How to build a deck

Overview

A deck carries real loads, so the structure matters more than the finish. The load path is simple: decking to joists to beams to posts to concrete footings in the ground. Get the footings below frost, flash the ledger, and follow local span tables, and the rest is straightforward framing.

Step 1: Plan and apply for permits

Before you buy lumber, confirm the deck size, footing depth, joist span and spacing, and guardrail height with your local building office. Most decks require a permit and an inspection, and local span tables govern how far joists and beams can reach. Deck collapses almost always trace back to a footing, ledger, or fastener shortcut.

Step 2: Set the footings

Dig holes at each post location and pour concrete footings below the frost line — frost heave will lift a shallow footing and rack the whole deck. Use the concrete calculator to estimate bags. Keep the tops of all footings level with each other so posts come out even.

Step 3: Attach the ledger

For a deck attached to the house, bolt a pressure-treated ledger into the house's rim joist — never just into siding — and install flashing above it so water drains over the top and can't get behind the connection. Missing or botched ledger flashing is one of the most common causes of deck failure and rot.

Step 4: Set posts and beams

Set each post in a galvanized base on its footing, plumb it in both directions, and brace it. Run beams across the posts with hangers or bolted connections, sized to your span from the local span tables.

Step 5: Install the joists

Hang the joists on the ledger and beam with joist hangers at the spacing your span calls for — 16 in is common. Tape the top of each joist with flashing tape before decking so moisture can't sit on the wood. Estimate joists and decking with the deck calculator.

Step 6: Lay the decking

Lay decking across the joists with a consistent gap for drainage and expansion, screwing into every joist — or use hidden fasteners if the decking allows. Keep cut ends sealed, and follow the manufacturer's spacing for composite boards.

Step 7: Add railings, stairs, and finish

Install railings to code — most jurisdictions require about 36 in tall with balusters spaced so a 4-in sphere can't pass. Build stair stringers with correct riser and tread ratios using the stairs calculator. Finish with a sealer or stain designed for decking, applied to all cut ends.

Cost and time

• Materials: roughly $15–$30 per square foot for a treated-lumber deck.
• Time: 2–5 days with two people, plus permit wait time.
• Tools: post-hole digger, circular saw, level, drill, joist hanger nailer, tape measure.

Safety and permitting notes

• Most decks need a permit and a framing inspection — schedule before you cover the structure.
• Set footings below the frost line; shallow footings heave and rack the deck.
• Flash the ledger properly — this is where decks rot and fail first.
• Follow local span tables for joists, beams, and posts.
• Guardrail height and baluster spacing are code requirements, not suggestions.