12×20 Deck Cost

Why this page exists

Two zones, one line

Twenty feet of length is what finally separates dining from lounging — each end gets a job, the middle stays a walkway.

Installed ranges for 240 sq ft

Pressure-treated, composite, and PVC, derived from the same rates as our interactive cost calculator.

Serves two doors

A 20 ft run often reaches both the kitchen door and the living-room slider — the layout trick that makes a deck feel built-in rather than bolted on.

Proportions checked by render

Long decks live or die by how they sit against the house line. See yours on a real photo before committing to the shape.

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.

12×20 Deck Cost

The answer up front: a 12×20 (240 sq ft) deck runs about $6,000 – $9,600 installed in pressure-treated pine, $10,800 – $16,800 in composite, or $14,400 – $21,600 in PVC. The long format spends its square footage differently than a square deck: you’re buying separation — a dining end and a lounge end that don’t share elbow room — at the cost of more railing and a longer beam line.

Installed cost by material

What the build takes

What moves the price

• Railing runs long. A raised 12×20 carries roughly 44 feet of railing — more than a squarer deck of similar area. In composite or aluminum rail that’s a four-figure line item on its own.
• Beam and footings. Twenty feet of beam wants 3–4 posts on footings. Long decks pay for their shape in the ground, not the boards.
• Stair placement. On a long deck, stairs at the far end force a 20 ft walk from the door; stairs mid-run split the zones. Neither is wrong — but it’s a decision to make on a render, not after framing.
• House line coverage. A 20 ft run covering two doors turns the deck into a second hallway of the house. If your slider and kitchen door are within 20 feet, this shape earns its keep.

Ranges are 2026 North American installed averages (materials plus contractor labor). Long attached decks at door height with full railing typically price mid-range and up.

Common questions

Is a 12x20 deck better than 16x16?

Nearly identical square footage, completely different decks. A 16×16 gives one deep room — best for a big sectional or one large gathering zone. A 12×20 gives two distinct zones and can serve two doors. Pick by how you’ll actually live on it, and render both on your yard before deciding.

Can I fit dining and lounging on a 12x20?

Yes — that’s the shape’s whole argument. A six-person table at one end, a loveseat-and-chairs lounge at the other, and the middle third as circulation. At 12 feet deep, keep furniture off the walk line along the railing.

Do I need a permit for a 12x20 deck?

Assume yes: 240 sq ft is over the common 200 sq ft exemption threshold even for low freestanding builds, and most 12×20s attach at door height anyway. Budget for the permit and a footing inspection in the timeline.

What does the framing look like for 12x20?

On 16-inch centers you’re setting 16 joists spanning the 12 ft depth, over a 20 ft beam line on 3–4 posts. Decking comes to about 287 linear feet with waste — the full table above has fasteners and railing too.