THE CODE
The code basically breaks down the method to meet the higher window load requirements in two ways: the window itself, and its installation. It says that the window must be able to withstand the “large missile impact” of a 9 pound 2×4 hitting the window at a speed of 34 miles per hour without penetrating the opening. The glass may break, but the opening must not be penetrated. Then, the windows and doors also have to withstand 9,000 cycles of positive and negative air pressure, such that a real hurricane could pull a regular windows right out of its frame.
THE WINDOW
To meet the penetration restriction, window manufacturer’s all use a similar type of impact window glass that’s much like a heavy duty car window. Florida’s Best Windows and Doors manufacturing process is basically the same as it is with most window manufacturer’s: their design consists of a clear plastic interlayer sandwiched between two panes of glass. Two types of interlayer are used: Polyvinyl butyral (PVB) and SentryGlas Plus (SGP). The SGP is more rigid and less likely to tear than PVB. For that reason, some manufacturers use it in their larger windows, or those windows designed for the highest wind zones.
The glazing system is also an important factor: a silicone sealant that may be strong enough to hold the glass in place in a Zone 3 impact test, but would likely fail in a Zone 4 test, causing the window to fly out of its frame. Windows in the higher test category would instead use something more like a construction adhesive for its glazing system. “The difference, says Kurt Mendez of Florida’s Best, is between Elmer’s glue and super glue.”
Window manufacturers also reinforce the frames in order to meet requirements. Lawson Industries uses a one piece sill plate (this also helps to prevent water leaks into the home) and interlocking meeting rails which ties the sash together when shut. Heavier locks also place a role in meeting impact tests, as they can be critical on certain types of windows, such as casements. For a casement window, the only thing holding the window sash in place under negative pressure is the hinge on one side and the lock on the other.
Today, virtually all of the major window manufacturers make a high-grade, impact-resistant window that has been certified to meet protective standards. The current gold standard in testing is the Miami-Dade County hurricane impact test (http://www.miamidade.gov/buildingcode/online_product_search.asp). Remember, it is your life and your property. Essentially all of Florida, and all the coastal regions of the United States should prepare for possible wind speeds of 110 mph or greater.
INSTALLATION
For the window to withstand hurricane conditions, something similar to the 9,000 cycles of positive and negative air pressure they undergo in impact testing, the installation is every bit as important as the quality of the window. Dave Olmstead, spokesman for PGT Industries in Venice, Florida, agrees that no matter how strong a window is the attachment to the building structure is critical. Olmstead says a window that is 53-inches by 76-inches would have 28 square feet of exposure, and with a wind speed of 146 mph from a category 4 hurricane would result in a load on the window equivalent to 1,958 pounds of pressure. For the window to perform correctly, the load has to be transferred to the building itself, which is done by using suitable anchors to transfer the load from the window or door frame to the rough opening without causing failure. Therefore, the installer needs to be knowledgeable in how to use this system and its different anchoring mechanisms.
Through the construction side of our business, we have had to make major repairs to structures as a result of poor window installations by other contractors – everything from using the wrong sealant to the extreme of installing regular windows instead of the hurricane impact windows the customer paid for. Something as small as the using the wrong sealant can cause significant damage to a home – rotting framing members, structural damage, mold, etc. Since leaks are often inside the walls long before a homeowner notices them inside the house, they are often not detected until there is major damage and then expensive repairs have to be made. This experience is invaluable for our installers. In addition to the installation training we give them, they get to experience firsthand the things that can go wrong with window and door installations and how to prevent them in the work that they do.
EXTRA BENEFITS
Benefits from impact-resistant windows extend beyond the storm belt to broader security and environmental concerns. Impact-resistant windows are considered to be security features because they are so difficult to penetrate or separate from their frames that they reduce break-ins, theft, and property damage. On top of physical and financial protection, impact-resistant windows also can preserve mental health. Who hasn’t been disturbed by car alarms, barking dogs or noisy neighbors?
“They do a good job of keeping outside noise outside,” Olmstead says. “With almost every homeowner, that’s the first thing they notice: How quiet the home [became]. Noise abatement is far more important than people realize.”
There are insurance breaks for new homes built with impact resistant windows, and for existing homes remodeled to include the tougher windows and frames. This discount can be as much as 50%. Check with your homeowner’s insurance carrier to see what kind of a discount is available.