Facade Impact Resistance Manual

Facade Impact Resistance Manual Page 1

2387 NW 57th St. Miami, FL 33142 | Tel 786 877 7108 Fax 954 457 3592 | www.B-E-C.us | [email protected]

Facade Impact Resistance Manual This manual is intended for designers designing

large facades in the high wind regions. The author

is a chairman of Building Enclosure Council (BEC) in

Miami, FL, covering the areas subjected to the peril

of wind‐borne debris impact; therefore, he

frequently responds to questions dealing with the

specifics of the hurricane‐proof façade design.

This manual is intended to clarify and respond to

some frequently asked questions, typically posed

by northern designers experiencing lack of

information regarding impact resistance design for

public, commercial, healthcare, cultural projects,

and other large projects.

The origins of the impact resistance requirements.

After Hurricane Alicia in 1983, the construction community started to slowly realize that the

hurricane wind is overrated, and what the wind carries, including the windborne debris, is often

more dangerous than the pure wind pressure. It took Hurricane Andrew to translate this awareness

into specific code requirements. The basic phases are listed below:

1. The design and engineering. The facades are

designed to withstand the pressure differential

between the exterior and the interior. Designers

assumed that the interiors of the building are fairly

wind‐pressure‐neutral (18%); therefore, a facade

was only designed for the fraction of the wind load

that a corresponding freestanding wall would see.

Also, the diagonal bracing was often value‐

engineered out of the facades. The original thought was that the sheathing would provide

the adequate lateral stability instead.

2. The wind event. A single shattered glass pane or an

impacted garage door would equalize the wind

pressure inside, significantly increasing the

pressure differential seen by the facade

components. All it took was a single pea of roof

gravel thrown at a window. The wind‐resistant

Windborne debris damage to the curtain wall glazing.

Miami Beach 2005

This manual is organized in four logical steps: Where, What, Why, and Design, explaining the steps a façade designer needs to follow in order to verify and address the elementary impact resistance requirements.



framing might never see its design wind load because the

components (e.g. glass pane or sheathing) which were supposed

to collect and transfer this load were already gone.

The sheathing collects the wind load; once the sheathing blew

off, it could no longer performs the function of the lateral

bracing it was assumed to perform. In turn the framing of the

building was compromised.

3. Conclusion: A facade is only as good as its weakest component.

The industry wasted thousands of tons of perfectly good aluminum, steel, and lumber to build

highly wind‐resistant fenestration framing which never

saw its full load because the glass was broken before its

load capacity could be used. Ironically, at the same time,

the secondary structure of opaque facades was found to

be inadequately engineered for the wind forces, not

taking into account the pressurization by openings.

4. The Result: After the Hurricane Andrew some of the

strictest requirements were imposed on glazing with

the intent of keeping interiors pressure‐neutral. Today,

glazing is often the safest place to hide behind during a

hurricane because opaque assemblies in Wind‐Borne

Debris Region do not need to meet same impact

requirements.

Curtain wall loss as a result of wind pressurization.

Fort Lauderdale, 2005, photo credit Alexandro Abate.

Glass breakage by windborne debris.

Curtain wall framing intact. Atlanta 2008

Roof loss as a result of wind pressurization. Atlanta, 2008



1. Where? What triggers the impact resistance requirements?

The first step is to determine the project requirements. A building must comply with the codes

having jurisdiction and requirements additionally imposed by the owner. We cannot encompass all

individual cases (e.g. specific requirements for Texas, Louisiana, etc.) but the two sets of

requirements are the most typical and they are presented below.

“Miami‐Dade” requirements – High Velocity Hurricane Zone (HVHZ)

Miami‐Dade County is exposed to the highest winds and therefore has

imposed very strict standards for approval of products used there. The

Florida Building Code embraced these requirements under the term

HIGH‐VELOCITY HURRICANE ZONE (HVHZ). This zone consists of

Broward and Dade counties in South Florida only.

Wind‐Borne Debris Regions (WDBR)�

If the building doesn’t happen to be located in

Broward or Dade counties and the owner has not

elected to voluntarily meet these requirements, you

would need to verify if the project is located in the

Wind‐Borne Debris Regions:

U.S. building codes derive the definition from the

ASCE/SEI 7 “Minimum Design Loads for Buildings

and Other Structures,” which describes: “Areas

within hurricane prone regions1 located:

1. Within 1 mile of the coastal mean high water

line where the basic wind speed2 is equal to or

greater than 110 mph and in Hawaii, or

2. In areas where the basic wind speed is equal to

or greater than 120 mph.”

Notes:

1 The Hurricane Prone Regions are defined as: “Areas vulnerable to hurricanes; in the United States

and its territories defined as:

1. The U.S. Atlantic Ocean and Gulf of Mexico coasts where the basic wind speed is greater than 90

mph.

2. Hawaii, Puerto Rico, Guam, Virgin Islands, and American Samoa.”

2 How do you figure out the base wind speed? This is often a challenge in the early stages of design. In

principal, you should figure it from the grainy maps published in ASCE/SEI 7 such as the one reproduced above

and from the respective statewide codes. In practice however, individual jurisdictions (counties and cities)

have the tendency to override these provisions in many ways, and getting the information often proves to be

very tricky. However, these modifications are typically minor ,and an approximation is often found good

enough for the early stages of design.

Map of High Velocity Hurricane Zone

(HVHZ) marked with red.

Base Wind Speed map copied from ASCE7‐



Word of explanation regarding codes and standards.

Unproportionately large part of this note deals with the code requirements, which may sound

overwhelming in spite of my best intentions to clarify them. The chief reason is the excruciatingly

obscure way in which the legislation is written:

In some countries, the code specifies the general intent its appendices list the requirements

comprising the qualifiers (what and where), pass/fail criteria (performance threshold) and the

referenced testing and calculation standards define the methods (procedures used to measure the

performance).

This way the general intent of the legislation is clear by reading the main body of a code, the specific

performance criteria are easy to revise in the subsequent editions of appendices, and only the

professionals are exposed to the detailed procedures written in separately developed standards. It

also affords a greater flexibility, with the stable code, regularly updated appendices, and scientific

standards published at their own pace. Such a transparent structure also offers some protection

against contradictory requirements because inconsistencies and conflicts are easily identifiable and

wetted out early. Such an organization is seldom seen in the U.S. as clearly demonstrated in this

manual.

Qualifiers placed in surprising places

Some codes and standards contain fairly specific inclusions and exclusions to their specific

requirements. You need to check with the specific jurisdiction. In the example below, the testing

procedure standard contains qualifiers and criteria which should be addressed by the code:

The ASTM E1996 “Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors,

and Impact Protective Systems Impacted by Windborne Debris in Hurricanes,” which provides testing

information, includes separate classifications of the following:

‐Wind Zones (referenced by ASCE7)

1. Wind Zone 1—110 mph (49 m/s) ≤ basic wind speed <120 mph (54 m/s), and Hawaii. 2. Wind Zone 2—120 mph (54 m/s) ≤ basic wind speed <130 mph (58 m/s) at greater than 1.6

km (one mile)from the coastline. The coastline shall be measured from the mean high water mark.

3. Wind Zone 3—130 mph (58 m/s) ≤ basic wind speed ≤ 140 mph (63 m/s), or 120 mph (54 m/s) ≤ basic wind speed ≤140 mph (63 m/s) and within 1.6 km (one mile) of the coastline. The coastline shall be measured from the mean high water mark.

4. Wind Zone 4—basic wind speed >140 mph (63 m/s)

‐Protection Levels

The separate classification called Levels of Protection lists three levels, including the “Enhanced Protection” corresponding roughly with the Occupancy Category IV , “Unprotected,” corresponding roughly with the Occupancy Category I, and “Basic Protection,” corresponding roughly with the Occupancy Category II.



2. What needs to be protected?

Once you found out where, the second step is to determine what: 1) what components of the

façade and 2) what requirements apply to them.

High‐Velocity Hurricane Zone (HVHZ)

The requirements embrace BOTH opaque assemblies and openings. Also, they apply not only below

but also ABOVE 60 feet (18.2 m) in height ( as opposed to Wind‐Borne Debris Regions).

The Florida Building Code (FBC). SECTION 1626 “HIGH‐VELOCITY HURRICANE ZONES—IMPACT TESTS

FOR WIND‐BORNE DEBRIS” requires that “All parts or systems of a building or structure envelope3

such as, but not limited, to exterior walls, roof, outside doors, skylights, glazing and glass block shall

meet impact test criteria or be protected with an external protection device4 that meets the impact

test criteria. Test procedures to determine resistance to wind‐borne debris of wall cladding, outside

doors, skylights, glazing, glass block, shutters and any other external protection devices shall be

performed in accordance with this section.”

This obscure requirement is followed by 8‐point long list of exceptions. Surprisingly, the section ends

with another list of exceptions, overlooked in the main article. Here are all the exceptions compiled

for you:

1. Roof assemblies for screen rooms, porches, canopies, etc. attached to a building that do not breach

the exterior wall or building envelope and have no enclosed sides other than screen.

2. Soffits5, soffit vents and ridge vents. Size and location of such vents shall be detailed by the designer

and shall not compromise the integrity of the diaphragm boundary.

3. Vents in a garage with four or fewer cars. Size and location of such vents shall be detailed by the

designer and shall not exceed the minimum required area by more than 25 percent.

4. Exterior wall or roof openings for wall‐ or roof‐mounted HVAC equipment.

5. Openings for roof‐mounted personnel access roof hatches.

6. Storage sheds that are not designed for human habitation and that have a floor area of 720 square

feet (67 m2) or less are not required to comply with the mandatory windborne debris impact

standards of this code.

7. Louvers as long as they properly considered ASCE 7 in the design of the building.

8. Buildings and structures for marinas, cabanas, swimming pools, and greenhouses.

9. Exterior concrete masonry walls of minimum nominal 8‐inch (203 mm) thickness, constructed in

accordance with Chapter 21 (High‐Velocity Hurricane Zones) of this code.

10. Exterior frame walls or gable ends constructed in accordance with Chapter 22 and Chapter 23 (High‐

Velocity Hurricane Zones) of this code ,sheathed with a minimum 19/32‐inch (15 mm) CD exposure 1

plywood and clad with wire lath and stucco installed in accordance with Chapter 25 of this code.

11. Exterior frame walls and roofs constructed in accordance with Chapter 22 (High‐Velocity Hurricane

Zones) of this code sheathed with a minimum 24‐gage rib deck type material and clad with an

approved wall finish.

12. Exterior reinforced concrete elements constructed of solid normal weight concrete (no voids), designed

in accordance with Chapter 19 (High‐Velocity Hurricane Zones) of this code and having a minimum 2‐

in. (51 mm) thickness.

13. Roof systems constructed in accordance with Chapter 22 or Chapter 23 (High‐Velocity Hurricane

Zones) of this code, sheathed with a minimum 19/32‐inch (15 mm) CD exposure 1 plywood or

minimum nominal 1‐inch (25 mm) wood decking and surfaced with an approved roof system installed

in accordance with Chapter 15 of this code. All connectors shall be specified by the building designer of

record for all loads except impact.



Note: These exceptions cause a lot of confusion, even with experienced and competent design

professionals. In one instance I know about, a famous building enclosure consultant from South

Florida requested the impact tests for the exterior masonry walls.

Notes:

3 Are the words “building” and “structure” used as adjectives or is the “building” a separate subject? I

guess the former is true. However, let me know if you found the definition of the “structure

envelope.” I did not. My educated guess is it should be read as either the “Components and

Cladding” as defined by ASCE/SEI 7.

COMPONENTS AND CLADDING: Elements of the building envelope that do not qualify as part of the

MWFRS.

BUILDING ENVELOPE: Cladding, roofing, exterior walls,glazing, door assemblies, window assemblies,

skylight assemblies,and other components enclosing the building.

4 This requirement may be also interpreted as an indirect definition of the “external protection

devices” by including and excluding them in two recitations of façade components, with and without

shutters. Identical, redundant recitations are repeated in three TAS standards: 201, 202, and 203.

Needless to say, I found no definition of a “protection device” in the code. Again, my guess it should

be read as “Impact Resistant Covering” defined in ASCE/SEI 7:

IMPACT RESISTANT COVERING: A covering designed to protect glazing, which has been shown by

testing in accordance with ASTM El886 and ASTM El996 or other approved test methods to withstand

the impact of wind‐borne debris missiles likely to be generated in wind‐borne debris regions during

design winds.

5 It is unclear why soffits (p.2) are excluded in HVHZ, since many exterior soffits in modern

architecture are not protected by structural slabs. The interested reader may also read the

discussion about opaque assemblies in the Design section below.

Wind‐Borne Debris Regions

The requirements embrace ONLY THE GLAZED OPENINGS, depending on their height above grade:

1. Below 30 feet. Glazed openings located within 30 feet (9144 mm) of grade shall meet the

requirements of the Large Missile Test.

2. Above 30 feet and below 60 feet Glazed openings located more than 30 feet (9144 mm) above

grade shall meet the provisions of the Small Missile Test.

3. Above 60 ft. Glazing above 60ft needs to be protected only if there is a potential source of debris

within 1,500 ft (457 m) of the new building. For example, loose roof aggregate that is not protected

by an extremely high parapet should be considered as a debris source. If loose roof aggregate is

proposed for the new building, it too should be considered as a debris source because aggregate can

be blown off the roof and be propelled into glazing on the leeward side of the building. (ASCE/SEI 7)

The Florida Building Code (FBC) lists the following exceptions:



1. Storage sheds that are not designed for human habitation and that have a floor area of 720

square feet (67 m2) or less are not required to comply with the mandatory windborne debris

impact standards of this code.

2. Openings in sunrooms, balconies or enclosed porches constructed under existing roofs or

decks are not required to be protected provided the spaces are separated from the building

interior by a wall and all openings in the separating wall are protected in accordance with

Section 1609.1.2. Such spaces shall be permitted to be designed as either partially enclosed

or enclosed structures.

3. Glazing in Occupancy Category I buildings including greenhouses that are occupied for

growing plants on a production or research basis, without public access shall be permitted to

be unprotected.

4. Glazing in Occupancy Category II, III or IV buildings located over 60 feet (18 288 mm) above

the ground and over 30 feet (9144 mm) above aggregate surface roofs located within 1,500

feet (458 m) of the building shall be permitted to be unprotected.

5. Louvers located within 30 feet of grade need to meet the Large Missile Test of ASTM E 1996.

The International Building Code (IBC) gave the third option: to qualify the glazing as an opening: 1609.1.4.1 Building with openings. “Where glazing is assumed to be an opening in accordance with Section 1609.1.4, the building shall be evaluated to determine if the openings are of sufficient area to constitute an open or partially enclosed building as defined in Section 1609.2. Open and partially enclosed buildings shall be designed in accordance with the applicable provisions of ASCE 7.”

However, the option of unprotected glazing was eliminated for most buildings in the 2005 edition of the ASCE7 standard to reduce the amount of wind and water damage to buildings during design wind storm events. The wind pressurization of the interiors often causes collapse of internal partitions which are seldom designed to withstand the exterior wind pressure. Note: It was reported that some framed walls built

according to the presciptive code requirements do not

p pass the glazing impact testing criteria, prompting the

ironic conclusion that windows are the safest place to

hide in case of a hurricane.

3. How? Methods of compliance.

General Concept.

Once you found where and what, the next question is how. The impact resistance is generally

demonstrated only by testing. The “rational analysis” is allowed by the codes but the industry lacks

the “sound engineering practices” to perform such analysis so far. Our computers are not fast

enough yet to perform such simulations.

There are number of test procedures quoted in legislation. All the impact test regimens have a

similar series of required tests: large missile, small missile, and cyclic loading.

Loss of a ceiling as a result of pressurization.



The large missile test, as its name implies, involves the use of a large object to test the glazing,

simulating the impact of windborne debris such as signage, yard furniture, and other common items

that may be picked up by high winds. A mockup of the assembly to be tested is installed in a

supporting frame and an 8’ long piece of 2”x4” lumber is fired from an air cannon.

The small missile test involves the use of small steel balls fired at the specimen in order to simulate

the effect of small windborne debris such as roof gravel easily lifted by high winds and thrown into

glazing.

Cyclic load testing is performed after the impact tests to simulate the action of the hurricane winds

on the impacted specimen. The pressure in the chamber can be altered by the use of a variable

speed fan to force air into or out of the chamber. The cyclic load is applied as a number of

fluctuations from the atmospheric pressure to positive pressure or negative pressure in an

incremental fashion with the number, duration and magnitude of the cycles specified by the test

standard and codes.

General Criteria of Acceptance.

The tested assemblies are generally required to reject missile impacts with no penetration and resist

the cyclic pressure loading with no crack forming longer than 5 inches. The HVHZ testing criteria are

stricter than the Wind‐Borne Debris Regions regarding the character and size of objects that may

pass thru the crack: 1/16” wide air stream in HVHZ versus 3” diameter sphere in Wind‐Borne Debris

Region.

Wind‐Borne Debris Regions – Specific Procedures

Florida Building Code (FBC), par. 1609.1.2 Protection of openings. States: “Glazed opening protection

for wind‐borne debris shall meet the requirements of SSTD 126, ASTM E 1886 and ASTM E 1996,

ANSI/DASMA 115 (for garage doors and rolling doors) or TAS 201, 202 and 203 or AAMA 5067

referenced therein.” The exception is made for louvers located within 30 feet of grade which need to

meet the Large Missile Test of ASTM E 1996.

Glazing (or its impact‐resistant cover) below 30' is subject to large missile impact tests, and above

30' and below 60' is subject to small missile impact tests. Three specimens shall be tested and three

impacts per specimen are required. Then the product is subjected to fatigue cyclic wind loading,

positive and negative.

You may feel a little dizzy after this recitation of acronims and digits above. As mentioned above, all

the impact test regimens have a similar series of required tests: large missile, small missile, and cyclic

loading. For the majority of applications (both walls and openings), either of the two basic test

protocols TAS or ASTM would apply.

Notes: 6 SSTD 12 is absolete. See below – under SBCCi.

7 This is voluntary (having option to go with ASTM E 1886 and E1996 standards). See below ‐ under

AAMA.



Testing Application Standards (TAS)

TAS stands for Testing Application Standards and is included in a separate volume of the Florida

Building Code (available free of charge online). TAS superseded PA (Product Approvals prepared

according to Miami Dade County Test Protocols). You will find plenty of references to PAs in many

publications. The trailing digits (201, 202, 203) remain the same. See also below under “Miami Dade

County Building Code Compliance Office Protocols ‐ Product Approvals (PA).”

The protocol TAS 201 covers procedures for conducting the impact test of materials. The large

missile test requires firing a 2x4 weighting 9lbs (which means it’s approximately 8ft long) at velocity

50 feet per second. The small missile impact test requires firing 30 solid steel balls of 5/16‐

in.diameter weighting 2 grams at velocity 130 feet per second.

Any specimen that passes the large missile impact test need not be tested for the small missile

impact test if the specimen has no opening that a 3/16 inch sphere can pass through.

The protocol TAS 202 covers procedures for conducting a uniform static air pressure test. It contains

its own water testing procedure and references ASTM E 283 for air tightness test.

The protocol TAS 203 covers procedures for conducting the cyclic wind pressure loading test.

Notes: Confusingly, it is impossible to read TAS without the referenced fragments of the Section

1625 and 1626 of Florida Building Code (FBC) which deal with the HVHZ and contain fragmentary

descriptions of the testing procedures mixed with the pass/fail criteria. Therefore, some of these

HVHZ procedures apply to Wind‐Borne Debris Regions by a reverse reference.

American Society for Testing and Materials (ASTM)

Two ASTM tests describe the small and large missile impact tests and the cyclic test, similar to the

ones described in the TAS 201 and TAS 203.

ASTM E 1996 “Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors,

and Impact Protective Systems Impacted by Windborne Debris in Hurricanes” provides the

information required to conduct the test method ASTM E 1886. Confusingly, it lists qualifiers (e.g.

building and location classifications) and pass/fail criteria in addition to the descriptions of the

procedure, specimens, reporting requirements, etc. These qualifiers and criteria are not addressed

by the Florida Building Code (FBC). See paragraph titled “Word of explanation…” above.

ASTM E 1886 specifies how the Large Missile Test is conducted. It describes the method, the

apparatus, its calibration, the test procedure, etc. in a much greater detail than TAS 201.

American Architectural Manufacturers Association (AAMA)

It’s a short pass‐thru document. AAMA 506 references the ASTM E 1886 and E1996 standards and

adds 8 additional requirements for specimens and reporting. It can be read as a voluntary option,

since it is listed as an alternative to ASTM E 1886 and E1996.

Standard Building Code (SBCCI)

The old 1997 SBCCI includes SSTD 12 “Standards for Determining Impact Resistance from Windborne

Debris” which is generally similar to the tests listed above. However, the SBCCI SSTD‐12 test allows

the use of a weighted pendulum to simulate the 2x4 impact in the large missile test. The SSTD 12



test standard is apparently no longer accepted although the requirement is incorporated in the FBC

2007.

Miami Dade County Building Code Compliance Office Protocols ‐ Product Approvals (PA)

They were superseded by Testing Application Standards (TAS) incorporated in the Florida Building

Code (FBC). See also above under “Testing Application Standards (TAS).”

High‐Velocity Hurricane Zone (HVHZ)

The testing criteria are stricter than the Wind‐Borne Debris Regions as noted above.

Florida Building Code (FBC), SECTION 1626 “HIGH‐VELOCITY HURRICANE ZONES—IMPACT TESTS FOR

WIND‐BORNE DEBRIS” contains 31 mixed fragments of the procedures and the criteria for small and

large missile impact that should be read in addition to the wind‐borne debris requirements and the

Testing Application Standard (TAS) 201. Some of these procedures apply to Wind‐Borne Debris

Regions by a reverse reference. Some are redundant with the standards.

We do not list them here for two reasons: 1)because the code is available free of charge online and

2)because the detailed testing procedures are of little interest to the average architect. They are

domain of testing laboratories and building enclosure professionals.

4. Design. Meeting the requirements.

The average architect is very limited in their choice of the facade products and systems. The list of

impact‐tested products is very short and contains chiefly almost identical products manufactured

and sold in the low‐rise market, such as accordion shutters and hung windows. Commercial

products’ sector experiences a similar misery. Last time I checked, only 62 skylights were tested and

most of them were small polycarbonate units commonly used in small commercial applications.

There are four components that architects typically ask about: glazing, opaque cladding, shutters,

and roofs.

1) Shutters or more generally “Impact Resistant Coverings.”

Permanent coverings may serve as shades and are highly

recommended to reduce the solar heat gain and protect

the interiors from burglars. There are plenty of types to

choose from, including stretched fabric nets installed in

front of a protected opening. Most of them is dedicated

to residential applications, but architects should become

familiar with them before designing custom systems

dedicated for commercial and public projects.

The most popular in South Florida are two types: metal

storm panels, and accordeon shutters. Metal panel is one

of the least expensive systemic options. It is typically

comprised of horizontal rails fixed above the head and

below the sill and a stock of corrugated metal panels stored

on site and bolted to the rails after a hurricane warning is

issued. The disadvantages include a dark interior, industrial

Metal storm panels – photo by Muhler

Window shades are often folded or

rolled down to protect the window from

impact of windborne debris.



look, cumbersome installation, the need

for a separate storage space, and a low

security of the solution.

Accordeon shutters eliminate the two last

disadvantages. They are permanently fixed

to their frame and unfolded in anticipation

of a storm, locked with key lock. Their

operation may require access from the

exterior, depending on the specific

configuration.

Many users discovered that due to cumbersome installation and operation as well as for the

security purposes, shutters are typically kept permanently closed, making opaque coverings

less desirable than translucent or transparent ones. Also, shutters may interfere with

window washing access.

Recently, we see the major influx of two types:

the vertical roller shades and translucent

polycarbonate storm coverings. The former are

used extensively in Europe, outside wind‐borne

debris areas, for their good security performance

and easy remote operation.

They also offer unobstrusive appearance if

incorporated properly in the design, with the coil

and side rails concealed within the depth of the

wall. This type is often used in commercial and

public buildings because it does not require

exterior access and can be tied into the central

computer system and electronically operated on

daily basis.

Polycarbonate storm coverings are popular due to

their translucency. They are intended to be stored

on site and installed in anticipation of a storm. In

practice, they are often left on windows

permanently.

Stuctural Panels. The least expensive and the most popular

version of opening protection is a simple plywood boarding.

It’s enough for a homeowner to keep a sufficient stock of

plywood around ready to attach when a hurricane is forecast,

to meet the code requirement.

Note: In Florida, shutters are typically owned by owners of

individual condominium units; therefore, a designer of a

Structural Panels – plywood boarding

Accordeon shutters – photo by A1A Garage Doors and Gates

Roll‐up retrofit shutters – photo by Metrix USA

Fabric covering – photo by Storm Smart Industries



multifamily building may want to address them holistically to avoid a patchwork appearance.

2) Glazing. Laminated glass is a prerequisite for the achievement of the impact resistance in

fenestration and the biggest factor influencing cost. Large expanses of glazing such as

curtain walls and high‐rise applications characterized by a challenging access may be

cumbersome to protect with standard shutters or portable protection means. Skylights and

sloped glazing are typically laminated anyway. Glass overhangs are defined by code as

skylights (not soffits) and need to be tested or protected as well to meet the code. The side

effect of the sturdy framing and

continuous structural silicone

joints that are necessary to pass

the tests is the increased water

and air‐tightness performance, in

spite of abysmal engineering and

detailing typically seen in catalogs

of the manufacturers selling to

this market. Laminated glass is

also a prerequisite for security

applications such as blast

protection.

3) Opaque Walls. Opaque cladding and louvers in HVHZ are typically excluded from testing if

the backing assembly itself meets the impact requirements. It is accepted that the cladding

can become destroyed as long as

the underlying structure is not

penetrated, per the criteria

described in testing procedures

listed above. The cladding should

remain positively attached to

avoid danger of becoming

windborne debris. Owners may

elect to have expensive and hard‐

to‐match cladding material such

as the natural stone either

produced and installed in thicker

veneer slabs or continuosly

backed with a stronger material, to increase their impact resistance and reduce the

frequency of replacements. Spandrel glazing in this case is treated as a vision glazing and

needs to either pass the impact tests or the opening must be equipped by a separate

protection device. Soffits and vents are surprisingly excluded by the code; however, we

suggest they are designed to the same standards as the respective vertical walls, particularly

in applications not protected by the stuctural slab (e.g., bottoms of protruding windows).

Foam core metal cladding damaged by a high wind.

Laminated glazing exposed to the high wind and impact stays In frame.

Note the deflection of the frame.



Flexible cladding, such as metal panels, flashings, etc. often mysteriously fail to wind in spite

of a seemingly sufficient attachment. They are subject to aeroelastic response distributing

wind reactions unevenly and overstressing fasteners, which is not addressed in codes.

4) Roofs. Roofs are typically excluded from impact testing by the virtue of a strong structural

deck or a prescriptive code path. They are typically designed, tested, and built to meet the

extreme wind uplift

requirements. Inverted roofing

systems are seldom seen in high‐

wind areas due to the practical

difficulties of keeping the roof

ballast from becoming a

windborne debris. For the same

reason, such a ballast is off‐limits

in HVHZ. From the impact

standpoint, the good practice is

to specify a roofing membrane

characterized by a high puncture

resistance, such as a build‐up

roofing system with four or more plies. This is particularly important in flat roofing

applications, which are challenging to effectively protect with tarps and other temporary

means. They become penetrated by numerous flying debris and left exposed to rain

sometimes for years after a wind event, resulting in consequential damages to interiors

exceeeding many time the cost of the roofing. Shortages of construction supplies and

building contractors are common in areas affected by wind events. Insurance adjustment

disputes and financial difficulties caused by high deductibles parallel to cash flow stoppage

due to business interruption may contribute to the delay. Another way is specification of a

roofing system that is characterized by the inherent high uplift resistance and easy water

intrusion detection, such as a seamless liquid applied roofing on a polyurethane spray foam.

Roof three days after a wind event. Atlanta, 2008

Roof perforation three years after a wind event.

New Orleans, 2008

Metal roof impacted by windoborne debris.

Pembroke Pines, 2007



5. References Miami ‐ Dade County, Florida ‐ Code of Ordinances

http://library.municode.com/index.aspx?clientId=10620&stateId=9&stateName=Florida

Miami ‐ Dade County, Florida –Product Control Search

http://www.miamidade.gov/buildingcode/pc‐search_app.asp

ASCE/SEI 7‐2005 “Minimum Design Loads for Buildings and Other Structures”

Florida Building Code (FBC) ‐2007

International Building Code (IBC) ‐2006

ASTM D5635 “Standard Test Method for Dynamic Puncture Resistance of Roofing Membrane

Specimens”

ASTM E1996 “Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors, and

Impact Protective Systems Impacted by Windborne Debris in Hurricanes”

About the author Karol Kazmierczak (Kaz), CSI, CDT, AIA, ASHRAE, NCARB, LEED AP, is the Senior Building Science Architect at Building Enclosure Consulting, LLC and the leader of the BEC Miami. He has 14 years of experience in building enclosure technical design, engineering, consulting, and inspection, with significant knowledge of curtain walls and architectural glass and a particular focus on thermodynamics. He can be contacted via e‐mail at info@b‐e‐c.us, webpage www.b‐e‐c.us and telephone (786) 877 7108. DISCLAIMER The author is not an attorney and any information derived or found in this material is NOT to be construed as legal advice and is for educational purposes only. Contact an attorney if you have any questions about statements in this material before you take any action on your own. The author’s comments about architects, engineers, attorneys, contractors, manufacturers, managers, administrators, and any other profession mentioned in this material are not meant to be any indictment of character or generalization about any group or any individuals. The author believes any and all statements in this material are true to the best of his knowledge. For no specific reason, other than to save space, we have used the male gender (his, he) in all places where the female gender (her, she) would fit equally as well. Any similarities to the actual situations, persons, jobs, constructions, and discussions are strictly coincidental. Limits of Liability and Disclaimer of Warranty: The author and publisher of this material have used their best efforts in preparing this information. They make no representation or warranties with respect to the accuracy, applicability, or completeness of this material and its contents. They disclaim any warranties either expressed or implied, merchantability, or fitness for any reason or particular purpose. The author, publisher, and the above mentioned companies shall in no event be held liable for any loss or other damages, including but not limited to special, incidental, consequential, or other damages. The advice of a competent legal professional should be sought if the reader has any questions what‐so‐ever.

Documents

Facade Impact Resistance Manual