Materials list for a DIY timber deck (Australia): boards, joists, screws
Short answer
For every square metre of deck you need about 11 lineal metres of 86 mm decking boards (or about 7 m of 140 mm boards) plus 10% for offcuts, around 50 decking screws, and joists at 450 mm centres. Under that you need bearers, posts and footings sized from the span tables, H3 treated timber above ground (H5 for structural posts in the ground), galvanised or stainless brackets and fixings, and deck oil. A 4 × 3 m deck in 86 mm boards takes about 145 lineal metres of decking (including 10% extra) and 600 screws.
A deck is the classic big-weekend DIY job, and most of the decisions are made before you lift a saw: board width, joist spacing, fixings and timber treatment. Get those right and the shopping list follows.
First, check approval. Many decks need council approval, depending on height above ground, size, distance from boundaries and your state. Read do I need council approval for a deck? before you buy.
Decking boards
Boards are sold by the lineal metre. Coverage depends on board width plus the gap between boards (usually 4–5 mm for hardwood):
| Board | Lineal metres per m² | 4 × 3 m deck (12 m²) + 10% |
|---|---|---|
| 86 × 19 mm | ~11.0 m | ~145 m |
| 90 × 19 mm | ~10.5 m | ~140 m |
| 140 × 19 mm | ~6.9 m | ~91 m |
| Composite (137 mm, typical) | ~7.0 m | ~93 m |
How the maths works: 1 ÷ (board width + gap, in metres). For 86 mm boards with a 5 mm gap: 1 ÷ 0.091 ≈ 11 m per m². Add 10% for offcuts and defects, more if you’re laying diagonally or picture-framing the edge.
Buy boards in lengths that suit your joists. Board joins must land on a joist, so choose lengths that minimise waste across the deck.
Joists, bearers and posts
The frame is the structural part, and it’s where you shouldn’t guess:
- Joists run under the boards, typically at 450 mm centres for 19 mm hardwood decking. Composite and thinner boards often need 400 mm or less. Follow the board manufacturer’s spacing.
- Bearers carry the joists, and posts or stumps carry the bearers. Their sizes and spacings depend on the timber grade, the spans and the deck height. Take them from the span tables in AS 1684 or your timber supplier’s span tables, not from a rule of thumb.
- Treatment: use H3 treated pine (or durability class 1–2 hardwood) for framing above ground. Structural posts set in the ground need H5 treatment or in-ground durability class 1–2 timber. H4 is for in-ground uses like fence posts and garden edging. Simplest of all: stand posts on galvanised stirrups in concrete, so no timber touches the ground.
- Footings are sized from the span tables and your soil. Most decks use concrete footings with galvanised post stirrups to keep timber off the ground.
Counting joists: deck width ÷ 0.45, plus one, gives the number of joists at 450 mm centres. A 4 m wide deck needs 10 joists.
Fixings and hardware
| Item | How many | Notes |
|---|---|---|
| Decking screws | ~50 per m² (2 per joist crossing, plus 10%) | Type 17 or specific decking screws; stainless steel within about 1 km of the coast. |
| Joist hangers / triple grips | 1–2 per joist end | Galvanised, fixed with the specified nails. |
| Post stirrups / stumps | 1 per post | Galvanised, set in concrete. |
| Bolts / coach screws | For ledger and bearer-to-post connections | Sized from the span tables or bracket specs. |
| Concrete | Per footing | Premixed bags are easiest for small decks. |
| Joist protection tape | Length of every joist | Optional; helps framing last longer under the boards. |
Finishing
- Deck oil or stain. Coverage varies widely by product and timber; the tin will give it per coat. Most decks need two coats, plus an oiling of the board ends before laying.
- End-grain sealer for cut ends.
Tools
- Drop saw (mitre saw) and circular saw
- Cordless drill and impact driver
- Spirit level, string line, tape measure and a square
- Post-hole digger or auger, shovel and wheelbarrow
- Decking spacers and board-straightening clamp
- Safety glasses, hearing protection and a dust mask
Jib’s AI Toolbox remembers which of these you already own.
What isn’t DIY
Building a deck on your own home is generally DIY-legal, subject to council approval and owner-builder value limits. Stormwater or drainage changes need a licensed plumber, and any lighting or power points on the deck need a licensed electrician. If the deck is high or attached to the house, get the design checked, and follow your approval’s conditions exactly.
Frequently asked questions
How many decking screws per square metre? About 50 for 86 mm boards on joists at 450 mm centres: two screws at every joist crossing, plus 10% spare.
What joist spacing for 19 mm decking? 450 mm centres is standard for 19 mm hardwood boards. Check the board manufacturer for composites and thinner boards, which often need closer spacing.
Hardwood, treated pine or composite? Hardwood looks and wears best but costs more and moves more. Treated pine is cheapest. Composite needs the least maintenance but has its own spacing and fixing rules, and costs the most per m².
Sources
Every rule on this page is taken from these official sources. If a rule has changed, please tell us and we’ll fix it.
This guide is general information, not legal or professional advice. Rules differ between states, councils and individual properties, and they change. Confirm with your state regulator or council before starting work, and if in doubt, get a licensed tradesperson.