Q: When grading kiln-dried hardwood lumber, our supplier says that he grades from the better face of the lumber rather than the poor face. He also says that the lumber only has to be 13/16 inches thick. Is this okay?
A: When grading kiln-dried hardwood lumber, following the rules of the National Hardwood Lumber Association (NHLA), you still use the poor face for grading on rough lumber. But if the lumber has been surfaced on both sides (clean surfacing or hit-and-miss), then you are supposed to the use the better face for grading. The rule book goes into more detail. The minimum thickness of non-kiln-dried 4/4 hardwood lumber is 1 inch.
For kiln-dried lumber, the lumber can be 1/16 inch thinner-15/16 inches minimum thickness. (The thickness applies to the area used in grading and would not include thin ends or edges that are not critical in determining the grade). For surfaced-two-sides (S2S) lumber, the minimum required thickness (free of most roughness-planer skip, chipped grain) is 13/16 inches. There are other specifications for other thicknesses. Keep in mind that the NHLA Rules are a starting point.
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