S&J Wackett Timber Merchants
Decking Calculator
Enter the size of your deck and we'll work out everything you need — boards, subframe, posts and fixings — with a live quote. Happy with it? Add the whole lot to your basket in one click.
1 Size of your deck
metres
metres
2 Choose your decking board
🌲 Timber
Pressure-treated softwood decking — the traditional look and the best value per m².
◼ Composite
Low-maintenance wood-plastic composite — no oiling or staining, colour-stable finish.
3 Deck construction
Ground-level deck
Subframe sits on a firm, level base. 47×100mm joists at 400mm centres.
Raised deck
Adds 90×90mm laminated support posts, concrete for footings and a heavier 47×150mm joist.
UC4 SmartFrame
Treated to Use Class 4 for ground contact — the belt-and-braces choice, with a longer service life in wet ground.
Standard treated carcassing (C24)
Pressure-treated C24 structural timber — the budget-friendly option, best kept clear of standing water.
4 Options
How we work it out
- Boards laid with a 5mm expansion gap (6mm for composite), joists at 400mm centres.
- Board lengths are chosen automatically (3.6m / 4.8m where stocked) to minimise cost and waste per row.
- Subframe allows for perimeter joists, a row of noggins every 1.8m, and fixings for both.
- Raised decks allow one support post per 1.5m grid, with 2 bags of Fast Set PostFix per post hole.
- Quantities are a guide for a straightforward rectangular deck — for complex shapes or site advice, give us a ring on 020 8801 9090.