How to install deck boards
Deck boards are the only part of the deck most people see, and the gap between them is the detail that decides whether the deck looks built or assembled. The right gap depends on the moisture content of the board, not on a fixed number.
Direction
Boards should run perpendicular to the joists. That is the structural requirement — a board running parallel to a joist is only fastened to the rim.
Beyond that, direction is a choice:
- Parallel to the house makes the deck look wider and pushes the eye away from the wall.
- Perpendicular to the house makes it look deeper and emphasises the length.
- Diagonal at 45° softens the rectangle and hides out-of-square framing, at the cost of 15% more material and closer joist spacing.
Gap size depends on moisture
| Material | Gap | Why |
|---|---|---|
| Pressure-treated, wet (S-GRN) | 1/8″–3/16″ | Board shrinks as it dries; the gap opens |
| Pressure-treated, kiln dried | 1/8″ | Little further movement |
| Cedar | 1/8″ | Stable once dry |
| Hardwood (ipe, cumaru) | 3/16″–1/4″ | Needs room for seasonal movement |
| Composite | Per manufacturer, usually 3/16″ | Expansion is specified, not estimated |
| PVC | 3/16″–1/4″, plus end gaps | Highest expansion of the synthetics |
A wet treated board installed tight will shrink and leave a 3/16″ gap on its own. A wet board installed at 3/16″ will leave a gap wide enough to catch a heel. If the boards are wet, gap them at 1/8″ and let them shrink.
Fastening
Two screws per joist crossing for a 5/4 board, three for a 2×6. Place them 1″ from the board edge and offset them slightly from each other so they do not split the grain.
- Face screws are the fastest and the most visible. Use a trim-head or a coloured head, and drive them flush, not countersunk.
- Hidden clips cost more and take longer, and they leave a clean surface. They also hold the board from the edge, which means the gap is set by the clip rather than by you.
- Ring-shank nails are faster than screws and back out over time. On a deck that will be re-surfaced in 15 years, screws come out; nails do not.
Pre-drill hardwood and any board within 2″ of an end. A screw driven into the end grain of ipe will split the board every time.
The two patterns worth the extra material
Picture frame. A border board runs around the perimeter, perpendicular to the field. It hides the cut ends and makes the edge look finished. Cost: 10–15% more material and a mitre at each corner.
Herringbone or basket weave. Field boards run in alternating directions in panels. It looks deliberate and it uses a lot of short offcuts, which makes it efficient if you already have them. It also requires blocking under every direction change.
Both need the frame to be laid out for them. A picture frame needs solid blocking at the perimeter, because the border board is fastened along its length to nothing but the rim.
Staggering end joints
End joints should land on a joist, and adjacent rows should not have their joints in the same bay. A random stagger looks better and distributes the fastening; a regular pattern of joints every second board reads as a mistake.
Order the boards by length before starting. Laying the longest boards first and filling with offcuts at the end produces a deck with all its joints in one place.
What this guide will not choose for you
- It does not choose a board. See composite vs wood for that decision.
- It does not cover stair treads or railing, which have their own sequencing.
- It does not cover the frame; decking is the last step, and the frame has to be square first.
- It does not give a gap for a specific composite product — those are manufacturer numbers and they matter.
Questions people actually ask
What gap should I leave between deck boards?
One eighth to three sixteenths of an inch for wood, wider if the boards are wet and will shrink. Composite and PVC gaps come from the manufacturer and are usually three sixteenths.
Should deck boards run parallel or perpendicular to the house?
Structurally they must run perpendicular to the joists. If the joists run away from the house, that means the boards run parallel to it, which is the usual layout.
How many screws per joist for deck boards?
Two for a 5/4 board, three for a 2×6. Place them about an inch from the edge and offset them so they do not follow the same grain line.
Is it better to use hidden fasteners?
They look better and hold the gap consistently. They cost more, take longer, and make it harder to replace a single board later, since the board is held from the edge rather than the face.