A 20×20 (400 sqft) deck costs $21,591–$34,988 installed in 2026, depending on material and state. The lower end is pressure-treated pine in an average-labor state; the upper end is premium hardwood in a high-labor metro. Most homeowners picking a mid-tier composite land at $29,011.
What a 20×20 deck fits
At 400 square feet, a 20×20 deck comfortably holds a large dining set, full lounge, a grill area, and room for a hot tub or fire table.
For perspective: a 4-person round dining table needs about 80 sqft clear space. A standard outdoor couch plus coffee table needs 50–70 sqft. A built-in grill station needs 20–30 sqft plus clearance. Add 6 feet of circulation paths on active sides.
Cost by material — 20×20 deck (US average)
Mid-height (4–6 ft) build, composite balusters, one stair run, permit, 8% contingency. Baseline uses a national average labor rate.
Pressure-Treated Pine
15–20 yrs · Stain every 2–3 yrs
$54/sqft
$21,591
Cedar / Redwood
20–25 yrs · Seal every 2–3 yrs
$61/sqft
$24,434
Composite (Trex, TimberTech)
25–30 yrs · Rinse yearly
$73/sqft
$29,011
PVC / Cellular
30+ yrs · Rinse yearly
$81/sqft
$32,545
Ipe / Cumaru Hardwood
40+ yrs · Oil annually (optional)
$87/sqft
$34,988
20×20 composite deck cost by state
Same 400 sqft composite build, state-by-state. Metro labor can shift these another ±5–15%.
A 20×20 (400 sqft) deck costs $21,591–$34,988 installed in 2026. Pressure-treated pine is the cheapest at ~$54/sqft; composite (Trex, TimberTech) runs ~$73/sqft; premium hardwood (ipe) runs up to ~$87/sqft. Labor is 40–55% of the total.
Can I build a 20×20 deck myself?+
Possibly, but a 20×20 deck at 400 sqft is on the larger side for DIY. Framing, ledger attachment, and stair construction are code-critical steps many jurisdictions require to be inspected. Expect to save 40–55% on labor if you're capable; add 10–15% to material budget for wasted cuts and mistakes.
Do I need a permit for a 20×20 deck?+
Yes in nearly all US jurisdictions. Decks over 30 inches off the ground or attached to the house require a building permit and at least a footing and final inspection. Permit costs typically run $100–$500; a 400 sqft deck lands in the middle of that range.
How long does a 20×20 deck take to build?+
3–4 weeks of active build time for a crew of 2–3 once permits are approved. Permit approval itself adds 2–6 weeks upfront. Composite and PVC installs run slightly faster than wood; multi-level or wraparound designs add another 1–2 weeks.
What shape should a 20×20 deck be?+
Rectangle is the cheapest and fastest to build. L-shape adds 10–15% cost but wraps around corners well. For footprints where 20×20 is the bounding box, check what fits inside — an L-shape or wraparound at a 20×20 envelope will have less actual deck surface than a solid 400 sqft rectangle.
Price your own 20×20 deck
Use the calculator to adjust material, shape, height, railing, and features for your state.