Glossary: Deck Board Spacing
The structural gap left between adjacent outdoor decking planks to allow for seasonal thermal expansion, wood shrinkage, and drainage.
Decking Expansion Gaps and Drainage Layouts
Wooden and composite deck boards expand when wet or hot and shrink when dry or cold. Leaving no board gaps leads to deck buckling, wood rot, and blocked drainage. Proper spacing is dictated by material type at installation:
- Pressure-Treated Wood: Often installed wet (high moisture content) and will shrink. Standard spacing is typically 1/8 to 3/16 inch at installation.
- Composite Decking: Experiences high thermal expansion along its length but does not shrink. Gap requirements (normally 3/16 to 1/4 inch) are critical for end-to-end framing junctions.
- Drainage: Gaps allow rainwater to drain through the deck structure rather than pooling on top of joists.