Eli5 Why is dimensional lumber not cut to its actual dimensions or why is it named something other than its actual dimension?
In: Engineering
It used to be cut to the actual size, as late as the 1960s. However, standards for straightness and smoothness were changed at that time, to make house building faster, and the wood industry didn’t think they should have to cut down more trees to meet the same demand. The solution was to adjust the sizes down a little so the same number of board feet of lumber could be produced per cubic foot of raw tree.
It is milled to its named dimension, then dried and planed to a slightly smaller size. A 4×4 is milled at 4″x4″, shrinks slightly during drying, and is then planed to 3.5″x3.5″
If you use homemade lumber (not planed) that actually measures full size, that is called rough-cut lumber and you can purchase hardware designed for those dimensions.
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