Attention to Building Envelope will Minimize Hurricane Damage

The six-month hurricane season is well underway and how your home weathers the onslaught will depend in large measure on how well your building envelope performs. Building envelopes (walls and roof) that remain intact during high wind events are less likely to experience catastrophic failure than those with breeched windows, doors and roof elements. APA - The Engineered Wood Association offers several recommendations to help builders and homeowners improve their structure's survival odds.

"The first measure of defense when building in high wind regions is to fully sheath the home with wood structural panels. Using plywood or oriented strand board (OSB) walls is the best-known way to strengthen wood frame buildings," said Bryan Readling, a staff engineer with APA's Field Services Division. Flying debris is a significant cause of damage with hurricanes and wood walls are a great defense against airborne projectiles.

As part of several damage assessment teams investigating tornado and hurricane aftermath, Readling has noted that fully sheathed wood homes experience far less debris penetration. "In many instances the wood panel sheathing helped keep the structure intact," said Readling. The second area of defense concerns the roof. APA recently updated Roof Sheathing Fastening Schedules for Wind Uplift, which provides recommended nailing schedules for wood structural panel sheathing -- plywood or oriented strand board (OSB). Developed through engineering analysis and full-scale laboratory testing of wet and dry panel specimens, the schedules give nailing recommendations for 90 mph, 120 mph and 150 mph wind conditions (3-second gust). The 150 mph schedules are appropriate for most hurricane oceanline regions in the Atlantic and Gulf Coast regions. Another important consideration is the wood species of the roof framing members. According to APA research, more dense species such as Douglas-fir or southern pine provide greater nail withdrawal resistance and significantly improve the performance of the sheathing nailing.

During high wind events, a home's garage opening is another vulnerable spot where breeches may occur. "We noted inadequate lateral capacity in walls adjacent to the garage opening as another mechanism which triggers large-scale failure," said Readling. Fully sheathed homes can take advantage of APA's prescriptive narrow garage wall details that permit 16-inch walls adjacent to the garage opening (International Residential Code 2006 IRC 602.10.5). APA's Narrow Walls That Work includes details for building over permanent foundations and raised wood floors. This site-built, bracing solution may be used in wind zones up to 109 mph.

Keeping the windows intact under a barrage of windborne debris is imperative to a home's survival. Wood structural panels provide an effective barrier to both flying debris and the sudden pressure changes that result from minor breeches in the building envelope. APA provides two alternatives for builders and homeowners in the 18-page Hurricane Shutter Designs. The first approach provides code minimum requirements for using wood structural panels as shutters. The second approach offers five designs, which provide additional strength and stiffness beyond code requirements. These designs include several attachment options for use with masonry block and wood framed structures.

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