Composite Deck Cost in Seattle
The full composite category in Greater Seattle — standard composite, capped composite, capped polymer PVC — with PNW lifecycle math against cedar and pressure-treated framing.
2026 Deck Cost Estimator
Directional range based on material tier, slope condition, jurisdiction, and current site state. Built from 2026 PNW dealer-installed cost data.
$18,400 – $46,000
Range covers materials and labor before permit fees, Washington 10.35% retail sales tax, and any project-specific engineering. We refine to a single open-book number after site visit and structural review.
Seattle SDCI valuation-based; SFI permits ~40% of plan review fee. Typical deck permit fee band runs $400-$1,800; ECA-overlay decks add geotech review costs separately. 2025-2026 saw inflation-adjusted hourly rates rise materially.
Range includes January 2026 Trex/TimberTech repricing — composite Signature and Transcend lines were lifted +7-15% YoY per manufacturer notices. Cost guides published before Q4 2025 do not reflect this adjustment.
Estimates are directional only. Final pricing requires site visit, structural review, and permit feasibility check. Slope and ECA conditions in particular shift the band substantially after stamped engineering enters the scope.
The composite tier ladder
“Composite” covers a wide cost band because it spans three distinct product categories: wood-plastic composite (WPC) with no cap, capped composite, and capped polymer PVC. PNW installed-cost bands below draw on 2026 national installed-cost medians (HomeGuide / Angi) and PNW dealer-installed benchmarks.
- Standard composite (uncapped or single-cap)$40-$80/sqft installed. Trex Enhance, MoistureShield Vision, Deckorators Vista. Adequate for shaded PNW conditions; entry tier with shortest warranty.
- Capped composite (premium)$75-$130/sqft installed. Trex Select, Trex Transcend Lineage, TimberTech Reserve. Sealed polymer cap resists moisture intrusion — the right call on covered PNW slopes and shaded north-facing sites.
- Capped polymer PVC$90-$150/sqft installed. TimberTech AZEK Vintage, AZEK Landmark. No wood content; ideal for waterfront and deep-shade rot exposure. Highest material cost, longest manufacturer warranty.
Sources: HomeGuide / Angi 2026 installed-cost data; PNW dealer-installed benchmarks (Premium Composite, PVC Decking).
2026 cost reality — what shifted, and where it shows up
The Greater Seattle composite cost band is materially higher in 2026 than in 2024. Four discrete shocks layered into quotes between Q1 2025 and Q2 2026, each documented in primary sources. None of them are contractor-margin moves — they are upstream from the local builder.
Permit fees first. King County (unincorporated) raised deck permit fees +49% on January 1, 2025 (Ord. 19857), then another ~14% on January 1, 2026 (Ord. 20021), plus a new $126 application screening fee. Seattle SDCI inflation-adjusted hourly billing rates rose +12-19% in 2025 and +18% in 2026. On a 400 sqft project in unincorporated KC, the permit line shifted from roughly $900 in early 2024 to $1,900-$2,500 today.
Manufacturer repricing second. Trex announced railing, fastener, and Signature/Transcend line increases +7-15% effective January 1, 2026. TimberTech AZEK followed with parallel mid-cycle adjustments. Installed Trex in Western WA now lands $28-$45/sqft for materials and labor on substructure plus boards on standard tiers.
Lumber third. Q2 2026 framing lumber rose +5.11%, with the national average around $916/MBF in April. PNW labor and supply constraints amplify the move. Composite finish does not exempt a deck from pressure-treated joists, beams, and posts in the substructure.
Code fourth. Washington adopted the 2021 IRC effective March 15, 2024. Section R507.10 requires guard loads to transfer to deck joists with a continuous load path and prohibits notched 4x4 guard posts at the connection point — both common pre-2024 practices. WA State separately requires a 42-inch minimum guard height on residential decks more than 30 inches above grade, against the IRC 36-inch baseline. The combined effect shifts railing system selection and stamped-engineering scope on any composite deck above 30 inches.
400 sqft Trex Select replacement, Bellevue flat lot
Representative project: tear-out of an aging 380 sqft pressure-treated deck, replaced with 400 sqft of Trex Select on concrete pier substructure, composite Select railing at the WA 42-inch spec, one stair flight, Bellevue permit pathway.
- Demolition & disposalTear-out of existing 400 sqft pressure-treated deck, transfer station fees$1,800 – $3,200
- Footings & substructureConcrete piers, pressure-treated framing to 60-psf live load, IRC R507.10 continuous load path$7,500 – $9,800
- Trex Select boards400 sqft of Select at $5.50-$7.50/sqft materials (post January 2026 repricing) + 10% waste$2,400 – $3,300
- Composite railing (42")55 linear ft Trex Select railing at WA 42-inch guard spec, posts and one gate$3,300 – $4,950
- StairsEngineered stringers, composite treads, code-compliant landing$1,800 – $2,800
- LaborPNW licensed carpenter crew, ~140 hrs at $50/hr blended$7,000
- Bellevue building permitValuation-based residential deck permit, plan review included$800 – $1,400
- WA 10.35% sales taxApplied to materials portion (combined retail rate)$1,400 – $1,800
- Total — directional range$26,000 – $34,250
Materials cost weighted to Trex’s January 2026 price sheet. Labor at PNW carpenter $50/hr blended. Permit and sales tax per the applicable 2026 jurisdiction fee schedule and WA Department of Revenue Bellevue/King retail rate.
2026 Permit Fee Matrix
Four core Greater Seattle jurisdictions, their deck permit thresholds, and the 2026 fee schedules behind every quote you receive.
| Jurisdiction | Permit Threshold | 2026 Fee Structure | Recent Change |
|---|---|---|---|
| Seattle SDCI | >18" above grade; any roof deck; any deck in an ECA overlay | Valuation-based sliding scale. SFI (Subject-to-Field-Inspection) permits run ~40% of the plan review fee. 2026 Fee Code and Fee Estimator published. | +12-19% in 2025, +18% inflation-adjusted hourly rates in 2026 |
| King County (unincorporated) | >30" above ground (uncovered decks at or below 30" outside critical areas exempt) | $772 application review + $2.46/sqft inspection (deck of 500 sqft or less) + new $126 application screening fee | +49% on Jan 1 2025 (Ord. 19857), +~14% on Jan 1 2026 (Ord. 20021) |
| Bellevue | >30" above ground (plan review included in permit) | Valuation-based. Reported by local contractors as relatively faster and less painful than King County unincorporated. | No major fee-schedule shock reported through Q2 2026 |
| Pierce County (unincorporated) | >30" above adjacent grade; guardrail required on all decks >30" | $69 for the first $2,000 of valuation + $12.21 per additional $1,000 up to $25,000. Fast Track available for pre-designed single-level decks up to 14 ft high. | Updated effective Feb 1, 2026 (Pierce County Code 17C.10.070) |
Source: Seattle SDCI 2026 Fee Code; King County Ord. 19857 / 20021; Bellevue Development Services; Pierce County Code 17C.10.070. Threshold and fee data current as of Q2 2026. Final permit cost on any project depends on valuation, site conditions, and whether structural engineering or geotechnical review is triggered.
Frequently asked
- Do I need a permit for a composite deck in Seattle?
- Inside the City of Seattle, any deck more than 18 inches above grade, any roof deck, and any deck in an Environmentally Critical Area (ECA) require a permit. In unincorporated King County, Bellevue, and Pierce County, the threshold rises to 30 inches above grade. Whether you finish in Trex, TimberTech, or Deckorators makes no difference — the permit attaches to the structure, not the finish material.
- What is the difference between $40/sqft and $120/sqft installed composite?
- Material tier and structural complexity. The $40/sqft band is standard composite (Trex Enhance / Select, MoistureShield, Deckorators Vista) on a flat lot with reusable framing and a simple railing. The $120/sqft band is premium capped composite or capped polymer PVC (Trex Transcend Lineage, TimberTech AZEK Vintage) on a slope or ECA site with new helical pile substructure, stamped engineering, and a 42-inch cable or aluminum railing system. Both are legitimate; they are not the same deck.
- Why is composite more expensive in the PNW than national averages suggest?
- Three reasons. PNW carpenter wages run $38-$52/hr against a national mean closer to $32/hr. Slope and shoreline parcels often require helical piles or geotech-stamped footings rather than simple concrete piers. And WA State requires a 42-inch guard height on residential decks more than 30 inches above grade, against the IRC 36-inch baseline, which shifts railing system pricing on per-linear-foot specs.
- How much does the WA 42-inch guard requirement add to cost?
- The 6-inch upgrade is rarely a headline driver, but it adds 8-15% to per-linear-foot railing system cost on cable, glass, and aluminum systems where the manufacturer prices to a specific height. On a 60-linear-foot perimeter that is typically $300-$900 versus the IRC 36-inch spec, depending on system.
- How does a January 2026 Trex tariff repricing show up on a quote pulled today?
- Trex repriced railing, fasteners, and several Signature and Transcend composite lines +7-15% effective January 1, 2026. TimberTech AZEK followed in parallel. Contractors quoting against old supplier price sheets will under-quote boards by hundreds to low thousands of dollars on a 400-600 sqft project. If your quote uses 2024 cost guide figures, expect a change order. Open-book contractors will show the current manufacturer price sheet as a line-item attachment.
- Is composite or cedar cheaper in PNW lifecycle terms?
- Cedar is cheaper at year one and more expensive at year fifteen. Western Red Cedar installs at $30-$90/sqft in the PNW, lasts 15-25 years with reseal every 1-3 years (~$1,000-$2,000 per reseal on a 400 sqft deck). Standard composite installs at $40-$100/sqft, lasts 20-30 years with annual rinse, no reseal. At year 18-25 the composite is structurally intact and the cedar typically is not.
Open-book quote. Permit in your name.
Every composite deck we build runs through Seattle SDCI, King County DPER, Bellevue, or the relevant municipal office under your name as the property owner. Tracking number on day one. Manufacturer price sheets attached as a line-item reference, so the Trex or TimberTech materials cost is not a black box.