Deck building, Greater Seattle Area
Five Tips Before Installing a New Outdoor Deck
The five things to decide before installing a new outdoor deck are the decking material, size and layout, height and permit, footings and ledger, and railing and stairs. In Seattle a deck needs a permit if it is more than 18 inches above grade, over a basement or story below, a roof deck, or in an environmentally critical area.
The code rules below are Seattle's. Other cities set their own. Book a Consultation and we check the rules for your address before we price the deck.
What decking material should you choose for a new deck?
Choose the boards first, because they set the price tier and the upkeep. On our Deck Builder Across the Greater Seattle Area page, Basic decks use pressure treated wood, Mid-Range decks use cedar or entry composite, and Luxury decks use premium composite or PVC. In Seattle a composite deck costs about 40% more than the same deck in wood. Composite needs far less upkeep. Wood needs regular cleaning and stain.
Composite boards have their own code rules. The 2021 Seattle Residential Code, Section R507.2.2, says composite deck boards, stair treads, guards and handrails "shall comply with the requirements of ASTM D7032 and this section". Section R507.2.2.1 requires a label with the allowable load and the maximum span. We are Trex certified and install listed products.
Pick the color with the house. A stain that suits the siding and trim makes a deck look like part of the house. On a Bellevue deck in 2021 we kept the boards and the white lattice railing, cleaned the gray surface and stained every board a deep red-brown. That refinish cost about $15,000.
How big should a new deck be, and how should it be laid out?
Size the deck for how you will use it. Spend time in the spot first: note where the afternoon sun falls and how much room the table, the grill and the chairs need. On our deck page, a new single level deck is typically 200 to 400 square feet, such as a 16 by 20 foot deck with steps to the yard. Elevated and multi level decks are typically 400 square feet and up.
Levels and steps change how a deck is used. In Mukilteo we replaced an old deck and pergola with a low platform deck that has angled corners and a step around the front edge, so it can be stepped onto from the lawn on three sides. It sits low enough to need no railing. That job cost about $10,000.
In Seattle, height also limits size and placement. The Seattle Department of Construction and Inspections (SDCI) Decks page (read October 2026) says a deck more than 36 inches above the ground counts toward lot coverage. A deck more than 18 inches above the ground cannot sit within 10 to 15 feet of the front property line or 3 to 5 feet of a side property line in neighborhood residential zones.
Does a new deck need a permit in Seattle?
Yes, unless it is a low platform on a lot outside an environmentally critical area. The 2021 Seattle Residential Code, Section R105.2, lists the work that needs no building permit. Item 7 reads: "Platforms, walks and driveways not more than 18 inches above grade and not over any basement or story below." A deck higher than that, or one over a basement or a story below, needs a permit. SDCI's Decks page also requires one for a roof deck, or for any deck in an environmentally critical area (ECA), such as a landslide prone slope. Section R105.2 says an exemption "does not authorize any work to be done in any manner in violation of this code or any other laws or ordinances of the City."
SDCI's Decks page says most decks need only a subject-to-field-inspection construction permit. The larger decks in the table below need a full addition or alteration permit. That page leaves out the basement clause. The adopted code governs.
Permit time depends on the city. Seattle permits through SDCI take 4 to 8 weeks, and Eastside cities usually take 2 to 4 weeks. For other remodel permits, read Do you need a permit to remodel in Seattle?
| Deck | What applies | Source |
|---|---|---|
| 18 inches or less above grade, not over a basement or story below | No permit, unless in an ECA | SRC R105.2 item 7; SDCI |
| Over 18 inches above grade, or over a basement or story below | Permit, usually subject-to-field-inspection | SRC R105.2; SDCI |
| Roof deck, or any deck in an ECA | Permit at any height | SDCI |
| Over 8 feet up, beams 14 feet or longer, roof deck, ECA, solid surface or over 750 square feet | Addition or alteration permit | SDCI |
Source: 2021 Seattle Residential Code, Chapter 1, and the SDCI Decks page, read October 2026.
What do deck footings and the ledger connection need?
The frame under the boards decides how long a deck lasts. Seattle designs decks for a live load of 60 pounds per square foot (2021 Seattle Residential Code, Table R301.5). Section R507.3 says "Decks shall be supported on concrete footings or other approved structural systems", and Section R507.3.2 says "Deck footings shall be placed not less than 12 inches (305 mm) below the undisturbed ground surface."
Where a deck meets the house, Section R507.8 of the 2021 code says the attachment "shall not be accomplished by the use of toenails or nails subject to withdrawal." Section R703.4, item 5, requires flashing "Where exterior porches, decks or stairs attach to a wall or floor assembly of wood-frame construction." Our elevated decks include ledger flashing at the house, and our Mid-Range resurface and single level decks add joist protection tape.
On a Mercer Island deck in 2022, the posts, joists, rim and rail boards had rotted under boards that only looked tired from above. We replaced the rotted wood, laid new deck boards and built a stained wood railing with black metal infill. That rebuild cost about $35,000.
How tall does a deck railing need to be, and what about deck stairs?
The deck's height sets the railing. Under the 2021 Seattle Residential Code, a guard is required where a walking surface is more than 30 inches above the grade below, and it must be at least 36 inches tall. SDCI's Decks page adds that a glass railing has special rules and may need a structural engineer. Stairs follow their own rules:
| Item | Rule | Section |
|---|---|---|
| Guard required | Open side more than 30 inches above grade within 36 inches of the edge | R312.1.1 |
| Guard height | At least 36 inches (34 inches on the open side of a stair) | R312.1.2 |
| Guard openings | A 4 inch sphere must not pass through | R312.1.3 |
| Stair riser | No more than 7 3/4 inches | R311.7.5.1 |
| Stair tread | At least 10 inches deep | R311.7.5.2 |
| Stair width | At least 36 inches clear | R311.7.1 |
| Handrail | On flights with four or more risers, 34 to 38 inches above the nosing | R311.7.8, R311.7.8.1 |
Source: 2021 Seattle Residential Code, Chapter 3, read October 2026.
How much does a new deck cost in the Greater Seattle area?
A new single level deck costs $25,000+ and an elevated or multi level deck costs $45,000+. Resurfacing a sound deck costs $15,000+.
Starting prices leave out permit fees, rot found in the house rim or ledger, engineering for steep slopes and hot tub support. On a Seattle home in 2023 we built a front entry landing and a raised rear landing, each with a stair, dark brown treads and white railings. That job cost about $30,000. Prices have risen since each of our past decks was completed.
| Deck type | Basic | Mid-Range | Luxury | Time on site |
|---|---|---|---|---|
| Resurface and refinish | $15,000+ | $25,000+ | $40,000+ | 1 to 2 weeks |
| New single level deck | $25,000+ | $40,000+ | $60,000+ | 2 to 4 weeks |
| Elevated or multi level deck | $45,000+ | $70,000+ | $100,000+ | 4 to 8 weeks |
Source: Deck Builder Across the Greater Seattle Area, deck prices, October 2026. Time on site is after permits.
Should you plan a roof cover with a new deck?
Decide on a roof cover before the deck is drawn. A solid roof cover over a deck starts at $20,000+ and adds 1 to 3 weeks on site. For heat, cover and lighting ideas, read How to Create a Winter-Friendly Outdoor Living Space.
We plan the cover, the deck and the permit together on jobs across King and Snohomish counties, from Seattle, Mercer Island and the Eastside north to Snohomish. See Home Remodeling Contractors in Seattle, WA for what else we build in the city.
Frequently Asked Questions
Who draws the deck plans for a Seattle permit?
SDCI's Decks page says "Deck drawings rarely require a professional's stamp" and that anyone with drafting skills may prepare them. We draw every deck we build and file the permit when the height, size or site calls for one.
What wood can touch the concrete footings?
SDCI's Decks page says you must use treated wood or wood that naturally resists decay for all wood in contact with concrete that is close to the earth.
Does replacing rotted deck boards need a permit in Seattle?
Usually not. The 2021 Seattle Residential Code, Section R105.2 item 2, exempts "in-kind or similar replacement of or repair of deteriorated members of a structure" when no changes are made to the building envelope.
What warranty comes with a new deck?
Every deck we build carries a 2-year workmanship warranty, which can be extended to 5 years. The decking and railing carry their manufacturer's warranty.
