Do I need a permit to build a deck?

Almost always, yes, for an attached deck or any deck more than a step or two off the ground. The permit process reviews your footings, ledger connection, framing, and railing — the exact things that fail on unpermitted decks. Freestanding ground-level platforms below a size threshold are sometimes exempt, but check with your local building department before you dig. Unpermitted decks also cause problems when you sell the house.

How deep do deck footings need to be?

Below the frost line for your area, which ranges from about 12 inches in the warm South to 48 inches or more in the northern states. Footings above the frost line heave up and down with freeze-thaw and rack the whole deck. Diameter depends on the load each footing carries and the soil, commonly 10–16 inches — your span and load determine it, and the inspection will check it.

Why do decks collapse?

The overwhelming majority of deck collapses are ledger failures — the board attaching the deck to the house pulls away because it was nailed instead of bolted, or wasn't flashed and rotted the house rim behind it. Get the ledger right (structural screws or through-bolts at the required spacing, proper flashing) and you've addressed the single biggest risk in deck building.

Should I use composite or wood decking?

Composite costs more up front (roughly 2–3x the board price) but needs no staining or sealing and lasts 25+ years, so it often wins on lifetime cost and weekends saved. Pressure-treated lumber is cheapest to buy but needs periodic cleaning and sealing and moves more with the weather. Cedar and hardwoods sit in between on cost and look. The framing underneath is the same either way — only the deck boards and fasteners change.

How to Build a Deck — Step-by-Step Guide

A seven-step guide covering permits, footings below the frost line, posts set in concrete, a properly flashed ledger, beam-and-joist framing, decking, and code railing — the structure-first sequence that keeps a deck safe for decades.

A deck is a structure, not a project you eyeball — it holds people in the air, and the two things that actually put people at risk, the ledger connection and the footings, are both buried under the pretty part and invisible once it's built. That is exactly why decks get permitted and inspected. Build it in the right order, get the ledger and footings right, and the rest is careful carpentry. Start by sizing materials: count deck boards with the Deck Board Calculator and the footing concrete with the Concrete Calculator before you order anything.

Tools & Materials

Tools: post-hole digger or a rented power auger, circular saw, cordless drill and impact driver, 4-foot and torpedo levels, framing and speed squares, batter boards and mason's line for layout, a socket wrench for ledger bolts, and a wheelbarrow or mixing tub for concrete. A deck is a two-person job for the framing and decking — line up a helper.

Materials (size with the calculators below):

Decking boards (composite or lumber) — count with the Deck Board Calculator
Concrete for the footings — size with the Concrete Calculator
Pressure-treated posts — the same set-in-concrete method as fence posts; the Fence Post Calculator sizes the concrete per hole
Pressure-treated beams and joists, sized to your spans; galvanized joist hangers and post bases
Ledger board, structural ledger screws or through-bolts, Z-flashing, and self-adhesive flashing tape
Hidden fasteners or deck screws; railing posts, rails, and balusters

Step 1: Plan the Deck and Pull a Permit

Draw the deck to scale — dimensions, joist and beam spans, footing locations, and railing. Then pull a permit: most attached decks require one plus inspections of the footings and framing, and those inspections check the exact connections that fail on DIY decks. Confirm two numbers before you finalize anything: your local frost depth (it sets how deep footings go) and the span tables for your joist and beam sizes (they set spacing). Planning around the code up front is far cheaper than tearing out failed inspections.

Step 2: Lay Out and Dig the Footings

Set the footing grid with batter boards and mason's line, and square the corners with the 3-4-5 method (a corner is square when a 3-foot and 4-foot leg make a 5-foot diagonal). Dig each footing below the frost line — anywhere from 12 inches in the South to 48+ in the North — and to the diameter your load and soil call for. A footing that stops short of the frost line heaves every winter and racks the whole deck. Call 811 for utility locates before you dig.

Step 3: Pour Footings and Set Posts

Pour the concrete footings, embed galvanized post bases, and let them cure before you load them. Size the concrete per hole with the Concrete Calculator (the same math the Fence Post Calculator uses for posts set in concrete). Set pressure-treated posts on the bases, never in direct soil contact— a post standing on a metal base sheds water and lasts; a post buried in dirt wicks moisture and rots from the bottom. Plumb each post and brace it until the framing locks it in.

Step 4: Flash and Attach the Ledger

The ledger is the most safety-critical connection on the deck. Bolt it to the house rim joist with structural screws or through-bolts at the required spacing — never nails. Then flash it: self-adhesive flashing tape on the wall behind the ledger and Z-flashing over the top, so water sheds out and away instead of running behind the board. A ledger that isn't flashed rots the house rim joist invisibly for years and then lets go — it is the number-one cause of deck collapses. This is the step to slow down on.

Step 5: Frame the Beams and Joists

Set the beam on the posts and fasten it, then hang joists from the ledger with galvanized joist hangers at 16 inches on center (or whatever your span table specifies), running out to the beam and rim joist. Sight down each joist and install it crown up so the deck settles flat, not into a valley. Check the entire frame for square and level before a single deck board goes on — every error here telegraphs straight into the finished surface.

Step 6: Install the Decking

Lay decking perpendicular to the joists, starting at the house and working outward, with a consistent gap between boards for drainage and expansion (follow the decking manufacturer's spec — composite and lumber differ). Fasten with hidden clips or deck screws, keeping the lines dead straight; a spacing tool between boards keeps the gaps uniform. Let the boards run long past the edge and snap a chalk line to trim the whole side flush at the end — it's faster and cleaner than cutting each board to length. Count your boards with the Deck Board Calculator so the last row isn't a sliver.

Step 7: Build the Railing

Install railing posts, rails, and balusters to code — typically 36-inch residential height with balusters spaced so a 4-inch sphere can't pass through. Railing is a life-safety element and a required part of the final inspection, so fasten the posts to the framing properly (blocked and bolted, not lag-screwed into a single rim). Add stair rails, any deck lighting, and then schedule the final inspection before you put furniture on it. The sign-off is what makes the deck legal and insurable.

Common Mistakes

Nailed or unflashed ledger. The single deadliest deck mistake. Bolt it, flash it, or don't stand on it.
Footings above the frost line. They heave with freeze-thaw and rack the whole structure. Go below the frost line, every footing.
Posts buried in soil. Direct soil contact rots posts from the bottom. Set them on galvanized bases above grade.
Skipping the permit. An unpermitted deck fails the exact connections inspections catch, and it becomes a problem at resale. Permit and inspect.
No board spacing. Decking butted tight has nowhere to drain or expand and cups, warps, and traps water. Leave the manufacturer's gap.

Cost: DIY vs. Contractor

DIY materials for a typical 12 × 16 ft attached deck (192 sq ft) run roughly $2,500–5,500 depending on decking: pressure-treated lumber lands near the bottom, composite near the top, with framing, footings, hardware, and railing on top of the boards. Decking is the biggest single line item, so size it precisely with the Deck Board Calculator. For how AceCalc sources the underlying material costs and why they vary by region, see our pricing methodology page.

Contractor-installed decks commonly run $30–60 per square foot — roughly $6,000–12,000 for the same 192 sq ft — more for composite, elevated decks needing tall posts and bracing, or complex shapes with stairs and multiple levels. Because the ledger and footings are safety-critical and inspected, many DIYers who take on the framing still have a pro verify the ledger connection. If a deck sits more than a story up, hiring out is the sound call.

Related Calculators

Deck Board Calculator — Count decking boards by area, board size, and gap
Concrete Calculator — Size footing concrete by hole diameter and depth
Fence Post Calculator — Size concrete per post for posts set in concrete
Pricing Methodology — How AceCalc sources material costs and why they vary by region

Written by Daniel McCarney — AceCalc