20×20 Deck Cost

Why this page exists

Whole-backyard pricing

Installed ranges for 400 sq ft in pressure-treated, composite, and PVC — a build that behaves like a small addition, priced like one.

Multi-zone by default

Dining, lounge, and grill each get a real station at 20×20 — the question shifts from what fits to how the zones talk to each other.

Where big ideas enter

Levels, pergolas, built-in benches, and hot-tub bays all start at this scale. We flag which ones move the budget 15–30% before they charm you.

Too big to guess at

At 400 sq ft a mistake is expensive and permanent. Render the deck on a photo of your actual backyard — with your material — before plans are drawn.

How it works

1. Upload a backyard photo. Use any phone photo of the build site. No measurements, no CAD file.
2. Mark the deck area. Drag to outline where the deck goes. Add stairs or a railing line if you want them.
3. Choose material and design. Pick composite, PVC, cedar, or pressure-treated. Compare looks on the same photo.
4. Generate the render and share. Get a photorealistic render in seconds. Send it to the homeowner or attach it to a proposal.

20×20 Deck Cost

Answer first: a 20×20 (400 sq ft) deck runs about $10,000 – $16,000 installed in pressure-treated pine, $18,000 – $28,000 in composite, or $24,000 – $36,000 in PVC. At this scale the deck is the backyard’s main event, and the build behaves accordingly: more beam line, more footings, and design decisions — levels, cover, built-ins — that swing the price more than the material does.

Installed cost by material

What the build takes

What moves the price

• Structure scales in the ground. Twenty feet of beam wants 3–4 posts, and the 20 ft joist span all but guarantees a mid-beam with its own row of footings. Excavation and concrete become visible line items at 400 sq ft.
• Levels and features. Multi-level layouts, a covered section, or a built-in bench run add 15–30% each. They’re also what makes a 400 sq ft deck feel designed rather than vast — pick one deliberately instead of three impulsively.
• Furnishing reality. A deck this size unfurnished looks like a stage. Budget honestly for the furniture program — or size down to 16×20 and spend the difference furnishing it well.
• Maintenance at scale. Staining 400 sq ft of wood every other year is a multi-day project or a recurring bill. This is the size where composite’s soap-and-water maintenance makes its strongest lifetime case.

Ranges are 2026 North American installed averages (materials plus contractor labor) for a single-level build. Levels, covers, and built-ins are additive — budget each at 15–30%.

Common questions

Is a 20x20 deck too big?

Only relative to the yard and the life on it. As a rule of thumb, a deck reads well under about a third of the visible backyard; past that it reads as paving. This is precisely what a render on your own photo answers in seconds — 400 sq ft looks radically different against different houses.

Should a 20x20 deck be multi-level?

If the grade drops, yes — levels turn a tall scary rail line into two friendly ones and give the zones architecture. On flat grade it’s an aesthetic (and 15–30% budget) choice. Render the single-level version first; add the level only if the flat render looks like a parking lot.

What does a 20x20 deck cost with a covered section?

A roofed section over a quarter to a third of the deck typically adds 20–30% to the project — posts, beams, roofing, and often electrical. Pergolas without roofing land cheaper. Both read beautifully in renders, which is the cheap place to try them.

Can a 20x20 deck hold a hot tub?

This is the first size where a tub integrates without eating the deck — but the structural rule is unchanged: 3,000–5,000+ lbs concentrated means engineered framing and dedicated footings under the tub bay, planned before framing. Many builders still prefer a grade-level pad with the deck wrapping it.