360 sqft · 18×20 ft

18×20 Deck Cost

An 18×20 deck (360 sqft) is upper-mid — generous for entertaining without fully committing to wraparound complexity. The calculator below is pre-loaded with these dimensions — change the state, finish tier, or scope to recalculate live.

Get 2–3 free quotes

360 sqft76 ft perimeter5 finish tiersAll 50 states2026-Q1 pricing

18×20·Footprint

360·Sq ft

76·Perimeter ft

<2s·Live calc

How much a 18×20 deck costs by material

Material$/sqft installed18×20 total (360 sqft)

Pressure-treated wood

Cheapest to build; re-stain every ~2 years.

$25–$40$9,000–$14,400

Cedar / premium PT

Warmer look than PT; ages to silver, re-stain every ~3 years.

$35–$55$12,600–$19,800

Composite — mid-range

Trex Enhance, Fiberon Good Life. Wash-only; best 25-year value for most.

$50–$80$18,000–$28,800

Composite / PVC — premium

Trex Transcend, TimberTech AZEK. Longest warranty, coolest underfoot.

$75–$110$27,000–$39,600

Tropical hardwood (Ipe)

Ipe, Cumaru. Stunning and dense; pre-drill every fastener.

$90–$140$32,400–$50,400

A 18×20 deck is 360 sq ft. In pressure-treated wood that runs about $9,000–$14,400 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 360 sq ft is $18,000–$28,800: roughly double the upfront, near-zero maintenance, and usually the lower 25-year cost.

Premium composite or PVC (Trex Transcend, TimberTech AZEK) lands around $27,000–$39,600, and tropical hardwood like Ipe tops out near $32,400–$50,400. 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.

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.

Inputs

Dimensions

Plan-view length × width.

Lengthft

Widthft

Area · 360 sq ft·Perimeter · 76 ft

Material tierinstalled $/sqft band

State2-letter · labor multiplier

Footprint shape1.00× complexity

AttachmentShares house structure

Deck heightinches

IRC R312 requires a 36″ guardrail above 30″.

Stairssteps

Site accessDriveway / wide-open backyard

Scope toggles

Project budget · Northeast

$28,025 – $49,256

$78–$137/ sq ft

360 sq ft · Mid composite · 1.22× labor · 1.10× complexity

Materials

Low $8,910

Labor

Low $13,286

Add-ons

Low $5,397

Soft costs

Permit · demo · design

Project advisories · IRC 2021

Guardrail included (deck 36″ off grade)

IRC R312

IRC R312 mandates a 36″ guardrail on open edges when deck height exceeds 30″. 56 lf priced at Mid composite tier.

Building permit included in budget

IRC R105

Northeast 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 specs

Mid 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

Materials29%$14,256
Labor43%$21,257
Add-ons18%$8,833
Soft costs1%$432
Contingency9%$4,478
Share of the high estimate. Switch tiers below to repaint the split.

Item

Qty

Total

Labor (Northeast, 1.22× national)

$13,286 – $21,257 (low – high estimate)

1.0 scope

$21,257

Labor (Northeast, 1.22× national)

$13,286 – $21,257 (low – high estimate)

1.0 scope

—

$21,257

Materials (decking + framing + hardware)

$8,910 – $14,256 (low – high estimate)

Home Depot Lowe’s

1.0 scope

$14,256

Materials (decking + framing + hardware)

$8,910 – $14,256 (low – high estimate)

Home Depot Lowe’s

1.0 scope

—

$14,256

Railing (56 lf, ledger 3-side)

$3,758 – $6,490 (low – high estimate)

1.0 scope

$6,490

Railing (56 lf, ledger 3-side)

$3,758 – $6,490 (low – high estimate)

1.0 scope

—

$6,490

Contingency (10% reserve)

up to $4,478

1.0 scope

$4,478

Contingency (10% reserve)

up to $4,478

1.0 scope

—

$4,478

Stairs (4 steps @ 9.0″ rise)

$1,640 – $2,342 (low – high estimate)

1.0 scope

$2,342

Stairs (4 steps @ 9.0″ rise)

$1,640 – $2,342 (low – high estimate)

1.0 scope

—

$2,342

Building permit (Northeast)

$432 flat

1.0 scope

$432

Building permit (Northeast)

$432 flat

1.0 scope

—

$432

Materials subtotal

$49,255

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.

Live preview

Visualize your deck

Photoreal 3D · plan view · framing breakdown. Color matches your tier selection.

PBR materialsHDR lightingMid composite

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DeckMath·20′ × 18′·360 sq ft

Trex Enhance·composite

Drag · pinch / scroll

Joists

16 × 18′

Beams

1 × 2-ply 2×10

Posts

4 × 6×6

Boards

40 rows

Project all-in

Materials (low – high)

Mid composite tier · Trex Enhance · Fiberon Good Life · TimberTech Prime+. ~$0.05/sqft/yr.

$8,910 – $14,256

Labor (installed)

Northeast · 1.22× national index

$13,286 – $21,257

Add-ons

Railing · stairs · lighting (only included items)

$5,397 – $8,833

Soft costs

Permit · demo · design (only included items)

$432 – $432

Contingency reserve (10%)

Industry-standard cushion for unforeseen scope

$4,478

Project total (low – high)

Plan around the high. Get 3 contractor bids — DeckMath should land within ±15%.

$28,025 – $49,256

Same dimensions, different tier

tap to switch

DIY savings

$23,602

vs mid-range contractor

Materials only: $14,256
Estimated hours: 540 hr
Skill required: advanced

Finance estimate

$998/month

60-month personal loan @ 7.99% APR

Principal: $49,256
Total interest: $10,654
Estimate only — shop 3+ lenders.

Composite/PVC installs use hidden-fastener clip systems — labor is 25–30% slower than face-screwing pressure-treated wood. That premium is already baked into the tier's installed $/sqft band.

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.

Open

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 — 18×20

The framing and decking a 18×20 (360 sqft) deck needs — board, joist, beam, post, footing, and railing quantities computed from the dimensions at 16″ joist spacing with a 10% waste factor.

Component

Quantity

How it's estimated

Decking boards (16′ × 5/4×6)

55 boards · 864 lf

360 sqft ÷ 5.5″ face × 10% waste

Joists (2×8 @ 16″ o.c.)

16 joists · 288 lf

⌈20′ × 12 ÷ 16″⌉ + 1, each 18′ long

Beam lumber (2× 2-ply built-up)

80 lf

2 beam lines × 20′ × 2 plies

Posts (6×6 PT) + footings

8 posts · 8 footings

2 lines × (⌈20′ ÷ 8⌉ + 1) posts at ≤8′ o.c.

Footing concrete (60-lb bags)

42 bags · 18.8 cu ft

8 piers @ 12″⌀ × 36″ deep — adjust depth to local frost line

Joist hangers (Simpson LUS)

16 hangers

one per joist at the ledger / beam connection

Railing run

56 lf

76 lf perimeter − 20′ ledger side

Decking face screws

≈ 1,729 screws

≈2 screws per board at each joist crossing

Decking

55 boards

864 lf incl. waste

Joists

16″ o.c. · 288 lf

Posts / footings

42 × 60-lb concrete

Railing

56 lf

76 lf perimeter

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).

FAQ — 18×20 deck

How much does a 18×20 deck cost?

A 18×20 deck (360 sqft) costs $9,000-$14,400 for budget pressure-treated construction, $18,000-$28,800 for mid-range composite, and $32,400-$50,400 for premium composite or tropical hardwood. National-average pricing — multiply by 0.92× for the South or 1.28× for West Coast labor.

How many boards do I need for a 18×20 deck?

Running 5/4×6 or 1×6 deck boards (5.5″ face, 1/8″ install gap) parallel to the long dimension: rows = ceil(18 × 12 ÷ 5.625) = 39 rows. Total LF = 39 × 20 × 1.07 (7% waste, parallel pattern) ≈ 835 LF. Round up to 20-ft stock for typical 42 boards.

How long does it take to build a 18×20 deck?

For a contractor crew (2-3 people), a 18×20 deck takes 4-6 days depending on complexity, including framing + decking + railing + inspection wait. DIY single-person build: 54-68 weekend days for composite, less for pressure-treated.

Do I need a permit for a 18×20 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 18×20 deck (360 sqft) exceeds the 200-sqft threshold and definitely requires a permit.