When lumber dries, how does it tend to shrink?

When lumber dries, it tends to shrink more in width than in length due to the structure of the wood’s fibers. Wood is an anisotropic material, meaning it has different properties in different directions. The cell structure of wood is such that it holds moisture differently across the grain compared to along the grain.

As the moisture content decreases during the drying process, the wood fibers contract. This contraction predominantly occurs in the tangential and radial directions (which correspond to the width of the board), rather than along the length of the grain. The length of the wood fibers remains relatively stable because the longitudinal fibers are compressed less by drying stresses.

Therefore, when considering the drying behavior of wood, it's clear that the greater shrinkage in width impacts various applications in construction and woodworking, influencing design decisions and requiring allowances for material movement.