During a wildfire, attached decks can be a vulnerable component of a building. If ignited by flames or by wind-blown embers, a burning deck could then ignite the adjacent building. An underdeck flame impingement exposure is used to evaluate deck performance as part of the current California State Fire Marshal and American Society for Testing and Materials (ASTM) standard test methods, as well as the California Building Code that applies to construction in wildfire-prone areas. To pass the California standard, a deck can ignite, but the heat released while burning cannot exceed the specified maximum heat release rate. Although the California State standard test method acceptance criteria includes the ability for a decking product to self-extinguish, it is not one of the requirements for compliance based on language in Chapter 7A of the California Building Code. The vulnerability and performance of decking subjected to an ember exposure is not considered. Given both the possible distance that wind-blown embers can travel and the typical size of most residential and commercial properties, it would not be possible to reduce the ember exposure to a deck with even the most effective defensible space on an individual property. Therefore, understanding the threat of an ember exposure to a deck is critical to understanding its vulnerability to wildfire.

The objectives of this study were to (1) evaluate the ability of an ember exposure to directly ignite combustible wood and plastic composite decking, and (2) evaluate the effectiveness of the standard underdeck flame impingement exposure test to predict the performance of combustible decking subjected to an ember exposure.