Decks are a potential source for spreading fire to the home, especially in areas at high risk of forest fires. A company called Trex has developed fire-resistant composite decking. It performed better than other composite-decking products when tested by fire officials, although there's variation in the flammability ratings of Trex's product lines. Trex has won approval as a building product in wildland-urban interfaces.
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Decks and Wildfires
Fires in the wildland-urban interface raise concerns about outdoor decks. Decking that's laid horizontally with gaps between can ignite from burning embers and spread flames to the house. Fire officials recommend clearing away flammable material within 30 feet of the house as part of a strategy to create defensible space. Decks constructed of flammable materials weaken that space. Most deck materials are tested for flame-spread rates, but these ratings don't tell fire officials about flammability and ignition under forest-fire conditions.
ASTM International, formerly called the American Society for Testing and Materials, describes a process for testing and evaluating the performance of building materials during ignition, combustion and burning phases of fire. The ASTM standards are used as a basis for building codes, insurance requirements and fire regulations. ASTM E84 - 11a is referred to when testing the response of materials or products to heat or flame under controlled conditions, but the standard doesn't include all the factors that a real fire would contain.
Flammability Tests for Composite Decks
The California Forest Products Laboratory tested the flammability of a number of wood, plastic and composite deck-building materials in 2002. The tests found that solid products such as redwood decking performed best. Several plastic-wood composites displayed runaway combustion and flaming debris, though Trex was one of the composite products that performed well. Firefighters in Flagstaff, Ariz., conducted an informal test for ignition, and found that out of four composite decks that had surface fires lit under them, the Trex deck was the most difficult to ignite.
Trex Product Ratings
Trex product lines are approved products in California's wildland-urban interface as a result of the tests by the California Department of Forestry and Fire Protection. Trex is listed as having Class A and Class B ratings for flame spread; Class A is the highest flame-spread rating in ASTM E84. Trex "Escapes" decking is rated Class A, and "Accents" and "Transcend" are rated Class B. Most significant is that fire officials approved Trex following testing for the burning hazards contained in forest fires.