Years after the record devastation caused by Hurricane Katrina, government agencies, code officials, and other policy makers are still debating how to ensure new construction in hurricane-prone areas is safe.
Homeowners and insurance executives are also anxious to find more durable building methods, as frame construction is relatively weak even when built to the new, stronger codes.
Perhaps the best option is to build with insulating concrete forms, or ICFs. Hurricanes pose three main threats to a structure—strong winds, storm surge, and flying debris—and ICFs stand up well to all three.
Strong Winds and Storm Surge – ICFs stand up to hurricane force winds easily, thanks to the mass of concrete in the exterior walls. A typical 16”x48” ICF, when filled with concrete, weighs about 400 pounds (6” core), or 75 pounds per square foot of wall. That’s heavy enough to withstand even the strongest winds. Concrete walls are also a superior choice for withstanding storm surge; breakwaters and sea walls around the world are made from the material.
ICF structures have another advantage: They are integrally tied to the footing or foundation slab with structural reinforcing steel. While frame walls use hurricane ties and/or anchor bolts to meet code minimums, ICF wall-footing connections are stronger by a factor of ten. Sometimes, the walls are poured monolithically with the footing, eliminating even the cold joint.
Likewise, all of the wall components above the footing are connected in a solid monolithic mass, eliminating flex, fatigue, and weak points. Photographs taken after Katrina prove the point dramatically: Often, a battered ICF homes stands relatively intact, even when the neighboring homes have been swept away or reduced to a bare slab.
One area of concern for code officials and the insurance industry are the roof attachments; it does little good to have hurricane-proof walls if the roof is compromised and belongings get ruined in the torrential rain. Once again, ICF homes have more hurricane-resistant alternatives available than other building methods.
Traditional roof trusses fastened into concrete are extremely sturdy. Steel trusses are even better. And ICFs are strong enough to support the most durable choice, a concrete roof system.
Flying Debris – The third major threat from hurricanes is flying debris. Dramatic photos show sheets of plywood skewering palm trees. Boards literally become missiles, and can puncture even brick walls.
Scientists at Texas Tech University have studied this issue extensively. In one experiment, eight-foot-long 2×4 studs were shot at various wall assemblies. They easily penetrated wood- and steel-frame walls at 50 mph. At 70 mph, the penetrated brick veneer. But nothing penetrated ICFs, even at 100 mph. The report concludes,
The strength and durability of concrete walls offer unmatched resistance to the devastation of major storms. Concrete homes are less likely to suffer major damage from debris than conventionally framed houses.
– ICF Builder Magazine, Sep/Oct 2012