Deck Board Spacing Guide
A one-page printable reference card with the correct gap spacing for every common decking material. Keep it on the job site so you never have to guess the right spacer size.
What's in the Cheatsheet
The printable deck board spacing guide covers four decking materials — pressure-treated wood, generic composite, Trex, and TimberTech — with the manufacturer-recommended side gap, end gap, fastener type, and maximum joist spacing. It also includes a temperature adjustment table so you can widen or narrow gaps based on the air temperature at the time of installation.
Gap Spacing by Material
| Material | Side Gap | End Gap | Fastener | Max Joist Spacing |
|---|---|---|---|---|
| Pressure-Treated Wood | 1/8″ | 1/8″ | Face screws | 16″ OC |
| Composite (generic) | 3/16″ | 1/4″ | Hidden clips | 16″ OC (12″ diagonal) |
| Trex | 3/16″ | 1/4″ | Hideaway clips | 16″ OC (12″ diagonal) |
| TimberTech | 3/16″ | 1/4″ | CONCEALoc clips | 16″ OC (12″ diagonal) |
Temperature and Thermal Expansion
Composite and PVC decking expand and contract with temperature far more than wood. A 20-foot Trex board can grow nearly 1/8″ between a cold morning install and peak summer heat. The standard 3/16″ side gap already accounts for moderate expansion, but installers in extreme climates should adjust. If you are installing composite boards when the air temperature is below 40°F, widen end gaps to 3/8″. Above 90°F, you can tighten to 3/16″ because the board is already near its expanded length. Pressure-treated wood does the opposite: it shrinks as it dries. Wet lumber delivered from the yard can be butted tight because gaps will open naturally as the moisture content drops over the first season.
Why the Gap Matters
Too-tight gaps cause buckling — boards push against each other during expansion and lift off the joists. The repair is expensive: you have to pull boards, trim ends, and refasten. Too-wide gaps let debris accumulate between boards, trap moisture against the joist frame, and create an uncomfortable surface underfoot. The manufacturer-recommended gap is the sweet spot that handles seasonal movement without compromising drainage or comfort.
Diagonal and Stair Restrictions
When laying composite boards on a diagonal (typically 45°), the span between joists increases. Most manufacturers require you to reduce joist spacing from 16″ to 12″ on center for diagonal layouts. TimberTech has an additional restriction: the CONCEALoc hidden clip system is not approved for stair treads, so face screws are required on stairs even when the rest of the deck uses hidden fasteners. The cheatsheet includes these restrictions so you do not discover them mid-build.
Calculate Your Deck Board Order
Once you have your spacing locked in, use the Deck Board Calculator to get exact board counts, fastener quantities, and cost estimates for your deck area and chosen material.