Fire-Safe Decking

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 surface fire, we exposed deck boards to an 80-kilowatt propane flame for three minutes. And to simulate burning embers landing on the deck, we used an ASTM E-108 “A” brand: a 1-square-foot, three-layer assembly of nailed-together 3/4-inch-square sticks that we set on fire and placed on the decking (the same method used to test roofing).

Our testing showed that a decking material’s fire performance was largely dependent on its cross-section (solid, channeled, or hollow), the plastic component used in its construction, and the presence or absence of a fiber reinforcement. Channeled deck boards tended to perform poorly in the under-deck tests, while hollow decking typically performed poorly in the burning-brand tests. Solid decking performed best overall; it’s worth noting that 2x6 heart-grade redwood, a common decking material in California, performed as well as or better than all of the plastic and composite decking products we tested.

These tests were conducted about eight years ago, and many of the plastic and composite lumber manufacturers have since modified how their deck boards are made in order to comply with the California requirements. Therefore, how any given product performed in our original testing isn’t necessarily an indication of how it would perform today.

There are several decking products that now meet the performance standards established by the CBC, such as TimberTech XLM (timbertech.com), a solid PVC product with a Class A flame-spread rating, and Trex Accents Fire Defense (trex.com), a wood-polyethylene composite with a Class B flame-spread rating. Also approved for use is nominal 2-by solid-wood decking in several species, including redwood and some types of cedar.

For a list of these products and information about the compliance criteria, you can download a free handbook, “Wildland Urban Interface Products,” at jlconline.com/firetested. Some of the products aren’t easy to find outside of California, but they may be available through special order at your local lumberyard.