In a major windstorm, such as a hurricane or a tornado, it's the windows and doors that usually hold a house together. “Once you breach the envelope, the air rushing in pressurizes the building just like blowing up a balloon,” explains Scott Schiff, civil engineering professor and director of Clemson University's Wind Load Test Facility. In the best case, intense wind pressures invading the home blow out the windows, equalizing the pressure before severe structural damage occurs, but more often, the roof or whole wall sections blow out. “The house literally explodes,” Schiff says.
The incidence of damage due to internal pressurization had a big effect on building codes in 1992 following Hurricane Andrew, and ushered in a new era for the window industry selling impact-resistant, laminated glass units. Since then, entry door manufactures have followed suit, offering product lines to meet new wind-loading standards based on AAMA 101/I.S. 2/A440 — the latest certification of exterior, side-hinged doors. But perhaps most important of all, sharp attention has been given to garage doors.
Because of their size, garage doors are highly susceptible to collapse, says Tim Reinhold, vice president of engineering at the Institute of Business and Home Safety (IBHS), a non-profit arm of the insurance industry that has assumed an increasingly important role guiding research in hurricane-protection. The bigger the door, the higher the wind pressure: This makes double-wide garage doors especially vulnerable.
After Hurricane Charley tore across Florida in 2004, Reinhold and colleagues conducted a study that correlated permits to the age of the door that was replaced. Of the four hurricanes in Florida that season, Charley was the only “design wind event” —meaning homes in the path of the storm faced wind speeds at or above the limits established in the building code. The study revealed that new garage doors built to meet the latest code requirements were unaffected by the storm, while older garage doors were likely to fail.
Replace vs. Reinforce The IBHS study was not able to determine the prior condition of the failed doors, but the evidence suggests that replacing older units with state-of-the-art doors is cost-effective. Mark Westerfield, manager of Product Development and Engineering for Clopay Building Products Co., concurs, pointing out that the only other option is to retrofit existing units to meet wind-load requirements. But this is problematic for several reasons:
- Impact-resistant garage doors usually require heavier vertical stiles, as well as added horizontal reinforcement. This reinforcement will change the doors' “springing weight.”
- When the springing weight is changed, the springs must be changed. Given the high-tension stresses on the springs and the special tools involved, this is work for a professional garage-door installer.
- More often than not, the track, the track attachments, the hinges, and the rollers must also be upgraded to properly transmit the loads from the door to the building. The need for these heavier-gauge tracks, hinges, and rollers may not be obvious to someone unless they're following detailed instructions or drawings, or they have been trained for garage door installation in high wind-load areas.
Although most remodelers are likely to sub out the installation of a new unit, keep in mind that any garage door is only as good as the supporting structure. In a high-wind zone, the opening must be braced to carry the extreme loads. This may require peeling back the siding on each side of the doors to increase the sheathing nailing and installing metal anchors that secure these small walls to the foundation and header. A one-page bulletin from APA — The Engineered Wood Association illustrates the essential details.