Estimate your 2026 Seattle deck build — pressure-treated, cedar, composite (Trex), PVC (TimberTech Azek), or ipe. Set the dimensions, height above grade, railing material, stairs, skirting, and deck shape, and the calculator returns an itemized material and labor breakdown. Decks built more than 18 inches above grade include Seattle's building permit, priced from the 2026 SDCI fee schedule.
This is the tool version of our Seattle Deck Cost 2026: $/sqft by Material + Permit Trigger Explained, which walks through the price matrix by size and material tier, SDCI permit rules, and a pre-project checklist. Read the guide for planning; use the calculator below for your specific footprint.
Is this a new deck build or renovation of an existing deck?
Project Configuration
Enter deck dimensions and select materials
Total area: 0 sq ft
Additional Features
Add safety railing around perimeter
Replacing a deck? We tear out the old one and haul it away
Add stairs to access deck
Select your deck configuration
Apply sealant to protect deck from weather
Your Estimate
Configure your project and click Calculate
Enter your project details to get started
How Our Deck Cost Calculator Works
Professional deck building estimates for Seattle and Pacific Northwest homes
Accurate Cost Estimation
Our deck cost calculator prices new decks, and repairs to existing ones, from Kolmo's own material catalog and labor rates. For a
new deck you enter the length, width and height, then choose the decking material (pressure-treated, cedar, composite and Ipe hardwood
among them), the framing lumber, the railing material and length, the number of stair steps, a finish, skirting and the deck shape.
Decking is ordered with a 10% waste allowance, framing lumber is sized by the board foot from the deck's area and height, and fasteners
and hardware are 5% of the decking and framing cost. Labor is billed by the hour at $75, from production rates for the deck surface,
railing, stairs, skirting and finish. Decks more than 3 feet above grade carry a height multiplier on labor, and L-shaped, angled-corner
and multi-level layouts add a percentage to materials, shown as its own line.
What The Calculator Includes
Every new-deck estimate is itemized: the decking material with its waste allowance, framing lumber (joists, beams and posts) by the
board foot, a fasteners and hardware line, the railing by the linear foot when you include it, and the labor hours at $75. Stain gallons,
skirting, a stair landing, a shape adjustment and tearing out the old deck appear as their own lines when you choose them. Stairs carry their stringers, treads, closed risers and
hardware in the decking and framing you pick, plus the labor: about $121 a step in pressure-treated lumber to $147 in Trex Enhance on a
ground-level deck. A deck more than 18 inches above grade carries Seattle's building permit, priced from the 2026 SDCI fee schedule on the
deck's material and labor (full plan review above 8 feet). A deck 18 inches or less above grade carries no permit line. The calculator does not price concrete footings, helical piles, flashing
or engineering; those are scoped on site. Tearing out and hauling away the deck you are replacing is $650 on 250 sq ft. The decking you pick moves the price: on a bare 250 sq ft deck 2 feet
above grade, pressure-treated boards come to $9,435, cedar to $10,764 and composite to $10,914.
Seattle-Specific Considerations
Seattle's wet climate drives most deck decisions. Boards that stay damp through the winter need rot resistance: cedar resists decay
naturally, pressure-treated lumber is treated against it, and composite decking does not rot the way untreated softwood does. Framing sits
closest to the moisture, which is why pressure-treated 2x6 is the framing lumber the calculator starts from. Many Seattle homes sit on
slopes, and a deck that stands higher above grade needs longer posts and more labor; the calculator reflects that through the height you
enter, with post lumber that grows with height and a labor multiplier above 3 feet. Footings, engineering for tall or hillside decks, and
anything a site visit turns up are priced after we see the lot. Whether your deck needs a permit, and what it costs, is set by the Seattle
Department of Construction and Inspections (SDCI); the calculator's permit line is SDCI's 2026 fee on the deck's value, and the city sets the final fee at intake. Washington requires deck
contractors to be registered with L&I, bonded and insured, and our estimates reflect only properly insured, bonded professionals.
Using The Calculator Effectively
For accurate estimates, measure your intended deck's length and width in feet and the height from the ground to the deck surface.
Height matters: above 18 inches the Seattle permit fee is added, above 3 feet the labor carries a multiplier, and above 8 feet the permit moves to full plan review. Select
your decking material based on budget and maintenance preferences: pressure-treated lumber offers the lowest upfront cost but requires
regular sealing; cedar provides natural beauty and rot resistance with upkeep; composite decking costs more per board but eliminates
staining and sealing. Enter the railing length you actually need rather than the full perimeter if one side runs against the house, and
choose the railing material with care: pressure-treated wood railing adds about $33 a linear foot, and stainless cable railing about $74.
Add stair steps, a finish and skirting if you want them. Change any input and recalculate to see how each choice moves the total; the
estimate lists the decking, framing, fastener, railing and labor lines and a time estimate in working days.
Deck Cost Calculator: common questions
How long does a deck last in Seattle's climate?
Pressure-treated lumber decks last 15-20 years with proper maintenance. Cedar decks can last 20-30 years when regularly sealed and maintained. Composite decking lasts 25-40 years with minimal maintenance. The Pacific Northwest's moisture requires diligent maintenance - unsealed wood decks deteriorate rapidly in our wet climate.
Do I need a permit for my Seattle deck?
It depends on the deck, and the Seattle Department of Construction and Inspections (SDCI) decides it for your lot, so check your address before you build. The calculator adds Seattle's building permit only for new decks built more than 18 inches above grade, priced from the 2026 SDCI fee schedule on the deck's material and labor: about $880 on a 16x20 Trex Enhance deck 3 ft up, with full plan review above 8 feet. A deck 18 inches or less above grade gets no permit line. SDCI sets the final fee at intake.
What's the best decking material for Seattle weather?
For Seattle's climate, Western Red Cedar offers natural rot resistance and weathers well if maintained. Composite decking such as Trex needs no staining or sealing. In this calculator composite costs 1.4% more than cedar on a bare 250 sq ft deck 2 feet above grade ($10,914 against $10,764) and 6.9% more on a 16x20 deck with 72 feet of matching railing and six steps ($18,865 against $17,642), most of that difference being the railing. Pressure-treated lumber works but requires annual sealing. Avoid untreated pine or hardwoods not rated for ground contact as they'll rot quickly in our wet conditions.
Why trust this deck building estimate?
Kolmo LLC, established 2025, is a licensed, bonded and insured Washington general contractor (License #KOLMOL*753JS) working across Seattle and King County. This deck building calculator prices from Kolmo's own material catalog and labor rates, not national averages. Every estimate returns an itemized breakdown of materials and labor, and the line items reconcile to the total so you can check the arithmetic yourself, and the cost of every option you switch on appears as its own line. Treat the result as a planning estimate rather than a quote: the final price is set after a walkthrough of the actual conditions, which is free and carries no obligation.
What this calculator captures
Installed price from this calculator for a 16x20 deck (320 sq ft), 3 ft above grade, with railing around the perimeter and one 6-step stair. Taller decks and cable or glass railing cost more; run the calculator for your layout.
Pressure-treated wood
From $15,100
Most affordable. Refinishing every 2-3 years. Best for rental properties or budget-sensitive projects.
Composite (Trex Enhance)
From $18,900
No refinishing, 25-year warranty. Common Seattle choice given the wet winters. Priced with composite railing.
Premium composite (Trex Transcend)
From $20,100
Trex's top line: deeper wood grain and more colors. Priced with composite railing.
Using this calculator
Does the estimate include the SDCI permit?
It includes Seattle's building permit for a deck built more than 18 inches above grade, priced from the 2026 SDCI fee schedule on the deck's material and labor: about $880 on a 16x20 Trex Enhance deck 3 ft up, on the field-inspection path. A deck more than 8 ft above grade is priced on full plan review. Check whether your deck needs a permit at your address with our Permit Assessment tool at /permits.
How does the calculator handle tear-off of an existing deck?
Turn on 'Tear Out the Old Deck' and the new-deck price includes tearing out the old deck and hauling it away, priced on the deck's square feet: $650 on 250 sq ft. Footings left in the ground are scoped on site. If the frame is sound, choose 'Existing deck' and 'Replace flooring': that price includes removing the old boards. New pressure-treated boards on 250 sq ft come to about $2,290; Trex Enhance composite about $3,660.
Are railings priced separately or bundled?
Railing is its own line: the material you pick, priced per linear foot, plus installation. On a new deck that comes to about $33/ft for pressure-treated wood, $43/ft for cedar, $44/ft for aluminum, $57/ft for composite, $74/ft for stainless cable, and $107/ft for glass. The calculator prices railing on the full deck perimeter.
How are posts and footings priced?
Posts are part of the framing line, sized from the deck's area and height. The calculator doesn't price helical piles, ground screws, or engineered footings; if your lot needs them, ask us for a site quote.
Can I model a covered pergola or roof over the deck?
No. The calculator prices the deck, railing, stairs, skirting, and finish. A pergola or roof needs its own framing and often a separate permit, so contact us for a custom quote.
