Fire-retardant-treated (FRT) plywood used as roof sheathing has exhibited strength degradation in some situations. The cause appears to be certain fire retardant chemicals that are activated under environmental conditions of high temperature and moisture content. This report describes how fire retardants are made, how they work, and what causes strength degradation of FRT wood. We present guidelines for selecting and using FRT wood and precautions to follow when designing roof systems with FRT plywood.
LeVan, Susan; Collet, Mary. 1989. Choosing and applying fire-retardant-treated plywood and lumber for roof designs. Gen. Tech. Rep. FPL-GTR-62. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 11 p.