Plywood treated with ammonium phosphate compounds as fire retardants has been disintegrating when used as roofing material. High heat and humidity catalyze the deterioration process. Another product, Dricon, an organic phosphate, causes some strength reduction of the wood but thus far does not appear to precipitate thermal degradation. Manufacturers present arguments that improper installation is the cause of the wood deterioration. (Abstractor's note: There was no report that this material has been used in either museum construction or in historic house repairs, but the restorer needs to be warned of the potential danger of this material.)