A deck looks simple, but its material list has more lines than most small jobs. Work from the ground up, and price each layer before moving to the next, so nothing is missed.
1. Layout and design decisions
Before counting anything, settle the basics: deck size and height, whether it's attached to the house with a ledger or freestanding, joist direction and spacing, beam positions, stairs and railings. Height matters most. A deck more than about 24" (600 mm) above the ground usually needs a guard, at least 36" (900 mm) high, or 42" (1070 mm) more than 5' 11" (1.8 m) up, and taller decks need bracing and bigger footings. Most Canadian municipalities require a building permit for a deck more than about 24" (600 mm) above the ground, and some also when it is attached to the house or over a set area, so check before you quote.
2. Footings and posts
Lay out the beam lines and post spacing first. Every post needs a footing: a poured pier in a form tube (Sonotube), sized for the load and set below frost depth, often 4 ft (1.2 m) in much of Canada and deeper on the Prairies. Helical piles are a popular alternative. Count footings, work out the concrete per footing, and add post bases or anchors. The pier calculator gives the concrete for any number of footings.
3. 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. Beams are usually two or three plies of joist-size lumber, so count those pieces too.
Joist and beam sizes and spans must come from the span tables in your provincial building code (Part 9), or an engineer. A calculator can count parts, but it can't size them. Composite decking often needs closer joist spacing, especially for diagonal boards.
4. Deck boards
Work in rows, not area. Rows = (deck width + gap) ÷ (board width + gap). Then choose a board length that suits the deck: a 16 ft deck with 16 ft boards wastes almost nothing, while a slightly longer deck forces joins in every row. Where joins are needed, stagger them and land them over doubled joists or blocking. Picture-frame borders and breaker boards add extra boards and extra framing, so count them separately.
5. Fasteners
Two screws per board at every joist. On a 16 × 12 ft deck that's around 650 screws. Hidden clip systems need one clip per joist crossing. Use stainless or coated fasteners rated for treated lumber, and the system made for composite boards.
6. Stairs and railings
Count stringers (one every 16" or so), treads and risers from the stair calculator. Railing posts, top and bottom rails, and balusters spaced under the 4-inch rule are a big part of the cost on raised decks. Railing posts must be through-bolted or fixed with approved hardware to resist the guard loads. A post screwed into the rim joist alone isn't enough.
7. The small stuff that adds up
- Joist tape on top of joists and beams
- Flashing and flashing tape for the ledger, so water can't get behind it
- Structural screws or bolts for the ledger
- End-grain preserver for cut ends of treated lumber
- Weed membrane and gravel under low decks
- Stain or oil for the first coat, if included
Waste
10% for boards and framing is typical. Go higher for diagonal boards, picture-frame borders, angled corners or curved edges.
A worked example
A 16 × 12 ft attached deck, joists 16" OC spanning 12 ft: 13 joists plus rims, a ledger and one doubled beam on three posts. Three 12" × 48" piers (about 0.27 m³, or about 21 bags of 30 kg mix). Boards: 26 rows of 5½" board at 16 ft, 29 boards with waste. Screws: about 680, or two boxes of 350.
Use the deck framing, deck board and baluster calculators, adding each to the same job, to build the whole quote in minutes.
Common questions
Composite or wood?
Composite costs more up front but needs no staining and lasts longer. Wood is cheaper and easier to work, but needs regular maintenance. Price both if the client is unsure.
How long does a deck take to build?
A simple ground-level deck of this size is often two to four days for a small crew. Raised decks with stairs and railings take longer.
This guide is general information for estimating. It is not engineering, legal or tax advice. Check local codes and your inspector for your project.