A.Peggi Clouston, associate professor of Building Materials and Wood Technology at the University of Massachusetts Amherst and a specialist in timber design, responds: Certainly, natural whole elements of a tree can be used safely as structural members in a building. Trees are, after all, innately structural. But instead of rules of thumb, the IBC requires inspection by a certified grading agency or the engineer of record to estimate just how strong a log actually is and whether it is suitable for a particular structural application (see Section 2303.1.10, 2006 IBC).

Complex grading rules establish limits on the size and number of strength-reducing growth characteristics — knots, checks, splits, holes, and the like — allowed for any particular species and for a number of anticipated end-uses. Stress grades — as shown on grade stamps — are a direct result of this grading process, and strength values derive...

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