Lateral shrinkage (Dutch: breedtekrimp), also called width shrinkage, is the dimensional reduction of wood across the grain as its moisture content decreases during drying. Wood shrinks significantly more in the tangential and radial directions than along its length, making lateral shrinkage the primary cause of warping, splitting, and joint failure in timber construction.
How lateral shrinkage works
Wood is a hygroscopic material that absorbs and releases moisture depending on the surrounding humidity. When freshly sawn timber dries below the fibre saturation point (approximately 28-30 percent moisture content), the cell walls begin to lose bound water and contract. The amount of shrinkage depends on:
- Grain direction — tangential shrinkage (parallel to the growth rings) is roughly twice the radial shrinkage (perpendicular to the growth rings)
- Species — softwoods generally shrink less than hardwoods
- Moisture content change — the greater the moisture loss, the greater the shrinkage
Typical shrinkage values
| Direction | Shrinkage (green to oven-dry) |
|---|---|
| Tangential | 6-12 percent |
| Radial | 3-6 percent |
| Longitudinal | 0.1-0.3 percent |
Minimising the effects of lateral shrinkage
- Kiln drying — reduce moisture content to the target level before use
- Acclimatisation — store timber on site until it reaches equilibrium moisture content
- Quarter-sawn boards — exhibit more uniform and lower shrinkage than flat-sawn boards
- Expansion gaps — allow room for seasonal movement in flooring and cladding
- Surface treatment — sealers and finishes slow moisture exchange and reduce dimensional changes
Application
Understanding lateral shrinkage is essential when designing timber floors, cladding, furniture, and joinery. Builders and carpenters account for expected movement by selecting appropriate timber grades, allowing expansion gaps, and orienting boards to minimise visible effects.
Related Terms
- Moisture content
- Fibre saturation point
- Quarter-sawn timber
- Timber drying
- Wood warping
More guides and plans available at fredsdiyplans.com