When a Category 3 or above hurricane sweeps through an area, the two parts of a house most vulnerable are wall openings (windows and doors) and the roof. People in Florida know this all too well. Beginning with Hurricane Andrew in August 1992, storm after storm ravaged the area, with seven major hurricanes in 2004-2005 alone. The increasing destruction has wrought changes in state building codes as well as caused insurance companies to tighten their standards for coverage.
And what engineers who have tested the effects of these storms on residential buildings and the products installed to protect exteriors find is that “if one component of the building fails, it can create a cascading effect,” says Florida engineer and University of Florida professor Dr. Forrest Masters. (See his recent study, “New Research on Wind Resistance to Asphalt Shingles.”)
How Wind Works
A single tear in the roof cover can allow wind to rip away whole layers of shingles. That can leave sheathing to resist torrential rains for as long as it clings to the frame. The failure of even a few shingles can create a domino effect, especially at the perimeter, says Naples, Fla., roofer Ken Kelly, president of Kelly Roofing. That effect usually starts with the flashing or “the first row of products,” he says.
But it isn’t replacing a roof that leaves insurance companies out of pocket so much as replacing and repairing what’s underneath that roof. For insurers operating in Florida, the largest percentage of hurricane dollars have been spent replacing contents and rebuilding interiors rather than replacing failed roofs.
In winds of 100 mph or greater, shattered windows significantly increase the prospect of roof failure. A window smashed by flying debris equalizes the pressure indoors and outdoors, says Steve Dawson, vice president of CGI Windows, the first manufacturer with an impact-resistant window code-approved by Dade County (way back in 1992). Once inside, he says, hurricane-force winds can “blow out windows and the roof can just pop off the house.”
Enhanced Standards in Code and Products
Manufacturers of shingles and of windows have, through testing and steadily enhanced new products, responded to the challenge of supplying products that can protect the envelope of the house from extreme weather. Meanwhile, code officials, insurance companies, and FEMA have adjusted standards for new construction and re-building and considerably increased inspection, oversight, and control. (For more information, see this report from the Florida Building Commission Department of Community Affairs investigating the causes roof failures in 2004.)
For instance, some insurance companies will grant homeowners who are installing a new roof discounts of as much as 35% on the windstorm portion of their homeowners policy for implementing even one of several changes in installation mandated by current Florida code. That code, Kelly says, requires an increase in the number of fasteners per shingle from four to six, the installation of a secondary water barrier, the reconstruction of decking using shank nails (not cut nails or staples) 6-inches on-center, and enhanced roof-to-truss connections.
More End-of-Life Testing Required
Masters says that his recent investigations indicate that the single most common cause of roof damage in a storm is the failure of the sealant strip that attaches one shingle to the next. Intense wind can get beneath the bleeding edge of the shingle below while acting on the shingle above to create “a vortex effect” in which the uplift pressure exceeds the capacity of the sealants. In field surveys of older roofs (as many as 30 years old) conducted as part of his research, Masters says he found that asphalt shingles begin to “unseal” after six or seven years, probably as a result of heat-driven expansion and contraction. The 2010 code, he says, leaves “the sealing issue” unaddressed.
As for windows, code changes now require either impact-resistant windows or some type of exterior protection such as hurricane shutters. Masters says that while changes in code and product leave Floridians substantially more well-protected in their homes than they were 20 years ago, or even five years ago, the process of evaluating the strength and efficiency of building products in the face of more storms of increasing strength should focus on testing products at the end of their service life rather than fresh out of the box. “An honest remodeler wants to know: Am I putting in something that will last?” Masters says.