Trex decking may appear like a regular wood surface, with its lumber shape and wood grain appearance, but Trex decks actually consist of a combination of wood, plastic and sawdust. Trex decks, despite their composite quality, can still burn like natural wood surfaces, so always avoid having an open flame near the deck.
Trex decking is classified as a Class C, or Class III, building material. As a result, Trex lumber will burn as wood does, even though it contains several other composite materials. Fire resistance ratings are determined by Underwriters Laboratories, an independent consumer safety company. An "A" rating indicates a high level of fire resistance, while a C rating refers to an average level of fire resistance. So if a fire occurs, your Trex lumber will burn just like the wood on any traditional wood deck.
In 2002, the California Forest Products Laboratory tested a variety of different decks, including those made of plastic, wood and composite materials. Trex composite decks withstood fire better than some other decks, particularly those made up of hollow materials. In general, solid decks (such as Trex decks) are better suited for withstanding fire than hollow decks. Certain decks suffered problems like combustion and dripping, but Trex decks did not experience these problems.
A Trex Fire Defense board is a special type of board used for additional fire resistance. As opposed to the standard Trex decking, which contains wood and plastic, Fire Defense boards contain 50 percent wood and 50 percent polyurethane. As a result, Fire Defense boards burn more slowly than traditional lumber but are still flammable. If you live in a dry or otherwise fire-prone environment, Fire Defense may offer added protection.
If you have concerns about fire, or if you live in a fire-prone area, look for a decking material with a Class A fire rating. Such composite decking material will likely cost you more than the more common Class C material. As of November 2011, Trex did not offer a Class A lumber, but some other composite manufacturers do. Trex decking, and especially Trex Fire Defense decking, can provide moderate fire resistance.