Protecting Homes From Hurricanes: Windborne Debris Resistant Windows, Doors and Skylights

The entire U.S. Atlantic Ocean and Gulf of Mexico coasts, and islands of Hawaii, Puerto Rico, Guam, Virgin Islands and American Samoa are all vulnerable to hurricanes.  Wind speeds exceeding 130 miles per hour during hurricane events can occur well inland in nearly all of those regions and over 140 mph or more in much of them.    One of the greatest hazards to homes and buildings in those regions when a hurricane strikes is windborne debris generated by extremely strong winds.  Glazing in windows, doors and skylights must be protected from it to help to ensure those structures as a whole are not severely damaged or destroyed.   That happens when unprotected openings are broken out leading to excessive pressurization inside of a structure that in turn can blow the roof off or the walls out or both, destroying it.

Driven largely by the devastation caused by Hurricane Andrew in 1992, structural requirements in building codes for those regions have been significantly beefed-up including requirements for exterior glazing to be protected from windborne debris.  That’s in addition to other stringent structural and installation requirements windows, doors and skylights must meet to resist hurricane force winds and wind driven rain.

The International Residential Code (IRC) and International Buildings Code (IBC), which most state and local jurisdictions base their codes on, define two areas where windborne debris protection is required for exterior glazing.  The first is areas within 1-mile of the coastal mean high-water line where wind speeds can exceed 130 mph.  That includes a mile inland for most of the Atlantic and Gulf coastlines up to Virginia, then from New York up into Massachusetts and all of Hawaii.  The second is all areas, regardless of how far inland, where wind speeds can exceed 140 mph or greater.  That adds nearly all of the southern half of Florida as well as all of Puerto Rico, Guam, Virgin Islands and American Samoa.  All together it’s a lot of real estate.

The IRC and IBC, which as noted is the basis for most state and local codes, allow for windborne debris protection to be provided by either impact resistive coverings or systems for windows and doors, or impact resistant window, door and skylight assemblies.  All must meet stringent requirements set forth in those codes to provide the same level of protection for the hurricane conditions they can be expected to encounter which the code identifies.  Jurisdictions can also impose even more stringent requirements with Miami-Dade County in Florida having the most stringent in the country.

All windborne debris protection options allowed by codes have their merits.  However, a big plus for using impact resistant windows, doors and skylights is that the protection is in place at all times. No action is required in preparation for a hurricane in order to protect those openings and the structure. Impact resistive coverings or systems on the other hand require specific actions to close, lower or install them.  With impact resistant window, doors and skylights there is also no obstruction of views to the outside for a lengthy period before and after a storm or at any time during it.

In order to comply with the windborne debris requirements of building codes, impact resistant windows, doors and skylights must first meet the requirements of two very stringent ASTM standards —  E1886: 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 and, E1996: Specification for Performance of Exterior Windows, Curtain Walls, Doors and Impact Protective Systems Impacted by Windborne Debris in Hurricanes.  As implied by their titles, they are both rigorous and complex and are used in conjunction with one another to specify what performance levels products must meet and how they are to be tested to demonstrate that they do.  Specified performance levels vary to an extent based upon the hurricane wind speeds that can be expected in the location where the product will be installed.   Testing is then based on the specified performance level and consists of firing small or large missiles at high speed targeting different locations on the glazing and frame to simulate windborne debris impacts.  The small missiles used for testing are generally ten steel balls which simulate roof gravel and tile, while 2×4’s, simulating framing materials are generally used for the large missile tests.  Products (the entire assembly) are then also subject to a series of positive and negative air pressure tests in the testing apparatus to ensure they stay in place in the opening even if damaged.  It’s all more complicated than that, but that is a good general overview of what is required.

As can be imagined meeting these requirements is a significant challenge for manufacturers especially given those products must also incorporate design and material elements to meet other code requirements such as those for energy efficiency.  Manufacturers must design and develop intricate combinations of laminated glazing, robust framing materials and hardware, and prescribe detailed requirements for the proper installation of the assembly to do so.  When tested, the product must experience no damage to the laminated glazing exceeding a five inch tear or a puncture large enough for a three inch or greater sphere to pass through.  The entire assembly must also remain in place during the additional pressure testing so even if the glazing is torn or punctured to the limited extent that is acceptable by the standards,  the window, door or skylight assembly will still protect the opening by staying in place and limit the internal pressurization potential that can lead to severe damage or destruction of a structure if the assembly is blown out.

Fortunately manufacturers have greatly advanced impact resistant technologies since Hurricane Andrew and there is a wide range of product types and styles that meet the ASTM standards. They continue to become stronger and more versatile and are a great option for complying with windborne debris code requirements in hurricane prone regions of the country.