Decks often fail due to overloading, if not from poor design and construction. However, one expert suggests being wary about another way decks can fail: swaying.
Unlike vertical forces, horizontal ones caused by side movement don’t need to reach maximum weight capacity to force a deck to give way. This type of deck failure, according to Washington State University’s Composite Materials and Engineering Center director Don Bender, is rarely reported in the news.
“For every deck collapse you hear about there are many more collapses that never make the news. It’s a serious national problem.”
What the IRC Says
Lateral forces are commonly attributed to tremors and high winds, although activity on the deck is also a factor. To prevent these forces from pulling the deck away from the adjacent structure, the 2009 International Residential Code (IRC) requires the installation of hold-down devices on at least two sections of a deck.
A hold-down device is a system comprised of a half-inch threaded rod attached to two tension ties on both ends. The device secures both deck and structure joists, reducing lateral movement and risk of lateral deck failure. The IRC requires the hold-down device to be capable of resisting lateral forces of no less than 1,500 lbs.
What Bender Says
However, Bender believes the penetration required to install the devices can be to the owner’s detriment. Besides the project’s cost, no clear evidence of its effectiveness exists.
Bender found a more traditional but cost-effective approach: building diagonal bracing. With the proper screws, simple diagonal braces can provide increased strength and stability to the deck without drilling a hole for the hold-down structure. His tests showed that with diagonal bracing, a fully loaded deck with lots of lateral movement barely budges.
Consult a Pro
At any rate, it would be wise to consult expert deck builders in San Francisco like Schafer Construction who can determine the best way to reduce lateral forces based on multiple factors, from the deck design to the materials used. You can be assured of quality construction that satisfies all safety and aesthetic requirements.
Having said all that, code compliant decks are prone to failure by gradual wear and tear. Even the smallest problems like missing screws and rotting wood can result in major freak accidents. Before the situation worsens, you would do well to coordinate with a deck builder such as Schafer Construction for quality deck repair in the Bay Area.
(Source: “Deck collapse: Swaying people can be worse than a hurricane,” Washington State University, June 4, 2014)