A deck looks simple, but its material list has more lines than most small jobs. Work from the ground up so nothing is missed.
1. Footings and posts
Lay out the beam lines and post spacing first. Every post needs a footing: a concrete pad or pier on firm ground below frost depth, typically at least 450–600 mm deep. Count footings, work out the concrete per footing, and add post bases and anchors.
2. Beams and joists
Joists = deck length ÷ joist spacing + 1. Add rim and end joists, and a ledger if the deck is attached to the house. Count hangers (two per joist at a ledger or flush beam) and ties where joists sit on beams.
Joist and beam sizes and spans must come from span tables, TRADA guidance or a structural engineer, and Building Control approval where needed. A calculator can count parts, but it can't size them.
3. Deck boards
Work in rows, not area. Rows = (deck width + gap) ÷ (board width + gap). Then choose a board length that suits the deck: a 4.8 m deck with 4.8 m boards wastes almost nothing, while a slightly longer deck forces joins in every row.
4. Fixings
Two screws per board at every joist. On a 4.8 × 3.6 m deck that's around 650 screws. Hidden clip systems need one clip per joist crossing. Use stainless or coated fixings rated for treated timber.
5. Stairs and railings
Count stringers (one every 400 mm or so), treads and risers from the stair calculator. Railing posts, top and bottom rails, and spindles spaced under the 100 mm rule are a big part of the cost on raised decks.
6. The small stuff that adds up
- Joist tape on top of joists and beams
- Flashing tape and flashing for the ledger
- Structural screws or bolts for the ledger
- End-grain preserver for cut ends
- Stain or oil for the first coat
Waste
10% for boards and framing is typical. Go higher for diagonal boards, picture-frame borders or lots of angles.
Use the deck framing, deck board and baluster calculators, adding each to the same job, to build the whole quote in minutes.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check the Building Regulations and Building Control for your project.