. 
Health care facilities, especially hospitals, are usually very complex 
building systems, because they accommodate diverse and highly 
specialized services in a strictly controlled environment. Hospital 
buildings must be designed to provide appropriate spatial arrangement 
for the flawless interaction between staff, patients, and 
visitors. They also require a complex network of technological infrastructure 
to support the hospitals functions. Even the smallest 
breakdown in this complex network can cascade into a serious disruption 
of operations.

Protecting the functionality of a hospital requires very careful facility 
planning and design that is in accordance with the most 
stringent flooding and high-wind mitigation requirements applicable 
to the site. The damage sustained by hospitals during 
Hurricane Katrina emphasized the fact that many of the Nations 
hospitals occupy old or inadequate buildings that may not be sufficiently 
protected against hazards. In particular, some of the 
hospitals were planned and built before mitigation against natural 
hazards became common practice. 

Considering the expanding gap between the functionality of 
aging hospitals on the one side, and the requirements of new 
technologies and the needs of a growing and aging population 
on the other, it is expected that many of the countrys hospitals 
will have to be replaced, upgraded, or rebuilt in the coming years. 
Some medical industry forecasts predict that by the end of the decade 
the United States will spend $20 billion annually for this 
purpose. Since new or rebuilt hospitals will have to last for a long 
time, the anticipated construction program provides an opportunity 
to rethink hospital planning and design, and to consider how 
to avoid hazard areas and reduce the vulnerability with improved 
hospital design.

The following observations are based on published sources at the 
time of Hurricane Katrina, and on the subsequent interviews with 
providers and regulators in both Louisiana and Mississippi. The 
damage assessments present a picture of common effects on the 
medical facilities, which are consistent across the region affected 
by Hurricane Katrina. Generous contributions by the following institutions 
and their staff are acknowledged:

 St. Tammany Parish Office of Homeland Security and 
Emergency Preparedness (Covington, Louisiana)
 Touro Infirmary (New Orleans, Louisiana)
 West Jefferson Medical Center (Jefferson Parish, Louisiana)
 Hancock Medical Center (Bay St. Louis, Mississippi)
 Garden Park Medical Center (Gulfport, Mississippi)
 Guest House of Slidell (Slidell, Louisiana)
 Slidell Memorial Hospital (Slidell, Louisiana)
 LSU Health Sciences Center (New Orleans, Louisiana)
 Charity Hospital (New Orleans, Louisiana)
 University Hospital (New Orleans, Louisiana)

4.2.2 Effects of Flooding


The damage caused by Hurricane Katrina flooding was significantly 
more serious than the damage caused by wind. Along the 
Gulf Coast, the storm surge was higher than previously experienced, 
which caught many health care providers by surprise (see 
Figure 1-2). In most places, the storm surge flooding receded in 
several hours, but in New Orleans the floodwaters remained for 
more than a week. Apart from the damage and disruption caused 
by floodwaters that penetrated the facilities lower levels, many 
hospitals in New Orleans were completely surrounded by floodwaters, 
which cut off all surface access.

As a result of the disrupted access, most hospitals had to manage 
on their own, without any assistance from the outside. Patients 
and visitors were stranded, along with staff that could not be relieved 
for days. The injured, and others in need of emergency 
care, could not be brought in for treatment. Family and friends 
of people stranded in the hospitals had no way of communicating 
with them. Food, water, medical, and other supplies could not be 
brought in except by small boats and helicopters, or in some instances, 
by military vehicles. The evacuation of the critically ill 
patients, and eventually others, was possible only by boat or by helicopter. 
Hospitals with dedicated or improvised elevated helipads 
managed the evacuation much better than others. 

Hospitals and nursing homes that were inundated during Katrina 
experienced the greatest damage. Hospital functions located in 
the areas exposed to floodwaters had to be shut down. In many 
cases, the elevators and other mechanical and electrical services 
were shut down by the floodwaters. 

Flooding caused considerable disruption of utility services in most 
hospitals in the New Orleans area. Sewers flooded or pumping 
stations shorted out, disabling sewage and liquid waste disposal. 

The water supply was interrupted and, in many instances, onsite 
sources were contaminated and could not be used for drinking 
purposes. Emergency generators and electrical switchgear equipment, 
as well as underground transformers flooded and were put 
out of commission.

In several instances, communications panels and other controls 
were located on the first floor and shorted out. The heat and the 
buildup of humidity in New Orleans ruined the telephone connections 
and the fire alarm systems in some hospitals, even though 
floodwaters did not contact sensitive communications equipment 
directly.

4.2.3 Effects of High Winds

In general, three types of wind damage affected the hospitals: 
damaged roof coverings, rooftop equipment, and window 
breakage. Damaged roof coverings that were either peeled off or 
punctured by wind-borne debris exposed the interior to rainwater 
penetration and additional damage. Similarly, rooftop equipment 
displaced by wind left unprotected roof openings exposed 
to rainwater penetration. Water damage ranged from saturation of 
interior surfaces, like walls and ceilings, to ruined equipment and 
considerable mold growth.

Window breakage during the storm was particularly dangerous, 
because it allowed the penetration of rainwater, and wind that can 
cause pressurization in the interior. Hospital patient rooms, however, 
faced the greatest risks from window breakage, because many 
of their occupants could not be moved away from monitors, medical 
gases, and other equipment.

4.2.4 Site Design

Although most of New Orleans is located in the lowlands that are 
protected by a system of canals and levees, the hospitals were not 
built to resist the flooding caused by levee failures. As a result of 
Hurricane Katrina and the failure of levees, only 3 out of more 
than 20 of the citys hospitals remained open during the storm 
(see Figure 4-1). Only one of these, the Touro Infirmary, was not 
completely surrounded by water, retaining access on one side. Access 
problems affected all hospitals. West Jefferson Medical Center 
had planned to deploy their staff in two shifts, to allow the second 
shift to stay at home until the storm had passed and then come to 
relieve the staff locked down in the hospital. Because of impeded 
access, the relief staff could not get to the hospital, which put an 
added burden on the initial staff, already nearing exhaustion.

Figure 4-1:University Hospital surrounded by 4 feet of 
water

Figure 4-2: Evacuation of New Orleans by helicopter

Hancock Medical Center in Bay St. Louis, Mississippi, although located 
outside of the 500-year floodplain, experienced 3-foot deep 
flooding as a result of the storm surge (see Figure 4-3). Access 
to the hospital was disrupted long before Katrina made landfall 
because, prior to the storm arrival, there was a 33-mile traffic back-
up on the road leading out of town. Access was important because 
all the functioning hospitals needed relief supplies, medical gases, 
water, and fuel for their emergency generators. In many cases, the 
only way to resupply the facilities was by air, using large Chinook 
helicopters. These helicopters are too heavy for most roof structures, 
and to use them for emergencies in the future, a second 
helipad may be necessary on the site, requiring sufficient glide angles 
for landing and takeoff of the largest aircraft.

Access to emergency services was also blocked by the water and, 
in some cases, by trees and utility lines that were knocked down. 
Once the hospitals had access restored, they were deluged by 
the injured from nearby communities. Slidell Memorial Hospital 
administered 40,000 tetanus shots in the days after the storm. 
Hancock Medical Center saw 600 to 700 patients a day for up to 2 
weeks after the surge water receded. 

Figure 4-3: The lobby of Hancock Medical Center was under 
3 feet of water.

Perhaps the most serious consequence of the impeded access was 
the way it affected the evacuation of hospitals in New Orleans. 
Serious disruptions in hospital operations required immediate 
evacuation, which could not take place because the streets were 
not accessible for up to 5 days. There was a critical need for a 
helipad, either on the roof or an equivalent landing area on a 
parking structure, with emergency lighting for night operation. 
Elevated parking structures were a great asset, providing both a 
protection for the vehicles and a convenient helicopter landing 
site on the roof. They were especially useful if the parking structure 
had an elevated pedestrian bridge to the hospital.

4.2.5 Architectural Design

A typical hospital configuration is based on access requirements 
that usually place the emergency department on the first floor 
in order to receive walk-in patients or those brought in by ambulances. 
Clinical laboratory and imaging are frequently on the 
first floor as well, as are surgery and intensive care units in many 
smaller hospitals. All of these are vital services in the event of an 
emergency and for providing routine patient care. Location on 
the first floor frequently exposes them to additional risks from 
natural hazards, especially flooding, as became evident during 
Hurricane Katrina.

Building configuration and general shape frequently contribute to 
high-wind damage. Protrusions and projections in walls and roofs 
cause additional wind turbulence that increases uplift pressures. 
The penthouse at West Jefferson Medical Center illustrates the 
vulnerability of projections and corners to high winds (see Figure 
4-4). Large portions of metal cladding came loose because they 
were not designed or constructed to resist these loads.

Canopies, which most hospitals have over drop-off areas, are particularly 
susceptible to uplift and other damage, if not designed to 
resist the loads (see Figure 4-5). Glass-enclosed lobbies and atria, 
common to many hospitals, also proved to be a hazard, because 
of the large areas of usually unprotected glazing that could easily 
shatter under the impact of wind-borne debris. In many cases, 
these areas were closed during the storm, thereby cutting off a 
major point of access to the hospitals.

At Louisiana State University Hospital, the emergency generators 
in the basement were flooded and shut down, which put the 
entire hospital out of commission. Similarly, all the major mechanical 
equipment in Charity Hospital in New Orleans was in the 
basement, including fifteen 5,000-watt emergency generators. The 
hospital had to be evacuated soon after the basement flooded and 
the emergency power supply failed. Touro Infirmary, however, had 
the emergency power generators located on the third floor. This 
allowed them to run most of the critical systems, including the 
air conditioning, without interruption until the generators broke 
down from prolonged use and contaminated fuel supplies. 

Figure 4-4: Penthouse at the West Jefferson Medical Center

Figure 4-5: Canopy soffit damage at West Jefferson Medical 
Center

Critical operations such as emergency and surgical departments, 
recovery rooms, ICUs, and other patient bed units and laboratories 
should not be located in areas below ground or below the 
elevation of possible flooding and storm surge. These critical 
functions should be located on upper floors or in areas where 
communication between floors is easily accomplished. These areas 
should have no windows, or should have protected glazing to prevent 
window breakage and rain water penetration.

4.2.6 Building Envelope

Building envelope damage during Hurricane Katrina was widespread 
and included uplifted roof coverings and flashing, roofing 
punctured by flying debris or overturned roof-mounted equipment 
that led to extensive rainwater penetration, wall cladding 
separation, and window and door breakage.

The building envelope on the Garden Park Medical Center in 
Gulfport, a relatively new building opened in 2000, sustained considerable 
damage from 130-mph winds during Hurricane Katrina. 
The estimated wind speed may appear to have been close to the 
current design wind speed of 135 mph for this facility, but the actual 
pressures were below the current design pressures as a result 
of the 1.15 importance factor required for hospitals. Wall cladding 
consisting of EIFS was blown off in several areas, allowing 
water to penetrate wall cavities (see Figure 4-6). Extensive use of 
EIFS, despite a long track record of failure during hurricanes, 
contributed to significant damage from water penetration. EIFS is 
a popular wall cladding system, but not strong enough to prevent 
damage from wind-borne debris in cases where EIFS is applied 
over studs. In addition, EIFS design or construction deficiencies 
frequently make it insufficiently resistant to suction pressures 
caused by high winds. This is especially significant for hospitals, 
where such damage can allow water penetration and trigger serious 
disruptions in the mechanical and electrical systems and 
damage the building interior. Hospitals in hurricane-prone regions 
that have EIFS should have field testing performed to 
evaluate its attachment. 

Hancock Medical Center suffered damage to the wall sheathing 
behind the exterior brick veneer. This damage resulted from 
standing water at significant depths in various locations around 
the building. The sheathing retained moisture long enough to 
compromise its integrity through swelling, and to support the 
growth of mold and bacteria. There have been numerous examples 
of the failure of brick veneer. The reasons for this include 
corroded brick metal ties, insufficient number of metal ties installed, 
or ties not adequately embedded in the mortar. 

Many hospitals have low-slope roofs. There have been many instances 
of failure of this type of roof, frequently beginning at 
the edge flashing and progressively spreading to other parts of 
the roof. Roofs are also susceptible to puncture, as happened at 
the Hancock Medical Center and Garden Park Medical Center 
(see Figure 4-7). Rubber walkway pads were blown away and the 
roof membrane was punctured in several places by displaced 
equipment and other flying debris. As a result, a substantial 
amount of water leaked through the roof openings into the top 
floor, causing considerable damage to the interior. In addition, 
the aggregate surfacing blew off, damaging glazing on surrounding 
buildings. 

Figure 4-6: Repair of EIFS wall covering on Garden Park 
Medical Center

Hancock Medical Center lost substantial portions of its metal 
roofing. Patients had to be relocated from the top floor to lower 
floors because of roof leakage (see Figure 4-8). West Jefferson 
Medical Center lost portions of roofing on the Psychiatry building, 
when the metal roof covering partially peeled off. The leading 
edge began to peel back, but did not go any further than the edge 
flashing, so a minimal amount of water penetrated through the 
roof. The psychiatry building was not occupied at the time because 
the hospital evacuated the building before the hurricane landfall.

Figure 4-7: Roof membrane starting to peel off at Hancock 
Medical Center.

Figure 4-8: Roof damage on Hancock Medical Center

The primary cause of window breakage was wind-borne debris. 
(see Figure 4-9). West Jefferson Medical Center had 76 windows 
broken, mainly by flying aggregate. Intensive care patients had to 
be moved to the recovery room in the interior of the building and 
away from windows. The Psychiatry building had rainwater penetration 
through windows, even though they were not broken. 

Although many important hospital functions are located away 
from the exterior windows, wind-blown rain can damage expensive 
equipment even when it is located some distance from 
the broken window (see Figure 4-10). At West Jefferson Medical 
Center, the fitness center building sustained $250,000 worth 
of damage that resulted from water driven through the broken 
windows and from 30 days of high humidity, before the air-conditioning 
was restored. 

Exterior doors were often pushed in by floodwaters and blown 
open and damaged by wind pressure. Breakaway doors are particularly 
vulnerable to opening in high-wind conditions, as wind 
pressure can build up through the unsecured doors. Ground 
floor entrance doors at Hancock Medical Center had to be 
blocked by sandbags and two-by-fours, both on the inside and the 
outside, to stay closed (see Figure 4-11). The penthouse door at 
Garden Park Medical Center in Gulfport was blown off its hinges 
by strong winds.

Figure 4-9: Broken windows at Touro Infirmary
Hancock Medical Center lost numerous fan cowlings and other 
rooftop equipment, which left openings in the roof. Water penetrated 
the building through these openings, reaching the first 
floor, and damaged boilers and other equipment. Vent openings in 
the elevator penthouse in Touro Infirmary were blown off, allowing 
water penetration. The water damaged the electrical and mechanical 
equipment and controllers, shutting down the elevators.

Figure 4-10: Broken windows at West Jefferson Medical Center

Figure 4-11: Blocked doors at Hancock Medical Center

West Jefferson Medical Center lost a number of cowlings and 
other covers causing water damage to equipment in the rooms 
below the roof. Some motors were sealed and continued to work 
during the storm. 

All rooftop equipment should be safely secured to the curb 
and stay in place during a high-wind event. Equipment that 
has a high failure rate in high-wind events includes air-conditioning 
condensers, HVAC units, exhaust fans and air intake 
and exhausts. 

4.2.7 Utility Plumbing Systems

Hospitals depend heavily on municipal services and other utilities. 
While it is possible to go into a minimal function mode and still 
maintain patient safety, certain utility systems must be operable. 
In many cases, Hurricane Katrina and the subsequent flooding 
pushed hospitals beyond the limits of even a minimal function 
mode. Many had to be shut down, and the patients and staff had 
to be evacuated. In addition to the loss of electrical power, the 
most common problem in maintaining the operations proved to 
be the failure of water supply and sewer systems. 

Most hospitals lost water within a day or two following Hurricane 
Katrinas landfall. Even when the water service was restored, 
it was suspected of contamination. Drinking water was in short 
supply in many hospitals. West Jefferson Medical Center received 
three truck loads of bottled water from a local retailer in the aftermath 
of the storm, but other hospitals suffered from serious 
shortages. A running water supply is critical for boilers to produce 
steam for sterilizing; for the chillers for the air-conditioning 
system; and for sanitary uses like toilets, washing dishes and 
linens, bathing patients, etc. The most successful hospitals had 
their own wells from which they pumped water using an emergency 
power supply. The hospitals that stayed without water and 
an emergency power supply had to evacuate patients as quickly 
as possible. As a consequence of this experience, West Jefferson 
Medical Center is planning to install two wells to provide both 
sufficient capacity and redundancy. One well will service the central 
plant boilers and chillers, and the other will be dedicated to 
hospital operations.

Potable water service will likely be shut down during and immediately 
after an event because of line breakages, lack of power to run 
pumping stations, or repair delays because of blocked roads and 
access routes. Hospitals, especially those in hurricane-prone regions, 
need a back-up water supply system in the form of:

 Wells for exclusive hospital use should be supplied with their 
own emergency generator to run the well pumps.
 Water storage or water recycling systems on site should serve as 
a back-up to the central water supply.
In many areas, the sewer system broke down shortly after the 
storm arrived, either because of loss of power required to run municipal 
pumping stations, sewage back-up or shut down of sewage 
treatment plants as a result of flooding, or because uprooted trees 
broke the sewer lines. When the water and sanitary waste systems 
were disabled, patients and staff were required to use hazardous 
waste bags (red bags) taped to buckets or toilet bowls to manage 
bodily waste. At West Jefferson Medical Center, used bags were 
stored in the hallways for several days and then buried on the hospital 
site for later disposal.

Hospital design in hurricane-prone regions should also take into 
consideration the need to provide an onsite sewage-diversion and 
storage system to prevent sewer backflows from disrupting hospital 
sanitary system operations. Field observations indicate that in situations 
where the sanitary sewer system may be damaged, causing a 
disruption in service, functionality may be protected by:

 Installation of an onsite septic tank as a sanitary back-up 
system 
 Installation of backflow devices in the sanitary lines to prevent 
sewage from backing up into the hospitalm Designating, as part of the operations 
plan, a limited number 
of sanitary systems to use in the hospital, so the onsite storage 
tank does not fill too quicklym Creating holding ponds for direct pumping of 
sewage, if sufficient site area is available

4.2.8 Mechanical and Electrical Systems

Hurricane Katrina struck at a time when the temperatures during 
the daytime reached 95F. Air-conditioning systems in hospitals 
were generally not connected to the emergency power supply, 
nor was there any flexibility to switch emergency power from one 
system to another to provide some relief. The heat build-up was a 
significant factor in creating difficult conditions for patients and 
staff (see Figure 4-12). 

Lack of air-conditioning also allowed humidity to build up, which 
caused problems with switchgear, computers, and other electronic 
equipment. In many cases dehumidifying and cooling 
could not resume for months after the event. The excessive humidity 
damaged the electronic components of mechanical 
and electrical equipment, such as fire alarm systems, elevator 
switchgear, or the telephone switchgear, as happened in Touro 
Infirmary. Mold growth in conditions of high temperatures and 
humidity caused further damage. At West Jefferson Medical 
Center, rainwater and high humidity caused considerable damage 
to the fitness center, requiring all the electrical equipment to 
be replaced. The ground floor at Hancock Medical Center was 
flooded 3 feet deep; enough to cover all electrical outlets close to 
the floor. The damage was irreparable.

Figure 4-12: Toppled HVAC equipment at Charity Hospital, New 
Orleans

Air-conditioning systems were also disrupted by a lack of water 
needed for water-cooled chillers, as happened in Garden Park 
Medical Center in Gulfport when the municipal water service 
was shut down. Loss of air-conditioning resulted in interior condensation, 
and warm and humid air interfered with the normal 
functioning of electronic medical equipment. 

Measures to provide sufficient HVAC capacity for patient-occupied 
and support areas and to protect the operation of the hospital 
from humidity-related damages include the following:

 Install emergency electrical generators with capacity to run the 
air conditioning system. This might also require water for the 
chillers if this is the method of delivering cold air. 
 Install sufficient controls in the hospital to be able to identify 
the areas with mold and mildew problems, and have them 
cordoned off quickly.
 Install HVAC duct cleanout locations, so that any mold or 
mildew that begins to grow in the ductwork can be easily 
cleaned out.
 Create air-conditioning zones (where practical), so that crucial 
operations can be cooled with a minimum amount of air-
conditioning. 

In a storm of Katrinas magnitude, it is expected that power would 
be lost almost immediately and for a considerable period of time 
thereafter. For example, Touro Infirmary lost power within minutes 
of being hit with wind gusts of about 60 mph. Since power 
is so vital to maintaining functionality in critical facilities during 
normal periods, it is of paramount importance to provide an 
emergency power supply for all critical hospital functions.

Most hospitals store up to 72 hours of emergency fuel on site. 
In the case of Hurricane Katrina, emergency generators needed 
to run continuously for 5 days or more. Many hospitals had 
to obtain fuel for their generators from outside sources, usually 
the military. West Jefferson Medical Center got fuel from a 
nearby Navy ship. Hancock Medical Center had one of their underground 
emergency generator fuel tanks flooded, with water 
covering the fill cap and all vent openings. They could not use 
this tank, fearing that contaminated fuel would damage the 
power generators.

The capability to switch power to different locations at different 
points in time is one of the most important features of 
emergency power supply systems. However, most of the wiring 
systems in facilities affected by Hurricane Katrina were not set 
up with this capability. Emergency power in most cases was not 
available to run the air-conditioning systems. Redundancy in the 
emergency power systems that would have allowed maintenance 
and repair without disruption was lacking in most cases.

Portable generators, where they existed, were invaluable. They 
could be moved around as needed, but the problem of outside 
ventilation was difficult to overcome when the power was 
required away from vent openings. Use of generators indoors 
is extremely dangerous and should not be attempted in any 
circumstances.

More and more hospitals are dependent on computerized systems 
for patient medical records, transmission of X-ray film and other 
images, reporting laboratory results, patient physiological monitors, 
and a myriad of other uses. Once the power is lost, these 
systems are shut down unless they are on emergency power. 

Piped oxygen and nitrous oxide supplies are essential for many 
patients. With electrical systems out, pumping of medical gas 
was not possible. Most of the hospitals maintained tanks of oxygen 
that could be brought to the bedside (Figure 4-13), but 
once the emergency supplies of medical gas ran out, the patients 
at serious risk had to be evacuated. 

The experience of hospitals during Katrina indicates that the 
requirements for emergency power should have high priority. 
Generators should be located above the base flood elevation, be 
protected from flying debris, and have appropriate exhaust vent 
systems installed. Fuel storage tanks should be located above 
the flood elevation, or adequately anchored to ensure that the 
tank will not float off its foundation under pressure from rising 
floodwaters. 

Hospitals in hurricane-prone regions should store 
sufficient fuel to support running generators at full load for at 
least 96 hours (4 days). Emergency power distribution systems 
should be able to provide power to every system in the hospital, 
and have switching capabilities to shift loads to different parts of 
the hospital as needed.

4.2.10 Communications Systems

Hospitals have a variety of communications systems in addition to the 
usual telephone and e-mail systems. Many of these are for emergency 
communications with ambulances and other emergency support 
services. These include satellite telephones, government line telephones, 
ham radios, internal radio systems, nurses call systems, and 
wireless systems of various sorts. Communications systems are critical 
for medical uses, but during a storm like Katrina, the ability to contact 
family members and friends to check on their status meant a lot 
to both the staff and the patients. The importance of being able to get 
news from outside, to request restocking of supplies, and to arrange 
evacuation of patients became obvious in the aftermath of Katrina.

One consistent theme in damage reports was that satellite dishes 
were toppled, rendering satellite phones, one of the main sources 
of emergency communications, inoperable. Antennae used for 
emergency communications frequently broke, disconnecting the 
hospital systems from the outside world. Hancock Medical Center 
lost not only the satellite dish, but also the dish for the education 
system and its television antennae. West Jefferson Medical Center 
lost only one antenna. 

Figure 4-13: Oxygen supplies at Hancock Medical Center

External communication isnt the only important link that 
can be broken during a hurricane. Internal communications 
(for example, from surgery to the nursing floor, or from the 
nursing floor to the supply storage areas) are critical to maintain 
functionality.

At Hancock Medical Center, the only means for internal communications 
were 5-Watt Motorola radios. These continued to work 
well, and were relied upon exclusively when the telephone switchgear 
flooded and broke down. West Jefferson Medical Center also 
used radio communication that continued to work throughout the 
storm. Cellular phones also worked, until the transmission tower 
was toppled. Hospitals that had ham radio operators bring their 
equipment in, or had a ham radio set-up in the hospital, found 
this system very important and useful. Several hospitals plan to 
have ham radios available for future emergencies. 

Charity Hospital and West Jefferson Medical Center lost their computers 
because the computer network power supplies were not 
wired into the emergency power supply grid. John Hancock Medical 
Center also lost its computers when the ground floor flooded 
(see Figure 4-14). 

Since many communication systems are dependent on external 
networks that may be out of commission, roof antennae should be 
well anchored, or mounted inside of penthouses. Satellite dish antennae 
may have to be taken down prior to a hurricane and put 
back after the storm had passed. Finally, redundancy of systems is 
important, as proven during Katrinaone system may work where 
others do not.

4.2.11 Nonstructural and Other Systems

Nonstructural systems, among others, include interior non-load-
bearing walls, ceilings, and floors. In hospitals flooded with storm 
surge, floors were destroyed and gypsum board walls were soaked. 
At Hancock Medical Center the water level reached 3 feet. The 
hospital must replace all the flooring material, rewire the outlets, 
and replace the wall sheathing at a level about 2 feet above the 
high water mark (see Figure 4-15).

In many hospitals humidity buildup damaged floor and ceiling 
tiles. Touro Infirmary had to replace 60,000 square feet of tile 
flooring and all of the ceiling tiles in the hospital because of humidity 
damage. The loss of air-conditioning at West Jefferson 
Medical Center caused the buildup of humidity in the air, leading 
to water condensation on terrazzo floors, making them very 
slippery.

Security was a major issue for most New Orleans hospitals. Members 
of the community naturally sought the hospital for shelter 
when their homes were destroyed. When the water rose, people 
trapped in the city followed the waters edge to the Touro Infir
mary and West Jefferson Medical Center, where crowds of people 
congregated on the front doorsteps. Attempted break-ins and 
looting were reported, which prompted hospitals to barricade 
doors, post armed guards at entrances, and lock down so that 
no one could either enter or leave. At University Hospital, the 
doors were removed and the entrances sealed up.

Figure 4-14: Damaged computer network equipment at 
Hancock Medical Center

Hospitals that allowed families to come in with the staff for the 
duration of the storm encountered numerous problems after a 
few days. Many of the family members became restless because 
hospitals had no appropriate accommodations for them. This became 
a security problem, as it was important to keep guests away 
from the patients and their caregivers. 

Fire safety should be a concern during a storm since the fire 
risks are usually greater than at other times. Although the fire 
alarms are normally connected to emergency power, other types 
of damage made them inoperable. At Touro Infirmary, the 
build-up of humidity knocked out the electronic components of 
the fire alarm system. After the storm, 470 points needed to be 
repaired before the system was fully operational again. At West 
Jefferson Medical Center, the fire alarm system was undamaged, 
but the line to the fire station was cut. Heat-activated fire suppression 
systems continued to function where sufficient water 
pressure was available, but dry standpipes might not have been 
supplied with water in the event of a fire. Directional signs in 
many hospitals were blown away. In the rush for care after the 
hospitals were accessible, it was necessary to put up temporary 
signage to route the large volume of visitors and patients to the 
right destination. 

Figure 4-15: Drying of flooded ground floor at Hancock Medical 
Center

4.2.12 Summary

The General Accounting Office (GAO) report to Congress on the 
evacuation of hospitals and nursing homes noted that administrators 
should consider several issues when deciding to evacuate 
or to shelter in place, including the availability of adequate resources 
to shelter in place, the risks to patients in deciding when 
to evacuate, the availability of transportation to move patients 
and of receiving facilities to accept patients, and the destruction 
of the facilitys or communitys infrastructure. For new facilities, 
most of these issues can and should be addressed during 
site selection, risk assessment, and application of the appropriate 
planning and design recommendations described in this manual. 
For existing facilities, careful evaluation and consideration of the 
recommendations provided in this manual should help ensure 
greater resilience during flooding and high-wind hazard events. 
In this way, communities can continue to depend on these facilities 
both for the care of existing patients and the care of people 
in disaster emergencies.

4.3 EDUCATIONAL FACILITIES 

4.3.1 Background

Educational facilities are considered critical facilities because, 
apart from their vital role in educating children, they are 
frequently used during and after a storm as emergency shelters, 
or as staging centers by the National Guard, law enforcement 
personnel, or critical infrastructure repair crews for emergency 
operations. Educational facilities, in this case mostly K-12 school 
buildings, are generally equipped with food preparation facilities, 
well distributed sanitary facilities, and ample space for personnel 
and equipment.
 
The primary function of a place of refuge shelter is the protection 
of the occupants during a storm. This function is dependent 
on preservation of the structural integrity of the building and 
the building envelope. The failure of a structural component or 
a breach in the building envelope can lead to casualties and can 
make the buildings unusable as a recovery shelter after the storm. 

Educational facilities planned for use as place of refuge shelters 
must, above all, protect the lives and well-being of evacuees. To do 
so, they must be constructed to withstand storm surge or inland 
flooding and wind impact. This means that they must be located 
in areas that minimize these storm effects. If they are located in 
the areas subject to flooding and high-wind hazards, they need to 
be constructed to preserve full functionality, with uninterrupted 
electricity, communications, water, and sanitary service. This will 
also allow them to serve as recovery shelters. Educational facilities 
that may not have served as shelters during the storm, because 
of their proximity to the coast or their susceptibility to inland 
flooding, may be useful as recovery shelters provided they are able 
to survive the hurricane intact. 

The primary function of a recovery shelter is to provide a location 
for resources and manpower after the storm has passed, to centralize 
the command and distribution functions for recovery work 
in the community. Recovery shelters require that all building functions 
and services remain usable in the aftermath of a storm. They 
are often used by the American Red Cross (ARC), National Guard, 
or other government agencies as a distribution point of first aid, 
food, water, and other supplies. They also serve as management or 
information dissemination hubs concerning recovery efforts.

The following facilities were visited for the preparation of this 
manual:

 Charles P. Murphy Elementary School (Pearlington, Mississippi)
 Pass Christian Middle School (Pass Christian, Mississippi)
 St. Stanislaus High School (Bay St. Louis, Mississippi)
 Northbay Elementary School (Bay St. Louis, Mississippi)
 Hancock High School (Kiln, Mississippi)
 Pineville Elementary School (Pass Christian, Mississippi)
 DIberville High School (DIberville, Mississippi)
 DIberville Middle School (DIberville, Mississippi)
 Lyman Elementary School (Gulfport, Mississippi)
 East Hancock Elementary School (Hancock County, Mississippi)
 Saucier Elementary School (Saucier, Mississippi)
 Port Sulpher School (Port Sulpher, Louisiana)

4.3.2 Effects of Flooding

The most devastating damage to educational facilities during Hurricane 
Katrina was caused by the storm surge. FEMA reported 
a storm surge of 20 to 30 feet above normal tide levels. In some 
places the flooding extended up to 6 miles inland. The effect on 
coastal communities was catastrophic, because most buildings 
within a quarter of a mile of the shore were virtually washed away, 
while most of the remaining buildings beyond this area were severely 
damaged. Virtually all of the educational facilities in Pass 
Christian, Mississippi, were heavily damaged as a result of their 
proximity to the coastline. 

Inland flooding occurred in low-lying areas farther away from the 
coastline. DIberville Middle School had approximately 8 feet of 
water, but was not used as a shelter because the school district 
staff was aware of the potential for flooding from past experience. 
The structural integrity of the school was not compromised by the 
flooding, but the water damage to the interior was substantial (see 
Figure 4-16). 

Figure 4-16: DIberville Middle School was flooded to the depth 
of 8 feet

The experience of Hurricane Katrina shows that the damage 
caused by rising water generally renders shelters uninhabitable 
and useless, further aggravating the recovery process. In most cases 
the mechanical and electrical systems were disabled as a result of 
flooding, which allowed the internal temperatures to reach intolerable 
levels. Additionally, the flood-induced back-flow of plumbing 
systems created unsafe sanitary conditions in most of the facilities.

4.3.3 Effects of High Winds

Hurricane Katrina reached maximum gust wind speeds of 130 
mph at landfall, with hurricane force winds extending outward 
105 miles from the center of the storm (FEMA, 2006). Numerous 
tornadoes were also spawned by the hurricane, contributing to 
further damage as the storm moved northward. There were 11 tornadoes 
recorded in Mississippi, with 17 more in Georgia, and 4 
in Alabama. Current model building codes in the areas affected 
by Hurricane Katrina generally require buildings to be designed 
to meet 120 to 150 mph design wind speeds. Some buildings, 
however, were constructed prior to the implementation and enforcement 
of the current model codes.

Wind damage was most evident on the building envelope, especially 
roofs, walls, doors, and windows, as well as other exterior 
elements, such as walkway canopies and exposed mechanical and 
electrical equipment. The extent of the damage was dependent 
on the force of the wind, the type of construction, and the configuration 
of the buildings. Once a building envelope was breached, 
the interior of the building sustained additional damage, both as 
a result of pressurization and rainwater penetration. The most severe 
damage in the interior was observed on the least durable 
finishes, such as acoustical ceilings, wood doors and trim, and 
building contents such as office equipment, furniture, and books. 

Most of the educational facilities used as place of refuge shelters 
suffered wind damage to the roofs and windows. When a portion 
of the roof was lost or a window was broken, rainwater was able 
to enter the building, causing damage to the interior. In some instances, 
the occupants were forced to relocate to other buildings 
during the storm, because of the danger of progressive building 
failure (see Figure 4-17).

4.3.4 Site Selection

Most educational facilities that were destroyed or severely damaged 
by Katrina were located in the areas subject to storm surge 
flooding. Ideally, educational facilities used as shelters should 
not be located in floodplains, but since they must be located in 
proximity to the neighborhoods they serve, some are built on 
flood-prone sites. Even if buildings can be elevated to reduce the 
potential for damage, the surrounding area remains susceptible 
to flooding, which could prevent access and disrupt the delivery 
of emergency aid. This also underscores the need to provide multiple 
routes to and from a facility, in case of roadway blockage 
following a storm.

Pineville Elementary School near Pass Christian, Mississippi, was 
used as a place of refuge during the storm, but when the water 
rose to a depth of 2 feet, the people had to be moved by school 
buses to another shelter (see Figure 4-18). The buses were driven 
by school bus mechanics struggling to maintain control in rising 
water and 80 mph winds.

Figure 4-17: Broken windows at DIberville High School

The schools in Pass Christianmostly one-story buildings located 
in mapped flood hazard areassustained heavy damage from 
storm surge flooding. The massive storm surge devastated parts of 
Northbay Elementary School in Bay St. Louis, Mississippi, a single-
story building located in a mapped flood zone. Exterior walls 
collapsed, and most of the interior and contents were destroyed 
(see Figure 4-19).

Figure 4-18: Pineville Elementary School shelter had to 
be evacuated when the floodwaters started to rise.

Figure 4-19: Exterior walls at Northbay Elementary School

St. Stanislaus High School in Bay St. Louis, although located right 
on the coast, was on naturally higher ground, and only the first 
floors were affected by the storm surge. Within a few months after 
the storm, the second floors in some of the buildings had been repaired, 
including restored power, water, and sanitary service, and 
were back in use (see Figure 4-20).

Considerable damage occurred in low-lying areas that were 
flooded by storm surge ranging in depth from 2 to 8 feet. Such 
was the case at DIberville Middle School in DIberville, Mississippi, 
which sustained severe damage, including the destruction 
of many exterior walls, when water rose to nearly 8 feet above the 
floor. Fortunately, it was not used as a shelter, unlike the nearby 
DIberville High School, which is a designated shelter. The high 
school is built on higher ground and was not affected by flooding.

4.3.5 Architectural Design

Generally, educational facilities have centrally located corridors 
(with classrooms or other spaces on both sides) that have ready access 
to sanitary facilities, are at least 8 to 10 feet wide, and are free 
of all obstructions. These features make them ideally suited for 

Figure 4-20: Lower floors washed away by the storm surge at St. 
Stanislaus campus

emergency shelter use. Although there are a few exterior openings 
that can be breached by a storm, the hallways are generally 
well protected from outside elements. It should be pointed out, 
however, that in situations where the roof or the exterior walls fall, 
interior corridor walls may collapse as well. The corridors are usually 
unfurnished and readily available for a variety of functions. 
They served well as safe areas during the storm, with only a few notable 
exceptions. At the DIberville High School, the corridors had 
unprotected windows at each end. These windows were broken 
during the storm and it was necessary to move people into another 
building. Unfortunately, there were no enclosed walkways or 
interior corridors connecting the buildings, and it was necessary 
to go outside into the storm to reach the other building. Similarly, 
when the roof structure at Lyman Elementary School shelter 
started to fail, it became necessary to take the refugees outside before 
they could reach safety in another building (see Figure 4-21).

For hurricane shelter safety, it would be beneficial to have all of 
the buildings connected with enclosed corridors, to allow safer 
movement between buildings during a storm. Other components 
of the building envelope would have to be sufficiently resistant 
to wind and wind-borne debris impact to protect the occupants 
and the services they need. School corridors in particular should 
either have impact-resistant (or protected) windows or none at all. 
All exterior doors should also be designed to meet hurricane wind 
loads and wind-borne debris impact requirements, as described in 
Section 3.4.3.1).

Figure 4-21: Collapsed portion of the Lyman Elementary School Building

4.3.6 Structural Systems

Most of the educational facilities observed were one-story buildings 
with concrete slab-on-grade foundations constructed using 
concrete masonry load-bearing walls and steel-framed roofs. 
The roof joists were supported either by masonry walls or steel 
beams. Some facilities, like the East Hancock Elementary School, 
used pre-engineered systems consisting of rigid steel frames supporting 
a standing seam metal roof. Pass Christian Middle School 
and Saucier Elementary School used structural steel frames 
with standing seam or built up roofs. St. Stanislaus High School, 
located on the coast, had a concrete structural frame where the 
first floor was heavily damaged by the storm surge, but the foundations, 
concrete structure, and the upper floors survived. This was 
because the buildings on campus were located on higher ground 
than the surrounding area. 

The storm surge exerted tremendous forces on the buildings in its 
path, first as the water rose, and again when it receded. The forces 
were strong enough to knock down exterior masonry walls, as happened 
in the Northbay, Charles B. Murphy, Pass Christian, and 
Plaquemines Parish schools (see Figure 4-22). In most cases, the 
main structural components survived with little or no damage. 

Figure 4-22: Damaged exterior walls at Charles B. Murphy 
Elementary School

Designing the connections between structural components according 
to loads is critical to maintaining the load path and 
the structural integrity of school buildings in hurricane-prone 
regions. 

4.3.7 Building Envelope

Newer educational facilities located some distance from the coast 
sustained mainly wind-induced damage to the building envelope, 
primarily to roof coverings and windows. Facilities located along 
the coastline were hit by the storm surge that destroyed most of 
the building envelope on the ground floor, including large sections 
of exterior walls. The walls collapsed under flood loads that 
exceeded all expectations. 

At Charles P. Murphy Elementary School, many of the infill masonry 
walls were displaced, and the concrete slabs on grade were 
uplifted and severely cracked in several classrooms (see Figure 
4-23). A similar slab failure also occurred at DIberville Middle 
School. The cause of this type of failure was an increase in upward 
hydrostatic pressure below the slab, causing it to burst upward.


Figure 4-23: Cracked concrete floor slab at Charles B. Murphy 
Elementary School

The St. Stanislaus High School campus consists of several buildings 
that used different exterior wall systems, including masonry 
and precast concrete panels. The masonry walls on the first floor 
were heavily damaged by the storm surge, but it appears that 
the precast concrete panels withstood the force of the hurricane 
much better (see Figure 4-24). Large sections of the exterior masonry 
walls at St. Stanislaus, as well as in Northbay Elementary in 
Bay St Louis and Port Sulphur schools in Plaquemines Parish, collapsed 
under the pressure from storm surge (see Figure 4-25).

Figure 4-24: Precast concrete paneling at St. Stanislaus High 
School

Figure 4-25: Collapsed exterior masonry wall at Port 
Sulphur school campus

The exterior brick veneer walls at the Pass Christian Middle School 
and at St. Stanislaus cracked and separated from the wall framing 
under the impact of storm surge (see Figure 4-26). This kind of 
damage usually results from a failure of brick ties that did not 
manage to hold the brick in place. In many cases these attachments 
can corrode and allow the brick veneer to move under lateral pressure. 
Such damage allows the penetration of water into the interior, 
where additional damage to building contents is inevitable.

The wind-induced damage was limited primarily to the roof components 
at the edge, such as flashing and coping. More substantial 
damage occurred on a building at St. Stanislaus campus and at 
Harrison 9th Grade gym, where large sections of metal roof covering 
were blown away (see Figure 4-27). The standing seam metal 
roof panels peeled back and away from the roof framing, exposing 
the interior to rainwater and additional wind damage. 

Typically, glazed doors, windows, and roof coverings are the 
building envelope components most susceptible to damage caused 
by wind-borne debris. Although glass or shutters designed to resist 
such wind-borne debris are available, none of the educational 
facilities had protection on the windows and doors. The corridor 
windows at DIberville High School were broken during the storm, 
which prompted the complete evacuation of the building.

Figure 4-26: Cracked brick veneer at St. Stanislaus High School

For buildings located in flood hazard areas, especially areas not 
subject to storm surge, elevation well above the predicted flood 
level is the most effective damage-reduction measure. Dry floodproofing 
may be used to provide some degree of protection, 
although if floodwaters rise higher than the designed level of 
protection, the damage can be catastrophic. This technique, generally 
feasible for flood depths of only 2 or 3 feet, is expensive 
and difficult to implement on existing buildings. Depending on 
the expected depth of water, local soil properties, and the size 
and location of openings, the facilities can be designed to limit 
water infiltration through the walls, openings, and conduits, and 
prevent envelope failure due to excessive hydrostatic pressure. 
Dry floodproofed buildings must have detailed emergency plans, 
with clear instructions for deployment of devices and other measures. 
Lack of periodic maintenance can render floodproofing 
measures ineffective.

Another alternative for minimizing structural damage to existing 
buildings is to provide wet floodproofing. This approach, which is 
not allowed for new construction, allows water to flood the lower 
floors protected with water-resistant materials and finishes that 
can be easily cleaned and restored.

Figure 4-27: Metal roof covering peeled away at a St. Stanislaus 
campus building

4.3.8 Utility Systems

Educational facilities are typically not equipped with emergency 
back-up systems, but are mostly dependent on municipal water 
and sanitary systems. The breakdown of municipal water and 
sewer services, caused by power outages which shut down water 
treatment plants and pumping stations, adversely affected most of 
the facilities. Although a few of the facilities affected by Hurricane 
Katrina were served by onsite wells and some had septic systems, 
lack of power prevented their full use. The sanitary sewer system 
backed up under pressure from floodwaters and, together with 
the loss of water service, created great difficulties inside facilities 
used as shelters. 

The sanitation problems, especially the unpleasant odors that permeated 
the facilities, combined with high humidity and heat, 
posed a serious health risk. At the DIberville High School, the 
loss of water prompted volunteers to haul buckets of water from a 
nearby ditch to be used for flushing the toilets. After the storm had 
passed, portable toilets and showers were brought in by the ARC. 

4.3.9 Mechanical and Electrical Systems

Most mechanical systems depend on the exterior equipment 
mounted on the roof or attached to the exterior walls. The exposed 
equipment is the most vulnerable element in the system, 
because it is commonly damaged by floodwaters, strong wind, 
and wind-borne debris. Rooftop equipment, such as air-handling 
units and exhaust fans, typically were not adequately anchored 
to meet the hurricane-force winds and were frequently damaged 
or toppled. Through-wall fan coil units installed below classroom 
windows at the Charles P. Murphy Elementary School in Pearlington 
were ruined by rising floodwaters (see Figure 4-28). 

As a result of HVAC failures, conditions in shelters became very 
unpleasant because of the heat build-up and the lack of ventilation. 
The interior temperatures and humidity rose to unbearable 
levels because of the hot weather that followed Hurricane Katrina. 
Without the advantage of sufficient natural ventilation, the 
atmosphere quickly became stuffy. Undamaged mechanical equip
ment, especially HVAC systems, was not operational because of 
the power outage and the lack of emergency power supply. At 
DIberville High School, the principal reported using a generator 
to run a large portable box fan in the corridors to provide some 
relief. The same generator also provided power for night-time 
lighting in the corridors.

The Harrison County School District office was one of the few 
buildings equipped with a generator, and for that reason it was 
used as an EOC. It served as a command center and provided 
sleeping and dining facilities for emergency crews. The success of 
this experience reinforces the importance of having emergency 
power generator systems and a sufficient fuel supply. Emergency 
generators should be in a protected enclosure and at an elevation 
high enough to prevent flooding.

4.3.10 Nonstructural and Other Systems

It is essential to the operation of educational facilities used as 
place of refuge and recovery shelters that communications systems 
remain operational. The place of refuge shelters had a 
variety of communications systems at their disposal at the beginning 
of the storm. This included the phone system, cellular 
telephones, school system radios, and police and fire radios. 
These systems proved to be unreliable during the storm when 
antennae and utility lines were damaged. Immediately after the 
storm, all communications had to be handled through messengers, 
until portable antennae were brought to restore both cell 
phone and radio service. The Harrison County school board 
is now considering the purchase of satellite phones to be used 
during emergencies.

Figure 4-28: Damaged HVAC unit at Charles B. Murphy 
Elementary School

Nonstructural components and contents of educational facilities 
sustained the greatest damage from flooding. At DIberville 
Middle School, all interior wood doors, frames, trims, casework, 
fan coil units, and furniture typically suffered severe damage 
from water exposure. 

The majority of interior walls were constructed of un-reinforced 
concrete masonry. Portions of these walls and some exterior non-
load-bearing walls at Charles P. Murphy Elementary School were 
knocked down by the storm surge (see Figures 4-29 and 4-30). If 
the buildings had been occupied during the storm, people could 
have easily been injured by falling debris. Although many of these 
walls are used as partitions and are consequently not load-bearing, 
their mass poses a threat to life and property should they collapse. 

Figure 4-29: Damaged non-load-bearing walls at Charles 
B. Murphy Elementary School

4.3.11 Equipment and Auxiliary Installations

School equipment is not necessarily important for the operation 
of emergency shelters, except for kitchen and dining facilities. 
Schools that sustained flooding damage usually had all their food 
preparation and refrigeration equipment ruined. The equipment 
stored outside consists mainly of buses and other vehicles. 

In Pass Christian, many of the school buses stationed in the town 
were destroyed by the storm surge (see Figure 4-31), although some 
of them were used during the storm to move people from Pineville 
Elementary School to another shelter because of rising water.

The Harrison County School District moved all of its buses farther 
inland before the storm, which ultimately proved prudent and allowed 
the buses to remain available for use after Katrina. In the 
aftermath, Harrison County School District had no fuel supply to 
operate the buses or other vehicles. Several years ago, the school 
district opted to issue gasoline cards to the bus drivers to fill up at 
various gas stations rather than at a central depot. After the storm 
there were few gas stations operating, and it became a time-consuming 
process to get fuel for any vehicle. In the future, Harrison 
County School District intends to have its own gasoline supply 
available on generator power to ensure that school vehicles are 
kept operational.

Figure 4-30: Interior damage at Charles B. Murphy Elementary 
School

4.3.12 Summary

Educational facilities intended to serve as emergency shelters, 
together with accompanying parking lots and access roads serving 
these shelters, should be located inland, away from the coast, and 
on high enough ground to avoid flooding. Educational facilities 
that are built closer to the shore because of the school district 
boundaries should be constructed with the first floor above the 
highest expected storm surge level. These educational facilities 
should not be used as shelters during a hurricane, but could 
serve as relief centers after the storm, as long as they do not 
sustain significant damage. No educational facilities should be 
constructed within the immediate area along the shore, where 
waves are the strongest.

Based on observations, the most resilient school buildings are 
built using reinforced concrete structural systems, or reinforced 
masonry construction. The best performing roof decks were 
cast-in-place concrete, precast concrete, or concrete topping 
over metal deck. Reinforced concrete or reinforced concrete 
masonry exterior and interior walls, including precast concrete 
panels and tilt-up concrete wall panels, seem to have sustained 
the least flood damage. Other observations indicate that the 
following measures may help reduce the damage in hurricane-
prone regions:

Figure 4-31: School bus washed away by the storm surge

 Doors should be designed to meet the positive and negative 
design wind pressure and impact resistance, as recommended 
in Section 3.4.3.1. Windows should use impact-resistant glazing 
or shutters.
 Educational facilities that will be occupied during a hurricane 
or needed within a few weeks afterwards should be equipped 
with an emergency generator.
 All shelters should have protected communications systems 
linked to the EOC.
 Exterior corridors should be enclosed to allow full access 
between buildings, so that no one is forced to go outside 
during a storm to get to another area of a building.
 All educational facilities intended for use as evacuation shelters 
should be designed according to FEMA 361 guidelines.

4.4 EMERGENCY RESPONSE FACILITIES 

4.4.1 Background

Emergency response facilities include EOCs, police stations, 
and fire rescue stations. All of these facilities are 
considered critical because they must remain functional 
to manage response and recovery operations during and after 
a hazard event. EOCs function as incident command centers 
for coordination and support of all emergency activities. 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, shelters, media, and other first 
responders, while providing Continuity of Government (COG) 
and Continuity of Operations (COOP).
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.

While each of the three types of emergency response facilities 
is used for different operational purposes and their needs are 
different, most of them require and depend on the following 
facilities:

Back-Up Communications Equipment: Conventional communications 
that rely on radio towers with repeater systems cannot be relied 
upon during high-wind events, because of the high probability 
that the towers will lose power, as occurred in many jurisdictions 
in Mississippi and Louisiana. All facilities need back-up communications 
systems such as very high-frequency (VHF) and ham 
radios, and adequate back-up communications equipment.

Accommodation Space: Adequate space for all the essential personnel 
to work, with provisions made for continuous operations, 
such as sleep areas, kitchens (with supplies for all duty personnel), 
laundry facilities, and shower facilities for all such personnel. It 
should also be noted that many residents view the local fire station 
as a point of shelter, and will seek it as a refuge when winds and 
conditions become dangerous in their own homes. 

Situation Rooms: Meeting rooms in which to conduct local government 
business as well as confer with community members, 
media, and government officials, and for press conferences and 
dissemination of information.

Safe Equipment Storage: Patrol and rescue vehicles and other equipment 
must be adequately protected from flood waters, wind-borne 
debris, and driving rain, and be accessible and readily available for 
emergency use.

The observations included in this section are based on the examination 
of the following facilities:

 Harrison County EOC (Gulfport, Mississippi)
 Jackson County EOC (Pascagoula, Mississippi)
 New Orleans EOC (New Orleans, Louisiana)
 Hancock County EOC (Bay Saint Louis, Mississippi)
 Orleans District Levee Board Police Department (New 
Orleans, Louisiana)
 New Orleans Police Department (New Orleans, Louisiana)
 Gulfport Police Department (Gulfport, Mississippi)
 Pass Christian Police Department (Pass Christian, Mississippi)
 New Orleans Fire Department (New Orleans, Louisiana)
 Gulfport Fire Department (Gulfport, Mississippi)
 Pass Christian Fire Department (Pass Christian, Mississippi)
 Cuevas Volunteer Fire Department (Pass Christian, 
Mississippi)
 Back Bay Fire Company #3 (Biloxi, Mississippi)

4.4.2 Effects of Flooding

Flooding during Hurricane Katrina, especially the impact of the 
storm surge and levee failures, caused heavy damage that disrupted 
the long-term functional capabilities of the emergency 
response system. 

The facilities damaged by rising water were generally rendered 
uninhabitable after the water receded. As a result, the 
emergency response teams were forced to relocate the operations 
elsewhere. Evacuation and relocation was common among 
damaged fire rescue and police facilities and affected their operations 
on many levels. Firstly, relocating farther away from their 
service areas meant that the response time to emergency calls increased 
substantially. Secondly, the response teams were forced 
to operate from temporary accommodations with inadequate facilities 
that were frequently overcrowded. Thirdly, new facilities 
lacked adequate supplies and services for the extra personnel, 
which required numerous improvisations, further hampering the 
operations.

4.4.3 Effects of High Winds

The highest gust wind speeds during Hurricane Katrina were typically 
below the design wind speeds for this area, which range 
from 120 to 150 mph. Despite this, many emergency response facilities 
sustained damage that disrupted their operations, and in a 
few cases shut down the facility. Most of the damage was confined 
to the building envelope. Portions of metal roofing were lifted 
and peeled off; aggregate roof surfacing was blown off, becoming 
wind-borne debris; and roof-mounted equipment, including communication 
towers and antennae, were toppled or broken. Metal 
wall-cladding panels detached or peeled off on a number of facilities, 
exposing the interior to pressurization and rainwater 
penetration. Doors and windows were damaged by wind-borne debris, 
allowing the penetration of wind-driven rain. 

4.4.4 Site Selection

Ideally, the emergency response facilities should not be located in 
a floodplain or a site exposed to other types of hazards. However, 
emergency response facilities, especially fire rescue and police stations, 
must contend with geographic limitations pertaining to size 
and adequate coverage of their service areas that frequently place 
them in hazardous locations. Many of the facilities flooded during 
Katrina were located in designated floodplains. However, this 
fact alone does not explain the catastrophic damage sustained by 
facilities such as the police and fire stations in Pass Christian, Mississippi 
(see Figure 4-32), because most of the facilities damaged 
by flooding were built above the minimum required elevations. 
The primary reason for the widespread damage is the catastrophic 
nature of the flooding, caused by extremely high storm surge and 
the failure of levees in New Orleans. 

In locations where the emergency response facilities were built to 
a higher standard than required by local regulations, the adverse 
effects of Katrina were substantially reduced. The Jackson County 
EOC occupies the second floor of a municipal building located 
in Pascagoula, Mississippi. An examination of the storm surge 
flooding associated with different hurricane scenarios indicated 
that the site would be inundated during a Category 3 hurricane. 
Consequently, the county decided to design the building to be 
approximately 4.5 feet above BFE (see Figure 4-33). During Hurricane 
Katrina, floodwaters rose to about an inch below the level 
of the lowest floor. The building was not evacuated prior to the 
storm, because it was believed that flooding would not exceed the 
maximum levels recorded during Hurricane Camille. As floodwaters 
started to rise, the decision was made to evacuate most of the 
occupants to another building across the street. Despite this action, 
the EOC operations were not hampered significantly. 

The Pass Christian police and west side fire station were less fortunate, 
as the storm surge flooding at these sites far exceeded the 
base flood elevation. It was estimated that the storm surge wave 
that hit the police building was at least 15 to 20 feet high, which 
rendered the building and the equipment stored inside totally unusable. 
The facility is currently looking at an alternative site on 
higher ground as a possible site for relocation and construction of 
a new station. 

The headquarters of the New Orleans Police Department had 
approximately 2- to 3-foot deep water on the first floor, and a completely 
flooded basement (see Figure 4-34). The surrounding 
areas were also under water, isolating the facility and preventing 
its normal operation. All operations had to be transferred to other 
police facilities in the city.

Figure 4-32: Police station in Pass Christian

The Hancock County EOC in Bay St. Louis, Mississippi, is located 
on naturally high ground outside mapped flood hazard areas. 
Nevertheless, the floodwaters inundated the ground level, damaging 
the interior finishes and practically destroying all equipment 
and contents (see Figure 4-35). Most of the EOCs operations were 
transferred to an alternate location prior to Katrinas landfall, 
most likely because the facility is mapped as part of an evacuation 
zone in case of a hurricane.

Figure 4-33: Jackson County EOC

Figure 4-34: New Orleans Police Department Headquarters

Site characteristics and landscaping contributed significantly to the 
extent and type of damage sustained by these facilities. The Gulfport 
Fire Station #5 in Gulfport, Mississippi, experienced significant disruption 
because of downed trees. One tree fell on the roof, causing 
minor damage, while two vehicles parked outside were severely damaged 
by the fallen trees. Furthermore, it took approximately 12 
hours of cutting the trees before firefighters were able to open 
the access road and start responding to emergency calls. This experience 
also underscores the need to provide multiple routes into 
and away from a site, in order to have redundancy and minimize the 
possibility of isolation as a result of roadway blockage.

The experience during Hurricane Katrina proved the efficacy of 
preventive evacuation of equipment and personnel to a safe and 
secure location. It also proved wise to organize back-up facilities in 
other locations or in adjacent jurisdictions to serve as alternative 
command and operation centers. Emergency response facilities 
that did so were better equipped to respond to citizens needs immediately 
after the storm. 

4.4.5 Architectural Design

Many buildings used as emergency response facilities were not 
initially designed for that purpose, or for operations under emergency 
conditions. During and after Hurricane Katrina, most of 
them experienced significant problems, irrespective of the level 
of damage. Some of these facilities are located in existing buildings 
designed as regular office space. These facilities performed 
poorly, and although they were able to adapt to the circumstances, 
they did not operate as efficiently as those designed for their particular 
functions.
 
Figure 4-35: Hancock County EOC

For example, EOC facilities in New Orleans were placed into civic 
center offices, which were not equipped with kitchens, showers, 
and other facilities essential for the smooth and continuous operation 
of an EOC (see Figure 4-36). As a consequence, the facility 
had to be relocated immediately after Katrina because the available 
accommodations were insufficient and poorly equipped. 
Some of the buildings occupied by first responders were originally 
designed for a different purpose and subsequently converted to 
their current use. 

Figure 4-36: New Orleans EOC in the City Hall building

Generally, any building, whether new or old, that is used as an 
emergency response facility should be carefully reviewed for compliance 
with the requirements for uninterrupted operation of 
the facility. Particular attention should be paid to issues that have 
historically caused problems in building or operational performance, 
such as: 

 Roof systems not designed for high winds and debris impact
 Rooftop equipment
 Unprotected exterior glazing
 Large, sectional and rolling doors not designed for high winds
 Communications towers
 Large roof overhangs
 Lack of facilities for an extended length of stay, especially 
emergency sanitary facilities and power supply
Basements are another design feature with a high damage potential, 
especially when important services and facility functions are 
located there. The basement at the New Orleans Police Department 
completely flooded, and all the essential equipment located there 
was severely damaged, crippling the facility for a long time. Observations 
indicate that essential functions and service equipment should 
be transferred from flood-prone basements to safer locations.

The relatively new Back Bay Fire Company #3 station in Biloxi, 
Mississippi, was built in 1996, and yet its design does not reflect 
the current needs of its occupants. The spaces are too small to accommodate 
the duty shifts. The kitchen is inadequate for longer 
stays, while the sleeping area has unprotected, large, storefront-
type windows that represent a serious hazard in high-wind 
situations (see Figure 4-37). These minor architectural deficiencies 
may be amplified during the times of crisis and adversely 
affect the operation of the facility, especially if combined with 
other building component failures.

4.4.6 Structural Systems

Concrete and reinforced masonry have traditionally been the most 
robust structural systems for hurricane-prone areas, since they 
have a much higher reserve structural strength than other systems. 
During high-wind conditions, the added weight of the concrete 
helps counteract the uplift forces, while the mass and depth of concrete 
and masonry walls provides reserve structural strength that 
prevents the walls from being breached during high winds and 
flood conditions. However, with precast concrete elements, attention 
to design and construction of connections is important. This 
was generally confirmed during Hurricane Katrina. 

The Jackson County EOC, located in Pascagoula, Mississippi, was 
built in 1977 and is an example of a structurally well-designed facility. 
The structure is composed of cast-in-place concrete, and 
performed remarkably well (see Figure 4-38). Although the EOC 
is located on the second floor of the building, water only came 
within 1 inch of the ground floor, which is approximately 4 to 5 
feet above the surrounding grade. Other structural systems proven 
to be resistant to flood and wind loads are steel or concrete frames 
that are covered with precast concrete panels. These systems have 
very high reserve capacities that perform extremely well during 
high winds and storm surges. 

Figure 4-37: Back Bay Fire Company #3

In contrast, pre-engineered metal buildings performed less well. 
Although the main structural components of most of these buildings 
remained standing, suffering only light damage, the rest 
of the building components were not able to resist the forces of 
storm surge. Two prime examples of these buildings are the Pass 
Christian Police Department Headquarters and the Gulfport Fire 
Department Station #7 (see Figures 4-32 and 4-39). Both of these 
buildings were severely damaged and all equipment stored inside 
was destroyed. 

Based on the observations, many existing structures can be retrofitted 
to perform better during high winds. Although such 
retrofits may be expensive and generally have limited capacity to 
strengthen the structure, they definitely increase the overall structural 
resistance. For example, roof decking can be retrofitted with 
additional connections to provide increased uplift resistance. Furthermore, 
roof decks should be attached securely to make the 
building diaphragm work as a unit and transfer loads adequately 
to the walls, while simultaneously preventing the deck from being 
pulled from the structure during high winds. 

Figure 4-38: Reinforced concrete building for Jackson County EOC

4.4.7 Building Envelope

When the building envelope is breached, the interior is no longer 
protected from the outdoor environment and the whole building 
is exposed to additional forces that may cause its progressive 
collapse. 

The Gulfport Police Department Headquarters and the Pass 
Christian Police Station are the prime examples of building envelope 
failure. Both buildings, located near the coast, were exposed 
to the storm surge that crushed the lightly built exterior walls and 
destroyed everything in the interior. Fire Station #7 was breached 
by the storm surge, and practically the entire building envelope 
was washed away, except for the roof deck. What remained of the 
building was just a shell (see Figure 4-40). The duty personnel and 
most of the vehicles were relocated to other facilities until a trailer 
was provided as a temporary place of operations. 

On the other hand, the Gulfport Police Department Headquarters 
building, constructed with heavy concrete masonry 
walls, sustained no significant damage to the building envelope. 
The building only required restoration of flooded building 
components. 

Figure 4-39: Gulfport Fire Station #7

Longbeach Police Station sustained heavy damage to its roof 
trusses, metal roof, and siding that allowed wind and rainwater 
to saturate the interior of the building. The police officers had 
to scramble to evacuate the prisoners and valuable records before 
they abandoned the building in the middle of the storm (see 
Figure 4-41).

Figure 4-40: Exterior walls on the Gulfport Fire Station #7 
washed away by the storm surge

Figure 4-41: Longbeach Police Station

Third District Fire Station in New Orleans is a newer one-story, 
structural steel-framed building with brick veneer walls, metal 
fascia panels, steel roof deck, rigid plastic foam roof insulation, 
and metal roof panels. The estimated maximum wind speed at 
this location during Hurricane Katrina was significantly lower 
than the design wind speed. Nevertheless, a large portion of the 
metal roof covering was blown off the apparatus bay (see Figure 
4-42). In some areas, the architectural metal wall panels with 
standing seams covered by snap-on battens were still in place, 
but the batten covers had broken away. In other areas, the batten 
covers were still attached, but they had liftedit appeared that fatigue 
cracks occurred along the standing seams (see Figure 4-43). 
Battens like these are frequently susceptible to blow-off, which allows 
water infiltration and may lead to panel blow-off. Both the 
battens and separated panels may become dangerous wind-borne 
debris. This station was occupied at the time of the storm, but 
because of the extensive damage to the interior, apparatus bay 
doors, and the equipment, it could not be used and was consequently 
evacuated. 

Figure 4-42: Metal roof and wall panels peeled off the Third 
District Fire Station in New Orleans

Although the estimated wind speed in Bay St. Louis was slightly 
lower than the design wind speed, the wind blew off most of the 
roof membrane from the Hancock County EOC, located in the 
city (see Figure 4-44). The damage was initiated with the separation 
of metal edge flashing that had an uncleated vertical face. In 
addition to roof damage, the hardware on the exterior door failed 
and the door blew inward. As a result of rainwater penetration and 
flooding, most of the interior was ruined. Although most of the 
facility operations were moved before hurricane landfall, the remaining 
building occupants had to be evacuated during the event. 

Jackson County EOC in Pascagoula experienced similar damage 
to its roofing when the metal edge flashing peeled off and lifted 
portions of the roof membrane. However, the roof damage did 
not cause water damage, because the cast-in-place reinforced concrete 
roof deck was capable of resisting rainwater penetration. 
The buildings reinforced concrete walls and roof deck resisted 
the wind loads very well. The walls and roof deck were also extremely 
resistant to wind-borne debris, as was the exterior glazing 
retrofitted with shutters that protected the openings.

The edge flashing on low-slope roofs that usually initiates 
the peeling of roof membranes can be easily retrofitted with 
additional screws, to prevent it from uplifting and causing a progressive 
failure of the roofing system.

Figure 4-43: Lifted batten covers on Third District Fire Station 
metal roof

Fire stations are especially susceptible to breaches of the building 
envelope, because of their large sectional and rolling doors that 
are usually not strong enough to resist wind forces, and even less 
so the hydrodynamic forces of storm surge. The apparatus bay 
doors failed in many fire stations affected by flooding. (see Figures 
4-39 and 4-45).

Water and wind from the storm were able to penetrate the buildings 
when the doors were breached, causing subsequent damage 
to other systems and equipment. Large doors should be designed 
to withstand wind pressures and windborne debris impact as recommended 
in Section 3.4.3.1.

All doors and windows can also be replaced with modern, impact-
resistant systems that would reduce the chances of building 
pressurization and rainwater infiltration, which resulted in heavy 
losses to equipment and contents during Katrina. Rooftop units 
that were blown off and damaged the building envelope by puncturing 
the roof covering should be securely anchored to prevent 
such damage in the future. 

Figure 4-44: Roof damage at Hancock County EOC

4.4.8 Utility Plumbing Systems

Failures of public utility systems during Katrina were very common. 
Many first responder facilities were forced to improvise short-term 
solutions until public utilities were restored. The Gulfport Fire Department 
Headquarters was able to back-feed water into its lines by 
isolating the buildings water supply lines from the public municipal 
supply system. They then fed water directly into the buildings 
water lines in order to have water to shower and wash during the 
two weeks that they were without water in the facility. This capability 
should be considered for all emergency response facilities, as 
it minimizes disruption of basic sanitary functions. 

In many facilities, flooding caused sewage to backflow into buildings, 
causing sanitary crises that directly affected their operations. 
Valuable time was spent cleaning up the facilities instead of 
helping others. To prevent this from occurring in future events the 
installation of backflow inhibitors (check valves) is recommended.

The Pass Christian Fire Department managed the loss of sanitary 
systems with plastic bags and buckets, while the staff at the Gulfport 
Police Department was able to acquire and use portable toilets 
and bottled water until public utility systems were restored. The 
Jackson County, Mississippi, EOC is equipped with a pressurized 
underground tank for toilets and washing, which supported the occupants 
during the 3 to 4 weeks that the facility was without water.

Figure 4-45: Damaged apparatus bay doors at Port Sulphur 
Volunteer Fire Department. 

The Cuevas Volunteer Fire Department in Pass Christian, Mississippi, 
was equipped with an underground septic tank, a drain 
field, and a well, and did not experience significant disruptions in 
its plumbing and fresh water systems. These independent septic 
and fresh water systems do not rely on public municipal systems, 
and are preferred where possible as they virtually eliminate the 
chances of disruption during widespread outages.

4.4.9 Mechanical and Electrical Systems 

Hurricane Katrina also affected facilities by damaging or destroying 
mechanical systems. Hurricane season occurs in the 
warmest months of the year, and many of these facilities were not 
designed to allow natural ventilation. For example, the New Orleans 
Police Department Headquarters Building is a multi-story 
building where the main circuitry for the HVAC system, which was 
located in the basement, was severely damaged by the flood. Since 
the building was designed as a closed structure, natural ventilation 
was a problem (see Figure 4-46). All the equipment located in the 
basement needed to be completely rebuilt or replaced before the 
building could be occupied again. In the interim, the entire department 
was forced to relocate its operations to other facilities in 
the city, placing a strain on facilities not intended to house additional 
personnel and take on additional responsibilities.

The inability to air-condition buildings because of damaged 
mechanical and electrical systems allowed internal temperatures 
and humidity to reach intolerable levels, and in many buildings 
mold began to form.

Loss of electrical power during and after Hurricane Katrina affected 
all other essential facility systems. Examples of this were 
evident at all of the sites visited. Utility, mechanical, and communications 
systems became partially or completely unusable, either 
because emergency power was not available, or it had to be rationed 
as a result of overload or breakdown of generators.

Cuevas Volunteer Fire Department, located inland at Pass Christian, 
Mississippi, was without municipal power for approximately 
2 to 3 days, but, since its generator functioned properly, their operations 
were only slightly affected by the storm. In contrast, the 
indoor generator and electrical panel at the Back Bay Fire Company 
#3 in Biloxi, Mississippi, became submerged in the flood, 
even though the generator was mounted several feet above the 
finished floor. The water flooded the building, putting all the mechanical 
and electrical equipment, including the generator, out 
of commission. As the water continued to rise, the firefighters and 
the local residents that sought refuge in the station had to climb 
to the top of fire engines until the floodwaters receded.

The New Orleans District 3 Fire Department Headquarters lost 
power as a result of flooding. The generator was located outside 
at grade level, and was ruined when approximately 2 feet of water 
flooded the area (see Figure 4-47). The firefighters were forced to 
relocate to the nearby West Bank facility for 4 months, until power 
was restored at the headquarters building. 

Facilities that escaped deep flooding were typically operational 
immediately upon restoration of power. The Gulfport Fire Department 
Station #1 had water barely enter the station, and was able 
to get by on their generator for 3 days until municipal power was 
restored. Although their radios worked intermittently, they were 
able to perform their search and rescue duties and use their newly 
acquired chainsaws to help clear the roads of debris.

Figure 4-46: Fixed windows on New Orleans Police Department 
Headquarters

The need to provide a back-up generator at a safe and elevated location 
is confirmed by the experiences during Hurricane Katrina. 
Many facilities were without power because of the low elevation 
and subsequent flooding of their generators. Jackson County EOC 
had its emergency power station elevated and protected in a separate 
enclosure, which allowed the facility to operate without 
interruption (see Figure 4-48). 

Figure 4-47: Generator mounted at grade level damaged by 
flooding

Figure 4-48: Jackson County EOCs elevated generator 
enclosure

4.4.10 Communications Systems

It is essential for the operation of emergency response facilities 
to keep their communications systems intact. Loss of communication 
capability prevents their primary function of responding to 
community needs and adversely affects their ability to coordinate 
their actions. If the communications system malfunctions or becomes 
unavailable, the coordination between command centers 
will be hindered, affecting management of the response and recovery 
operations during and after an event. Many jurisdictions 
in New Orleans and along the Gulf Coast were cut off from each 
other and could not communicate, even with their own departments. 
For example, one police officer from the Orleans District 
Levee Board Police Department was in the heart of New Orleans 
when the city was flooded, and had no way of communicating with 
the senior officials in his department. He worked for days with the 
officers of the New Orleans Police Department (NOPD) assisting 
the remaining residents in the city. For a period of days, he and 
his partners from NOPD were operating without communications 
capabilities of any sort until the military arrived and issued them 
new radios. It took approximately 2 to 3 weeks for communications 
to be re-established in a manner that resembled normalcy.

The command and communications center for the police and fire 
rescue departments in Pass Christian, Mississippi, was located in 
the police department building, and was crippled as a result of the 
destruction of their headquarters (see Figure 4-49). The landline 
communications at the Jackson County, Mississippi, EOC continued 
to function for a day or two, and other communications 
systems only experienced minor problems. The building was used 
during and after the storm.

Hurricane Katrina experience indicates that alternative forms of 
communication need to be available during and in the aftermath 
of a storm. High-frequency and ham radios that do not rely on repeater 
systems should be in place, along with detailed instructions 
and plans for their use in emergencies. Emergency power supply 
for communications systems must be available at all times. This 
relatively low-cost solution would reduce the loss of communications 
during and after future events.

4.4.11 Equipment and Auxiliary Installations

Specialized equipment such as vehicles, rescue equipment, and 
fire pumps were the most common types of equipment lost during 
Hurricane Katrina. Damage to vehicles and other equipment seriously 
affected the operations, and frequently prevented speedy 
rescue and response efforts. 

In many cases throughout Mississippi and Louisiana, the vehicles 
were stored immediately outside on facility parking lots while most 
of the specialized equipment was stored inside in apparatus bays. 
In other cases, as in Pass Christian, Mississippi, the police department 
stationed its vehicles in a remote location that was thought 
to be safe, but the entire area flooded and all vehicles were rendered 
useless. In Pass Christian the fire department, located 
approximately a quarter of a mile from the coastline, had four 
firefighting trucks and two rescue trucks ruined during the storm, 
hampering firefighters efforts in responding to emergencies that 
required the use of their equipment. Gulfport Police Department 
and the New Orleans District Levee Board Police Department deployed 
their vehicles all over the area to ensure that the vehicles 
would be available on short notice after the storm.

Figure 4-49: Broken communications masts at Pass Christian 
Police Station

For the 2006 hurricane season, Pass Christian emergency response 
plans include the evacuation of all vehicles to a staging site away 
from the coastline, and away from trees and other objects that may 
become wind-borne debris. This geographic distancing of vehicles 
from the coastline (and the area affected most by the storm and 
its surge) will protect key equipment and reduce the impact of a 
future storm by allowing the first responders to be mobile shortly 
after the event. It should be noted, however, that many jurisdictions 
in low-lying areas do not have safe staging sites at higher 
elevations or away from the coastline. 

Based on conversations with many emergency response crews that 
were affected by Katrina, the protection of their equipment and 
vehicles was a main consideration prior to the storm. Many jurisdictions 
throughout Mississippi and Louisiana decided to spread 
their vehicles out to many locations thought to be safe, in order to 
be certain that at least some of them would remain operational. 
This practice proved prudent and enhanced their abilities to respond 
in the immediate aftermath of the disaster. The vehicles 
should be sheltered in an area that is safe from flooding hazard 
and easily accessible after the event. 

4.4.12 Summary

Emergency response services are at the backbone of a communitys 
ability to protect and save the lives and property of its citizens 
in any crisis. The provision of these services depends on the uninterrupted 
operation of emergency response facilities during 
and after a hazard event. This means not only that the buildings 
that house the crews and equipment must survive the onslaught 
of flooding and high winds with minimal damage, but that all the 
equipment and systems necessary for emergency operations must 
remain fully functional. 

Hurricane Katrina showed that emergency response facilities 
have a better chance of protecting their operations if they occupy 
solidly constructed buildings with sufficient reserve structural 
capacity that cannot be easily overwhelmed by a storm of this magnitude. 
It also showed that facilities with functional generators 
were better equipped to respond after the storm than those that 
were left completely without power. Since the facilities cannot operate without 
adequate emergency power supply, all electrical 
systems should be connected to power back-ups, and emergency 
generators should be elevated and protected against floodwaters 
and wind-borne debris. 

Mechanical systems need to be located in a sheltered area, where 
they will not be damaged by wind and flooding. Plumbing systems 
should be equipped with backflow inhibitors to prevent sewage 
from entering the structure during a flood. Provisions should also 
be made to allow the isolation of the buildings water supply, so 
that it is possible to feed water directly into the buildings water 
lines until municipal water supplies are restored. 

Finally, the lines of communication between community command 
centers and individual facilities must remain functional at 
all times. The basic communications systems need to be protected 
against the effects of flooding and high-winds as much as possible, 
but as this storm showed, system redundancy is still the best 
policy. In the event of damage, the facilities should have alternative 
means of communication that do not depend on local systems 
and networks that could be damaged in the storm.

[End of Chapter 4]



Acronyms 

AASHTO American Association of State Highway and Transportation Officials

ABFE Advisory Base Flood Elevation

ADA Americans with Disabilities Act 

ARC American Red Cross

ASCE American Society of Civil Engineers 

ASTM American Society for Testing and Materials

ASCE/SEI American Society of Civil Engineers Structural Engineers Institute 

BFE Base Flood Elevation

BIA Brick Industry Association 

BUR Built-Up Roof 

C&C Components and Cladding 

CMU Concrete Masonry Unit

DFE Design Flood Elevation 

EIFS Exterior Insulation Finish Systems 

EOC Emergency Operation Center

EPDM Ethylene Propylene Diene Monomer

FEMA Federal Emergency Management Agency

FIRM Flood Insurance Rate Map 

FIS Flood Insurance Study 

FMA Flood Mitigation Assistance 

FMG Factory Mutual Global

FMR Factory Mutual Research 

HMGP Hazard Mitigation Grant Program 

IBC International Building Code 

ICC International Code Council 

ICU Intensive Care Unit

LPS Lightning Protection System

MEPS Molded Expanded Polystyrene 

MOB Medical Office Building 

MWFRS Main Wind-Force Resisting System 

NBC National Building Code 

NEHRP National Earthquake Hazard Reduction Program

NFIP National Flood Insurance Program 

NFPA National Fire Protection Association

NSSA National Storm Shelter Association

OSB Oriented Strand Board 

PA Public Assistance

PDM Pre-Disaster Mitigation

PMR Protected Membrane Roof

PNP Private Non-Profit 

SBC Standard Building Code
 
SEAW Structural Engineers Association of Washington

SHMO State Hazard Mitigation Officer

SPF Sprayed Polyurethane Foam 

UBC Uniform Building Code

[End of Appendix A]



Glossary of terms 

100-year flood. See base flood.

A

Alluvial Fan. A fan-shaped deposit of alluvium formed by a stream where its 
velocity is abruptly decreased, as at the mouth of a ravine or at the foot of a 
mountain.

Astragal. The center member of a double door, which is attached to the fixed or 
inactive door panel.

B

Base flood. The flood having a 1-percent chance of being equaled or exceeded in 
any given year, commonly referred to as the 100-year flood. The base flood is 
the national standard used by the NFIP and all Federal agencies for the purposes 
of requiring the purchase of flood insurance and regulating new development. 

Base flood elevation (BFE). The height of the base (1 percent or 100-year) flood 
in relation to a specified datum, usually the National Geodetic Vertical Datum 
of 1929, or the North American Vertical Datum of 1988. 

Basic wind speed. A 3-second gust 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.) Note: Since 1995, 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 speed could be 
associated with a given windstorm (e.g., a particular storm could have 
a 40-mph peak gust speed), or a 3-second peak gust speed could be associated 
with a design-level event (e.g., the basic wind speed prescribed in ASCE 7).


Building, enclosed. A building that does not comply with the requirements for 
open or partially enclosed buildings.

Building, open. A building having each wall at least 80 percent open. This 
condition is expressed by an equation in ASCE 7.

Building, partially enclosed. A building that complies with both of the 
following conditions:

1. The total area of openings in a wall that receives positive external pressure 
exceeds the sum of the areas of openings in the balance of the building envelope 
(walls and roof) by more than 10 percent.
2. The total area of openings in a wall that receives positive external pressure 
exceeds 4 square feet, or 1 percent of the area of that wall, whichever is 
smaller, and the percentage of openings in the balance of the building envelope 
does not exceed 20 percent.These conditions are expressed by equations in ASCE 
7.
Building, regularly shaped. A building having no unusual geometrical 
irregularity in spatial form.

Building, simple diaphragm. An enclosed or partially enclosed building in which 
wind loads are transmitted through floor and roof diaphragms to the vertical 
main wind-force resisting system.

C

Components and cladding (C&C). Elements of the building envelope that do not 
qualify as part of the main wind-force resisting system.

Coping. The cover piece on top of a wall exposed to the weather, usually made of 
metal, masonry, or stone, and sloped to carry off water.

D

Design flood. The greater of the following two flood events: (1) the base flood, 
affecting those areas identified as special flood hazard areas on a communitys 
Flood Insurance Rate Map (FIRM); or (2) the flood corresponding to the area 
designated as a flood hazard area on a communitys flood hazard map or otherwise 
legally designated.

Design flood elevation (DFE). The elevation of the design flood, including wave 
height, relative to the datum specified on a communitys flood hazard map.

Dry floodproofing. An adjustment, modification, or addition of a feature, or any 
combination thereof, that eliminates or reduces the potential for flood damage 
by sealing walls and closing openings to keep water from entering a building. 

E

Erodible soil. Soil subject to wearing away due to the effects of wind, water, 
or other geological processes during a flood or storm or long-term exposure. 

Escarpment. Also known as a scarp. With respect to topographic effects, a cliff 
or steep slope generally separating two levels or gently sloping areas. 

Exposure. The characteristics of the ground roughness and surface irregularities 
in the vicinity of a building. ASCE 7 defines three exposure categories
Exposures B, C, and D. 

Extratropical storm. A cyclonic storm that forms outside of the tropical zone. 
Extratropical storms may be large, often 1,500 miles (2,400 kilometers) in 
diameter, and usually contain a cold front that extends toward the equator for 
hundreds of miles.

F

Federal Emergency Management Agency (FEMA). The Federal Emergency Management 
Agency is the Federal agency which administers the National Flood Insurance 
Program (NFIP).

Fetch. Distance over which wind acts on the water surface to generate waves.

Flashing. Any piece of material, usually metal or plastic, installed to prevent 
water from penetrating a structure.

Flood Insurance Rate Map (FIRM).   The official map of a community on which FEMA 
has delineated both the special hazard areas, and the risk premium zones 
applicable to the community.

Flood Insurance Study (FIS). An engineering study performed by FEMA to identify 
flood hazard areas, flood insurance risk zones, and other flood data in a 
community; used in the development of the FIRM.

Floodplain. Any land area, including the watercourse, that is susceptible to 
partial or complete inundation by water, from any source.

Floodplain management regulations. Zoning ordinances, subdivision regulations, 
building codes, or special-purpose ordinances that set flood-resistant standards 
for new construction, land use, and development.

Flood profile. A graph of computed flood elevations at points located along a 
riverine waterway. A flood profile typically is available for a waterway that 
has Base Flood Elevations (BFEs) shown on the Flood Insurance Rate Map (FIRM). 
Flood profiles are usually found in the Flood Insurance Study (FIS) report.

Floodway. The channel and that portion of the floodplain that is to be reserved 
to convey the base flood, without cumulatively increasing the water surface 
elevation more than a designated height.

Floodway fringe. The area of the floodplain outside of the floodway, where 
floodwaters may be shallower and slower. 

Freeboard. A factor of safety, usually expressed in feet above a flood level, 
for purposes of floodplain management. Freeboard also compensates for the many 
unknown factors that could contribute to flood heights greater than the height 
calculated for a selected size flood and floodway conditions, such as wave 
action, constricting bridge openings, and the hydrological effect of 
urbanization of the watershed. A freeboard of 1 to 3 feet is often applied to 
critical facilities.

Frontal dune. Ridge or mound of unconsolidated sandy soil, extending 
continuously alongshore landward of the sand beach and defined by relatively 
steep slopes abutting markedly flatter and lower regions on each side.

G

Glazing. Glass or a transparent or translucent plastic sheet used in windows, 
doors, and skylights.

Glazing, impact-resistant. Glazing that has been shown, by an approved test 
method, to withstand the impact of wind-borne missiles likely to be generated in 
wind-borne debris regions during design winds.

H

Hurricane-prone regions. Areas vulnerable to hurricanes; in the United States 
and its territories defined as:

1. The U.S. Atlantic Ocean and Gulf of Mexico coasts, where the basic wind speed 
is greater than 90 miles per hour.
2. Hawaii, Puerto Rico, Guam, U.S. Virgin Islands, and American Samoa.
Human intervention. The presence and active involvement of people necessary to 
enact or implement floodproofing measures prior to the onset of flooding.

Hydrodynamic load. Loads imposed by water flowing against and around an object 
or structure, including the impacts of debris and waves.

Hydrostatic load. Load (pressure) imposed on an object or structure by a 
standing mass of water; the deeper the water, the greater the load or pressure 
against the object or structure.

I

Impact-resistant covering. A covering designed to protect glazing, which has 
been shown by an approved test method to withstand the impact of wind-borne 
missiles likely to be generated in wind-borne debris regions during design 
winds.

Importance factor, I. A factor that accounts for the degree of hazard to human 
life and damage to property. Importance factors are given in ASCE 7.

L

Lowest floor. The lowest floor of the lowest enclosed area (including basement). 
An unfinished or flood resistant enclosure, usable solely for parking of 
vehicles, building access, or storage, in an area other than a basement area, is 
not considered a building's lowest floor, provided that the enclosure is 
compliant with flood-resistant requirements. 

M

Main wind-force resisting system. An assemblage of structural elements assigned 
to provide support and stability for the overall structure. The system generally 
receives wind loading from more than one surface.

Mean roof height, (h). The average of the roof eave height and the height to the 
highest point on the roof surface, except that, for roof angles of less than or 
equal to 10 degrees, the mean roof height shall be the roof eave height.

Missiles. Debris that could become propelled into the wind stream. 

N

National Flood Insurance Program (NFIP). A Federal program to identify flood-
prone areas nationwide, and make flood insurance available for properties in 
communities that participate in the program. 

Noreaster. Noreasters are non-tropical storms that typically occur in the 
eastern United States, any time between October and April, when moisture and 
cold air are plentiful. They are known for dumping heavy amounts of rain and 
snow, producing hurricane-force winds, and creating high surfs that cause severe 
beach erosion and coastal flooding. A noreaster is named for the winds that 
blow in from the northeast and drive the storm up the east coast along the 
Gulf Stream, a band of warm water that lies off the Atlantic Coast. 



O

Openings. Apertures or holes in the building envelope that allow air to flow 
through the building envelope. A door that is intended to be in the closed 
position during a windstorm would not be considered an opening. Glazed openings 
are also not typically considered openings. However, if the building is located 
in a wind-borne debris region and the glazing is not impact-resistant or 
protected with an impact-resistant covering, the glazing is considered an 
opening.

R

Racking. Lateral deflection of a structure resulting from external forces, such 
as wind or lateral ground movement in an earthquake.

Ridge. With respect to topographic effects, an elongated crest of a hill 
characterized by strong relief in two directions.

S

Scour. Removal of soil or fill material by the flow of floodwaters. The term is 
frequently used to describe storm-induced, localized erosion around pilings at 
building corners and other foundation supports where the obstruction of flow 
increases turbulence. 

Seiche. A wave that oscillates in lakes, bays, or gulfs from a few minutes to a 
few hours as a result of seismic or atmospheric disturbances.

Sheetflow. Rainfall runoff that flows over relatively flat land without 
concentrating into streams or channels.

Stillwater elevation. The elevation that the surface of coastal flood waters 
would assume in the absence of waves, referenced to a datum.

Storm surge. Rise in the water surface above normal water level on the open 
coast due to the long-term action of wind and atmospheric pressure on the water 
surface.

Substantial damage. Damage of any origin sustained by a structure, whereby the 
cost of restoring the structure to its pre-damage condition equals or exceeds 50 
percent of the market value of the structure before the damage occurred (or 
smaller percentage if established by the authority having jurisdiction). 
Structures that are determined to be substantially damaged are considered to be 
substantial improvements, regardless of the actual repair work performed. 

Substantial improvement. Any reconstruction, rehabilitation, addition, or other 
improvement of a structure, the cost of which equals or exceeds 50 percent of 
the market value of the structure (or smaller percentage if established by the 
authority having jurisdiction) before the start of the improvement. 

T

Tsunami. An unusually large sea wave produced by submarine earth movement or a 
volcanic eruption.

W

Wave runup. Rush of wave water up a slope or structure. The additional height 
reached by waves above the stillwater elevation. 

Wet floodproofing. Permanent or contingent measures and construction techniques, 
applied to a structure or its contents, that prevent or provide resistance to 
damage from flooding while allowing floodwaters to enter the structure. 
Generally, this includes properly anchoring the structure, using flood-resistant 
materials below the BFE, protection of mechanical and utility equipment, and the 
use of openings or breakaway walls. 

Wind-borne debris regions. Areas within hurricane-prone regions located:

1. Within 1 mile of the coastal mean high water line where the basic wind speed 
is equal to or greater than 110 mph and in Hawaii.
2. In areas where the basic wind speed is equal to or greater than 120 mph.


[End of Appendix B]




FEMA Mitigation Programs

Federal funding for mitigation is available 
on a regular basis for pre-disaster mitigation 
activities and as federal assistance 
following a presidential disaster declaration. 
Table 1 provides a side-by-side comparison of 
available funding programs administered by 
FEMA. Although each program is constrained 
in a number of ways, as explained below, the 
following sources of federal funding may be 
available for mitigation projects for critical 
facilities:
-- Section 406 Public Assistance (PA) is a post-disaster program 
established under Section 406 of the Stafford Actit is 
jointly administered by FEMA and individual states. As part 
of the reimbursements made to restore damaged public 
facilities and certain private non-profit (PNP) facilities, public 
assistance funds may be made available for cost-effective 
mitigation measures undertaken as part of the recovery. The 
amount of Section 406 Mitigation funds made available in 
any given disaster is not computed by a formula, but is based 
on a project-by-project evaluation of the feasibility and cost-
effectiveness of mitigation measures. 
-- Section 404 Hazard Mitigation Grant Program (HMGP) is a post-
disaster program established under Section 404 of the Stafford 
Act. It offers funding to states, communities, and other eligible 
Many other federal and state funding 
sources may be available to support 
planning and construction (or upgrades) of 
some critical facilities, but this manual does 
not identify or list such sources. Owners, 
planners, and community leaders are 
encouraged to contact appropriate state 
agencies to learn more.

Programs grant recipients to invest in long-term measures that will 
reduce vulnerability to future natural hazards. The states have 
a strong role in administering HMGP, with FEMA providing 
oversight. Contact the State Hazard Mitigation Officer 
(SHMO) for state-specific information. General guidelines and 
resources for this program can be found on the FEMA website 
(www.fema.gov/fima/hmgp). 

Pre-Disaster Mitigation (PDM), established under Section 203 
of the Stafford Act, is a nationally competitive grant program 
designed to assist states and communities to develop mitigation 
plans and implement mitigation projects. PDM funds are 
appropriated annually. FEMA convenes national panels to 
evaluate eligible applications. Applications are submitted 
by states following the state selection process. Communities 
should contact the SHMO for state-specific PDM procedures. 
PDM program guidance and other information can be found 
on the FEMA website (www.fema.gov/government/grant/
pdm/index.shtm).

Flood Mitigation Assistance (FMA) is a grant program funded by 
the National Flood Insurance Program (NFIP) and focused 
on buildings that are insured by the NFIP, with particular 
attention to buildings that have received multiple claim 
payments. As with the HMGP, FMA is state-administered, 
and information and assistance is available from the SHMO. 
General guidelines and resources for this program can be 
found on the FEMA website (www.fema.gov/government/
grant/fma/index.shtm). 

As part of the Hurricane Katrina recovery in Mississippi and Louisiana, FEMA 
initiated a post-disaster Partnering Mitigation Programs initiative to combine 
funding from Section 406 and Section 404 where possible. Section 406 mainly 
funds the repair and restoration of storm damage; thus, some building elements 
may remain exposed to future damage. The initiative fosters a cooperative 
approach to making decisions to use both PA and HMGP funds to 
accomplish recovery as well as mitigation of facilities as whole buildings in a 
seamless fashion. 

Table 1: Side-by-Side of FEMA Programs
ITEM
Eligible Applicants and Sub-applicants for Project Grants
PA(406)
State and local governments; PNP organizations or institutions that own or 
operate a PNP facility (as defined in regulation); Indian tribes or authorized 
tribal organizations and Alaska Native villages or organizations, but not Alaska 
native corporations with ownership vested in private individuals.
HMGP (404)
State and local governments; PNP organizations or institutions that own or 
operate a PNP facility (as defined in regulation); Indian tribes or authorized 
tribal organizations and Alaska Native villages or organizations, but not Alaska 
native corporations with ownership vested in private individuals.
PDM (203)
State-level agencies; local governments, Indian tribes, authorized tribal 
organizations, and Alaska Native villages; public colleges and universities; 
tribal colleges and universities. PNP organizations and private 
colleges and universities are not eligible sub-applicants, but a relevant state 
agency or local government may apply on their behalf.
FMA
State agencies, NFIP-participating communities (have zoning and building code 
jurisdiction), and local authorities designated to plan and implement projects. 
Item
Eligible Activities
PA(406)
Basic assistance to repair the damaged elements of public facilities and 
infrastructure. Eligible mitigation activities are only those that protect 
against direct physical damages to structures, building, and contents. 
HMGP (404)
Eligible activities include structural and nonstructural mitigation measures 
that are feasible and cost-effective. Projects may count benefits in terms of 
building and contents damages, displacement costs, loss of function, and 
casualties and loss of life.
PDM (203)
Eligible measures must be cost-effective and designed to reduce injuries, loss 
of life, and damage and destruction of property, including damage to critical 
services and facilities under the jurisdiction of the states 
or local governments.
FMA
N/A

Item
Cost Share
PA(406)
75 percent federal
25 percent non-federal
HMGP (404)
75 percent federal
25 percent non-federal
PDM (203)
75 percent federal
25 percent non-federal
Small, impoverished communities may be eligible for 90 percent federal share.
FMA
75 percent federal
25 percent non-federal
FMA
Item
Funding Source
PA (406)
The Disaster Relief Fund after a presidential disaster declaration; public 
assistance must be authorized specifically as 
part of the disaster declaration.
HMGP (404)
The Disaster Fund after a presidential disaster declaration; HMGP must be 
authorized specifically as part of the 
disaster declaration.
PDM (203)
An annual appropriation by Congress.
FMA
Annual appropriation by Congress, by transfer of income from the National Flood 
Insurance Fund.
Item
Planning Requirement
PA (406)
For categories C-G assistance, a state must have an approved mitigation plan.
HMGP (404)
For disasters declared after 11/1/04, state and local governments must have an 
approved mitigation plan.
PDM (203)
State and local mitigation plans must be adopted and approved by FEMA prior to 
the beginning of the selection 
process, as a precondition for receiving project grants.
FMA
Recipient must have adopted a mitigation plan approved by FEMA prior to receipt 
of grant funds.

Item 
Application Deadline
PA (406)
Project worksheets usually are due no later than 60 days after a formal briefing 
presented by FEMA and the state 
(extensions may be granted in unusual circumstances).
HMGP (404)
Applications must be submitted to FEMA within 12 months of the disaster 
declaration date (extensions may be 
granted in unusual circumstances).
PDM (203)
Varies by year; contact state agency for additional information.
FMA
Usually late spring; specific date varies by year, contact state agency for 
additional information.
[End of Table 1]


Public Assistance (Section 406)

Following a presidential disaster declaration, the PA program 
provides assistance for debris removal, emergency protective measures, 
and permanent restoration of publicly owned infrastructure. 
Eligible recipients of this assistance include state and local governments, 
Indian tribes or authorized tribal organizations, and 
Alaska Native villages. Certain PNP organizations may also receive assistance. 
Eligible PNPs include educational, utility, irrigation, emergency, medical, 
rehabilitation, 
temporary or permanent custodial care facilities (including those for the aged 
and disabled), and other PNP facilities that provide essential services of a 
governmental nature to the general public. Certain PNPs that provide critical 
services may apply directly to FEMA, including PNPs that provide power, sewer, 
wastewater treatment, communications, emergency medical care, and water 
(including water provided by an irrigation organization or facility).
As soon as practical after the declaration, the state, assisted by 
FEMA, conducts Applicants Briefings for state, local, and PNP 
officials, to inform them of the assistance available and the application 
procedure. A request for public assistance must be filed 
with the state within 30 days after an area is designated eligible for 
assistance. 

Following the Applicants Briefing, a kickoff meeting is conducted 
with each eligible grant recipient, where specific damages 
are discussed, needs assessed, and a plan of action put in place. 
A combined federal/state/local team proceeds with project formulation
the process of documenting eligible facilities and 
determining the cost for fixing the identified eligible damages. 
The team prepares a project worksheet for 
each project. Eligible projects fall into the 
following categories:

Category A: Debris removal 

Category B: Emergency protective measures

Category C: Roads and bridges

Category D: Water control facilities

Category E: Public buildings and contents

Category F: Public utilities

Category G: Parks, recreational, and other

FEMA reviews and approves the project worksheets and obligates 
the federal share of the costs to the state, which, in turn, disburses 
the funds to local applicants. The federal share is not less than 75 
percent of the eligible project costs (except in extraordinary circumstances, 
when some costs are eligible for 90 or 100 percent 
reimbursement). 

[text box]
The facility owner must pay for all costs 
that are not eligible for Section 406 
reimbursement. The non-federal share 
can be a combination of cash and in-kind 
resources. Federal funding from other 
sources cannot be used as matching funds, 
with the exception of federal funding 
provided to states under the Community 
Development Block Grant program from 
the Department of Housing and Urban 
Development.
[end of text box]

Section 406 provides FEMA with the authority 
to fund mitigation measures in conjunction 
with the repair of damaged facilities involving 
permanent restorative work (Categories 
C, D, E, F, and G projects). The mitigation 
measures must be related to the eligible disaster 
damages and must directly reduce the 
potential of future, similar damages to the eligible 
facility. In providing this discretionary 
authority, Congress recognized that the post-
disaster period offers unique opportunities 
to prevent the recurrence of similar damage 
in future disasters. These measures are additional 
to any other measures undertaken for 
the purpose of compliance with applicable 
codes and standards, although such compliance, 
itself, could be considered a form of 
mitigation. The following are examples of the 
types of mitigation required for compliance 
with building codes that are eligible under 
Section 406:

Improved building materials such as impact-resistant windows 
or flood-resistant materials 

--Anchoring of rooftop equipment
--Improved installation methods or techniques
--New or higher elevation (for flood-prone facilities)

Owners of eligible public facilities often wish to repair and restore 
a damaged facility in ways that exceed the current building 
code requirements, in order to further reduce or eliminate future 
damage. Where it can be demonstrated that doing so is cost-effective, 
the added costs of such actions are eligible under FEMA 
Policy 9526.1 governing the implementation of the Section 406 
program. Unfortunately, this approach rarely meets all the identified 
mitigation needs, because the funding can be used only for 
the damaged elementsmitigation of vulnerable but undamaged 
elements is not allowed. For example, a police station with some 
damaged windows can use Section 406 funds to replace the damaged windows with 
impact-resistant windows, but cannot replace 
undamaged windows. To address this limitation, facility owners 
should seek other sources of mitigation funding, such as the 
Hazard Mitigation Grant Program described below. 

[Text box]
Damaged buildings that are in a mapped 
floodplain and insured by NFIP may have 
access to an insurance payment to help 
cover the cost of mitigation, provided the 
damage caused by flooding is determined 
to be substantial damage. A building 
is substantially damaged when the value 
of the work required to repair it to its pre-
damaged condition equals or exceeds 
50 percent of the market value of the 
building. In these cases, increased cost 
of compliance coverage in NFIP flood 
insurance policies provides to owners 
up to $30,000 to bring the building into 
compliance with floodplain management 
requirements. This payment may be used 
as part of the non-federal match of grant-
funded mitigation projects designed to 
address flood hazards.
[end of text box]

All mitigation activities funded with Section 406 funds must be 
cost-effective. To facilitate recovery, FEMA can apply one of several 
tests to determine cost-effectiveness:

--Measures may cost to up to 15 percent of the total eligible cost 
of the eligible repair work on a particular project.
--Certain pre-approved mitigation measures identified in FEMA 
policies will be determined to be cost-effective, as long as the 
cost of the mitigation measure does not exceed 100 percent of 
the eligible cost of the repair project.
--For measures that do not meet the first or second test, the 
project applicant must demonstrate cost-effectiveness using 
an acceptable benefit/cost analysis. FEMA developed benefit/
cost models that are specific to hurricanes, coastal flooding, 
riverine flooding, earthquakes, and tornadoes. 

Hazard Mitigation Grant Program (Section 404)

Section 404, HMGP, is FEMAs primary hazard mitigation program 
to help implement long-term mitigation measures following major 
disaster declarations. Under HMGP, each state manages its own 
program, and eligible participants include state and local governments, 
tribes, and PNP organizations. The program funds up to 
75 percent of the costs of individual FEMA-approved projects. The 
total amount of funding made available after specific disasters depends 
on several variables. 

HMGP funds have been used for many types of projects, including 
the following:

Wind-resistant Retrofits. Existing facilities that were built before 
current code requirements may be eligible to be retrofitted to 
resist high winds. For any given building, applicable measures 
are identified by conducting an evaluation of the building. 

Critical facilities have been retrofitted with shutters for 
windows and doors, and anchoring of architectural features 
and rooftop equipment. 

Floodproof Retrofits. Depending upon the nature of the 
flood risk, elevating an existing flood-prone structure or 
incorporating dry floodproofing techniques may be the most 
practical approach to meet NFIP requirements and those 
administered by states and local governments. 

Code Upgrades. Certain measures intended to provide a level 
of protection that exceeds the minimum requirements of the 
applicable building code may be eligible. This approach to 
mitigation is especially applicable for critical facilities that 
serve vital post-disaster functions.

Relocation. In some cases, it may be viable to physically move a 
structure to a new location outside of high-risk flood hazard 
areas. Relocated buildings must be placed on a site located 
outside of the 100-year floodplain and any regulatory erosion 
zones, in conformance with all applicable state or local land 
use regulations.

Acquisition and Demolition. The community purchases the flood-
damaged property and demolishes the structure. The acquired 
property must be maintained as open space in perpetuity.
Pre-Disaster Mitigation (Section 203) 

PDM provides funds to state and local governments for hazard 
mitigation planning and the implementation of cost-effective 
mitigation projects unrelated to a specific disaster. PDM is 
administered directly by FEMA. Eligible applicants include 
states, tribes, territories, and local governments (PNPs can apply 
if sponsored by an eligible applicant). Grants are awarded on 
a nationwide competitive basis and without a formula-based 
allocation.

Similar to HMGP, PDM has funded numerous projects that improve 
wind- and flood-resistance of critical facilities such as 
emergency operations centers, hospitals, fire stations, police stations, and 
wastewater treatment plants. 
Specific measures include strengthening exterior 
walls, anchoring rooftop equipment, 
installing shutters, and elevation of facilities 
or equipment above the 100-year flood elevation. 
Other types of projects may be eligible, 
provided they meet the program requirements 
and are cost-effective. Each year, FEMA 
issues PDM program guidance with specific 
criteria.

Flood Mitigation Assistance Program

FMA is designed to fund mitigation projects that are cost-effective 
and in the best interest of NFIP. Funds are provided annually from 
income collected from flood insurance policyholders. Each state 
manages its own program. Eligible grant recipients must have a 
FEMA-approved mitigation plan. Eligible recipients include communities 
that have land use authority and participate in the NFIP, 
certain other local authorities, and state agencies. The program 
funds up to 75 percent of certain eligible costs for measures that 
reduce or eliminate flood damage to buildings that are insured by 
the NFIP, including buildings and facilities owned by public agencies 
and PNP entities. 

Eligible activities under the FMA program include acquisition, 
increased elevation, relocation, demolition, floodproofing, and 
activities that bring nonresidential structures into compliance 
with minimum NFIP requirements and state and local codes, and 
minor physical activities such as drainage improvements. As with 
HMGP, if an NFIP-insured building is damaged by a flood and 
found to be eligible for the increased cost of compliance claim 
payment to bring the building into compliance, the payment can 
be used as part of the required non-federal match for FMA grants. 


[text box]
Cost Share for Small, Impoverished 
Communities

PDM grants awarded to small, 
impoverished communities may receive 
a federal cost share of up to 90 percent 
of eligible costs. To qualify, a community 
must meet several eligibility criteria related 
to population, average annual income, 
unemployment rate, and other conditions. 
[end of text box]

[End of Appendix C]