20×20 Deck Cost

Why this page exists

Whole-backyard pricing

Installed ranges for 400 sq ft in pressure-treated, composite, and PVC, for a build that behaves like a small addition and is 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. Have each feature priced separately before including it in the design.

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. Show us your space. Upload a clear backyard photo. Tell us where the deck should go and what you want to change.
2. Check your brief. Review your photo and choices, then buy your Deck Ideas Pack for US$19. No subscription.
3. Compare and refine. Explore three concepts. Use your two remaining refinements to develop a favorite.
4. Take the next step. Download clean images and compare before and after. Share your ideas with family or a builder.

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 4–5 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 and built-in benches require separate design and pricing. They’re also what makes a 400 sq ft deck feel designed rather than vast, so 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.

U.S. planning allowances in USD for a simple, single-level deck, including ordinary materials and contractor labor. These are PaperPlan editorial assumptions, not surveyed averages or a local quote. Stairs, railing and elevated or complex framing need separate quotes; see the scope and sources below.

Fastener benchmark: Trex Hideaway Universal clip coverage. Check the fastener system and joist spacing for your chosen boards.

Cost assumptions and sources

U.S. planning allowances in USD for a simple, single-level deck, including ordinary materials and contractor labor. These are PaperPlan editorial assumptions, not surveyed averages or a local quote.

• Pressure-treated: $25 – $40 / sq ft installed (USD)
• Composite: $45 – $70 / sq ft installed (USD)
• PVC: $60 – $90 / sq ft installed (USD)

Multiply deck area (width × length in feet) by the selected installed rate, then round each end of the range to the nearest $100.

Demolition, permits and engineering, taxes, stairs, railing, roofs, unusual foundations and difficult site access need separate quotes. Location, product selection and labor can put a real bid outside these ranges. Canadian projects need local CAD pricing.

The manufacturer sources below explain scope and cost drivers; they do not validate PaperPlan’s exact installed-rate bands. Supplier material estimates should not be compared directly with an installed project budget.

• Trex: deck material cost calculator: Estimates materials and explicitly excludes labor; prices vary with location, season and design.
• TimberTech: understanding deck costs: Separates decking, railing, labor and substructure, and explains the impact of site and project features.

Sources and assumptions reviewed 2026-09-09. Confirm the scope and current price with local contractors before budgeting a build.

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 can answer, since 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, weigh the appearance against separately quoted framing, stairs and railing costs. 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 covered section needs a separate design and quote for supports, roofing, connections and any electrical work. A pergola has a different scope. Neither is included in the base deck platform allowance.

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.