A deck succeeds or fails on paper. The layout decisions — board direction, joist spacing, gap size — are all made before the first cut, and every materials count flows from them. This guide walks through the decisions in the order a builder makes them.
Choose the board direction
Boards usually run along the longest dimension or out from the house, whichever gives fewer butt joints. If the deck is longer than the longest board you can buy (commonly 16 ft), butt joints are unavoidable — stagger them across different joists in a random pattern, never in a line. Diagonal layouts look striking but waste 15 percent or more and require closer joist spacing.
Set the joist spacing to the board
Timber boards on a straight layout span 16 inches on centre comfortably. The same boards run diagonally need 12 inches. Many composite boards specify 16 inches for straight runs but flex noticeably — their manufacturers often recommend 12. Build the frame to the board's specification sheet, not to habit.
Gap honestly
Treated timber is often installed slightly damp and shrinks as it dries, so a 1/4 inch gap at installation closes toward 1/8. Kiln-dried and composite boards behave oppositely with temperature. The gap is drainage as much as movement: a tight deck holds water and debris in every joint.
Count fasteners and finishing parts early
Two screws at every board-to-joist crossing is the planning rule, and a mid-size deck passes 500 screws without noticing. Add fascia boards, post bases, ledger flashing against the house and end-grain treatment to the same order — the small parts stop more decks mid-weekend than the boards ever do.
Frequently asked questions
Do I need a permit for a deck?
Rules vary by location and by deck height and size. Ground-level decks often need none; raised decks attached to the house frequently do. A quick check with your local building office before ordering avoids expensive surprises.
Timber or composite boards?
Timber costs less up front and needs oiling or staining every year or two. Composite costs more, needs only washing, and demands closer attention to joist spacing and clip systems. Over ten years the total cost converges for many owners.