Risk Management Series
Design Guide for Improving Hospital Safety in Earthquakes, Floods, and High 
Winds
FEMA 577 / June 2007


CHAPTER 4  MAKING HOSPITALS SAFE FROM HIGH WIND

4.1 GENERAL DESIGN CONSIDERATIONS

Wind with sufficient speed to cause damage to weak hospitals can occur anywhere 
in the United States and its territories. [footnote 1] Even a well-designed, 
constructed, and maintained hospital may be damaged by 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 hospitals should be designed, 
constructed, and maintained to minimize wind damage (other than that associated 
with tornadoes  see Section 4.5). 

[Begin footnote 1] The U.S. territories include American Samoa, Guam, Northern 
Mariana Islands, Puerto Rico, and the U.S. Virgin Islands. ASCE 7 provides basic 
wind speed criteria for all but Northern Mariana Islands. [end footnote]

This chapter discusses structural, building envelope, and nonstructural building 
systems, and illustrates various types of wind-induced damage that affect them. 
It also presents six case studies. Numerous examples of best practices 
pertaining to new and existing hospitals 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.

The recommendations presented in this manual are based on field observation 
research conducted on 25 hospitals that were struck by hurricanes. [footnote 2] 
The recommendations are also based on numerous investigations of other types of 
critical facilities and other types of buildings exposed to hurricanes and 
tornadoes, and on literature review. Some of the 25 hospitals were exposed to 
extremely high wind speeds, while others experienced moderate speeds. 
Approximately 88 percent of the 25 hospitals experienced roof covering damage 
(many of which also experienced damage to rooftop equipment), and windows were 
broken on approximately 50 percent of them. Because of wind damage and 
subsequent water leakage, one of the hospitals was totally evacuated after a 
hurricane (Figure 4-1). Another hospital was also evacuated after a hurricane, 
but evacuation was prompted by flooding. Five other hospitals were partially 
evacuated after the storm because of interior water damage. None of the main 
hospital buildings on these 25 campuses experienced structural failure, although 
a few auxiliary buildings did collapse.

[Begin footnote 2] The research on the 25 hospitals was conducted by a team from 
Texas Tech University (Hurricane Hugo, Charleston, South Carolina, 1989), a team 
under the auspices of the Wind Engineering Research Councilnow known as the 
American Association for Wind Engineering (Hurricane Andrew, South Florida, 
1992), and teams deployed by FEMA (Hurricane Marilyn, U.S. Virgin Islands, 1995; 
Typhoon Paka, Guam, 1997; Hurricane Charley, Port Charlotte, Florida, 2004; 
Hurricane Frances, east coast of Florida, 2004, Hurricane Ivan, Pensacola, 
Florida, 2004; and Hurricane Katrina, Louisiana and Mississippi, 2005). [end 
footnote]

Figure 4-1 is a photo showing how Deering Hospital was evacuated after Hurricane 
Andrew due to water infiltration caused by roof covering, window, and door 
damage. [end figure]

[Begin text box]
The 200-bed Deering Hospital opened shortly before Hurricane Andrew struck south 
Florida in 1992. Aggregate from the hospitals built-up roofs broke several 
windows, the roof covering was blown off in some areas (Figure 4-9), and the 
entrance doors at the emergency room were blown away. Because of extensive 
interior water damage, the entire hospital was evacuated after the storm and 
remained closed for 9 months.
[End text box]

4.1.1 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 straight-line winds, 
down-slope winds, thunderstorms, downbursts, northeasters (nor'easters), 
hurricanes, and tornadoes. For information on these storm types, refer to 
Section 3.1.1 in FEMA 543, Design Guide for Improving Critical Facility Safety 
from Flooding and High Winds. [footnote 3]

[Begin footnote 3] Available at the FEMA Web site. See 
www.fema.gov/library/viewRecord.do?id=2441 [end footnote]


Of all the storm types, hurricanes have the greatest potential for devastating a 
large geographical area and, hence, affect the greatest number of people. See 
Figure 4-2 for hurricane-prone regions. 

Figure 4-2 is a map of hurricane-prone regions and special wind regions
Source: Adapted from ASCE 7-05 [end figure]

4.1.2 PROBABILITY OF OCCURRENCE

Via the importance factor [footnote 4], ASCE 7 requires Category III and IV 
buildings to be designed for higher wind loads than Category I and II buildings. 
Hence, hospitals designed in accordance with ASCE 7 have greater resistance to 
stronger, rarer storms. When designing a hospital, design professionals should 
consider the following types of winds.

[Begin footnote 4] The importance factor accounts for the degree of hazard to 
human life and damage to property. Importance factors are given in ASCE 7. [end 
footnote]

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

[Begin text box]
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 4.3).
[End text box]

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 Crefer to 
Section 4.1.3) 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: Hospitals 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 4.3.3.1, 4.3.3.3, and 
4.3.3.5. 

[Begin text box]
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.
[End text box]

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 
described in Section 4.5, 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). 

Well-designed, constructed, and maintained hospitals should experience little if 
any damage from weak tornadoes, except for window breakage. However, weak 
tornadoes often cause building envelope damage because of wind-resistance 
deficiencies. Most hospitals 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. See Section 4.5 for recommendations pertaining to tornadoes. 

4.1.3 Wind/Building Interactions

When wind interacts with a building, both positive and negative (i.e., suction) 
pressures occur simultaneously. Hospitals 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: exposure, basic wind speed, topography, building height, 
internal pressure, and building shape. For general information on these factors, 
refer to Section 3.1.3 in FEMA 543, Design Guide for Improving Critical Facility 
Safety from Flooding and High Winds. A description of key issues follows. 

Wind Speed: In the ASCE 7 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 4-3. 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.

Figure 4-3 is a chart showing wind pressure as a function of wind speed

[Begin text box]
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.
[End text box]

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 4-4 illustrates 
these aerodynamic influences. The negative values shown in Figure 4-4 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. 

[Begin figure]
Figure 4-4 is an illustration of 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. 
[end figure]

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 4-5 and 
4-6. Figure 4-5 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 4-6 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 4-6, 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 4-7. Wind load increases due to building 
irregularities can be identified by wind tunnel studies; however, wind tunnel 
studies are rarely performed for hospitals. 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.

[Begin figures]
Figure 4-5 is a photo of aggregate blow-off associated with building 
irregularities. Hurricane Hugo (South Carolina, 1989)

Figure 4-6 is a photo 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 4-7 is a plan view of a portion of the building in Figure 4-6 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
[End figures]

[Begin text box]
Information pertaining to load calculations is presented in Section 4.3.1.2. 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.
[End text box]

4.1.4 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 from 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 hospital.

4.1.4.1 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, hospitals 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 on all buildings. 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 widespread 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.

[Begin text box]
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.
[End text box]

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).

4.1.4.2 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 hospitals.

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, hospitals 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 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.

- Hospitals need to perform at a higher level than required by codes and 
standards. 

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 
hospitals. 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; and (5) they do not account for 
interruption of water service or prolonged interruption of electrical power. All 
of these elements are of extreme importance for hospitals, which need to remain 
operational before, during, and after a disaster. Guidance to overcome these 
shortcomings is given in Section 4.3 and 4.4.

- 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 to the 
2006 IBC pertaining to some of the test methods used to assess wind and wind-
driven rain resistance of building envelope components. For example, there is no 
test method to assess wind resistance of gutters. Further, the test method to 
evaluate the resistance of windows to wind-driven rain is inadequate for high 
wind events. However, before testing limitations can be overcome, research needs 
to be conducted, new test methods need to be developed, and some existing test 
methods need to be modified.

- Except to the extent covered by reference to ASCE 7, the 2006 IBC does not 
address the requirement 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.

- The 2006 IBC does not account for tornadoes; therefore, except for weak 
tornadoes, it is ineffective for this type of storm. Guidance to overcome this 
shortcoming is given in Section 4.5.




4.2 HOSPITALS EXPOSED TO HIGH WINDS

4.2.1 Vulnerability: What High Winds Can Do to Hospitals

This section provides an overview of the common types of wind damage and their 
ramifications.

4.2.1.1 Types of Building Damage

When damaged by wind, hospitals typically experience a variety of building 
component damage. For example, at the hospital shown in Figure 4-8, the roof 
covering was severely damaged, windows were broken, and rooftop equipment was 
blown away. The subsequent water infiltration required that most of the hospital 
be evacuated. The most common types of damage are discussed below in descending 
order of frequency. 

Figure 4-8 is a photo of a field military hospital in tents set up to replace 
evacuated hospital in U.S. Virgin Islands following Hurricane Marilyn (1995) 
[end figure]

Roof: Roof covering damage (including rooftop mechanical, electrical, and 
communications equipment) is the most common type of wind damage, as illustrated 
by Figure 4-9. In addition to blowoff of the roof membrane (yellow arrow), 
ductwork blew away (red circle), a gooseneck was blown over (red arrow), and 
wall panels at an equipment enclosure were blown off (blue arrow). The cast-in-
place concrete deck kept most of the water from entering the hospital. 

[Begin figure]
Figure 4-9 is a photo of a damaged roof membrane and rooftop equipment. Typhoon 
Paka (1997). 
[end figure]

Glazing: Exterior glazing damage is very common during hurricanes and tornadoes, 
but is less common during other storms. The glass shown in Figure 4-10 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).

[Begin figure]
Figure 4-10 is a photo showing how the outer window panes were broken by 
aggregate from a built-up roof. Hurricane Hugo (South Carolina, 1989) 
[end photo]

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. Wall covering damage is shown at the hospital complex 
described in the West Florida Hospital case study, Section 4.1.3.

Wall collapse: Collapse of non-load-bearing exterior walls is common during 
hurricanes and tornadoes, but is less common during other storms. At the 
hospital shown in Figure 4-11, a portion of the non-load-bearing wall collapsed. 
Several windows were also broken by aggregate ballast blown from the hospitals 
roof (see Figure 4-5).

[Begin figure]
Figure 4-11 is a photo showing the collapse of non-load-bearing wall (red 
circle) and broken glazing from roof aggregate (red arrow). Hurricane Hugo 
(South Carolina, 1989) 
[end figure]

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 4-12).

[Begin figure]
Figure 4-12 is a photo showing how this building in Northern Illinois was 
heavily damaged by a strong tornado in 1990. 
[end figure]

4.2.1.2 Ramifications of Damage

The ramifications of building component damage on hospitals 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. As illustrated by Figures 4-1 and 4-8, 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). 

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.

[Begin text box]
Modest wind speeds can drive rain into exterior walls. Unless adequate 
provisions are taken to account for water infiltration (see Sections 4.3.3.1  
4.3.3.6), damaging corrosion, dry rot, and mold can occur within walls.
[End text box]

Ancillary buildings (such as storage buildings) adjacent to hospitals are also 
vulnerable to damage. Although loss of these buildings may not be crippling to 
the operation of the hospital, debris from ancillary buildings may strike and 
damage the hospital. 

Injury or death: Although infrequent, hospital occupants or people outside 
hospitals may be injured and killed if 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. If a hospital, or a portion of a hospital, needs to be evacuated due 
to wind-related damage, patients may be exposed to risk of injury or death 
during their relocation.

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 hospitals can include lack of 
medical care, and the costs to rent temporary facilities. These additional costs 
can be quite substantial.

[Begin text box]
Although people are not usually outside during hurricanes, it is not uncommon 
for people to seek medical care during a storm. Missiles, such as roof aggregate 
or tile shedding from a hospital, could injure or kill people before they have a 
chance to enter the building.
[End text box]

4.2.1.3 The Case of West Florida Hospital, Pensacola, Florida

The case of West Florida Hospital illustrates a variety of building performance 
problems. The 531-bed West Florida Healthcare facility (also called the 
Pavillion) includes the 400-bed acute tertiary West Florida Hospital, the 58-bed 
Rehabilitation Institute, and a 73-bed behavioral health facility. The Pavillion 
is located north of downtown Pensacola, approximately 3 miles west of Escambia 
Bay and 7 miles north of Pensacola Bay. West Florida was struck by Hurricane 
Ivan in 2004. The estimated peak gust wind speed at this site was 105 to 115 
mph. [footnote 6] The design wind speed in the 2005 edition of ASCE 7 for this 
location is 135 mph. 

[Begin footnote 6] The 105 to 1115 mph speeds were estimated for Exposure C. 
[end footnote]

The West Florida Hospital (J on Figure 4-13) and several of the other buildings 
on the campus experienced a variety of damages during the storm. The roof 
membrane was punctured in several places by windborne missiles and by damaged 
rooftop equipment (see Figures 4-14 to 4-16). 


[Begin figure]Figure 4-13 is an illustration of the West Florida Hospital. 
[end figure]

Exterior insulation finish system (EIFS) blew off the hospital and caused 
significant glass breakage in the MOB (Figure 4-17) and the walkway connecting 
the hospital to the MOB. Some of the lower-level windows may have been broken by 
wind-blown aggregate ballast from the roof over the dialysis unit and urgent 
care facility. In addition, some window frames were reportedly blown out. These 
failures were likely caused by the development of high internal pressure after 
windows on windward surfaces were broken by missiles, combined with suction 
pressure on the exterior surface of windows on the leeward side of the building. 
Glass damage to the MOB, and subsequent wind and water damage to the interior, 
resulted in closure of several offices. 

In addition to the window breakage, EIFS blew off the elevator enclosure, the 
stair tower, and the spandrels. The single-ply roof membrane was damaged and the 
Lightning Protection System (LPS) on the MOB was also displaced. 

The hospital originally had exposed concrete walls. However, in a subsequent 
refurbishing, the walls were faced with EIFS. Steel hat channels were installed 
over the concrete, followed by gypsum board, insulation, and synthetic stucco. 
In areas where the EIFS blew off, the gypsum board typically pulled over the 
screw heads and blew away (Figure 4-23). The screws and hat channels were 
moderately corroded. Although the corrosion could have eventually caused loss of 
the EIFS, it did not play a role in this failure.

With loss of the EIFS wall covering, wind-driven rain destroyed the elevator 
control equipment (see Figure 4-22). Water damage to the elevator control 
equipment resulted in failure of the MOB stair tower elevator. As a result, 
several people were trapped in the MOB stair tower elevator shown in Figure 4-18 
during the hurricane. Fortunately, the MOB had another bank of elevators in the 
core of the building that was not damaged, so vertical transportation was still 
possible, although handicapped by the loss of the stair tower elevator. At the 
MOB stair tower, some of the gypsum board on the interior side of the studs 
collapsed into the stairway, thus trapping a maintenance worker who had gone to 
the mechanical penthouse during the hurricane. 

Glass shards from the MOB punctured the ballasted single-ply membrane over the 
regional dialysis unit and urgent care facility (item L on Figure 4-13). 
Although the roof membrane had been punctured in numerous areas (Figure 4-20), 
the concrete deck (concrete topping over metal decking) over the dialysis 
unit and urgent care facility acted as an secondary line of protection against 
water leakage and was effective in minimizing water infiltration into the 
facility, thereby minimizing interrupted use of these facilities. By quickly 
performing emergency roof repairs and cleaning up the interior, the dialysis 
unit was non-operational for only 1 day. 

At the cancer treatment facility (H on Figure 4-13), asphalt shingles were blown 
from the roof hips and some eave edge metal lifted. Additionally, sewage backed 
up at this facility because of power loss to a lift station. Sewage backup was 
cleaned up quickly and the facility was non-operational for only 1 day.

At the imaging center (F on Figure 4-13), there were some broken windows and a 
fan cowling blew away. Some large parking lot light fixtures also collapsed 
because the bottoms of the tubes were severely corroded (Figure 4-21).

Communications outside of the hospital were lost about an hour after the arrival 
of high winds because of damage to the communications antenna; the LPS was also 
displaced (Figure 4-15). A canopy at the loading dock was blown away, which 
caused difficulties in materials handling.

Because of rapid emergency response by construction and clean-up crews, the 
hospital and other facilities on campus remained functional. However, the damage 
was very costly and created many hardships for hospital staff. 

[Begin figures]
Figure 4-14 is a photo showing numerous repairs where the modified bitumen roof 
membrane was punctured by missiles. Water from the punctured membrane entered 
the surgical suite. 

Figure 4-15 is a photo showing damaged rooftop equipment, collapsed antenna 
(circled), and displaced LPS

Figure 4-16 is a photo showing damaged rooftop equipment. Although some of this 
damage may have been caused by wind pressure, some of it was caused by missiles. 
Note the open ducts (red arrows).

Figure 4-17 is a photo showing broken windows in the MOB. Wood studs and gypsum 
board had been temporarily installed after the hurricane to prevent patients 
from inadvertently falling out of the MOB. 

Figure 4-18 is a photo showing broken windows in the connecting walkway between 
the hospital (right) and MOB (left). Also note the broken windows and loss of 
EIFS (including the gypsum board on both sides of the studs) at the elevator 
enclosure (blue arrow).

Figure 4-19 is a photo showing EIFS debris blown off the hospital building (Item 
J on Figure 4-13) in the background (red square) broke numerous windows in the 
MOB (item G on figure 4-13) in the foreground. 

Figure 4-20 is a photo looking down at the one-story roof to the right of the 
MOB in Figure 4-19. The small dark areas are locations where emergency patches 
had been placed to repair punctures from falling glass shards. (Note: At the 
time the photo was taken, the ballast had been repositioned into rows in 
preparation for removal)

Figure 4-21 is a photo of a collapsed light fixtures caused by severe corrosion 
(see inset). The cancer treatment facility is beyond to the left.

Figure 4-22 is a photo showing the only remaining portion of the exterior wall 
surrounding the elevator penthouse on the MOB was the steel studs. 

Figure 4-23 is a photo of close-up of the damaged EIFS at the hospital. In this 
area most of the insulation and gypsum board was blown from the steel furring 
channels.
[End figures]

4.2.2 Evaluating Hospitals 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 hospitals. The procedures 
presented below establish guidelines for evaluating the risk to new and existing 
buildings from windstorms 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 hospitals.

In the case of tornadoes, neither the IBC nor ASCE 7 requires buildings 
(including hospitals) to be designed to resist tornado forces, nor are occupant 
shelters required in buildings located in tornado-prone regions. Constructing 
tornado-resistant hospitals 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 hospital 
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 hospital. See 
Section 4.5 for recommendations pertaining to hospitals in tornado-prone 
regions.

4.2.2.1 New Buildings

When designing new hospitals, a two-step procedure is recommended for evaluating 
the risk from windstorms (other than tornadoes).

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 4.3).

Step 2: For hospitals in hurricane-prone regions, refer to the design, 
construction, and maintenance enhancements recommended in Sections 4.3.1.5, 
4.3.2.1, 4.3.3.2, 4.3.3.4, 4.3.3.6, 4.3.3.8, 4.3.4.2, 4.3.4.4, 4.3.5, and 4.3.6. 

For 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 hospitals could severely affect patients. Some of the 
recommendations in the sections pertaining to hurricane-prone regions may 
therefore be prudent.

4.2.2.2 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 
4.4.




4.3 REQUIREMENTS AND BEST PRACTICES IN HIGH-WIND REGIONS 

4.3.1 General Hospital Design Considerations

The performance of hospitals 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 4 
emphasizes the building envelope components and the nonstructural systems. 
According to National Institute of Building Sciences (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 windstorms. 
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 hospitals. 

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. 

Hospital Design Considerations in Hurricane-Prone Regions

Following the general design and construction recommendations, this manual 
presents recommendations specific to hospitals located in hurricane-prone 
regions. These recommendations are additional to the ones presented for 
hospitals located outside of hurricane-prone regions, and in many cases 
supersede those recommendations. Hospitals 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. 

Hospitals in hurricane-prone regions require special attention because they 
normally have vulnerable occupants (patients) at the time of a hurricane, and 
afterwards, many injured people seek medical care. Significant damage to a 
hospital can put patients at risk and jeopardize delivery of care to those 
seeking treatment. In order to ensure continuity of service during and after 
hurricanes, the design, construction, and maintenance of hospitals should be 
very robust to provide sufficient resiliency to withstand the effects of 
hurricanes.

[Begin text box]
Because of advanced warning of impending land fall, with the exception of 
Hurricane Katrina (Louisiana and Mississippi, 2005), the death toll from 
hurricanes in the U.S. has been extremely low for the last several decades. 
However, large numbers of people are often injured and seek care at hospitals. 
Blunt-force trauma injuries caused by wind-borne debris, falling trees, 
collapsed ceilings, or partial building collapse occur during hurricanes. But 
most of the hurricane-related injuries typically occur in the days afterward. 
These injuries are typically due to chainsaw accidents, stepping on nails, 
lacerations incurred while removing debris, vehicle accidents at intersections 
that no longer have functional traffic lights, people falling off roofs as they 
attempt to make emergency repairs, and carbon monoxide poisoning or electrical 
shock from improper use of emergency generators. Therefore, at a time when many 
hospitals in an area may be functionally impaired or no longer capable of 
providing service due to building damage (Figures 4-1 and 4-8), hospital staffs 
are faced with a higher than normal number of people seeking treatment. Before 
arrival of a hurricane, hospitals also often receive an influx of women in their 
third trimester of pregnancy, so that they will already be at the hospital in 
case they go into labor during the storm or shortly thereafter, when getting to 
the hospital could be hazardous or impossible.
[End text box]

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. 

4.3.1.1 Site 

When selecting land for a hospital, sites located in Exposure D (see ASCE 7 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. [footnote 7]

[Begin footnote 7] 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. [end footnote]

Trees with trunks larger than 6 inches in diameter, poles (e.g., light fixture 
poles, flagpoles, 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 hospital and injure the occupants 
(see Figure 4-24). Large trees can crash through pre-engineered metal buildings 
and wood frame construction. Falling trees can also rupture roof membranes and 
break windows.

[Begin figure]
Figure 4-24 is a photo of the roof membrane on this hospitals materials 
management facility was ruptured by falling trees. Hurricane Ivan (Florida, 
2004) 
[end figure]


Street signage should be designed to resist the design wind loads so that 
toppled signs do not block access roads or become wind-blown debris. AASHTO LTS-
4-M (amended by LTS-4-12 2001 and 2003, respectively) provides guidance for 
determining wind loads on highway signs. 

Providing at least two means of site egress is prudent for all hospitals, but is 
particularly important for hospitals 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.

4.3.1.2 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 
hospital 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 hospitals.

[Begin text box]
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.
[End text box]

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 hospitals is required to be 1.15. However, some 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 facilities on a hospital campus.

[Begin text box]
Uplift loads on roof assemblies can also be determined from FM Global (FMG) Data 
Sheets. If the hospital 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).
[End text box]

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 hospitals 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 determine a reasonable safety factor in order to select 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.

[Begin text box]
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).
[End text box]

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 4.2.2, as appropriate.

[Begin text box]
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.
[End text box]

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 4-25 shows a load path discontinuity between 
a piece of HVAC equipment and its equipment stand. The equipment on this new 
building blew away because it was resting on vibration isolators that provided 
lateral resistance, but no uplift resistance (also see Figure 4-92).

[Begin figure]
Figure 4-25 is a photo of emporary coverings placed over two large openings in 
the roof that were left after the ductwork blew away. Hurricane Katrina 
(Mississippi, 2005)
[end figure]

Figure 4-26 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.

[Begin figure]
Figure 4-26 Illustration of load path continuity 
[end figure]

As part of the detailed design process, special consideration should be given to 
the durability of materials and water infiltration.

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. 

[Begin text box]
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).
[End text box]

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 4.3.3.1 and 4.3.3.5, and Figure 4-45 
for further discussion and an example. 

[Begin text box]
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. 
[End text box]

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 4-45, 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 hospital:

- Is located in an area where the basic wind speed is greater than 90 mph (peak 
gust).

- Will incorporate a tornado shelter.

4.3.1.3 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.

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 magnitude of the results 
of the risk assessment described in Section 4.2.2, complexity of the facility, 
and the competency of the general contractor, subcontractors, and suppliers.

4.3.1.4 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 (such as a 
thunderstorm with wind speeds of 70 mph peak gust or greater). The purpose of 
the inspection is to assess whether the 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.

4.3.1.5 Site and General Design Considerations in Hurricane-Prone Regions

Via ASCE 7, the 2006 edition of the IBC has only one special wind-related 
provision pertaining to hospitals 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 hospital during a hurricane, nor does it ensure a hospital will remain 
functional during and after a hurricane. A hospital 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 
4.3.2.1, 4.3.3.2, 4.3.3.4, 4.3.3.6, and 4.3.3.8. 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 striking 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 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 (see Figure 4-27).

[Begin figure]
Figure 4-27 is a photo showing how open walkways do not provide protection from 
wind-borne debris. (Hurricane Katrina, Mississippi)
[end figure]

4.3.2 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 hospitals 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 (Figure 4-34). 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 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). 

The following design parameters are recommended for structural systems:

- 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. 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. 

- 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 4-28 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 4-29 and 4-30 show problems with 
acoustical decking attached with powder-driven pins. The pin shown on the left 
of Figure 4-30 is properly seated. However, the pin at the right did not 
penetrate far enough into the steel joist below. 

[Begin figures]
Figure 4-28 is a photo of a 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 4-29 is a photo looking down at a sidelap of a deck attached with powder-
driven pins. The washer at the top pin blew through the deck.

Figure 4-30 is a photo of a view looking along a sidelap of a deck attached with 
powder-driven pins. The right pin does not provide adequate uplift and shear 
resistance.
[End figures]

- 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.

- 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 4-31 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.

[Begin figure]
Figure 4-31 is a photo of portions of this waffled precast concrete roof deck 
were blown off. Typhoon Paka (Guam, 1997)
[end figure]

- 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 4-32, 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.

[Begin figure]
Figure 4-32 is a photo of a Twin-Tee roof panel lifted as a result of the 
combined effects of wind uplift and pre-tension. Tornado (Missouri, May 2003)
[end figure]

- 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).

[Begin text box]
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.
[End text box]

- 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 
4-33). Wind-borne debris from damaged canopies can damage nearby buildings and 
injure people, hence these elements should also receive design and construction 
attention. 

[Begin figure]
Figure 4-33 is a photo of the destroyed walkway canopy in front of this building 
became wind-borne debris. Hurricane Ivan (Florida, 2004) 
[end figure]

4.3.2.1 Structural Systems in Hurricane-Prone Regions

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.

[Begin text box]
If precast concrete is used for the roof or wall structure, the connections 
should be carefully designed, detailed, and constructed.
[End text box]

If these recommendations are not followed for hospitals 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 4.3.3.2). 

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 
vertically with #4 rebars at 16 inches on center, and precast concrete that is a 
minimum 6-inches-thick and reinforced equivalent to the recommendations for 
cast-in-place walls.

4.3.3 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.

The design considerations for building envelope components of hospitals 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. Design considerations specific to hurricane-prone 
regions are discussed in Sections 4.3.3.2, 4.3.3.4, 4.3.3.6, and 4.3.3.8.

4.3.3.1 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 4-34). 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 (see Figure 4-35). 

[Begin figures]
Figure 4-34 is a photo of a door on a hospital penthouse blown off its hinges 
during Hurricane Katrina (Mississippi, 2005)

Figure 4-35 is a photo showing how this new rolling door failed because the CMU 
spalled at the door frames expansion bolts, which were too close to the end of 
the CMU. Hurricane Charley (Florida, 2004)
[End figures]

[Begin text box]
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).
[End text box]

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.

[Begin text box]
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).
[End text box]

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. 

[Begin text box]
Where corrosion is problematic, anodized aluminum or galvanized doors and 
frames, and stainless steel frame anchors and hardware are recommended. 
[End text box]

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.

[Begin text box]
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.
[End text box]

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 4.3.3.3 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 
4-36). It is recommended that designers use ASTM E 2112 as a design resource.
Weatherstripping

Figure 4-36 is an illustration of a door sill pan flashing with end dams, rear 
leg, and turned-down front leg [end figure]

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 4-37 and 4-38). Alternatively, a door sweep can be specified (see 
Figure 4-38). For high-traffic doors, periodic replacement of the neoprene 
components will be necessary.

[Begin figures]
Figure 4-37 is an illustration of a drip at door head and drip with hook at head

Figure 4-38 is an illustration of a door shoe with drip and vinyl seal (left). 
Neoprene door bottom sweep (right)
[End figures]

Door shoes and bottoms: These are intended to minimize the gap between the door 
and the threshold. Figure 4-38 illustrates a door shoe that incorporates a drip. 
Figure 4-39 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.

[Begin figure]
Figure 4-39 is an illustration of an automatic door bottom 
[end figure]

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 4-40), or thresholds can 
have a stop and seal (see). 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 during construction (see Figure 4-40).

[Begin figures]
Figure 4-40 is an illustration of an interlocking threshold with drain pan

Figure 4-41 is an illustration of a threshold with stop and seal
[End figures]

Adjustable jamb/head weatherstripping: This type of weatherstripping is 
recommended because the wide sponge neoprene offers good contact with the door 
(see Figure 4-42). The adjustment feature also helps to ensure good contact, 
provided the proper adjustment is maintained.

[Begin figure]
Figure 4-42 is an illustration of an adjustable jamb/head weatherstripping
[End figure]

Meeting stile: At the meeting stile of pairs of doors, an overlapping astragal 
weatherstripping offers greater protection than weatherstripping that does not 
overlap. 

4.3.3.2 Exterior Doors in Hurricane-Prone Regions

Although the ASCE-7 wind-borne debris provisions only apply to glazing within a 
portion of hurricane-prone regions, it is recommended that all hospitals 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. 

[Begin text box]
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: ASTM E 1996D
Missile Weight: 9 pound 2x4 lumber
Impact Speed: 50 feet per second (34 mph)
Momentum: 14 lbf -s*

Missile: ASTM E 1996E
Missile Weight: 9 pound 2x4 lumber
Impact Speed: 80 feet per second(55 mph)
Momentum: 22 lbf -s*

Missile: FEMA 361 (Shelter Missile)
Missile Weight: 15 pound 2x4 lumber
Impact Speed: 47 feet per second (100 mph)
Momentum: 68 lbf -s*

*lb sub-f -s = pounds force per second
[End text box]

4.3.3.3 Windows and Skylights

This section addresses general design considerations for exterior windows and 
skylights. For additional information on windows and skylights located in 
hurricane-prone regions, see Section 4.3.3.4, and for those in tornado-prone 
regions, see Section 4.5.

[Begin text box]
For further general information on windows, see the National Institute of 
Building Sciences Building Envelope Design Guide 
(www.wbdg.org/design/envelope.php).
[End text box]

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 4-
43). 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.

[Begin figure]
Figure 4-43 is a photo of two complete windows, including frames, blew out as a 
result of an inadequate number of fasteners. Typhoon Paka (Guam, 1997)
[end figure]

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.

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.

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.

[Begin text box]
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.
[End text box]

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 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 4-44). 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 
4-45. The stop protects the sealant from direct exposure to the weather and 
reduces the possibility of wind-driven rain penetration.

[Begin figures]
Figure 4-44 Illustrative view of a typical window sill pan flashing with end 
dams and rear legs Source: ASTM E 2112 

Figure 4-45 Illustration showing how protecting sealant retards weathering and 
reduces the exposure to wind-driven rain.
[End figures]

4.3.3.4 Windows and Skylights in Hurricane-Prone Regions 

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 4-46 and 4-47). At the hospital shown 
in Figure 4-46, 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. At the hospital shown in 
Figure 4-47, several of the skylights tempered glass outer panes were broken by 
wind-blown aggregate from the hospitals aggregate ballasted single-ply 
membrane. The inner laminated glass panes were not broken. Note that some of the 
copings were also blown off (blue arrow).Some of the glazing may have been 
damaged by wind-blown copings. At the grey hospital on the other side of the 
street, much of the roof membrane was blown away (yellow arrow).

With broken windows, a substantial amount of water can be blown into a building, 
and the internal air pressure can be greatly increased, which may damage the 
interior partitions and ceilings. 

[Begin figures]
Figure 4-46 is a photo of plywood panels (black continuous bands) installed 
after the glass spandrel panels were broken by roof aggregate. [footnote 9] 
Hurricane Katrina (Mississippi, 2005) 

Figure 4-47 is a photo showing how the outer glass panes of the skylight were 
broken by roof aggregate (red arrow). Hurricane Hugo (South Carolina, 1989)
[End figures] 

[begin footnote 9] Glass spandrel panels are opaque glass. They are placed in 
curtain walls to conceal the area between the ceiling and the floor above. [end 
footnote

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.

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 hospitals 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 4.3.3.2). 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. 

[Begin text box]
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/envelope.php).
[End text box]

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 4.4.2.2.

4.3.3.5 Non-Load-Bearing Walls, Wall Coverings, and Soffits

[Begin text box]
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).
[End text box]

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 4.4.3.6 for additional 
information pertaining to hospitals located in hurricane-prone regions, and 
Section 4.5 for additional information pertaining to hospitals located in 
tornado-prone regions. 

[Begin text box]
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 (see 
Figures 4-22 and 4-48). The restoration of elevator service can take weeks, even 
with expedited work.
[End text box]

[Begin figure]
Figure 4-48 is a photo showing how the wall covering blew off the penthouse at 
this hospital complex, allowing rainwater to destroy the elevator controls. 
Hurricane Ivan (Florida, 2004)
[end figure]

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.

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 Figures 4-49 and 
4-50). 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 can cause significant damage and the collapse 
of ceilings. 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.

[Begin text box]
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.
[End text box]

[Begin figures]
Figure 4-49 is a photo showing how this suspended metal soffit was not designed 
for upward-acting wind pressure. Typhoon Paka (Guam, 1997)

Figure 4-50 is a photo showing Hospital canopy damage. Hurricane Katrina 
(Louisiana, 2005) 
[end figures]

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. 

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 4-51). By doing so, wall collapse may be prevented if 
the building envelope is breached. This recommendation is applicable to 
hospitals located in areas with a basic wind speed greater than 120 mph, and to 
hospitals in tornado-prone regions that do not have shelter space designed in 
accordance with FEMA 361.

[Begin figure]
Figure 4-51 is a photo of red arrows showing the original location of a CMU wall 
that nearly collapsed following a rolling door failure. Hurricane Charley 
(Florida, 2004)
[end figure]

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: [footnote 10] 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 4-52). 
Common failure modes include tie (anchor) fastener pull-out (see Figure 4-53), 
failure of masons to embed ties into the mortar, poor bonding between ties and 
mortar, a mortar of poor quality, and tie corrosion.

[Begin footnote 10] The brick veneer discussion is from Attachment of Brick 
Veneer in High-Wind RegionsHurricane Katrina Recovery Advisory (FEMA, December 
2005). 

[Begin figures]
Figure 4-52 is a photo showing how the brick veneer failure on this building was 
attributed to tie corrosion. Hurricane Ivan (Florida, 2004)

Figure 4-53 is a photo showing how this tie remained embedded in the mortar 
joint while the smooth-shank nail pulled from the stud.
[end figures]

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 4-
54). 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.

[Begin figure]
Figure 4-54 is an illustration of how misalignment of the tie reduces the 
embedment and promotes veneer failure.
[end figure]

Corrugated ties typically used in residential veneer construction provide little 
resistance to compressive loads induced by positive and negative pressure. The 
use of compression struts would likely be beneficial, but off-the-shelf devices 
do not currently exist. Two-piece adjustable ties (Figure 4-55) provide 
significantly greater compressive strength than corrugated ties.

[Begin figure]
Figure 4-55 is an illustration of examples of two-piece adjustable ties 
[end figure]

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:

- 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, 2005). A stud spacing of 16 inches on center is recommended 
so that ties can be anchored at this spacing.

- Ring-shank nails are recommended in lieu of smooth-shank nails for wood studs. 
A minimum embedment of 2 inches is suggested.

- 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 28BBrick 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.

- 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 they are used, bend the ties 
at a 90-degree angle at the nail head to minimize tie flexing when the ties 
cycle between tension and compression loads (Figure 4-56).

- 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 (Figure 4-57). 

[Begin figures]
Figure 4-56 is an illustration showing bend ties at nail heads

Figure 4-57 is an illustration showing tie embedment 
[end figures]

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. When the base of the 
brick veneer occurs near grade, the grade should be designed so that it occurs 
several inches below the weeps so that drainage from the weeps is not impeded. 
Also, landscaping should be kept clear of weeps so that vegetation growth does 
not cause blockage of weeps. At the hospital shown in Figure 4-58, 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. 

[Begin figure]
Figure 4-58 is a photo showing how water leaked inside along the base of the 
brick veneer walls (red arrow). Hurricane Katrina (Louisiana, 2005) 
[end figure] 

EIFS: Figure 4-59 shows typical EIFS assemblies. Figure 4-48 and several figures 
in Section 4.2.1.3 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 or hat channels. The gypsum board detached from the studs/hat 
channels, which is a common EIFS failure mode. 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. 

[Begin figure]
Figure 4-59 is an illustration showing typical EIFS assemblies
[end figure] 

At the hospital shown in Figure 4-60, 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. Glazing damage can be very 
devastating, as shown and discussed in Section 4.2.1.3.

[Begin figure]
Figure 4-60 is a photo showing EIFS blown off a cast-in-place concrete wall. 
Note the damaged rooftop ductwork. Hurricane Ivan (Florida, 2004)
[end figure] 

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 for 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.

Stucco over studs: Wind performance of traditional stucco walls is similar to 
the performance of EIFS, as shown in Figure 4-61. 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 4-61 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.

[Begin figure]
Figure 4-61 is a photo showing how the stucco wall failure was caused by 
inadequate attachment between the stud tracks and the buildings structure. 
Hurricane Ivan (Florida, 2004)
[end figure]

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 be by either 
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. Figure 4-62 illustrates metal wall 
panel problems. At this building, 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. Water entry was facilitated by lack of a moisture barrier and solid 
sheathing behind the metal panels (as discussed below).

[Begin figure]
Figure 4-62 is a photo showing how the loss of metal wall panels allowed a 
substantial amount of wind-driven rain to penetrate this building. Hurricane 
Ivan (Florida, 2004)  
[end figure]

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. 

[Begin text box]
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.
[End text box]

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 4-62 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.

4.3.3.6 Non-Load-Bearing Walls, Wall Coverings, and Soffits in Hurricane-Prone 
Regions 

In order to achieve enhanced missile resistance of non-load-bearing exterior 
walls, the wall types discussed in Section 4.3.2.1 (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 hospitals 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 interior non-load-bearing masonry walls in hospitals located where the basic 
wind speed is greater than 120 mph, see the recommendations given in Section 
4.3.3.5.

4.3.3.7 Roof Systems

[Begin text box]
For further general information on roof systems, see the National Institute of 
Building Sciences Building Envelope Design Guide 
(www.wbdg.org/design/envelope.php).
[End text box]

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 4.3.3.8 for additional information pertaining to 
hospitals located in hurricane-prone regions, and Section 4.5 for hospitals 
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. 

[Begin text box]
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 4.3.3.8, be specified over the 
elevator penthouse roof deck. 
[End text box]

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 4.1.3. 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. 

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.

[Begin text box]
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.
[End text box]

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 4-10 
and 4-81). 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 Figures 4-5, 4-46, and 4-47). 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 
building shown in Figure 4-63, 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 4-64, 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 the entire uplift load because of the decks 
inability to transfer any significant load to adjacent flanges. Hence, at the 
joists shown in Figure 4-64, 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.

[Begin figures]
Figure 4-63 is a photo of how the orientation of the membrane fastener rows led 
to blow-off of the steel deck. Hurricane Marilyn (U.S. Virgin Islands, 1995)

Figure 4-64 is a photo of a 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. 
[End figures]

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.)

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 4-65 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. 

[Begin figure]
Figure 4-65 is a photo of how an ink pen shows an opening that the wind can 
catch, and cause lifting and peeling of the membrane. 
[End figure]

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 hospitals. For FMG-insured 
facilities, FMR-approved flashing should be used and FM Data Sheet 1-49 should 
also be consulted. 

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 4-66) and subsequent lifting and peeling of the roof 
membrane. When a vertical flange disengages and lifts up, the edge flashing and 
membrane are very susceptible to failure. Normally, when a flange lifts the 
failure continues to propagate and the metal edge flashing and roof membrane 
blows off.

[Begin figure]
Figure 4-66 is a photo showing that the metal edge flashing on this hospital 
disengaged from the continuous cleat and the vertical flange lifted. Hurricane 
Hugo (South Carolina, 1989)
[End figure] 

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 4-67 was attached with 1/4-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.

[Begin figure]
Figure 4-67 is a photo showing that both vertical faces of the coping were 
attached with exposed fasteners instead of concealed cleats. Typhoon Paka (Guam, 
1997)
[End figure]

Gutters 

Storm-damage research has shown that gutters are seldom constructed to resist 
wind loads (see Figure 4-68). 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 4-69 was initiated by gutter uplift. The gutter was similar to 
that shown in Figure 4-68. The membrane blow-off caused significant interior 
water damage.

[Begin figures]
Figure 4-68 is a photo showing that 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)

Figure 4-69 is a photo showing that 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)
[End figures] 

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.

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 4-70). 
Therefore, it is imperative that the base flashing loads be calculated, and 
attachments 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.

[Begin figure]
Figure 4-70 is a photo showing that if mechanically attached base flashings have 
an insufficient number of fasteners, the base flashing can be blown away. 
Hurricane Andrew (Florida, 1992) 
[End figure]

When the roof membrane is specified to be adhered, it is recommended that fully 
adhered base flashings be specified in lieu of mechanically attached base 
flashings. Otherwise, if the base flashing is mechanically attached, ballooning 
of the base flashing during high winds can lead to lifting and progressive 
peeling of the roof membrane.

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).

4.3.3.8 Roof Systems in Hurricane-Prone Regions

The following types of roof systems are recommended for hospitals 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.

- When fully adhering boards to concrete decks, it is recommend that a planar 
flatness of a maximum of 1/4-inch variation over an 10 foot length (when 
measured by a straightedge) be specified. Prior to installation of the roof 
insulation, it is recommended that the planar flatness be checked with a 
straightedge. If the deck is outside of the 1/4-inch variation, it is 
recommended that the high spots be ground or the low spots be suitably filled.

- 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 4-72 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. 

[Begin text box]
When fully adhering insulation boards, it is recommended that the boards be no 
larger than 4 feet by 4 feet. It is also recommended that the board thickness 
not exceed 2 inches ( 11/2 inches is preferable). Use of small thin boards makes 
it easier for the contractor to conform the boards to the substrate. At the 
hospital shown in Figure 4-71, 4 foot by 8 foot insulation boards were set in 
hot 
asphalt over a concrete deck. A few of the boards detached from the deck. The 
boards may have initiated the membrane blow off, or the membrane blow off may 
have been initiated by lifting and peeling of the metal edge flashing, in which 
case, loss of the insulation boards was a secondary failure. 
[End text box]

Figure 4-71 is a photo of how blown off insulation may have initiated blow off 
of the roof membrane. Hurricane Ivan (Florida, 2004) [end figure]

[Begin figure]
Figure 4-72 is a photo showing that the secondary membrane prevented leakage 
into the ICU after the copper roof blew off. Hurricane Andrew (Florida, 1992) 
[End figure]

- 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 4-79) 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 
hospitals in hurricane-prone regions where the basic wind speed exceeds 130 mph. 

- 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, 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 1/2:12. 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 4-73, 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.
Figure 4-73 is a photo showing significant interior water damage and facility 
interruption occurred after the standing seam roof blew off. Hurricane Marilyn 
(U.S. Virgin Islands, 1995)

[Begin figure]
Figure 4-73 is a photo showing significant interior water damage and facility 
interruption occurred after the standing seam roof blew off. Hurricane Marilyn 
(U.S. Virgin Islands, 1995)
 [End figure] 

- 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. 

In order to avoid the possibility of roofing components blowing off and striking 
people arriving at a hospital during a storm, the following roof systems are not 
recommended: aggregate surfacings, either on BUR, single-plies or SPF; 
lightweight concrete pavers; cementitious-coated insulation boards; slate; and 
tile (see Figure 4-74). 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. 

[Begin figure]
Figure 4-74 is a photo of how brittle roof coverings, like slate and tile, can 
be broken by missiles, and tile debris can break other tiles. Hurricane Charley 
(Florida, 2004)
[End figure] 

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 hospitals in hurricane-prone regions. At the 
building shown in Figure 4-75, 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 missile puncture and 
are not recommended unless they are ballasted with pavers. At the hospital shown 
in Figure 4-76, several missiles, including exhaust fans and copings struck the 
roof. 

[Begin figures]
Figure 4-75 is a photo showing how mechanically attached single-ply membrane 
progressively tore after being cut by wind-borne debris. Hurricane Andrew 
(Florida, 1992)

Figure 4-76 is a photo showing how this fully adhered single-ply roof membrane 
was struck by a variety of missiles. Hurricane Marilyn (U.S. Virgin Islands, 
1995) 
[End figures] 

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 4-77. 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.

[Begin figure]
Figure 4-77 is an illustration showing 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)
[End figure] 

Walkway pads: Roof walkway pads are frequently blown off during hurricanes 
(Figures 4-78 and 4-82). Pad blow off does not usually damage the roof membrane. 
However, wind-borne pad debris can damage other building components and injure 
people. Currently there is no test standard to evaluate uplift resistance of 
walkway pads. Walkway pads are therefore not recommended in hurricane-prone 
regions.

[Begin figure]
Figure 4-78 is a photo showing how several rubber walkway pads were blown off 
the single-ply membrane roof on this hospital. Hurricane Katrina (Mississippi, 
2005)
[End figure] 

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 4-96) 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 4-79). 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 4-62). 

[Begin figure]
Figure 4-79 is a photo of base flashing protected by metal panels attached with 
exposed screws. Hurricane Katrina (Mississippi, 2005)
[End figure]

4.3.3.9 The Case of DeSoto Memorial Hospital, Arcadia, Florida

The case of DeSoto Memorial Hospital illustrates damage caused by aggregate-
surfaced roofs. The 82-bed hospital is located just off Florida Highway 17 in 
Arcadia, approximately 30 miles east of Floridas gulf coast. The hospital was 
constructed in 1964, though the current emergency room (ER), ICU, and third 
floor patient rooms were added in 1984. A separate pre-engineered storage 
building was constructed in 1979.

The facility was struck by Hurricane Charley in 2004, with an estimated peak 
gust wind speed between 125 to 140 mph. [footnote 11] Since the design wind 
speed in the 2005 edition of ASCE 7 for this location is 110 mph, the estimated 
speeds at this site were above current design conditions. Also, even with the 
1.15 importance factor, the actual wind pressures were above the design 
pressures.

[Begin footnote 11] The 125 to 140 mph speeds were estimated for Exposure C.

The hospital sustained damage to windows, rooftop equipment, and a freestanding 
storage building on the campus. Thirty-three windows were broken, including 
patient room windows and windows at three of the eight ICU rooms (Figures 4-80 
and 4-81). Windows were also broken in many vehicles in the parking lot. The 
majority of the glass breakage was caused by aggregate blown from the hospitals 
built-up roofs. Some of the glass breakage may have been due to blown off 
gutters and walkway pads from the hospitals roof (Figure 4-82) or other 
missiles such as tree limbs; blown off gutters can be high-momentum missiles 
that can travel a substantial distance (see Figure 4-81). 

As a result of the window breakage the entire ICU was evacuated during the 
hurricane and closed for about 2 weeks before repairs were completed and the 
unit reoccupied. Some patients were moved to lower floors; the elevator could 
not be used so the patients were either carried down or slid down the stairs on 
mattresses. Fortunately, no one was injured during the evacuation.

A portion of the roof covering was blown off and the satellite dish was nearly 
blown off too. The LPS was displaced in a few areas (see Figure 4-83). As a 
result of the damage to the roof covering and to rooftop equipment, water leaked 
into the building in several areas, which caused the closing of the operating 
room (OR), sterile processing, portions of the lab, and numerous offices. The OR 
was temporarily relocated to the Caesarian section (C-section) room. It was 
about a month before the OR was repaired and reoccupied. 

The metal storage building that contained the hospitals supplies, maintenance 
shop, environmental services, and shipping and receiving collapsed, and its loss 
was significant for the hospital operations. Almost all of the tools and stock 
materials for repairs were lost (Figure 4-84). Tents were set up after the 
hurricane to provide storage. Because of subsequent storms in the next several 
weeks (including two hurricanes), the stored items had to be moved in and out of 
the tents on several occasions. 

Municipal power and water were lost during the hurricane. The hospital ran on 
its generators for about 5 days before power was restored. Municipal water 
service was out for about 2 weeks, but fortunately the hospital had a secondary 
well for potable water, so water service was not interrupted. 

Access to the hospital was not hampered by fallen trees or by flooding. However, 
some staff and emergency medical service (EMS) personnel were unable to get to 
the hospital quickly after the storm because of downed trees or floodwaters in 
their neighborhoods. Landline telephone service was not lost, but paging and 
cell phone services were. The homes of many staff members were no longer 
habitable after the storm, so tents were set up on the hospital campus to house 
staff and volunteers that came to provide assistance. This in turn required 
additional security services and shower and laundry facilities.

The hospital did not have a contingency plan to cope with the damages, and 
therefore, did not have pre-arranged contracts with contractors to perform 
inspections and emergency repairs. Fortunately, there were no problems finding 
contractors quickly after the storm, although the building materials needed for 
repairs were in short supply. 

[Begin figures]
Figure 4-80 is a photo of the second floor beyond the canopy houses the ICU. 
Several windows along the two ICU walls that are visible were broken. 

Figure 4-81 is a photo of a view of the ICU from the third floor roof. The 
gutters (red arrow) are from the back side of the third floor roof.

Figure 4-82 is a photo of a view of the back side of the third floor roof where 
the gutter and an asphalt plank walkway pad were blown away. The loose aggregate 
surfacing was also blown away.

Figure 4-83 is a photo showing how this satellite dish was held down only with 
CMU. Note the displaced LPS at the corner (circled).
 
Figure 4-84 is a photo showing how this pre-engineered storage building 
contained the hospital supplies and maintenance shop. 
[End figures]

4.3.4 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 
Figure 4-85). The most common problems typically relate to inadequate equipment 
anchorage, inadequate strength of the equipment itself, and corrosion.

[Begin figure]
Figure 4-85 is a photo showing how 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)
 
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. Specific information pertaining to 
hospitals located in hurricane-prone regions is presented for each of the 
nonstructural component sections below.

4.3.4.1 Exterior-Mounted Mechanical Equipment

This section discusses loads and attachment methods, as well as the problems of 
corrosion and water infiltration.

Loads and Attachment Methods [footnote 12]

[Begin footnote 12] Discussion is based on: Attachment of Rooftop Equipment in 
High-Wind Regions - Hurricane Katrina Recovery Advisory (May 2006, revised July 
2006) [end footnote]

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 hospitals. 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 4-86 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. The inset at Figure 4-86 shows the curb upon which the unit was 
attached. A substantial amount of water entered the building at the curb 
openings before the temporary tarp was placed.

[Begin text box]
Mechanical penetrations through the elevator penthouse roof and walls must 
possess adequate wind and water resistance to ensure continuity of elevator 
service (see Section 4.3.3.5). 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.
[End text box]

[Begin figure]
Figure 4-86 is a photo showing that although this 18,000-pound HVAC unit was 
attached to its curb with 16 straps, it blew off during Hurricane Ivan. 
(Florida, 2004)
[end figure]
 
To anchor fans, small HVAC units, and relief air hoods, the minimum attachment 
schedule provided in Table 4-1 is recommended. The attachment of the curb to the 
roof deck also needs to be designed and constructed to resist the design loads. 
The cast-in-place concrete curb shown in Figure 4-87 was cold-cast over a 
concrete 
roof deck. Dowels were not installed between the deck and the curb, hence a weak 
connection occurred.

[Begin figure]
Figure 4-87 is a photo showing how the gooseneck on this hospital remained 
attached to the curb, but the curb detached from the deck. Typhoon Paka (Guam, 
1997)
[End figure]

[Begin table]
Table 4-1: Number of #12 Screws for Base Case Attachment of Rooftop Equipment

Case No: 1
Curb Size and Equipment Type: 12 x 12 Curb with Gooseneck Relief Air Hood
Equipment Attachment: Hood Screwed to Curb 
Fastener Factor for Each Side of Curb or Flange: 1.6

Case No: 2
Curb Size and Equipment Type: 12 x 12 Gooseneck Relief Air Hood with Flange 
Equipment Attachment: Flange Screwed to 22 Gauge Steel Roof Deck 
Fastener Factor for Each Side of Curb or Flange: 2.8

Case No: 3
Curb Size and Equipment Type: 12 x 12 Gooseneck Relief Air Hood with Flange
Equipment Attachment: Flange Screwed to 15/32 OSB Roof Deck
Fastener Factor for Each Side of Curb or Flange: 2.9

Case No: 4
Curb Size and Equipment Type: 24 x 24 Curb with Gooseneck Relief Air Hood
Equipment Attachment: Hood Screwed to Curb 
Fastener Factor for Each Side of Curb or Flange: 4.6

Case No: 5
Curb Size and Equipment Type: 24 x 24 Gooseneck Relief Air Hood with Flange
Equipment Attachment: Flange Screwed to 22 Gauge Steel Roof Deck 
Fastener Factor for Each Side of Curb or Flange: 8.1

Case No: 6
Curb Size and Equipment Type: 24 x 24 Gooseneck Relief Air Hood with Flange

Equipment Attachment: Flange Screwed to 15/32 OSB Roof Deck
Fastener Factor for Each Side of Curb or Flange: 8.2

Case No: 7
Curb Size and Equipment Type: 24 x 24 Curb with Exhaust Fan
Equipment Attachment: Fan Screwed to Curb
Fastener Factor for Each Side of Curb or Flange: 2.5

Case No: 8
Curb Size and Equipment Type: 36 x 36 Curb with Exhaust Fan
Equipment Attachment: Fan Screwed to Curb
Fastener Factor for Each Side of Curb or Flange: 3.3

Case No: 9
Curb Size and Equipment Type: 5-9 x 3- 8 Curb with 2- 8 high HVAC Unit
Equipment Attachment: HVAC Unit Screwed to Curb
Fastener Factor for Each Side of Curb or Flange: 4.5*

Case No: 10
Curb Size and Equipment Type: 5-9x 3- 8 Curb with 2- 8 high Relief Air 
Hood
Equipment Attachment: Hood Screwed to Curb
Fastener Factor for Each Side of Curb or Flange: 35.6*

Notes to Table 4-1: 
1. The loads are based on ASCE 7-05. The resistance includes equipment weight.

2. The Base Case for the tabulated numbers of #12 screws (or  pan-head screws 
for flange-attachment) is a 90-mph basic wind speed, 1.15 importance factor, 30 
building height, Exposure C, using a safety factor of 3. 

3. For other basic wind speeds, multiply the tabulated number of #12 screws by _ 
to determine the required number of #12 screws (or  pan-head screws) required 
for the desired basic wind speed, VD (mph). 

4. For other roof heights up to 200, multiply the tabulated number of #12 
screws by (1.00 + 0.003 [h - 30]) to determine the required number of #12 screws 
or  pan-head screws for buildings between 30 and 200.
- Example A: 24 x 24 exhaust fan screwed to curb (table row 7), Base Case 
conditions (see Note 1): 2.5 screws per side; therefore, round up and specify 3 
screws per side.
- Example B: 24 x 24 exhaust fan screwed to curb (table row 7), Base Case 
conditions, except 120 mph: 1202 x 1  902 = 1.78 x 2.5 screws per side = 4.44 
screws per side; therefore, round down and specify 4 screws per side.
- Example C: 24 x 24 exhaust fan screwed to curb (table row 7), Base Case 
conditions, except 150 roof height: 1.00 + 0.003 (150 - 30) = 1.00 + 0.36 = 
1.36 x 2.5 screws per side = 3.4 screws per side; therefore, round down and 
specify 3 screws per side.

* This factor only applies to the long sides. At the short sides, use the 
fastener spacing used at the long sides.
[End table

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 4-88). 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 4-89) are 
recommended to avoid cowling blow-off. For fan cowlings less than 4 feet in 
diameter, one half-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. 

[Begin text box]
To avoid corrosion-induced failure (Figure 4-21), 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.
[End text box]

[Begin figures]
Figure 4-88 is a photo showing how cowlings blew off two of the three fans. Note 
also the loose lightning protection system conductors and missing walkway pad 
(red arrow). Hurricane Charley (Florida, 2004) 

Figure 4-89 is a photo showing how cables were attached to prevent the cowling 
from blowing off. Typhoon Paka (Guam, 1997)
[end figures]

Ductwork: To avoid wind and wind-borne debris damage to rooftop ductwork, it is 
recommended that ductwork not be installed on the roof (see Figures 4-16, 4-60, 
and 4-124). 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. 

Condenser attachment: In lieu of placing rooftop-mounted condensers on wood 
sleepers resting on the roof (see Figure 4-90), 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 4-91).

[Begin figure]
Figure 4-90 is a photo showing a sleeper-mounted condensers displaced by high 
winds. Hurricane Katrina (Mississippi, 2005) 

Figure 4-91 is a photo showing how this condenser had supplemental attachment 
straps (see red arrows). Typhoon Paka (Guam, 1997)
[end figure]

[Begin text box]
Three publications pertaining to seismic restraint of equipment provide general 
information on fasteners and edge distances: 
- 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) 
[End text box]

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 4-92). 

[Begin figure]
Figure 4-92 is a photo showing the 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)
[end figure]

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 4-93, 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.

[Begin figure]
Figure 4-93 Three of the five stacks that did not have guy-wires were blown 
down. Hurricane Marilyn (U.S. Virgin Islands, 1995) 
[end figure]

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 4-94). 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. 

[Begin figure]
Figure 4-94 Equipment screen panels, such as these blown away at a hospital, can 
break glazing, puncture roof membranes, and cause injury. Hurricane Ivan 
(Florida, 2004)
[end figure]

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.

4.3.4.2 Nonstructural Systems and Mechanical Equipment in Hurricane-Prone 
Regions

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 4.3.3.5, 4.3.3.7, and 4.3.4.1, because of the greater 
likelihood that at least one of the elevators will remain operational and 
therefore allow the facility to function as intended, as discussed in Section 
4.2.1.3.

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 4-94) 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 4.3.2.1, 
4.3.3.6, and 4.3.3.8.

4.3.4.3 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 4-21 and text 
box in Section 4.3.4.1 regarding corrosion).

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 hospitals be 
designed as Class III structures.

Collapse of both large and small communication towers at hospitals is quite 
common during high-wind events (see Figures 4-15 and 4-95). 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 hospital, unless the roof system incorporated a 
secondary membrane (as discussed in Section 4.3.3.8). At the tower shown in 
Figure 4-95, 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. 

[Begin figure]
Figure 4-95 is a photo showing how 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) 
[end figure]

See Sections 4.3.1.1 and 4.3.1.5 regarding site considerations for light fixture 
poles, power poles, and electrical and communications towers.

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 4-96, 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 Figures 4-83 and 4-97). 

[Begin figures]
Figures 4-96 is a photo of a common anchoring method for satellite dish. 
Hurricane Ivan (Florida, 2004)

Figure 4-97 is a photo showing how a satellite dish anchored similarly to that 
shown in Figure 4-96 was blown off this five-story building. Hurricane Charley 
(Florida, 2004) 
[end figures]

Lightning protection systems: For attachment of building lightning protection 
systems higher than 100 feet above grade, and for buildings located where the 
basic wind speed is in excess of 90 mph, see the following section on attaching 
LPS in hurricane-prone regions.

4.3.4.4 Lightning Protection Systems (LPS) in Hurricane-Prone Regions

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 4-98 and 4-99). 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. 

[Begin figures]
Figure 4-98 is a photo showing an air terminal debonded from the hospitals 
roof. Displaced air terminals can puncture tough membranes, such as this 
modified bitumen membrane. Hurricane Ivan (Florida, 2004)

Figure 4-99 is a photo showing a view of an end of a conductor at a hospital 
that became disconnected. Hurricane Katrina (Mississippi, 2005) 
[end figures]

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 4-100). 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.

[Begin figure]
Figure 4-100 is a photo showing how the conductor deformed the prongs under wind 
pressure, and pulled away from the connector. Hurricane Katrina (Mississippi, 
2005)
[end figure]

To enhance the wind performance of LPS, the following are recommended: [footnote 
13]

[Begin footnote 13] Discussion is based on Rooftop Attachment of Lightning 
Protection Systems in High-Wind RegionsHurricane Katrina Recovery Advisory (May 
2006, Revised July 2006).[end footnote]

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 4-101). 

[Begin figure]
Figure 4-101 is a photo showing how this conductor was attached to the coping 
with a looped connector. Hurricane Katrina (Mississippi, 2005)
[end figure]

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 4-102).

[Begin figure]
Figure 4-102 is plan showing conductor attachment 
[end figure]

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 4-103). 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).

[Begin figure]
Figure 4-103 is a illustration of adhesively attached conductor connector that 
does not use prongs
[end figure]

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 4-101). 

[Begin text box]
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.
[End text box]

Conductor splice connectors: In lieu of pronged splice connectors (see Figure 4-
104), bolted splice connectors are recommended because they provide a more 
reliable connection (see Figure 4-105). 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.

[Begin figures]
Figure 4-104 is a photo showing how if conductors detach from the roof, they are 
likely to pull out from pronged splice connectors. Hurricane Charley (Florida, 
2004) 

Figure 4-105 is a photo showing how bolted splice connectors are recommended to 
prevent free ends of connectors from being whipped around by wind. Hurricane 
Katrina (Mississippi, 2005)
[end figures]

4.3.4.5 The Case of Martin Memorial Medical Center, Stuart, Florida

The case of Martin Memorial Hospital illustrates the importance of elevator 
penthouse envelopes. Martin Memorial Medical Center is a 244-bed facility 
located on the south bank of the St. Lucie River in Stuart, Florida. The 
original hospital building, opened in 1939, is still in use but not for patient 
care. Currently the main hospital building is the six-story North Tower 
constructed in the early 1970s. MOBs and a cancer treatment facility are also 
located on the hospital campus. In 2004 the facility was struck by Hurricane 
Frances, and about 3 weeks later by Hurricane Jeanne.  The estimated peak gust 
wind speed at this site during Hurricane Frances was 100 mph. [footnote 14] The 
design wind speed in the 2005 edition of ASCE 7 for this location is 140 mph.

The hospital sustained damage to the elevator penthouse, roof covering, and 
roof-mounted equipment. Many of the metal panels on the elevator penthouse of 
the North Tower that were blown off during Hurricane Frances (Figure 4-106) tore 
the roof membrane on the tower roof  as well as on lower roofs. Mechanical 
equipment was damaged on the tower roof (Figure 4-107) and on lower roofs. The 
LPS was displaced on the tower roof (Figure 4-108) and on lower roofs. Unlike 
the windows on the first floor that were protected with shutters, the upper-
level windows were not protected. However, none of them were broken, although a 
significant amount of water leaked through many of these windows. The second 
hurricane (Jeanne) caused additional water infiltration and interrupted 
reconstruction work.

[Begin figures]
Figure 4-106 is a photo showing a view of the reconstruction of the damaged 
walls at the elevator penthouse

Figure 4-107 is a photo of damaged HVAC equipment. Work is underway on the 
elevator penthouse beyond. 

Figure 4-108 is a photo of displaced LPS
[end figures] 

[Begin footnote 14] The 100 mph speed was estimated for exposure C. [end 
footnote]

Loss of the elevator penthouse panels allowed water infiltration into the 
elevator equipment room, which destroyed the control equipment. Water also 
leaked into the nursing floors, which made it necessary to evacuate the 
patients. 
Because of significant interior water damage and lack of vertical 
transportation, many patients had to be evacuated by helicopter. 

As dramatically illustrated at this hospital, water infiltration and the lack of 
elevator service can take portions of the hospital offline for several weeks. 
Rather than simply replace the elevator penthouse walls, an engineer was 
retained to design a more wind-resistant wall covering system. The new design 
for the elevator penthouse wall system was developed and new elevator control 
equipment was installed, bringing the 5th floor back online about 4 weeks after 
the first hurricane struck. The remaining floors (2, 3, 4, and 6) were brought 
back online at a rate of about one floor every 2 weeks after the 5th floor was 
reopened. It cost $3,733,233 to repair the North Tower. In addition to this 
expenditure, the hospital lost a significant amount of patient revenue. 

Electrical service was interrupted for 36 hours (generators were used during 
that time), though there was no disruption of site access or water, sewer, and 
communications services. The hospital had an existing contingency plan, which 
was helpful during the response to these hurricanes. For instance, the hospital 
had contractors on site the day after the hurricane struck to perform emergency 
repairs; some of these contractors were under a pre-arranged contract with the 
hospital. The contingency plan was updated and modified based on experiences 
with these two hurricanes. 

4.3.5 Municipal Utilities in Hurricane-Prone Regions

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. Hospitals should be designed to prevent the disruption of services 
arising from prolonged loss of municipal services.

4.3.5.1 Electrical Power 

It is recommended that buildings on hospital campuses 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, because 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 4.3.2.1, 4.3.3.2, 4.3.3.6 and 4.3.3.8) so that they 
are not susceptible to damage from debris or tree fall. Locating generators 
outdoors or inside weak enclosures (see Figure 4-138) 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. If a screen wall is 
used, it should be designed to allow adequate air flow to the generator in order 
to avoid overheating the generator. 

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).[footnote 15] If at any time it appears that 
refueling won't 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 3 
recommendations.

[Begin text box]
It is recommended that a minimum of 96 hours (4 days) of onsite fuel storage be 
provided for boilers. Storage tanks, piping, and pumps should be located within 
wind-borne debris resistant buildings or be placed underground (if site is 
susceptible to flooding, refer to Chapter 3).
[End text box]

[Begin footnote 15] The 96-hour fuel supply is based in part on the Department 
of Veterans Affairs criteria. [end footnote]

4.3.5.2 Water Service 

It is recommended that hospitals be provided with an independent water supply  
a well or onsite water storage. 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. 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). 
[footnote 16]

[Begin footnote 16] The 96-hour fuel supply is based in part on the Department 
of Veterans Affairs criteria. [end footnote]

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.

[Begin text box]
It is recommended that onsite storage of medical gases be sized to provide a 
minimum of 96 hours (4 days) of service.
[End text box]

4.3.5.3 Sewer Service 

It is recommended that hospitals be provided with an alternative means of waste 
disposal, such as a temporary storage tank that can be pumped out by a local 
contractor. It is also recommended that back-flow preventors be provided.

4.3.6 Post-Design Considerations in Hurricane-Prone Regions

In addition to adequate design, proper attention must be given to construction, 
post-occupancy inspections, and maintenance. 

4.3.6.1 Construction Contract Administration 

It is important for owners of hospitals 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 hospitals that are not in hurricane-
prone regions.

4.3.6.2 Periodic Inspections, Maintenance, and Repair 

The recommendations given in Section 4.3.1.4 for post-occupancy and post-storm 
inspections, maintenance, and repair are crucial for hospitals 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. 




4.4 REMEDIAL WORK ON EXISTING FACILITIES

Many existing hospitals 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. 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 5 years  see 
Figure 4-109). It is particularly important to perform vulnerability assessments 
on hospitals located in hurricane-prone and tornado-prone regions.

[Begin figure]
Figure 4-109 is a photo showing how the roof on this 5-year-old hospital blew 
off. Water leaked into the patient floor below. The floor was taken out of 
service for more than a month. Hurricane Katrina (Mississippi, 2005) 
[end figure]

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, 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. 

[Begin text box]
Although it is unlikely, a hospital may occupy a building that was originally 
intended for another use. 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 hospital is located in a building not 
originally designed for a critical occupancy, especially if the hospital is 
located in a hurricane- or tornado-prone region.
[End text box]

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 hospital operations after a storm. For example, a vulnerability 
assessment on a hospital such as that shown in Figure 4-110 may identify 
weakness of the roof membrane and/or rooftop equipment. Replacing weak 
components before a hurricane is much cheaper than replacing them and repairing 
consequential damages after a storm, and proactive work avoids the loss of use 
while repairs are made.

[Begin text box]
Before beginning remedial work, it is necessary to understand all significant 
aspects of the vulnerability of a hospital 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. Mitigation efforts can be very ineffective if they do not 
address all items that are likely to fail.
[End text box]

[Begin figure]
Figure 4-110 The roof membrane and some of the rooftop equipment blew off. 
Although the deck was cast-in-place concrete, water leaked into the patient 
floor below. Hurricane Charley (Florida, 2004)
[end figure]

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. 

4.4.1 Structural Systems

As discussed in Section 4.1.4.1, 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 Figures 4-111 and 4-132. 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, as well as precast concrete 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 4-112, because older 
codes provided inadequate uplift criteria.

[Begin figures]
Figures 4-111 is a photo showing how the built-up roof blew off after one of the 
cementitious wood-fiber deck panels detached from the joists. Hurricane Katrina 
(Mississippi, 2005) 

Figure 4-112 is a photo showing how the cementitious wood-fiber deck panels 
detached from the joists along the overhangs and caused the built-up membranes 
to lift and peel. Hurricane Katrina (Mississippi, 2005)
[end figures]

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 4-113.

[Begin figure]
Figure 4-113 is a photo showing how the steel truss superstructure installed as 
part of a steep-slope conversion blew away because of inadequate attachment. 
Hurricane Marilyn (U.S. Virgin Islands, 1995)
[end figure]

4.4.2 Building Envelope 

The following recommendations apply to building envelope components of existing 
hospitals.

4.4.2.1 Sectional and Rolling Doors

Sectional and rolling doors (e.g., at hospital loading docks and ambulance 
garages), 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 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 building shown in 
Figure 4-114 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.

[Begin figure]
Figure 4-114 is a photo showing how 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)
[end figure]

4.4.2.2 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 4-115). 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.

[Begin figure]
Figure 4-115 is a photo showing how wind pressure caused the window frames on 
the upper floor to fail (red arrow). Hurricane Katrina (Mississippi, 2005)
[end figure]

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 4.3.3.4. Shutters are typically a more economical approach 
for existing facilities. There are a variety of shutter types, all illustrated 
by Figures 4-116 to 4-118. Accordion shutters are permanently attached to the 
wall (Figure 4-116). When a hurricane is forecast, the shutters are pulled 
together and latched into place. Panel shutters (Figure 4-117) 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 4-118) can be motorized or pulled down manually. 
Figure 4-118 illustrates the benefits of shuttering. Two of the unprotected 
window units experienced glass breakage and the third window unit blew in. 

[Begin figures]
Figure 4-116 is a photo showing how this building has accordion shutters. 
Hurricane Ivan (Florida, 2004)

Figure 4-117 is a photo that illustrates a metal panel shutter. Hurricane 
Georges (Puerto Rico, 1998) 

Figure 4-118 is a photo showing how the lower window assembly was protected with 
a motorized shutter. Hurricane Ivan (Florida, 2004)
[end figures]

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.

4.4.2.3 Roof Coverings

For roofs with weak metal edge flashing or coping attachment, face-attachment of 
the edge flashing/coping (as shown in Figure 4-67) 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 
(Figures 4-5, 4-46, and 4-47). 

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 4-119), 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 4-119 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 4-126). 

[Begin figure]
Figure 4-119 is a photo showing how the built-up roof was blown off after a few 
of the rotted wood planks detached from the joists. Hurricane Katrina 
(Mississippi, 2005)
[end figure]

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 4-120). 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 4-79), which permit drying of the 
brick.

[Begin figure]
Figure 4-120 is a photo showing hoe failed base flashing adhered directly to the 
brick parapet. Hurricane Katrina (Louisiana, 2005) 
[end figure]

If the parapet is constructed of masonry, it is recommended that its wind 
resistance be evaluated and strengthened if found to be inadequate. The masonry 
parapet shown in Figure 4-139 fell onto the roof. Had it fallen in the other 
direction, it would have blocked the entry and would have had the potential to 
cause injury.

4.4.3 Exterior-Mounted Equipment

Exterior-mounted equipment on existing hospitals should be carefully examined 
and evaluated.

4.4.3.1 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 4-
121. 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 (red arrow in Figure 4-121).

[Begin figure]
Figure 4-121 is a photo showing how the antenna at this hospital collapsed and 
was whipped back and forth across the roof membrane. Hurricane Andrew (Florida, 
1992) 
[Begin figure]

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.

[Begin text box]
Fastening rooftop equipment to curbs, as discussed in Section 4.3.4.1, is a 
cost-effective approach to minimize wind-induced problems.
[End text box]

4.4.3.2 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 hospitals more than 100 feet above 
grade, it is recommended that attachment modifications based on the guidance 
given in Section 4.3.4.4 be used. 

4.4.4 The Case of Baptist Hospital, Pensacola, Florida

The case of Baptist Hospital illustrates the challenges faced by older 
facilities. Baptist Hospital is a 492-bed tertiary care hospital located in 
downtown Pensacola on West Moreno St. approximately 2 miles north of Pensacola 
Bay. This hospital campus, which dates back to the 1950s, includes the hospital 
itself, a psychiatric hospital, and MOBs. 

This facility was also struck by Hurricane Ivan. The estimated wind speed and 
design wind speed at this hospital are the same as the case study presented in 
Section 4.2.1.3. Figure 4-122 shows the site plan and Figure 4-123 is a general 
view from the northwest (looking southeast).

[Begin figure]
Figure 4-122 is a site plan

Figure 4-123 is a photo showing a general view.
[end figure]

Water entered the hospital at damaged rooftop equipment (Figure 4-124), and at 
areas where the roof membrane blew off (Figures 4-125 and 4-126) and where it 
was punctured. The roof failure shown in Figure 4-126 was caused by an 
inadequately attached edge nailer anchored to the brick wall. Failure of the 
nailer caused a progressive lifting and peeling of the roof membrane. Gutters 
and downspouts were blown off and a few windows were broken. The elevator 
penthouse roof was damaged at the psychiatric hospital (Figure 4-127) and the 
MOBs (Figure 4-125).

[Begin figures]
Figure 4-124 is a photo showing how this hospital had a substantial amount of 
rooftop ductwork. Ductwork and fan units were damaged in several locations (see 
inset). Some of the windows in this area were also broken. Note the missing 
downspout (yellow arrow). 

Figure 4-125 is a photo showing how the roof covering blew off  an emergency 
roof covering had been installed (yellow arrow). Note the damaged MOB penthouse 
beyond (red arrow).

Figure 4-126 is a photo showing how the roof covering blew off  an emergency 
roof covering had been installed (blue arrow). The failure was caused by the 
inadequately attached nailer (see inset). The leaning mast at the right is a 
ladder (yellow arrow), with an extension for communications and an anemometer 
for the nearby heliport. 

Figure 4-127 is a photo showing how an emergency roof covering had been 
installed over the elevator penthouse at the psychiatric hospital.
[end figures]



4.5 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. 

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 4-128 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. 

[Begin figure]
Figure 4-128 is a photo showing how a violent tornado showered the roof with 
missiles. (Oklahoma, 1999)
[end figure]

Besides the case studies presented in Sections 4.5.1 and 4.5.2, there is little 
documentation regarding tornado-induced damage to hospitals. Most of the damage 
reports on critical facilities 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 Administration [footnote 17] 
identified four hospitals that were struck by tornadoes between 1973 and 1976. 
Table 4-2 (taken from that report) further illustrates the effects tornados can 
have on hospitals. 

[begin footnote 17]
A Study of Building Damage Caused by Wind Forces, McDonald, J.R. and Lea, P.A, 
Institute for Disaster Research, Texas Tech University, 1978. [end footnote]


[Begin Table]
Table 4-2: Examples of Ramifications of Tornado Damage at Four Hospitals

Location and Building Characteristics: Mountain View, Missouri (St. Francis 
Hospital). One-story steel frame with non-load bearing masonry exterior walls.
Tornado Characteristics: The tornado crossed over one end of the hospital. 
Damage: Metal roof decking was blown off, some windows were broken, and rooftop 
mechanical equipment was displaced.
Ramifications of Damage: Patients were moved to undamaged areas of the hospital.

Location and Building Characteristics: Omaha, Nebraska (Bishop Bergen Mercy 
Hospital). Five-story reinforced concrete frame. 
Tornado Characteristics: Maximum wind speed estimated at 200 mph. Proximity to 
hospital not documented.
Damage: Windows were broken, and rooftop mechanical equipment was damaged and 
displaced. Communications and electrical power were lost (emergency generators 
provided power). 
Ramifications of Damage: A few minor cuts; double walled corridors provided 
protection for patients and staff. Some incoming emergency room patients 
(injured elsewhere in the city) were rerouted to other hospitals. Loss of 
communications hampered the rerouting.

Location and Building Characteristics: Omaha, Nebraska (Bishop Bergen Mercy 
Hospital  Ambulatory Care Unit). One-story load bearing CMU walls with steel 
joists. 
Tornado Characteristics: See above.
Damage: The building was a total loss due to wall and roof collapse.
Ramifications of Damage: Patients were evacuated to the first floor of the main 
hospital when the tornado watch was issued.

Location and Building Characteristics: Corsicana, Texas (Navarro County Memorial 
Hospital). Five-story reinforced concrete frame with masonry non-load bearing 
walls in some areas and glass curtain walls. 
Tornado Characteristics: The tornado was very weak.
Damage: Many windows were broken by aggregate from the hospitals built-up 
roofs. Intake duct work in the penthouse collapsed.
Ramifications of Damage: Two people in the parking lot received minor injuries 
from roof aggregate. Electrical power was lost for 2 hours (emergency generators 
provided power).

Location and Building Characteristics: Monahans, Texas (Ward Memorial Hospital). 
One-story load bearing CMU walls with steel joists. Some areas had metal roof 
deck and others had gypsum deck.
Tornado Characteristics: The tornado passed directly over the hospital, with 
maximum wind speed estimated at 150 mph. 
Damage: The roof structure was blown away on a portion of the building (the bond 
beam pulled away from the wall). Many windows were broken. Rooftop mechanical 
equipment was damaged.
[end table]

[Begin text box]
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 4-129). However, an owner of a 
hospital may decide to use other frequency values (e.g., 1 or greater, 16 or 
greater, or greater than 25) in defining whether the hospital is in a tornado-
prone area. In this manual, tornado shelters are recommended for all hospitals 
in tornado-prone regions.
Where the frequency value is 1 or greater, and the hospital does not have a 
tornado shelter, the best available refuge areas should be identified, as 
discussed at the end of this Section.
[End text box]

[Begin figure]
Figure 4-129 is a map showing Frequency of recorded F3, F4, and F5 tornadoes 
(1950-1998)
[end figure]

For hospitals located in tornado-prone regions (as defined in the text box), 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 
4.3.3.5. 

- 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 hospitals in tornado-prone regions. 

- To minimize disruption from nearby weak tornadoes and from strong and violent 
tornados that are on the periphery of a hospital, the following are recommended:

1) For the roof deck, exterior walls, and doors, follow the recommendations 
given in Sections 4.3.2.1, 4.3.3.2, and 4.3.3.6. 

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.

[Begin text box]
It is recommended that hospitals have a National Oceanic and Atmospheric 
Administration (NOAA) weather radio, so that they will be aware of tornado 
watches and warnings. It is also recommended that hospitals have a plan to 
distribute notice of watches and warnings received via the radio to hospital 
staff.
[End text box]

Existing Hospitals without Tornado Shelters 

Where the number of recorded F3, F4, and F5 tornadoes per 3,700 square miles is 
one or greater (see Figure 4-129), the best available refuge areas should be 
identified if the hospital 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 hospitals, it is very important that the best 
available refuge areas be identified by a qualified architect or engineer. 
[footnote 18] 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 4-
142, sometimes provide protection, but they can also be death traps. 

[Begin footnote 18] 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. [end footnote]

Retrofitting a shelter space inside an existing hospital 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 because of the difficulty of accommodating patients with different 
medical needs. 

4.5.1 The case of Kiowa County Memorial Hospital, Greensburg, Kansas

The case of Kiowa County Memorial Hospital illustrates damage that is indicative 
of smaller, older facilities that are struck by strong tornadoes. The hospital 
is a 28-bed, one-story facility. The original hospital comprised three separate 
buildings (two of these are shown in Figure 4-131): a patient wing, a kitchen 
facility, and an equipment building, and was constructed in 1950. Additions were 
built in 1965 and 1982. A separate ambulance garage was built prior to 1979, 
and a separate pre-engineered metal storage building was added in 2006. The 
original buildings had precast twin-tee roof structures and at the time of the 
storm, they had aggregate ballasted single-ply membrane roof systems. The 
additions all had different structural systems. The 1965 patient wing addition 
had a concrete topping slab over metal form deck over steel roof joists. The 
1982 addition, which housed the emergency room, semi-intensive care, operating 
room, MRI, lab, medical records, and business offices, had a plywood roof deck 
over wood joists. The ambulance garage had a precast twin-tee roof structure. 

[Begin figure]
Figure 4-131 is a photo of the building housing the generator is shown by the 
yellow arrow. The kitchen facility is shown by the blue arrow. The red arrow 
shows the collapsed storage building. 
[end figure]

Except for the storage building, the majority of the exterior walls were brick 
veneer over unreinforced CMU. A finished basement was built under portions of 
the 1965 and 1982 additions (the two basements were not interconnected). 

Figure 4-130 shows the site plan.

[Begin figure]
Figure 4-130 is site plan
[end figure]

The hospital was struck by a tornado in 2007. The National Weather Service rated 
a portion of the track as an EF5 (with an estimated peak gust speed in excess of 
200 mph). At the hospital site, the damage was indicative of an EF3 (with a 
speed between 136 and 165 mph). The 2005 edition of ASCE 7 lists the design wind 
speed for this location as 90 mph. Therefore, the speeds at this site were well 
above current design conditions.

[Begin text box]
Using the Damage Indicators in the Enhanced Fujita Scale (EF-Scale) for the main 
portion of the hospital, the Degree of Damage (DOD) indicated an expected wind 
speed during the tornado of 142 mph (with lower and upper bounds ranging from 
119 to 163 mph). Failure analysis of the precast twin-tee that blew off the 
hospital indicated that a speed of approximately 147 mph was needed to blow off 
the tee, and a speed of approximately 193 mph was needed to toss it the 80 feet 
that it traveled.
The DOD at the pre-engineered storage building indicated an expected wind speed 
of 155 mph (with lower and upper bounds ranging from 132 to 178 mph). 
Thus, the DOD of the hospital, the DOD of the storage building and the failure 
analysis of tee blow off indicate essentially the same estimated speed (142, 
147, and 155 mph). The upper bound values of the DODs (163 and 178 mph) are 
lower than the 193 mph speed that was calculated to have tossed the tee. Based 
on the EF-Scale DODs, the 193 mph speed appears to be high.
[End text box]

One of the precast twin-tees from the original building blew off and flew 
approximately 80 feet (Figures 4-132 and 4-133). Where the tees rested on the 
bearing wall, steel bearing plates were embedded in the tees beams, and bearing 
plates were embedded on top of the wall. At the wall in the foreground of Figure 
4-132, the bearing plates had not been welded together. Hence, at that end of 
the tee, no uplift resistance was provided other than the tees dead load. At 
the opposite bearing wall, the bearing plates were welded, but the bolts 
anchoring the plates to the wall failed in tension as the tee lifted. Both of 
the bearing plates had two small anchor bolts (about 3/8-inch diameter).

[Begin figure]
Figure 4-132 is a photo of the view of the end of the patient wing where the 
twin-tee blew off. Note the missing window. 

Figure 4-133 is a photo showing how the missing tee shown in Figure 4-132 landed 
about 80 feet away (red oval). The red arrows show tees that were blown from the 
ambulance garage. Note the missing wood roof structure on the 1982 addition 
(yellow arrow). 
[end figures]

The hospital complex was struck with a very large number of missiles. Virtually 
all of the hospitals exterior glazing was broken. Figure 4-134 shows a damaged 
door at the kitchen facility. A piece of built-up roof (BUR) membrane struck the 
right door. Although the doors were out-swinging, the missile pushed the door 
inward. The lower right hinge was broken, and the right side of the door frame 
buckled and pulled from the rough opening. The laminated glass in the door was 
broken, but remained in place.


Figure 4-134 is a photo showing how the BUR missile (red arrow) struck the right 
door. Missiles also punctured the siding and wood sheathing (red oval).
[end figure]

Aggregate from the ballasted single-ply membrane roofs broke several windows 
(Figure 4-135), and pieces of the large aggregate (11/2-inches in diameter, 
nominal) were found inside the building. Windows were also broken by 2x wood 
framing (Figure 4-136).

[Begin figures]
Figure 4-135 All six panes of glass were broken. The craters shown in the right 
center pane and at the vehicle windshield were caused by the large aggregate 
blown from the ballasted single-ply membranes.

Figure 4-136 is a photo showing how a large missile (2x framing) penetrated this 
patient room. Note the debris on the bed in the inset (the arrow shows the same 
2x missile).
[end figures]

Figure 4-137 illustrates an opening through the entire exterior wall.

[Begin figure]
Figure 4-137 is a photo showing how a missile impact created an opening in the 
brick veneer and unreinforced CMU.
[end figure]

The building shown in Figure 4-131 (yellow arrow) and in Figure 4-138 housed the 
emergency generator. The sectional door collapsed and allowed wind-borne debris 
to strike the generator. All window panes in the wall adjacent to the sectional 
door were broken (see inset at Figure 4-138). The wall louver adjacent to the 
window, which served the generator room, escaped damage. 

[Begin figure]
Figure 4-138 is a photo showing how the sectional door (red arrow) at the 
generator building was blown in and windows were broken by debris. 
[end figure]

There was no apparent structural damage to the 1965 addition. However, the 
unreinforced brick/CMU parapet shown in Figure 4-139 fell onto the roof, rather 
than in the other direction, where it would have blocked the entry and possibly 
could have caused injuries. Virtually all of the exterior windows were broken 
(see Figures 4-135 and 4-136). The roof insulation and aggregate-ballasted 
single-ply roof membrane were blown off. The wood roof structure blew off the 
majority of the 1982 addition (Figures 4-133 and 4-140), and virtually all of 
the exterior windows were broken. 

[Begin figures]
Figure 4-139 is a photo showing a collapsed unreinforced masonry parapet. Note 
the broken windows. 

Figure 4-140 is a photo showing the loss of the wood roof structure at the 1982 
addition. 
[end figures]

The precast twin-tees on the ambulance garage blew off and landed against the 
wall of the 1982 addition (Figures 4-133 and inset at 4-141). The garage door 
and virtually all of the exterior unreinforced brick/CMU bearing walls collapsed 
(Figure 4-141). Where the tees rested on the bearing wall, steel bearing plates 
were embedded in the tees beams. However, bearing plates had not been embedded 
on top of the support walls. Rather, where the tees beams rested on the wall, a 
piece of roof membrane had been installed between the beams and the wall. Hence, 
at the ends of the tees, no uplift resistance was provided other than the tees 
dead load. 

[Begin figure]
Figure 4-141 is a photo showing a view of the collapsed ambulance garage. The 
twin-tees (red arrows) flew to the left, as shown in the inset.
[end figure]

There were 20 patients and 10 staff in the facility when the tornado struck 
around 9:45 p.m. Fortunately, the staff was aware of the tornado warning that 
was issued by the National Weather Service. Patients and staff took refuge in 
the basement of the 1965 addition per the hospitals tornado plan. Because of 
the extensive structural and non-structural damage, it was necessary to 
completely evacuate the hospital after the storm. Evacuation was completed by 
around 2:45 a.m. (about 5 hours after the tornado). None of the occupants were 
injured during the storm or evacuation. The ambulance shown in Figure 4-141 was 
not usable because of missile damage. Even though some portions of the facility 
could be salvaged, significant demolition and reconstruction will be necessary.

The loss of life and avoidance of injuries was attributed to three factors. 1) A 
tornado warning was issued by the National Weather Service about 20 minutes 
before the tornado struck, and the hospitals staff was aware of the warning. 2) 
The hospital had a tornado evacuation plan and there was sufficient time to 
execute the plan. 3) Although it is believed that the basement was not 
specifically designed as a tornado shelter, it provided a safe area of refuge 
for patients and staff. For hospitals located in tornado-prone regions, the 
experience from this tornado demonstrates the importance of having a pre-
identified, best available refuge area (or preferably a FEMA 361-compliant 
shelter). Although small interior rooms and corridors sometimes provide adequate 
protection during tornadoes, unless specifically designed as a tornado shelter, 
they often provide inadequate protection, as shown in Figure 4-142.

[Begin figure]
Figure 4-142 is a photo showing a view of a main corridor in the 1982 addition  
[end figure]

[Begin text box]
It was determined that with minimal work, the basement under the 1965 addition 
could be used as an interim, best available refuge area for the city. In the 
weeks and months following the storm, several hundred people would be in the 
city performing demolition, salvaging personal items, and conducting 
reconstruction. Much of this work would occur during the time of year when 
tornado activity is high. Hence, although severely damaged, a portion of the 
hospital continued to serve the community by providing an interim refuge area.
[End text box]

The damage investigation of this facility validates several of the 
recommendations provided in Section 4.5, summarized below:

- Incorporate a tornado shelter within the facility.

- Don't use aggregate roof surfacing.

- Use roof decks, exterior walls, and doors as recommended in sections 4.3.2.1, 
4.3.3.2, and 4.3.3.6.

- Use laminated glass window assemblies that are designed to resist the test 
Missile E.

4.5.2 The case of Sumter Regional Hospital, Americus, Georgia 

The previous case study reported on a smaller, older hospital that was struck by 
a tornado. The case of Sumter Regional Hospital illustrates the performance of a 
much larger and newer hospital. This hospital is a 143-bed, four-story facility 
built in 1953, and expanded in 1975, 1983, and 1999. The 1999 addition had a 
cast-in-place concrete roof deck. All of the other buildings had steel roof 
decks. Roof coverings included single-ply membranes (exposed and aggregate-
ballasted) and aggregate surfaced built-up. Exterior walls included brick veneer 
(over unreinforced CMU and over steel studs) and EIFS over steel studs.  

[Begin figure]
Figure 4-143 is an aerial view of the facility after it was struck by the 
tornado. The red arrow indicates the general direction of the tornado. The blue 
arrow shows the 1953 building, and the yellow arrow shows the 1999 building. The 
1975 and 1983 additions are adjacent to and behind the 1953 and 1999 buildings. 
Courtesy of the National Weather Service. 
[end figure]

The hospital was struck by a tornado in 2007. The National Weather Service rated 
a portion of the track as an EF3 (with an estimated peak gust speed between 136 
and 165 mph). At the hospital site, the damage was indicative of an EF2 (with a 
speed between 111 and 135 mph). The 2005 edition of ASCE 7 lists the design wind 
speed for this location as 90 mph. Therefore, the speeds at this site were well 
above current design conditions.

[Begin text box]
Using the Damage Indicators in the Enhanced Fujita Scale (EF-Scale), the Degree 
of Damage (DOD) at the hospital indicated an expected wind speed during the 
tornado of 131 mph (with lower and upper bounds ranging from 110 to 152 mph).
[End text box]

As the tornado approached the southwest side of the hospital, numerous tree 
branches from trees in front of the hospital were thrown against the building. 
Missiles broke virtually all of the glass in the southwest walls (Figures 4-144 
and 4-145), and missiles penetrated the EIFS and landed inside the building. 
Roof decking and steel joists were blown off of portions of the 1953 building, 
and the roof membrane was blown off of several different areas of the facility. 

The right (curved) portion of the building in Figure 4-144 is the 1999 addition. 
This portion of the first floor housed waiting and exam rooms. Offices were on 
the second floor, and medical offices were on the third floor. Figures 4-144 and 
4-146 also show part of the 1953 building. Offices were on the first floor, and 
patient rooms were on the second and third floors. 

[Begin figures]
Figure 4-144 is a photo showing the 1999 addition on the right, and the 1953 
building to the left. Virtually all of the glass on these facades was broken.

Figure 4-145 is a photo showing how one window frame was blown away (red 
circle). The EIFS was penetrated by many missiles, and in some areas, the entire 
wall (except the studs) was blown away (arrows).

Figure 4-146 is a photo showing how several of the window frames were blown 
away, along with some of the brick veneer (1999 addition).
[end figures]

Broken glass showered the rooms along the exterior walls. The breach of the 
building envelope allowed strong winds to enter the rooms and corridors, which 
led to the collapse of suspended acoustical ceilings and light fixtures. Figure 
4-147 illustrates the extent of the interior damage.

[Begin figure]
Figure 4-147 is a photo showing glass shards and other debris in the lobby area 
housing retail shops and offices. 
[end figure]

Damage also occurred on other facades, including collapse of a glass curtain 
wall and a portion of a brick veneer/unreinforced CMU wall. (Figure 4-148). A 
large unreinforced brick chimney collapsed on a roof, and a large rooftop air 
handling unit (20 x 7 x 9 feet) was shifted several feet. A substantial amount 
of water entered the building at various places where the envelope was breached. 

[Begin figure]
Figure 4-148 is a photo of a collapsed brick veneer/CMU wall at a mechanical 
room. The cast-in-place concrete wall (arrow) remained, but the brick veneer was 
blown away.
[end figure]

Much of the aggregate ballast (11/2-inch nominal diameter) was blown from the 
roof, and broke numerous vehicle windows in the parking lot.

There were 54 patients in the facility when the tornado struck around 9:15 p.m. 
Staff was not aware of the approaching tornado until just before it struck. Most 
of the patients and newborn infants were moved into hallways as the tornado 
struck the building. Some remained in their beds during the few seconds of the 
tornado impact. People were injured, but none seriously. Because of the 
extensive damage, it was necessary to completely evacuate the hospital after the 
storm. Evacuation was completed by around 2:00 a.m. (about 5 hours after the 
tornado).

Within a couple of days, an urgent care facility was temporarily set up in a 
tent. Temporary modular buildings were also brought in to provide space for an 
expanded array of healthcare services for the community. After approximately 3 
months of study, it was decided to demolish the entire hospital complex and 
build a new facility. An interim facility was expected to be completed by the 
fall of 2007. 

[Begin text box]
In addition to the impacts on delivery of healthcare to the community, the 
damage had potential impacts on the economy. The hospital had approximately 700 
employees and was one of the largest employers in the county. Had there been 
significant interruptions in meeting payroll, or had it been decided to close 
the facility and rely on a hospital that was approximately 40 miles away, the 
loss of jobs would likely have been difficult on the community.
[End text box]

As with the previous case study, the damage investigation of this facility 
validates several of the recommendations provided in Section 4.5. In particular, 
this case study validates the recommendations pertaining to use of roof decks, 
exterior walls, and doors, as recommended in sections 4.3.2.1, 4.3.3.2, and 
4.3.3.6, and the use of laminated glass window assemblies that are designed to 
resist the test Missile E. In those instances where there is little or no 
warning of an impending tornado strike, maintaining building envelope integrity 
is crucial to providing protection to patients and staff, and in minimizing 
disruption of services.




4.6 CHECKLIST FOR BUILDING VULNERABILITY OF HOSPITALS EXPOSED TO HIGH WINDS 

The Building Vulnerability Assessment Checklist (Table 4-3) 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.

[Begin table]
Table 4-3: Checklist for Building Vulnerability of Hospitals Exposed to High 
Winds

Vulnerability Section: General

Vulnerability: What is the age of the facility, and what building code and 
edition was used for the design of the building?

Guidance: 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.

Vulnerability: Is the hospital older than 5 years, or is it located in a zone 
with basic wind speed greater than 90 mph?

Guidance: 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.

Vulnerability Section: Site

Vulnerability: What is the design wind speed at the site? Are there topographic 
features that will result in wind speed-up?

Guidance: ASCE 7

Vulnerability: What is the wind exposure on site?

Guidance: Avoid selecting sites in Exposure D, and avoid escarpments and hills

Vulnerability: Are there trees or towers on site?

Guidance: Avoid trees and towers near the facility. If the site is in a 
hurricane-prone region, avoid trees and towers near primary access roads.
Road access Provide two separate means of access.

Vulnerability: Is the site in a hurricane-prone region?

Guidance: ASCE 7. If yes, follow hurricane-resistant design guidance.

Vulnerability: If in a hurricane-prone region, are there aggregate surfaced 
roofs within 1,500 feet of the facility?

Guidance: Remove aggregate from existing roofs. 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).

Vulnerability Section: Architectural 

Vulnerability: Will the facility be used as a shelter?

Guidance: If yes, refer to FEMA 361.

Vulnerability: Are there interior non-load-bearing walls?

Guidance: Design for wind load.

Vulnerability: Are there multiple buildings on site in a hurricane-prone region?

Guidance: Provide enclosed walkways between buildings that will be occupied 
during a hurricane.

Vulnerability: Are multiple elevators needed for the building?

Guidance: Place elevators in separate locations served by separate penthouses.

Vulnerability Section: Structural Systems - Section 4.3.2

Vulnerability: Is a pre-engineered building being considered?

Guidance: 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.

Vulnerability: Is precast concrete being considered?

Guidance: 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.

Vulnerability: Are exterior load-bearing walls being considered?

Guidance: If yes, design as MWFRS and C&C. 

Vulnerability: Is an FM Global-rated roof assembly specified?

Guidance: If yes, comply with FM Global deck criteria.

Vulnerability: Is there a covered walkway or canopy?

Guidance: 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. 

Vulnerability: Is the site in a hurricane-prone region?

Guidance: A reinforced cast-in-place concrete structural system, and reinforced 
concrete or fully grouted and reinforced CMU walls, are recommended.

Vulnerability: Is the site in a tornado-prone region?

Guidance: If yes, provide occupant protection. See FEMA 361.

Vulnerability: Do portions of the existing facility have long-span roof 
structures (e.g., a gymnasium)?

Guidance: Evaluate structural strength, since older long-span structures often 
have limited uplift resistance.

Vulnerability: Is there adequate uplift resistance of the existing roof deck and 
deck support structure?

Guidance: 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.

Vulnerability: Are there existing roof overhangs that cantilever more than 2 
feet?

Guidance: Overhangs on older buildings often have inadequate uplift resistance.

Vulnerability Section: Building Envelope - Section 4.3.3

Vulnerability: Exterior doors, walls, roof systems, windows, and skylights.

Guidance: Select materials and systems, and detail to resist wind and wind-
driven rain.

Vulnerability: Are soffits considered for the building?

Guidance: Design to resist wind and wind-driven water infiltration. 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.

Vulnerability: Are there elevator penthouses on the roof?

Guidance: Design to prevent water infiltration at walls, roof, and mechanical 
penetrations.

Vulnerability: Is a low-slope roof considered on a site in a hurricane-prone 
region?

Guidance: A minimum 3-foot parapet is recommended on low-slope roofs .

Vulnerability: Is an EOC, healthcare facility, shelter, or other particularly 
important hospital in a hurricane-prone region?

Guidance: If yes, a very robust building envelope, resistant to missile impact, 
is recommended.

Vulnerability: Is the site in a tornado-prone region?

Guidance: To minimize generation of wind-borne missiles, avoid the use of brick 
veneer, aggregate roof surfacing, roof pavers, slate, and tile.

Vulnerability: Are there existing sectional or rolling doors?

Guidance: Older doors often lack sufficient wind resistance. 

Vulnerability: Does the existing building have large windows or curtain walls?

Guidance: If an older building, evaluate their wind resistance.

Vulnerability: Does the existing building have exterior glazing (windows, glazed 
doors, or skylights)?

Guidance: If the building is in a hurricane-prone region, replace with impact-
resistant glazing, or protect with shutters.

Vulnerability: Does the existing building have operable windows?

Guidance: If an older building, evaluate its wind-driven rain resistance.

Vulnerability: Are there existing exterior non-load-bearing masonry walls?

Guidance: If the building is in a hurricane- or tornado-prone region, strengthen 
or replace.

Vulnerability: Are there existing brick veneer, EIFS, or stucco exterior 
coverings?

Guidance: If the building is in a hurricane-prone region, evaluate attachments. 
To evaluate wind resistance of EIFS, see ASTM E 2359 (2006).

Vulnerability: Are existing exterior walls resistant to wind-borne debris?

Guidance: If the building is in a hurricane-prone region, consider enhancing 
debris resistance, particularly if dealing with an important hospital.	

Vulnerability: Are there existing ballasted single-ply roof membranes?

Guidance: Determine if they are in compliance with ANSI/SPRI RP-4. If non-
compliant, take corrective action.

Vulnerability: Does the existing roof have aggregate surfacing, lightweight 
pavers, or cementitious-coated insulation boards?

Guidance: If the building is in a hurricane- prone region, replace the roof 
covering to avoid blow-off.

Vulnerability: Does the existing roof have edge flashing or coping?

Guidance: Evaluate the adequacy of the attachment. 

Vulnerability: Does the existing roof system incorporate a secondary membrane?

Guidance: If not, and if the building is in a hurricane-prone region, reroof and 
incorporate a secondary membrane into the new system. 

Vulnerability: Does the existing building have a brittle roof covering, such as 
slate or tile?

Guidance: If the building is in a hurricane-prone region, consider replacing 
with a non-brittle covering, particularly if it is an important hospital.

Vulnerability Section: Exterior-Mounted Mechanical Equipment

Vulnerability: Is there mechanical equipment mounted outside at grade or on the 
roof?

Guidance: Anchor the equipment to resist wind loads. If there is existing 
equipment, evaluate the adequacy of the attachment, including attachment of 
cowlings and access panels.

Vulnerability: Are there penetrations through the roof?

Guidance: Design intakes and exhausts to avoid water leakage.

Vulnerability: Is the site in a hurricane-prone region?

Guidance: If yes, place the equipment in a penthouse, rather than exposed on the 
roof.

Vulnerability Section: Exterior-Mounted Electrical and Communications Equipment 

Vulnerability: Are there antennae (communication masts) or satellite dishes?

Guidance: 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.

Vulnerability: Does the building have a lightning protection system?

Guidance: See Sections 3.3.4.4 and 3.4.4.2 for lightning protection system 
attachment. For existing lightning protection systems, evaluate wind resistance 
(Section 3.6.3.1)

Vulnerability Section: Municipal Utilities

Vulnerability: Is the site in a hurricane-prone region?

Guidance: See Section 4.3.5.1 for emergency and standby power recommendations.

Vulnerability: Is the emergency generator(s) housed in a wind- and debris-
resistant enclosure?

Guidance: If not, build an enclosure to provide debris protection in a 
hurricane-prone region.

Vulnerability: Is the emergency generators wall louver protected from wind-
borne debris?

Guidance: If the building is in a hurricane-prone region, install louver debris 
impact protection.

Vulnerability: Is the site in a hurricane-prone region?

Guidance: If yes, an independent water supply and alternative means of sewer 
service are recommended, independent of municipal services. 
[end table]




4.7 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, ASCE, The Masonry Society, Building Code 
Requirements for Masonry Structures, ACI 530/ASCE 5/TMS 402, 2005.

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 Institute, 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 RegionsHurricane 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 RegionsHurricane Katrina 
Recovery Advisory, Washington, DC, May 2006, rev. July 2006.

FEMA, Rooftop Attachment of Lighting Protection Systems in High-Wind Regions
Hurricane 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.