Windows Designed to Take Some Hits
A specialist on hurricane windows and doors gives us the low-down on high-impact protection.
Considerable research has been done to evaluate both hurricane damage and its causes. The research indicated that
the failure of windows and doors was a leading cause of total building
failure during high-wind events. Further, it became evident that windows and doors very often fail not as a result of wind forces themselves, but due to the impact of flying debris. Consequently, a concerted effort was made to develop products that would help shore up these structural
vulnerabilities, and impact-resistant windows and doors are the latest
products to have evolved from this research.
Impact-resistant windows meet the same test standards as shutters and
offer a range of additional benefits, usually at a cost comparable to
most high-quality windows. The benefits include passive protection that, once installed, is always in place; enhanced 24-hour security,
considerably improved outside noise abatement; and 100% protection from ultraviolet light, which is the portion of the spectrum that can
contribute to color fading in furnishings.
When Rob Thompson's West Palm Beach house (a 2001 This Old House project) was built in 1925, there were no building codes addressing the issue of hurricane protection. Now, however, Palm Beach County building codes require hurricane protection systems for all new construction and major renovations. Rob had a decision to make. Hurricane protection systems come down to two basic options: shutter systems, or impact-resistant windows and doors. And since Rob wanted to preserve the look of the home without shutters, he chose to go with the latter, selecting single-hung windows, casement
windows, architectural fixed glass and French doors as replacement
It hasn't been without a journey, however, that hurricane-resistant
windows and doors arrived at the state of the art available
for Rob's renovation. In the initial research and development following
Andrew, storm shutters were the first area to be explored. There were
several different kinds that worked as intended, but all had a few
drawbacks. Both roll-down and accordion shutters don't tend to look very good attached to the outside of a home, and also are expensive. Panel
shutters, on the other hand, are a less expensive option and require
less obtrusive mounting hardware, but their installation and removal are
labor-intensive, and a significant amount of space is also needed to
In light of these challenges, glass manufacturers began investigating
their own solutions. In the end they resorted to an old technology, born
out of safety issues that arose in the automotive industry in the 1930s.
It turned out that laminated glass had the potential for solving the
problem. Most automotive windshields use laminated glass consisting of a 3/100-of-an-inch plastic interlayer sandwiched on each side by regular glass. The challenge was to develop this glass product further in order to meet new hurricane protection requirements put in place after Andrew.
The Miami-Dade Building Code and Compliance Office initiated a rigid
standard of test protocols for impact protection in windows and doors.
Eventually, by increasing the interlayer thickness threefold to 9/100 of an inch, two companies developed glass products that could survive the Miami-Dade test protocols. Although the glass in hurricane-resistant windows and doors does break when impacted at high velocities, it is not
penetrated, and because the shattered glass adheres to the plastic interlayer, the hazard of flying shards is practically eliminated.
The Miami-Dade test protocols consist of two impacts on windows and four impacts on doors by a nine-pound two-by-four traveling at 50 feet per second, followed by up to 9,000 cycles of positive and negative
wind-loading. After the glass companies developed a component to pass the tests, the next step was to develop window and door assemblies that would pass these same tests.
Since then, a complete product line has been developed that, combined
with the glass component and proper installation methods, can
successfully meet the Miami-Dade test requirements. When installed in a one- or two-story residential dwelling, these window and door products can now be reasonably expected to withstand winds up to 130 miles per hour, including impacts by flying debris. Subsequent tests have also led to code changes in Florida, Texas, and the Carolinas.
Finally, given the violent nature of these tests, it was necessary to
develop installation methods that would provide adequate anchorage to the structure to allow the products to perform correctly. In fact, this
is where a problem developed with Rob's house. I inspected the
75-year-old wood casement windows and found they were in fairly poor shape. There was a lot of dry rot, termite damage, and no solid
structure to anchor to. Fortunately the general contractors were able to
use two-by-fours to thoroughly reinforce the openings and provide
correct anchorage for all Rob's replacement products.
When the winds won't come a-blowing in south
Florida, Rob will know his house has the windows to stand up to them.
Dave Olmstead of PGT Industries inspected and consulted on the windows at the West Palm Beach house, a 2001 This Old House project.