A.Stephen Quarles, a University of California Cooperative Extension advisor in Richmond, Calif., responds: For truly noncombustible decking, you could use an aluminum product like AridDek (ariddek.com), Last-Deck (lastdeck.com), or Lock Dry (lockdry.com). But there aren’t currently any wood, plastic, or wood-plastic composite deck boards that have a noncombustible rating. Keep in mind, though, that even in California, where homes built in wildfire-prone areas must comply with the state’s stringent, newly adopted fire code, deck boards don’t have to be “noncombustible”; they just have to meet certain minimum performance criteria (see Chapter 7A of the 2007 California Building Code).

Those standards — and the fire-test protocols used to establish them — were developed by researchers (including myself) at the University of California Forest Products Laboratory. We tested several different types of commercially available plastic and wood-plastic composite deckboards, as well as solid redwood decking. To simulate an under-deck...

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