How Much Does a Deck Cost in the Seattle Area?

A professionally built cedar deck in the Seattle area runs $40–$75 per square foot installed; composite runs $60–$110. A mid-size 300 square foot deck lands roughly $15,000–$30,000 depending on material, height and railing. A covered deck adds structure and roofing and commonly runs $25,000–$60,000+ all-in.

Those are the regional numbers. What makes a Seattle deck cost what it does — and what makes one last here — is mostly about water, and the rest of this guide is about that.

What actually drives the price here

• Height. A deck more than a step or two above grade needs guards, longer posts, larger footings and usually stairs. Height is the single biggest multiplier after square footage.
• Railing. Residential guards here are a minimum 36 inches with balusters spaced so a 4-inch sphere cannot pass. Wood railing is the cheap end; cable, glass and aluminium each add thousands on a typical run and are exactly what view lots ask for.
• Footings and drainage. Frost is not the issue in the Puget Sound lowlands; saturated ground is. Footings sized for wet soil and set with gravel drainage cost more than minimum code and stay level.
• Access. Materials carried through a side gate to a hillside backyard cost more to build with than a run where a truck backs to the site.
• Stairs and landings. Each flight is a small structure of its own with its own guards.

Cedar or composite, in a climate that is wet for eight months

Cedar is the regional material and the cheaper one up front. It needs a clean and seal every year or two here; skip that on a north-facing deck under trees and it greys, holds moisture at the board ends and starts to go soft at the fasteners. Maintained, it is beautiful and lasts.

Composite costs more and asks almost nothing afterwards. It does not rot, splinter or need sealing, though cheap boards can hold surface moisture and get slick, and dark colours run hot in the two months a year that matters. Over a fifteen-year horizon the totals land closer than the install prices suggest — the honest question is whether you want a maintenance task on the calendar. The same trade applies to fencing, and people who choose composite for one usually choose it for both.

Whichever you pick, the framing underneath is pressure-treated lumber, and the joist tape and flashing on that framing decide the deck’s life far more than the surface does.

The ledger: where Northwest decks actually fail

The ledger is the board that bolts the deck to the house. It penetrates the wall at exactly the height where water sits, and a ledger that was lag-screwed through siding without proper flashing is the most common structural failure we see on older decks here — and the most common cause of rot in the wall behind it.

A deck built properly today has the ledger flashed into the weather barrier, through-bolted to the rim joist, with a spacer or a free-standing design where the wall cannot take it. It costs a little more. It is also the difference between a deck and a deck that takes the siding with it. The October exterior checklist includes probing an existing ledger for exactly this reason.

Permits in Snohomish and King County

Most jurisdictions here require a permit once a deck is attached to the house, sits more than 30 inches above grade, or exceeds roughly 200 square feet — which covers nearly every deck worth building. Expect the plan review to look at footings, ledger attachment, guards and stairs. We pull the permit and meet the inspector as part of the job, and permit timelines by city covers how long review takes in each office.

Sloped and view lots

The hillside lots through Mukilteo, Edmonds and Bothell are where decks earn their keep — and where they cost more. A deck cantilevered over a slope needs taller posts, bracing and often an engineer’s stamp. The payoff is a level outdoor room on a lot that has none, and on a water-facing elevation it is usually the best money spent on the house. The same grade logic that makes daylight-basement conversions cheap makes high decks expensive; it is worth knowing which side of it your lot is on.

Covered decks

A roof over the deck is the upgrade that changes how many months a year you use it, and it changes the project: posts sized for roof load, a roof that has to tie into the house correctly at the wall, gutters, and often a permit review closer to an addition than a deck. $25,000–$60,000+ is the realistic band, and the roof-to-wall flashing is the detail to ask about in any bid.

The timing trick nobody uses

Deck crews are booked solid from April to September and quiet from November to February. Framing in the dry weeks of winter is perfectly normal work, and a deck booked in January is usually cheaper and finished before anyone else has had an estimate. Our seasonal guide covers the same pattern across the trades.

Comparing bids

Check each one names the footing design, the ledger attachment and flashing, the railing system, who pulls the permit, and the surface and framing materials by brand or grade. A deck bid that is cheaper because it is vaguer is not cheaper. The twelve questions cover the rest.

Get a number for your yard

We build decks across Snohomish and King County, and the free estimate walks the grade, the access and the wall the ledger will meet before it prices anything.

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