A.The idea that "wood structures are way overbuilt" may be the greatest myth in the wood construction field. It is possible that at one time in history wood structures were overbuilt, but it is certainly not true today. The safety factor for bending strength for visually graded dimension lumber is 1.3; by contrast, the safety factor for structural steel, which has much less variability from piece to piece, is as much as 2.

So how are safety factors applied? To arrive at the design values used in wood design, thousands of pieces of lumber of representative sizes, grades, and species have been tested. These tests are run for about ten minutes to determine the stress that will cause a piece of lumber to fail. The test data for every piece of lumber of a given grade,...

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