Wind Loads and Decks

Is it a safe assumption that hold-down hardware at the ledger is adequate to counteract wind loading? Most deck builders don't pay much attention to this question when they design and build decks. Even if they did, they wouldn't find answers in the codes or in DCA6, which specifically states that its guidelines don't address wind, seismic loads, or snow loads. As part of a larger project to characterize lateral loads on residential decks from these and other forces, Washington State University engineering professor Don Bender and his team used procedures contained in Minimum Design Loads for Buildings and Other Structures (ANSI/ASCE 7-10), the standard reference for general structural design, to calculate possible wind loads that decks might experience at different wind speeds.

The design wind speed in most of the United States is 115 mph, though that number increases to 180 mph for jurisdictions located at the tip of Florida. What the WSU researchers discovered in their study is that even under hurricane conditions, wind loads on a 12-foot by 12-foot  square deck would be less than 1,300 pounds, requiring hold-down forces of 650 pounds at each lateral load anchor point. This is considerably less than the 1,500-pound hold down force per anchor required by the current lateral load provision contained in the IRC. And in most areas, wind loads—and therefore hold-down forces—would be considerably less.

So if you're building to code, your deck shouldn't have any trouble staying attached to the house, even under hurricane conditions. To read the actual study and see for yourself exactly how to use ASCE 7 to determine wind loads on a residential deck, click on the PDF link above.