20 × 20 deck cost & materials
Short answer
A 20 × 20 ft deck is 400 square feet. In composite it costs about $12,000–$24,000 installed and needs roughly 61 deck boards and 16 joists.
Area
400 sq ft
Composite cost
$12,000–$24,000
Deck boards
61
Joists
16
What a 20 × 20 deck costs
A 20 × 20-foot deck is 400 square feet. In low-maintenance composite it runs about $12,000–$24,000 installed and needs roughly 61 deck boards on 16 joists. Board material is only part of it — the framing, footings, and labor underneath are the same work whatever decking you choose.
Because the substructure is fixed, moving to a cheaper board saves less than the per-square-foot gap suggests, and a bigger deck scales the framing and footing count too. Height off the ground is the other big lever: a raised 20 × 20 deck adds posts, more footings, and usually a railing and stairs.
Add permits and inspection, local labor rates, and any features — built-in benches, lighting, a pergola — and your 20 × 20 deck can swing well above the base composite figure. Compare bids itemized into framing, decking, and railing so a low board price isn't hiding pricier labor.
What affects your price
| Factor | Effect on cost |
|---|---|
| Deck area | 20 × 20 ft = 400 sq ft; cost scales per square foot |
| Decking material | Pressure-treated to PVC roughly doubles the per-sq-ft board price |
| Height & stairs | A raised deck adds posts, footings, railing, and stairs |
| Substructure | Footings and ~16 joists are the same under any decking |
| Features | Built-in benches, lighting, and pergolas add cost on top of the base deck |
| Permits & region | A deck permit, inspection, and local labor rates change the total |
20 × 20 deck cost by material
| Material | Installed | Lifespan | Upkeep |
|---|---|---|---|
| Pressure-treated wood | $6,000–$10,000 | 10–15 yr | Clean + re-stain every 1–2 yr |
| Cedar / redwood | $8,000–$15,200 | 15–20 yr | Clean + seal every 2–3 yr |
| Composite (Trex-style) | $12,000–$24,000 | 25–30 yr | Wash occasionally; no staining |
| PVC / vinyl | $14,000–$28,000 | 30+ yr | Wash occasionally; no staining |
Change size or material
Open the deck calculatorOther sizes
Frequently asked questions
How many deck boards for a 20 × 20 deck?
About 61 16-ft boards (5½" wide) for 400 sq ft, including 10% waste. Longer boards mean fewer pieces but more offcuts.
How much does a 20 × 20 deck cost?
A composite 20 × 20 deck costs about $12,000–$24,000 installed. Pressure-treated wood is cheaper; PVC costs more.
How many joists for a 20 × 20 deck?
About 16 joists at 16" on center, plus 8 footings. Enter your exact size and spacing in the calculator.