Building a deck and not sure what actually goes on the shopping list? Here's a practical rundown of the materials that turn up on almost every deck build – and how to get the right quantities so you don't run short halfway through the weekend.
Most decks use the same core materials. The quantities depend on the size of the deck, but the list usually looks like this:
| Material | Typical choice | Note |
|---|---|---|
| Deck boards | 21–28 mm thick, 14 cm wide | The surface you walk on. Count depends on area + waste. |
| Joists | 45 × 95 mm, pressure-treated | Support beams under the boards, usually 40–60 cm apart. |
| Deck screws | Stainless A2/A4, 50–60 mm | 2 screws per board per joist. Plan for 25–30 per m². |
| Weed membrane (geotextile) | Roll, laid underneath | Keeps weeds down beneath the deck. |
| Footings | Concrete pad, pedestal or posts | Chosen by height and ground. Keeps joists stable. |
| Posts (raised deck) | 9 × 9 cm, pressure-treated | Only for raised decks or soft ground. |
To get exact quantities from your own measurements, let the deck calculator work out boards, joists and screws for you.
The surface you walk on. Available in treated softwood, larch, hardwood and composite. The board width (typically 14 cm) and the gap between boards decide how many you'll need.
The support beams under the boards. They run perpendicular to the boards, usually 40–60 cm apart, and should be pressure-treated because they sit in damp shade. Read about joist spacing.
Always use corrosion-resistant deck screws (stainless A2, or A4 near the coast). Ordinary steel screws rust and leave ugly streaks. Plan for 2 screws per board at every joist crossing.
A weed membrane (geotextile) goes on the ground to keep weeds down. The footings – concrete pads, adjustable pedestals or sunken posts – keep the joists stable and clear of the soil so the timber can breathe and dry out.
The most common mistake is buying exactly the calculated amount. Boards get cut at edges and corners, some are slightly warped, and a couple get damaged along the way. So add:
It's also smart to keep a couple of spare boards. If you need to replace a damaged board in a few years, matching the exact colour and batch again is almost impossible.
Enter your deck dimensions, pick a board type and get the exact board, joist and screw count – with waste included. You can take the result with you as a shopping list.
Deck boards, joists (the supporting beams), corrosion-resistant screws and a stable base. Most people also add a weed membrane and either concrete footings, adjustable pedestals or posts depending on the height.
Add 5–10 % on boards for a simple rectangular deck, and around 15 % if you have angled corners or a patterned layout. Buy 5–10 % more screws than calculated too – a few always end up on the floor.
The joists, yes – they sit in damp shade, so use pressure-treated timber. The boards can be treated softwood, larch, hardwood or composite depending on your budget and the look you want.
It's a good idea. A weed membrane (geotextile) keeps weeds down and makes it easier to keep the space under the deck tidy. It's cheap and quick to roll out before you set the joists.
Measure the deck and use the deck calculator. It works out boards, joists and screws from your dimensions and adds waste, so you can take a finished shopping list to the store.
Keep going with one of these – they pair well with what you just read.
Deck joist spacing guide
How far apart should deck joists sit? It depends on board type, thickness and load – with clear rules of thumb.
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Read guide →Create a free account and use the deck calculator, material list and budget in MyPlanDIY.
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