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SESK: Stuff Everyone Should Know · sesk.info/wood-fiber-saturation-30

At about what moisture content does a drying board begin to shrink?

At roughly 30%, the fiber saturation point.

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  1. About 30% ✔
  2. About 12%
  3. About 6%

Why: Shrinkage starts near the fiber saturation point, when the cell walls are full of water but the cell cavities are empty. If you do not know the species figure, 30% is the standard estimate.

Huh, didn't know that: A board's surface dries first, so the outside can shrink while the average moisture content of the whole piece is still above that point.

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References

Answer: About 30%. Shrinkage starts near the fiber saturation point, when the cell walls are full of water but the cell cavities are empty. If you do not know the species figure, 30% is the standard estimate.

  1. Wood Handbook: Wood as an Engineering Material, FPL-GTR-282 (USDA Forest Products Laboratory, 2021) research.fs.usda.gov/treesearch/62200
    If MCfs is not known, 30% MC can be used as an approximation.
    Checked 2026-10-10.
  2. Wood Handbook: Wood as an Engineering Material, FPL-GTR-282 (USDA Forest Products Laboratory, 2021) research.fs.usda.gov/treesearch/62200
    shrinkage normally begins at about the fiber saturation point and continues in a fairly linear manner until the wood is completely dry
    Checked 2026-10-10.

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Trades & ShopWhich direction does wood shrink the most as it dries?Trades & ShopAs wood loses moisture, how much does a board shrink along its length?Trades & ShopUnder the American Softwood Lumber Standard, softwood is "dry" at what maximum moisture content?

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