Fire Retardant Treated (FRT) Lumber (circa 1960 to 1980) Can Experience Sudden Structural Failure When Exposed to High Humidity

摘要

When exposed to high heat and humidity conditions, as often found in unventilated attic/ceiling cavities, certain phosphate and sulfate chemicals used for fire retardant treated (FRT) lumber between approximately 1960 and 1980 can react with wood and cause unexpected failure. This condition caused a roof failure due to an enclosed attic cavity having no means of ventilation within the plenum. Similarly constructed roof trusses adjacent to the failure were open with no ceiling below. These were not exposed to elevated humidity and did not fail. This paper will discuss visual conditions, the analysis procedure used, findings, and lessons learned from the investigation of the failed roof trusses.