Securing all home openings–windows, garage and regular doors, sliding glass doors, skylights, and vents–is necessary to protect a home during hurricane events
Once a window or door has been breached by hurricane winds, tremendous pressure is brought to bear on interior walls and upward pressure on the building’s roof. This can lead to roof failure which exposes the entire contents of the building to the storm. Much of the damage and building failure in Hurricane Andrew could have been prevented by well installed hurricane shutters over windows and doors.
Openings can be breached in two ways. They can be caved in by the enormous pressure of the wind, and by storm debris such as flying lumber.
The Florida Department of Community Affairs has excellent suggestions http://www.floridadisaster.org/mitigation/rcmp/hrg/content/openings/openings_index.asp on how to secure your home’s openings. All windows, doors, and shutters should be certified as both large-missile resistant and/or wind-pressure rated.
A product is tested for large-missile resistance by exposure to various impacts with a piece of lumber weighing approximately 9 pounds, measuring 2″ x 4″ x 6’ (no more than 8′) in size, traveling at a speed of 50 feet per second (34 mph). Hurricane winds of 110-150 mph exert pressures of 30-50 pounds per square foot. A 110 mile-per-hour wind would exert 450 ponds on a 3 X 5 foot window; 840 pounds on 4 X 7 foot door; and 3,780 pounds on a 7 X 18 foot garage door.
They key point for cosumers is to buy products recognized by government and insurance companies as meeting wind pressure and/or large-missle standards. The Florida Department of Community Affairs http://www.floridabuilding.org/pr/pr_app_srch.aspx has a list of storm rated windows, skylights, shutters, regular and garage doors. Note that insurance companies will not give a windstorm insurance discount unless all your house’s openings are protected by an approved product.
Manufacturer Members of the International Hurricane Protection Association, a not-for-profit trade association, have all submitted for independent testing and engineering. Member Manufacturers produce products that have the necessary Texas Department of Insurance, Miami-Dade and/or Florida Building Code approvals for use in Florida and Texas.
An impact resistant window is stronger than a car windshield. Its extraordinary strength is created by a 1/10 inch thick sheet of tough plastic sandwiched between two panes of glass. The glass might shatter if a heavy object crashes into it, but it won’t break to bits.
Laminated glass is used in glass doors, skylights, and automobile windshields. In hurricane-prone areas, laminated glass is often used in exterior storefronts, exterior window-walls of high-rises, and residential windows.
A hurricane impact resistant window provides protection from wind-borne debris. It prevents wind-borne debris from penetrating the envelope of a home. If debris breaks a hole in a window, the hurricane strength winds could create interior pressure severe enough to blow its roof off. This has proved to be a major cause for the destruction of homes during hurricanes.
The advantages of impact resistant windows are numerous: no shutters to put up, no plywood to cut and put up- – in other words, continuous protection. Likewise, the windows are structurally part of the building so it is much more difficult for wind to get behind the windows and pull them off, which can occur for shutters and plywood. Impact resistant hurricane windows provide the added advantage of letting light in.
In a recent Miami-Dade, post-Hurricane Wilma study, buildings glazed with impact resistant laminated glass were surveyed to determine the extent of glass breakage and resulting damage to the property. A wide variety of windows in residential and commercial buildings were surveyed.
Projects, that reported broken or damaged laminated glass from windborne debris, only experienced fractures of the glass layers. There were no reports of laminated glass failures resulting in breaches of the building envelope. The laminated glass performed as was intended and consistent with the pass-fail criteria of the Florida Building Code. “The requirement that all structures must have windborne debris protection represents the greatest success story regarding damage mitigation,” concluded Miami-Dade County’s 2006 Post Hurricane Wilma Progress Assessment.
Impact resistant windows have other significant benefits. They deter intruders and are and are significantly quieter than non-laminated windows. A laminated window reduces exterior noise by 44 dB and sounds four times, quieter than a non-laminated two-pane window with a decibel reduction of 31 dB.
The key ingredient of an impact resistant window is laminated glass, a type of safety glass, that holds together when shattered. In the event of breaking, it is held in place by an interlayer, typically of polyvinyl butyral (PVB), between its two or more layers of glass.
The interlayer keeps the layers of glass bonded even when broken, and its high strength prevents the glass from breaking up into large sharp pieces. This produces a characteristic “spider web” cracking pattern when the impact is not enough to completely pierce the glass.
This window combines laminated glass and a pane with a low e-coating.
This is the gold standard for a hurricane zone. It keeps the home cool and provides protection from strong winds and flying debris.
The laminated glass transmits most of the sun’s energy to the interior pane of glass. The interior glass pane passes visible light, but reflects infrared light back outside. The laminated glass prevents hurricane wind and windborne debris, such as two-by-fours from penetrating into the interior.
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The Florida Department of Community affairs website has s detailed guide to the purchase and installation of storm shutters http://www.floridadisaster.org/mitigation/rcmp/hrg/content/openings/openings_index.asp.
The best way to protect your existing windows and glass doors from damage in hurricanes is to install tested and government-approved storm shutters. Much of the damage and building failure in Hurricane Andrew could have been prevented by well-installed hurricane shutters over windows and doors.
There are two basic kinds of shutters – porous ones which resist debris impacts that are not wind proof (e.g. Bahama shutters) and non-porous panels which resist both hurricane winds and airborne debris.
The easiest retrofits are typically those that simply cover the door or window opening with an approved wind-and impact-rated structural panel. In addition to commercial products that are professionally installed, there are a wide variety of do-it-yourself options, which may or may not qualify for windstorm insurance discounts.
The Florida Department of Community affairs website has a detailed guide to the methods for protecting window and door openings
http://www.floridadisaster.org/mitigation/rcmp/hrg/content/openings/openings_index.asp.
Because garage doors are so big, their survival is very important to the survival of your house. When garage doors in older houses fail in hurricane winds, a lot of additional damage follows.
The large areas of doors exposed them to huge amounts of wind pressure. At 30-50 pounds per square foot (from winds 110-150 mph), a garage door might have 2-3 tons of pressure and a large exterior door around 1 ton of pressure.
All exterior doors, without shutters, should be certified to be both large-missile resistant and wind-pressure rated to withstand the maximum hurricane winds expected in their locality.
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