Lessons From Ike
After a year-long study of the damage caused by last year's Hurricane Ike in coastal Texas, the Institute for Business and Home Safety (IBHS) released a report on the storm in October, including recommendations for upgrading homes to better withstand similar storms. Here is the first of three stories outlining the IBHS recommendations.
As with most hurricanes, only a minority of homes in Ike's path suffered the devastating effects of storm-surge wave action or extreme winds. Generally, the IBHS report notes, the most common risk to houses from hurricanes is simple water intrusion, caused by a combination of 70-mph to 100-mph wind and rain. And so the obvious place to start improving existing houses is to upgrade roofs, roof coverings, and roof vents against the action of wind-driven rain. In a section called "Tier 1: The Roof and Water Intrusion," the report recommends a series of measures to toughen roofs. The basic concept is to install high-wind-rated roof covering over securely attached sheathing, to ensure a strong attachment for ridge and soffit vents, and to provide for quick and easy deployment of temporary vent coverings if a storm approaches. If replacing the roofing is cost-prohibitive, and it's not time for a routine re-roof, then the report suggests a series of steps building owners can take between re-roofs. If you are re-roofing, IBHS recommends re-nailing roof sheathing to bring it up to a stronger spec. Use 8d ring-shank nails spaced at maximum 4 inches on-center near roof edges, overhangs, and at the corners of hip roofs; space nails no farther than 6 inches on-center for the rest of the roof. Because shingles might get blown off, it's important to seal the gaps between roof sheathing panels as a backup against rain intrusion. You can apply peel-and-stick membrane to the entire roof or just apply 6-inch-wide strips of peel-and-stick to the cracks. But make sure you get good adhesion — some OSB is coated with a waxy water repellent that can keep membrane products from sticking down. In that case, you'll have to use a special primer to prep the OSB before applying the membrane (most membrane manufacturers can also supply a recommended primer for this situation). Finally, use wind-rated shingles. Asphalt shingles are now tested for compliance with ASTM Standard D 7158, and receive a rating for resistance to wind uplift. You can use shingles with a Class F rating if your design wind speed is 110 mph or less, but you want a Class G rating for design wind speeds up to 120 mph, and a Class H rating if the design wind speed is higher than 120 MPH. If you're not re-roofing, you can still seal the roof sheathing gaps and strengthen the sheathing attachment, by applying adhesive foam sealant from the inside. Spray a closed-cell, urethane-based foam onto the joints between panels and at the joint where sheathing meets the rafters or truss top chords. (Information on one product, Foam Seal from ITW, is available at www.foamsealamerica.com.) And whether you're re-roofing or not, it's a good idea to strengthen the attachment of gable-end roof "lookouts," which are vulnerable to being peeled back by high wind, leading to water intrusion and gable-end structural failure. The IBHS report provides a detail (see page 37) for upgrading this framing element using steel connectors at the gable end and at the joint where the lookout framing end meets an interior truss. Next issue, we'll take a look at the IBHS recommendations for protecting window and door openings and strengthening porches and carports.
