If a fire occurs below the roof deck the most important thing the roofing assembly can do is to not spread the fire. The first line of defense is the material the roof deck is made of. When re-roofing the building it is highly unlikely to consider replacing the entire structural deck component just in case a fire might happen. The roof assembly is a different story. The most fire resistant material should be next to the roof deck. The most common material we see is a gypsum like board from Georgia-Pacific called Dens-Deck. There are other competitors that also perform well in a fire. With the more stringent enforcement of fire prevention systems and practices, and insulation materials tested and fire rated, we see less coverboards immediately above the roof deck specified by architects, consultants or roofing companies.