As poles dry, they lose moisture from the surface, but shrinkage occurs only when the moisture content drops below what percent?

• A. 10%
• B. 20%
• C. 30%
• D. 40%

Answer: (C)

Wood shrinks as it dries when its moisture content falls below the fiber saturation point, which is about 30 percent. Above 30%, drying mostly removes free water in the cell cavities and doesn’t change the dimensions much. Once moisture content drops under roughly 30%, water tied to the cell walls is released, and the wood begins to shrink in volume and dimensions. That’s why the threshold is 30 percent—the point at which bound water loss starts to cause measurable shrinkage. So drying down to around 40% won’t cause noticeable shrinkage yet, whereas going below about 30% leads to contraction. The other numbers (10% or 20%) are below the threshold, where shrinkage would occur, but the standard reference point for when shrinkage begins is about 30%.