Recent Experience with Wood Truss Systems Constructed with Fire Retardant Treated Lumber

Fire retardant treated (FRT) lumber has been used in building construction in the United States since the 1940s. This paper reports on a recent experience where a significant number of fractures developed in fire retardant treated plate-connected wood trusses in a large elementary school. These fractures occurred after approximately twelve years of service. A material test program indicated that the in situ wood strength was still within original design parameters. A review of the fracture locations indicated that the fractures occurred in truss members with low calculated forces and members with moderate to high forces. Observations and analysis indicated an increased frequency of fractures occurring in fire retardant treated members containing juvenile wood.