What's Wrong with Metal-Plate-Connected Wood-Roof Trusses?

Metal-plate-connected wood-roof-trusses (trusses) are used extensively, both within the housing industry and in commercial buildings. With engineering that is fine-tuned and precise, trusses are part of most contemporary wood-frame buildings, and often support the roof over masonry buildings as well. With truss use so widespread, a practice in forensic engineering that includes wood structures wilt inevitably lead to calls about buildings with wood-roof-trusses. In reviewing the nature of building problems where trusses are present, and in working on the design of new buildings that incorporate trusses, I have begun to consider what it is about the trusses themselves; in their specification, design and engineering, and in their deployment that makes them different, possibly more prone to problems, but in any case special. This paper identifies some of the consequential changes that result from the use of manufactured trusses. In addition to the obvious structural substitutions, there are systemic changes that may go unnoticed. Further, the paper explores the nature of some of the most prevalent problems that its author has encountered in working with trusses and studying the buildings that employ them. Considering their widespread use overall, trusses and the buildings that exploit them seem to find their way into trouble only rarely, but when they do, the reasons may reflect shortcomings in their design and fabrication, in the flow of communication between and collaboration among participants in the design and construction industry, or misunderstanding about their use. This paper explores some of the reasons why and how using trusses differs from other practices, it reviews the truss design process, and identifies conflicts inherent in the current design-fabrication-erection process, and it proposes some steps to reduce the risks associated with using trusses. Throughout, the paper notes that there are ongoing efforts within the truss industry trade organizations that address many of these problems.