Where can I find lumber treated for both flame retardancy and preservation?
We are not aware of commercially available treated wood for exterior applications that meets AWPA requirements for preservative-treated wood and the requirements for fire-retardant-treated wood. Borates are used both in preservative treatments and fire-retardant treatments. Some Interior Type Fire Retardant Treated Wood (FRTW) also contain borates that are registered with the EPA as wood preservatives and can meet both fire-retardant and preservative requirements of the model building codes. Interior Type FRTW and borate-treated wood should be used only in applications where the wood is kept free from rainwater, standing water, and ground contact. Some inorganic preservative treatments are known to have the tendency to promote glowing combustion after flames are extinguish. For applications where the wood is not required to meet the building code definition of fire-retardant-treated wood, one option is to use a fire-retardant coating on wood that is pressure treated with preservatives.
