How it works
The deck is the surface the concrete is poured on: boards laid side by side (a 1×12 board covers about 0.093 m² per running foot) or 8 × 4 ft marine boards (2.97 m² each). Bearers run under the deck at the spacing you choose, and props (round poles) hold the bearers up on a square grid. Timber is sold by the running foot, so the result is in feet.
Step by step
- Multiply the slab length by its width for the deck area.
- Divide the area by the board width (or by 2.97 m² per marine board) for the decking.
- Count bearer lines across the width at your spacing and multiply by the slab length.
- Count props on a square grid under the bearers, then add wastage to boards and timber.
Worked example
An 8 × 6 m slab (48 m²) on 1×12 boards: 48 ÷ 0.0929 = 517 ft of boards, plus 10% = 569 ft. Bearers at 0.6 m: 11 lines × 8 m = 88 m = 289 ft of 3×4, plus 10% = 318 ft. Props at 1.2 m: 8 × 6 = 48 round poles.
Questions
Shuttering boards or marine boards?
Shuttering boards are cheaper and are reused a few times. Marine boards give a smoother soffit, go up faster and last more pours if they are cleaned and oiled.
How far apart should props be?
About 1.0–1.2 m for an ordinary 150 mm slab. Thicker slabs need closer props; your engineer confirms the spacing.
Why is timber priced per foot?
Timber is cut to different lengths, so it is sold by the running foot. The calculator gives feet for each size.