An aerial ladder master stream may stop vertical fire spread from auto-exposure at much higher levels. The roof covering of a type II building can be a layer of asphalt water proofing, with a combustible felt paper covering. Another layer of asphalt may be mopped over the felt paper. A combustible foam insulation may be placed on top of the asphalt, and another layer of asphalt mopped over the foam insulation. When a fire occurs inside a type II building, flames rising to the underside of the steel roof deck may conduct heat through the metal and ignite the combustible roof covering above.
Conduction is the transfer of heat through a solid.
The asphalt, felt paper and foam insulation may bum and spread fire along the roof covering. After a fire has been extinguished inside a type II building, the officer should go to the roof and examine the roof covering directly above for extension. If necessary, a hoseline should be stretched to the roof for extinguishment. III buildings have combustible membrane roof coverings which are more combustible than the asphalt roof covering. It has masonry-bearing walls but the floors, structural framework and roof are made of wood or other combustible material.