Increased Frequency of Fracturing Occurring in Roof Truss Systems Constructed with Fire Retardant Treated Lumber

During the winter of 2003–2004, a significant number of partial and full fractures were observed in fire retardant treated plate-connected wood roof trusses which spanned over a ten year old elementary school. A test program indicated that the wood strength was still within the parameters of the original design. Review of the fractures indicated that they occurred in both truss members with low calculated stresses as well as those with moderate to high stresses. Close inspection of the members with full fractures revealed that a large percentage of the members contained juvenile wood. Observations, tests and analysis indicated an accelerated frequency of fractures occurring in fire retardant treated members containing juvenile wood. This paper reviews the findings of this investigation and provides a discussion of the contributing factors to the observed distress.