Dry Rot, a decay that occurs in damp lumber and timbers. It is caused by a fungus that enters the wood through a crack or split and destroys the cellulose, leaving the wood discolored and crumbling. The fungus has rhizomorphs(cords of hyphae, or rootlike projections) that conduct water to the body, or fruit, of the organism. Rhizomorphs will travel across brick, stone, and metal to reach damp lumber. These tough, fibrous filaments can crack wood siding and panelling. Diseased wood must be removed and replaced with dry, well-seasoned lumber that has been impregnated with fungicide.

Poria incrassata, building poria, is especially destructive in the Gulf States, the Pacific Northwest, and areas of the Midwest. It attacks lumber made from conifers and broad-leaved trees. Merulius lacrymans does extensive damage to oak and mahogany structures in Europe, the northeastern United States, and Canada. Both species are bracket, or shelf, fungi, belonging to the subclass Homobasidiomycetes of the class Basidiomycetes.