Impact-resistant windows consist of impact-resistant glass surrounded by a heavy-duty frame that is securely fastened to the interior window header and frame. Their construction and anchoring keep hurricane winds and debris from breaching your home's outer envelope.
The idea for shatter-resistant glass windows for homes came from the automotive field, where laminated glass has been in use for years to protect occupants. There are two common types of impact-resistant glazing for your windows. The first is laminated glass consisting of two sheets of glass with an inner shatter-proof membrane between them. Once the glass receives a significant impact, it may shatter but the inner membrane holds the pieces firmly in its frame so that the barrier is not broken. These windows are designed to handle wind-borne debris hurled at high wind speeds, as well as repeated impact from would-be intruders. In both cases, penetration of wind or water is nearly impossible. Interior lamination varies from .015 inch to .090 inch in thickness and the inner film can be ordered in a variety of color tints helping to reduce or eliminate sun fading and UV damage in your home.
The second, less-hardy variety of impact-resistant glass uses window film applied to the surface of the glazing. With filmed windows, shatter-resistant film is placed over the glass to keep the window shards in place if broken. Since these films are added to the glazing, they may not function as a complete system. Their durability really depends on how well the glass and protective laminate stay in the frame and window assembly.
Protecting the Building Envelope
Windows offer a significant opportunity for combined wind and water damage in hurricanes, but manufacturers originally came up with impact-resistant windows to save structures from destruction. A broken window provides a point of entry for wind, which enters the house, increases pressure, and seeks another way out. “When a building envelope is breached, the difference in air pressures inside and out will cause a building to lose a roof or a wall, and when that happens, the building is done for,” says Brian Hedlund, national product marketing manager for Jeld-Wen Windows & Doors. The only way to protect against damage from wind entry is to keep it out. This means deflecting wind and driving it around the building. This is why hurricane measures have been enacted in Florida for new building in hurricane zones. Residents must install impact-resistant windows or a permanent shutter system.
For homeowners in existing homes, replacing standard glass windows with impact-resistant windows brings peace of mind. “Take Florida for example,” Hedlund says. “Typically you have homeowners living there who will leave the state for periods of up to six months. If they know that a hurricane is coming, they have to return before it hits to either put shutters or plywood over the windows. If they have impact resistant windows, however, they have the peace of mind that they don't have to take any special precautions and that their windows won't be breached.”
Frames Add Strength to Glazing
It takes an entire window system to make an impact-resistant opening. Frames for impact-resistant windows or doors may be constructed from wood, metal, vinyl, or any combination thereof. However, frames are generally heavier than for regular residential windows, because although the glass may not break, a strong force could hit the window hard enough to cause the entire frame to give way.
“The frame can be any material, but they have stiffeners and reinforcement inside to help them bear the impact,” Hedlund says. “A lot of the windows have frames that are reinforced with steel, which makes a really solid structure. It takes much more to make an impact-resistant window than just putting in the glass,” he adds.
Testing for Total Security
Not every window on the market can claim to be impact resistant. There are testing standards set forth by the American Society for Testing & Materials (ASTM) that must be met before the window is certified as being impact-resistant. One of the most stringent of the requirements comes from the South Florida Building Code, which has been concerned over the increase in the number and force of hurricanes in recent years. Beginning in July 2001, the South Florida Building Code required that every exterior opening in a house be protected against flying debris either by shutters or impact resistant windows.
Also, according to the code, the windows must meet requirements for large and small missiles. It specifies that for large missiles, the window has been tested with an impact from a six-foot-long 2×4 weighing nine pounds, traveling at 50 feet per second. The test is done in a laboratory setting with the lumber fired from a cannon into the window. The window glazing must remain intact after the impact.
The small missile test exposes the window to a variety of impacts with 30 pieces of roof gravel traveling at approximately 80 feet per second or 50 miles per hour in order to meet the certification requirements. Current tests actually use steel ball bearings for uniformity in test conditions.
The windows are marked and graded according to the South Florida Building Code to ensure that you are getting exactly what you're paying for. You can rest assured when buying impact-resistant windows that the product will perform as advertised when installed according to manufacturer's specifications.