20×20 Deck Cost
A 20×20 square deck (400 sqft) is a favorite for outdoor kitchens + dining + lounge — the smallest size where 3 zones comfortably coexist. The calculator below is pre-loaded with these dimensions — change the state, finish tier, or scope to recalculate live.
How much does a 20×20 deck cost?
- PT installed
- $10,000–$16,000
- Mid composite
- $20,000–$32,000
- Per sqft
- $25–$140
How much a 20×20 deck costs by material
A 20×20 deck is 400 sq ft. In pressure-treated wood that runs about $10,000–$16,000 installed — the cheapest way to get a deck this size, though you'll re-stain it every couple of years. Step up to mid-range composite (Trex Enhance, Fiberon Good Life) and the same 400 sq ft is $20,000–$32,000: roughly double the upfront, near-zero maintenance, and usually the lower 25-year cost.
Premium composite or PVC (Trex Transcend, TimberTech AZEK) lands around $30,000–$44,000, and tropical hardwood like Ipe tops out near $36,000–$56,000. These are installed (material + labor) for a simple rectangle — an L-shape adds ~10%, a wraparound ~22%, and a tall or hard-to-access deck up to 40%. Regionally, the South runs about 8% under these national figures and the West Coast about 28% over.
Cost per square foot
Installed, that's about $25–$40/sq ft in pressure-treated, $50–$80/sq ft in mid-range composite, and up to $90–$140/sq ft in tropical hardwood.
Materials vs. labor
Labor runs $10–$20/sq ft — about $4,000–$8,000 on this 400 sq ft deck: roughly half a pressure-treated build, about a third of a composite one.
The calculator below itemizes a complete project — framing, footings, railing, stairs, permit, and contingency — so its total runs higher than the surface-and-labor bands above for the same size.
What fits on a 20×20 deck?
At 400 sq ft, a 20×20 deck comfortably seats about 22 for dining, or fits a sectional, a grill, and a clear walkway. Above 200 sq ft it needs a building permit in most US jurisdictions (IRC 2021 R105).
Does a 20×20 deck add home value?
A new deck recovers roughly 65–75% of its cost at resale, per Remodeling's Cost vs. Value report. On a 20×20 that's about $6,500–$24,000 back into home value — wood tends to recover the most, composite a bit less but with far lower upkeep.
Sources: IRC 2021 (structural + permit thresholds), RSMeans 2026-Q1 residential labor indices, HomeAdvisor / Angi 2026 material pricing, and Remodeling Cost vs. Value.
Dimensions
Plan-view length × width.
IRC R312 requires a 36″ guardrail above 30″.
400 sq ft · Mid composite · 1.22× labor · 1.10× complexity
Project advisories · IRC 2021
Guardrail included (deck 36″ off grade)
IRC R312IRC R312 mandates a 36″ guardrail on open edges when deck height exceeds 30″. 60 lf priced at Mid composite tier.
Building permit included in budget
IRC R105Northeast typical permit fee is in the budget. Most jurisdictions require a permit for decks > 200 sqft, > 30″ above grade, or attached to the house.
Hidden-fastener install premium baked in
Manufacturer specsMid composite uses hidden-fastener clip systems (Cortex / CamoClip / Trex Universal) — labor takes 25–30% longer than face-screwing PT. Already inside the tier's installed $/sqft band.
Cost breakdown
| Cost component | Share | Amount |
|---|---|---|
| Materials | 29% | $15,840 |
| Labor | 44% | $23,619 |
| Add-ons | 17% | $9,296 |
| Soft costs | 1% | $474 |
| Contingency | 9% | $4,923 |
| Total (high est.) | 100% | $54,152 |
Share of the high estimate. Switch tiers below to repaint the split.
National-median pricing (2026-Q1). Local prices vary ±15%. Materials line uses Mid composite tier; switch tiers to repaint the budget. Includes 10% contingency reserve on the high estimate.
Visualize your deck
Photoreal 3D · plan view · framing breakdown. Color matches your tier selection.
Project all-in
Same dimensions, different tier
tap to switchDIY savings
- Materials only: $15,840
- Estimated hours: 600 hr
- Skill required: advanced
Finance estimate
- Principal: $54,153
- Total interest: $11,713
- Estimate only — shop 3+ lenders.
Need exact board counts?
The Deck Material Calculator gives you a permit-ready bill of materials — every joist, hanger, fastener, and footing — validated against IRC 2021 span tables.
Estimates use 2026-Q1 national-median pricing (Home Advisor, Angi, RSMeans). Expect ±15% variance vs your local market. Always get 3 contractor bids before signing. This calculator is not a substitute for a licensed inspector or structural engineer.
Estimated material takeoff — 20×20
The framing and decking a 20×20 (400 sqft) deck needs — board, joist, beam, post, footing, and railing quantities computed from the dimensions at 16″ joist spacing with a 10% waste factor.
Estimated quantities for planning and budgeting — round up when ordering. Beam sizing, post spacing, and footing depth must follow your local code and a stamped plan (frost line, soil, and snow load vary by region per IRC 2021 / AWC DCA-6).
What the 20×20 footprint means for framing
At 20′ deep, this footprint is past a practical single joist span — which is why the takeoff above frames it on 3 beam lines: each joist bay runs about 6′8″, inside the 2×6 SPF @ 16″ o.c. limit of 7′11″ in the IRC 2021 R507.6 span table. The extra beam lines are also what moves the foundation bill on a deck this size: 12 posts on 12 footings, versus 4–6 on a small single-beam deck. Check your exact joist setup with the joist span calculator and size the beams with the beam span calculator.
Sizing up or down? See how much a 16×24 deck costs (384 sqft) or how much a 20×24 deck costs (480 sqft).
FAQ — 20×20 deck
How much does a 20×20 deck cost?
A 20×20 deck (400 sqft) costs $10,000-$16,000 for budget pressure-treated construction, $20,000-$32,000 for mid-range composite, and $36,000-$56,000 for premium composite or tropical hardwood. Those bands price a simple rectangle — decking surface plus labor — at national-average rates built from HomeAdvisor / Angi 2026 material pricing over RSMeans 2026-Q1 residential labor indices, so multiply by roughly 0.92× in the South or 1.28× on the West Coast. Labor itself is $10-$20/sqft ($4,000-$8,000 on this footprint) of whichever band you pick. The caveat: a full permitted project also carries framing extras, footings dug to your local frost depth (IRC R403.1.4), guardrail once the surface sits over 30″ (IRC R312), the permit fee, and a contingency — which is why the calculator's all-in total runs above these surface bands for the same 20×20 footprint.
How much is labor for a 20×20 deck?
Deck labor typically runs $10–$20 per square foot, so the build labor on a 20×20 deck (400 sqft) is roughly $4,000–$8,000. Labor is about half the installed cost of a pressure-treated deck and closer to a third of a composite one, since the composite boards themselves cost more per foot. Old-deck tear-out, tall framing, or hard site access push labor toward the top of that range.
How much does a 20×20 composite deck cost?
A 20×20 composite deck (400 sqft) runs about $20,000–$32,000 installed in mid-range boards (Trex Enhance, Fiberon Good Life) and $30,000–$44,000 in premium composite or PVC (Trex Transcend, TimberTech AZEK). That's roughly double a pressure-treated build up front, but with wash-only maintenance it is usually the lower 25-year cost of ownership.
Is it cheaper to build a 20×20 deck yourself?
Yes — labor is the single biggest line item, so a DIY 20×20 build saves roughly $4,000–$8,000 (the labor portion), bringing a pressure-treated deck down to about $5,500–$9,600 in materials. That labor band is the RSMeans 2026-Q1 residential rate of $10-$20 per square foot — about half the installed cost of a pressure-treated deck and closer to a third of a composite one, where the boards themselves carry more of the budget. Before committing, know the two places DIY decks most often fail inspection: under-depth footings (they must reach below your local frost line per IRC R403.1.4) and missing guards on surfaces over 30″ above grade (IRC R312). Budget a permit, an inspection visit or two, and several weekend days of work — and if the deck ledger-attaches to the house, consider hiring out just that connection, since the ledger is the most common structural failure point on DIY builds.
How many boards do I need for a 20×20 deck?
Running 5/4×6 or 1×6 deck boards (5.5″ face, 1/8″ install gap) parallel to the long dimension: rows = ceil(20 × 12 ÷ 5.625) = 43 rows. Total LF = 43 × 20 × 1.07 (7% waste, parallel pattern) ≈ 921 LF. Round up to 20-ft stock for typical 47 boards.
How long does it take to build a 20×20 deck?
For a contractor crew (2-3 people), a 20×20 deck takes 4-7 days depending on complexity, including framing + decking + railing + inspection wait. DIY single-person build: 60-75 weekend days for composite, less for pressure-treated.
Do I need a permit for a 20×20 deck?
In most US jurisdictions, yes. IRC 2021 R105 requires a permit for any deck above 30″ off grade, attached to the house, or larger than 200 sqft. A 20×20 deck (400 sqft) exceeds the 200-sqft threshold and definitely requires a permit.
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