A.Stephen Smulski, president of Wood Science Specialists in Shutesbury, Mass., responds: It takes specialized knowledge, an experienced eye, and a mix of field and lab work to, first, determine whether timbers exposed to conditions favorable to wood-rotting fungi are still structurally sound, and, second, to estimate their load-carrying capacity.

An inspector first looks for timbers with obvious advanced rot, insect damage, and signs of structural distress. These are marked for replacement, and no more time is expended on them.

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