Hey, I always want plywood on my decks for sheathing...and a lot of guys bitch about it, cause plywood costs more. But deck coating manufacturers stipulate plywood for a reason, and here's a good enough one for me...when it comes to fire, using the best fire resistant materials I can is my goal.
Click the headline to read about other construction methods and materials that may cause fire to spread or make it more difficult to fight.
They All Fall Down 
Critical Fireground Factors for New Residential Construction
by John Brunacini
The majority of all new residential construction uses lightweight construction materials. Let’s take a look at the different features of this construction type that directly effect the decision making process of firefighting strategy and tactics at these structures.
Oriented Strand Board (OSB) is now the construction industry’s predominate sheeting material; it has replaced plywood for roof decking, flooring decks and siding. OSB is assembled by gluing together small pieces of wood and wood chips at extreme pressures. After curing, they are cut into shapes (usually 4' x 8' sheets measuring 3/8" to ½" thick). OSB is structurally sound, cheaper and more readily available than plywood. But like a lightweight truss, it also fails much faster under fire conditions. The glues and resins that hold OSB together start to decompose rapidly at relatively low temperatures (+300°F). These moderate temperatures will decompose the adhesives holding the wood chips together, and the sheet will quickly delaminate (fall apart). The released glue and resin vapors are also very flammable and contribute to the combustion process. This phenomenon is causing faster attic flash-over times and quicker roof failure times once the fire has entered into the truss space.
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