WINDOWS, DOORS, AND OPENING PROTECTION Windows, Doors, and ...

WINDOWS, DOORS, AND OPENING PROTECTION 10

Windows, Doors, and Opening Protection

10.1 Introduction

W indows, skylights, vents, and glazed portions of doors are critical components of a building's envelope. Codes and standards use the term glazing to address all windows and openings containing glass. Specifically, ASCE 7-05 (which is incorporated by reference into both the IBC and IRC) provides the following definition for glazing:

GLAZING: Glass or transparent or translucent plastic sheet used in windows, doors, skylights, or curtain walls.

Glazing systems simultaneously allow natural light to enter the building's interior and provide a scenic view of the coast. However, these systems are very vulnerable to damage from wind forces and windborne debris unless specifically designed to resist such forces and impacts. Recent MAT investigations and laboratory tests have shown windows and doors are also susceptible to wind-driven rain penetration. Special consideration should be given to these features of the building envelope. In all areas where buildings are constructed, windows and doors tend to be more vulnerable to damage than other portions of a building's envelope. In coastal areas--where high winds, windborne debris, and wind-driven rain are common and often intense--their vulnerabilities are more pronounced.

This chapter presents actions needed to ensure that windows and doors can resist the hazards common to coastal areas. This chapter describes typical failures in windows and doors, discusses requirements contained in national codes and standards, outlines the nuances of window- and door-testing and certification, and discusses some best-practices approaches to installing and protecting windows and doors. The chapter finishes with a discussion of garage doors.

10.2 Window and Door Failure

In coastal environments, numerous post-disaster investigations conducted by FEMA have shown that windows and glazed portions of doors are vulnerable to impact from windborne debris. This impact force is the principal failure mode for these systems. Debris from the natural environment (e.g., tree limbs) and from the built environment (e.g., roofing material, siding material, sawn lumber, etc.) can become windborne debris and break window and door glazing. Once broken, windows and glazed portions of doors can allow wind, windborne debris, and rain into the interior of the building. This can result in the following:

nLarge amounts of water may enter a building and damage its contents and finishes. There is also the possibility that the water could compromise certain structural members. If water intrusion occurs, action will not only be needed to eliminate the water-induced damages on appurtenances (such as carpets, cabinets, and floors), but also to mitigate all potential long-term moisture problems associated with certain construction materials.

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nWind forces or pressures inside a building are dramatically increased when the building's envelope is breached. It is not uncommon to observe significant damage to structural and nonstructural building elements from this internal pressurization. Such damage may remain isolated to a small area or room or it may result in damage severe enough to initiate the complete structural failure of the building.

Water leakage around windows and doors is also quite common but because the effects of leakage are often subtle, the full effects of leakage are often not readily apparent. Leakage from poor flashing or weather stripping, from improper installation, or from doors or windows being inadequate to resist local conditions can allow water to enter a building's interior--even when the structure of the window or door remains intact. Water intrusion can cause rot and fastener corrosion that weaken the window or door frame or the wall framing itself. Leakage can also cause damage to interior finishes and facilitate mold growth.

Wind-pressure failure of glazing is also occasionally observed. Windows and doors can fail if they are not strong enough to resist wind pressures from a high-wind event or if forces exerted on the doors or windows exceed the strength of their anchorage. Figure 10-1 shows how the failure of a large window led to the loss of the roof structure. When strength is inadequate, the window or door's glazing or frames fail; when anchorage is inadequate, the entire door or window unit can be torn from its mounting. Negative pressure (i.e., suction) failures are more common but positive pressure failures can occur as well. Figure 10-2 shows a window separated from its frame due to positive pressures acting inward on a window system.

Figure 10-1. PUNTA GORDA, FLORIDA: Failure of a roof structure from pressurization of a house when the window failed on the windward face. (Source: FEMA 488)

New and older buildings may have windows broken by debris if windows are not protected. Figure 10-3 shows a window on a home under construction that was broken by windborne debris, while Figure 10-4 shows an oceanfront home that experienced window breakage when unprotected glazing was impacted by windborne debris. Properly addressing these failures requires doors and windows to be: 1) correctly designed and anchored to resist wind pressures, 2) adequately protected to resist windborne debris, 3) sufficiently flashed and weather-stripped to limit water infiltration, and 4) appropriately selected to resist local conditions.

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Figure 10-2. PUERTO RICO, 1998: Failure due to inadequate pressure rating of window. The window frame remained attached to the wall but the glazed portion was blown inward by positive pressures. (Source: FEMA 55)

Figure 10-3. PUNTA GORDA, FLORIDA: Glazing failure due to windborne debris from displaced roofing. (Source: FEMA 488)

Figure 10-4. Glazing failure due to windborne debris. An oceanfront home damaged during Hurricane Ivan due to windows being broken by windborne debris. (Source: FEMA 489)

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10.3 Windborne Debris Protection Systems NOTE

Damage to glazing systems can be prevented, or at least minimized, by using glazing or opening protection systems that have been designed to resist wind and windborne debris forces specified in the building code. Impact-resistant (i.e., debris-resistant) systems provide protection through the use of laminated glass or polycarbonate glazing systems. The use of physical-opening protection systems such as shutters, screens, or structural wood panels (as allowed by the IBC and IRC in certain hazard areas) is also a common means of achieving protection for glazing.

By far, the most effective solution is impact-resistant glazing systems.

It is very important to note that shutters, screens, and other panel systems that protect glazing from debris impacts are rarely, if ever, rated to reduce wind pressures on the windows they protect. A system that typically has been rated for a pressure rating has been rated to resist that pressure in order to avoid blow-off or excessive deflection--not to decrease pressure on a window or door that the system protects.

These systems provide "in-situ" protection and require no human

action or involvement after installation; the protection system is in place at all times and does not need to

be installed prior to storm events. Further, these systems do not need to be closed, lowered, or installed

like storm panels or shutter systems. While impact-resistant glazing systems are one of the more expensive

options for debris protection, their use may be determined to be appropriate for high-end homes (where

the relative cost of laminated systems as compared to the total building cost can be low) and for buildings

used for vacation homes (which are not continuously occupied). Their application may also be appropriate

on the upper levels of homes or buildings, where the installation of shutters may prove difficult.

Shutters, screens, and panel systems are the next-most-desirable option after impact-resistant systems. These systems protect vulnerable glazing from windborne debris but only when installed in place before the event strikes. Some styles of shutters (e.g., roll-up or accordion-style) are made to be deployed or positioned to protect glazing with little effort; many have electric-powered motors that facilitate their operation. Of course, electrically operated shutters need power to run and occasionally power is lost early during a storm. Other styles, often called "storm panels," are designed to be easily removed and kept in storage and installed only when a storm is approaching. If in place during a high-wind event, properly tested and certified shutters, screens, and storm panels are as effective as laminated, in-situ systems. However, installing these panels requires more effort and planning by home and property owners.

Wood structural panels (which include plywood and OSB) are allowed by the IBC and IRC in certain applications. Often these panels are large, single panels that are unwieldy and difficult to install-- particularly when winds begin to build and the panels need to be installed in order to protect upper-floor windows, glazing, or skylights. It is also difficult to prevent a homeowner from using wood structural panels if these custom wood panels meet the deflection requirements for which they are used. Wood structural panels, however, are relatively inexpensive and may be the most appropriate method for lowcost housing.

10.3.1 Impact-resistant Glazing Systems

Laminated glazing systems typically consist of assemblies fabricated with two (or more) panes of glass and an interlayer of a polyvinyl butyral (or equivalent) film laminated into a glazing assembly. Laminated systems are non-porous and have slightly different pass/fail criteria in ASTM E1996. During impact testing, the glass panes in the system can fracture but the interlayer must remain intact to prevent water

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and wind from entering the building. Depending upon the level of protection (i.e., enhanced or basic),

tears are allowed in the film used in windows but tears must be less than /1 16 inch wide and less than 5

inches long and cannot allow a 3-inch-diameter ball to pass through the tear. After impact testing, the laminated glazing systems must resist the cyclic pressure tests of ASTM E1886.

Polycarbonate glazing systems are also used in place of traditional laminated glazing systems. Polycarbonate systems typically consist of plastic resins which are molded into sheets which provide lightweight, clear glazing panels with high impact-resistance qualities. The strength of the polycarbonate sheets is much higher than non-laminated glass (i.e., more than 200 times stronger) or acrylic sheets or panels (more than 30 times stronger). Several brands of polycarbonates used as glazing (such as Lexan? and Makrolon?) are commonly available. Both impact-resistant windows and shutter systems may be constructed using polycarbonates.

10.3.2 Shutter, Screen, and Panel Systems

Shutters, screens, and non-wood panel systems are separate systems and are tested independently from the glazed portions of the windows and door they protect. While certified shutters protect glazing from debris impact for an identified missile at a prescribed impact speed, most shutter systems are porous and do not significantly reduce wind pressures on the glazing itself. Glazing protected by shutters does not need to be debris-impact-resistant but it does need to be strong enough to resist design wind pressures.

During testing, the shutter system must withstand the impact of the test missile while preventing the missile from penetrating the "innermost plane" of the test specimen. Also, after successful testing, there can be no openings formed that allow a 3-inch-diameter ball to pass through them.

To be effective, shutters should fully cover the glazing they are meant to protect. In retrofit installations, shutters are occasionally observed that do not cover the entire window or are obstructed by window unit air conditioners or other appliances (see Figure 10-5).

Also, as a best-practices approach, shutters should be anchored to the wall surrounding the window, and not to the window or door frame itself. Shutters should never be anchored to the window frame unless: 1) the window is properly anchored to the wall in a fashion that resists imposed wind pressures, and 2) the shutter is certified to perform properly when attached to the window or door frame. Typical installation of shutters, screens, and panels requires brackets or other mounting devices (such as anchors) to be secured to the walls or other elements that surround the window and not the window or door itself.

Shutters installed on upper floors or in difficult-to-reach areas can be challenging to install or operate. Several motorized styles are available to facilitate the operation and deployment of shutters in difficult-toreach areas. If motorized shutters are used, the shutter system should also be manually operable. If not, loss of electrical power can render the shutters ineffective prior to an event and might prevent opening after an event.

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