Installed, about $25 to $40 a square foot for pressure-treated, $30 to $50 for cedar, and $35 to $55 for mid-grade composite. On a 16 by 20 that works out to roughly $6,000 to $15,500 in pressure-treated and $13,000 to $24,000 in composite.
Now the part that costs contractors money. Those per-square-foot figures price the deck surface, and the surface is not where deck estimates go wrong. The footings are. The same six holes that go 12 inches down in Savannah go 48 inches down in Boston, and that difference alone is $300 to $800 before anyone has picked a board. Quote a deck off square footage and you have priced the visible half of the job.
What does a deck cost per square foot?
Installed, including labor and the structure underneath:
| Material | Per sq ft installed | 16x20 deck (320 sq ft) |
|---|---|---|
| Pressure-treated pine | $25 - $40 | $6,000 - $15,500 |
| Cedar | $30 - $50 | $9,600 - $16,000 |
| Composite, entry to mid | $35 - $55 | $13,000 - $24,000 |
| PVC | $50 - $85 | $16,000 - $27,000 |
Those ranges are wide for a reason, and the reason is not the decking. Within any single material, what moves the number is height off grade, footing depth, and whether a truck can get near the site. A ground-level deck on flat ground in sandy soil and a second-story deck over a slope are the same square footage and nothing like the same job.
Why do deck estimates get lost in the substructure?
Because it is the part you cannot see when you are standing in the yard giving a number.
Footings follow the frost line, and the frost line is local. IRC R403.1.4.1 requires footings to bear on undisturbed soil below the frost line. In practice that runs from about 12 inches in the deep south to 48 inches or more in northern jurisdictions - Maryland sits around 30, central and northern Iowa require 42. Every extra foot is spoil to dig, haul and dispose of, and more concrete per hole.
The ledger is the line nobody bills properly. A ledger has to anchor through the sheathing into the band joist, with flashing. It cannot go into siding and it cannot go into studs. Improperly installed ledgers are the most common cause of deck failure, which means the correct method is also the slow method - pulling siding, checking what is actually behind it, flashing it properly. If your estimate has a line for framing and no line for opening up the wall, you priced the fast version and you will build the right one.
Then the things nobody writes down. Spoil removal from eight footing holes. Concrete delivery or 40 bags carried around the back. Stair stringers, which cost more per step than any square foot of decking. Railing, priced per linear foot and easy to underestimate on an L-shaped deck.
Do you need a permit for a deck?
Almost always, and it is worth saying so in the estimate rather than discovering it later.
Most jurisdictions require a permit when the deck is over 30 inches above grade, attached to the house, or larger than roughly 200 square feet. That covers nearly every deck someone hires a contractor for. Free-standing ground-level platforms are the usual exemption.
The fee is the small part. The schedule is the expensive part: footing inspections have to happen after the holes are dug and before concrete goes in, so an inspector who cannot come until Thursday is a crew standing around, or open holes taking on rain. Price the calendar, not just the permit.
Is composite worth it over pressure-treated?
For the homeowner, sometimes. For your estimate, it changes less than people expect.
Wood runs about 27% less up front. Against that, a wood deck costs $300 to $800 a year in staining, sealing and replacing warped boards - $7,500 to $20,000 across 25 years. Whether composite wins depends entirely on whether the owner is the sort of person who actually re-stains on schedule, and most are not.
What matters to you is that composite does not change the framing. Same footings, same ledger, same joists - and on many composite systems the joist spacing tightens to 12 inches on center for diagonal runs, which is more lumber and more labor, not less. Contractors who quote composite as a straight material swap lose the extra framing.
What this misses
Every range here is national. Labor rates in a metro can run double a rural county, and these figures blend both. Use them to sanity-check your own numbers, not to set them.
Demolition of an existing deck is not in any of it. Tear-out, disposal and repairing whatever the old ledger did to the wall is its own scope, and the wall damage is not knowable until the old deck is off.
Neither is anything below the surface. Rock, a high water table, tree roots, or a buried utility line will change footing costs in a way no per-square-foot table can predict. That is an exclusion to write down, not a risk to absorb quietly.
The pattern with decks is the same one every trade runs into: the estimate covers what you can see, and the money goes on what you cannot. Getting every line written down is half of it, and getting the markup right is the other half. BidWalk builds the line items while you walk the job, which is the point at which you are actually looking at the slope, the siding and the access - and it works the same way for general contractors pricing a deck as part of a larger scope.
