Cedar wins on visible decking surfaces in Seattle. Pressure-treated lumber wins in the structural frame — posts, joists, and beams. Most professional deck builds in King County use both materials for exactly this reason. Here's what that means for your project, with real cost ranges and 20-year maintenance math.
Why Most Seattle Decks Use Both Materials
The question homeowners usually ask is: "Should I build my deck in cedar or pressure-treated wood?" The question most Seattle contractors actually answer is: "Which material goes where?"
Pressure-treated (PT) lumber is treated with ACQ (alkaline copper quaternary) or similar preservatives that prevent rot and insect damage. That makes it the right choice for any component in contact with the ground or trapped moisture — posts set in concrete, ledger boards against the house, joists and beams in the substructure. You want PT lumber in those locations because the structural frame is what you're not replacing for 30 years.
Cedar, specifically western red cedar, is naturally rot-resistant and dimensionally stable. It's also beautiful, workable, and what most Seattle homeowners actually want to look at when they step outside. Cedar shines as the visible surface — the decking boards you walk on and the railings you grip.
The hybrid approach — PT frame, cedar surface — is what most quality King County contractors build as a standard. The debate about which material to choose only becomes a real choice when you're deciding whether to surface a deck entirely in cedar, entirely in PT, or to skip both and go with composite.
Cedar Decking in Seattle: Performance, Cost, and What to Expect
Western red cedar is Washington State's home material. It grows here, it performs here, and when it's properly maintained it looks genuinely beautiful for 15–20 years in King County conditions.
**What cedar handles well in the PNW:** - Natural tannins provide meaningful rot resistance without chemical treatment - Low density means it stays cool underfoot compared to composite in summer - Accepts stain readily and can be refinished to look nearly new - Works with standard fasteners (unlike PT, which requires specific hardware — more on this below)
**What cedar demands in Seattle's 38 inches of annual rainfall:** - Cleaning and re-sealing every 1–2 years, without exception — Seattle's extended wet season accelerates the degradation cycle - Immediate attention to any cracks, checks, or end grain exposure where water can penetrate - Annual inspection for moss and algae colonization, which spreads on unmaintained cedar faster than on composite
**Cedar material and installation cost in Seattle (2026):** - Clear vertical-grain cedar decking: $8–$14 per linear foot (material only) - Installed cedar deck, 300–400 sqft, ground-level: $15,000–$28,000 all-in (includes PT substructure, permit, labor) - Annual maintenance cost: $300–$700 for a mid-size deck (cleaning products, sealer/stain, or contractor service)
Cedar decks in Seattle that are consistently maintained look excellent for two decades. Cedar decks that go two or three seasons without re-sealing begin showing gray weathering, board checks, and moss — and can reach replacement condition within 8–10 years. We replace aging cedar decks regularly; the ones that failed early almost always show a maintenance gap in the first five years.
Pressure-Treated Decking in Seattle: What It's Actually Good For
Modern PT lumber — ACQ or MCQ treated — is not the arsenic-based CCA lumber of the pre-2004 era. Today's PT is safe for residential use and significantly more rot-resistant than untreated wood.
**Where PT earns its place in a Seattle deck:** - Any below-grade or ground-contact component: post bases, buried blocking - Ledger board attachment points where flashing can't fully eliminate moisture contact - Structural frame: joists, beams, blocking - Stair stringers that run close to the ground
**PT as a visible decking surface:** It can be done and it's cheaper upfront. The realistic lifespan for PT decking boards in Seattle's climate is 10–15 years with consistent maintenance — shorter than cedar on the surface because PT lacks cedar's natural tannins and tends to check, warp, and splinter more aggressively through PNW humidity swings.
PT surface decking also presents an aesthetic compromise. New PT lumber is green-tinted from the preservative treatment and must dry for 6–12 months before it holds stain properly. It weathers to a grayish-brown that homeowners frequently find less appealing than cedar's warm tones.
**PT decking cost comparison:** - Pressure-treated pine decking boards: $3–$6 per linear foot (material only) - Installed PT surface deck, 300–400 sqft, ground-level: $12,000–$22,000 all-in - The upfront savings vs. cedar: roughly $3,000–$6,000 on a mid-size project
Cedar vs. Pressure-Treated: Side-by-Side Comparison
| Factor | Cedar (Surface) | Pressure-Treated (Surface) | |---|---|---| | Material cost (decking boards) | $8–$14/linear ft | $3–$6/linear ft | | Installed cost, 300–400 sqft | $15,000–$28,000 | $12,000–$22,000 | | Seattle-area lifespan | 15–20 years (maintained) | 10–15 years (maintained) | | Maintenance frequency | Seal every 1–2 years | Seal every 2–3 years | | Annual maintenance cost | $300–$700 | $200–$500 | | Appearance | Warm natural tones | Green-tinted new; gray-brown weathered | | Rot resistance | Natural tannins | Chemical treatment required | | Splinter risk | Low (clear-grain) | Higher (checks under humidity swings) | | Special hardware required | No | Yes (ACQ-compatible only) | | Best use in PNW | Visible surface decking | Structural frame, ground contact |
The Hardware Problem Most Homeowners Miss
This is one of the most overlooked issues in PT construction. Modern ACQ-treated lumber reacts chemically with standard galvanized hardware — joist hangers, post bases, deck screws. The copper in ACQ accelerates corrosion of standard zinc-coated hardware within 2–3 years in Seattle's wet climate.
**What PT lumber requires:** - Hot-dipped galvanized (HDG) or stainless steel joist hangers and post bases - Stainless steel or specifically ACQ-rated deck screws for any PT-to-PT connections - ACQ-compatible flashing at ledger board connections
A deck built with PT lumber and standard hardware will show fastener failure — staining from corroded screws, loose joist hangers — within a few years. This is a legitimate quality concern that budget-focused contractors sometimes cut corners on.
Cedar used as surface decking does not require special hardware — standard hot-dipped galvanized screws work correctly. If you're building a cedar surface over a PT substructure (which is standard practice), the hardware spec applies to the frame connections, not the cedar surface fasteners.
20-Year Cost of Ownership in Seattle's Climate
When we run the numbers for Seattle homeowners, the 20-year picture often surprises them:
**Cedar deck, 350 sqft, maintained consistently:** - Initial installed cost: $20,000 - Annual maintenance (stain/seal, cleaning): $450 average - Maintenance over 20 years: $9,000 - Board spot-replacements at year 10–12: $2,000 estimate - **20-year total: ~$31,000**
**PT surface deck, 350 sqft, maintained consistently:** - Initial installed cost: $16,000 - Annual maintenance: $350 average - Maintenance over 20 years: $7,000 - Full resurfacing at year 12–15 (typical): $8,000–$12,000 - **20-year total: ~$33,000–$37,000**
The upfront savings on PT surface decking frequently disappear in the mid-cycle resurfacing that most PT decks in Seattle require. Cedar maintained on schedule typically outlasts PT surface boards, making the long-term ownership math closer than the initial price gap suggests.
For a complete breakdown of Seattle deck cost variables, our [deck cost guide](/deck-cost-seattle) covers every factor that moves the number.
When Cedar Surface Decking Still Makes Sense
Cedar is the right choice for King County homeowners who: - Have the discipline to maintain it on schedule (or will hire someone to do it) - Want natural wood appearance and the warmth it brings underfoot - Are building on a covered or partially shaded structure where UV and rain exposure is reduced - Have a budget that fits cedar but not composite - Want a material they can sand and refinish rather than replace
In neighborhoods like Mercer Island, Madison Park, and Laurelhurst where architectural character and natural materials are premium, cedar is a legitimate premium choice that composites don't fully replicate aesthetically. Our [cedar decking page](/cedar-decking) covers the full scope of what a cedar build entails in PNW conditions.
Why Many Seattle Homeowners Choose Composite Instead
After walking through this comparison in consultations, a significant portion of Seattle homeowners land on a third option: fully capped composite decking.
The pitch is simple: capped composite — a polymer shell encasing a composite core on all four sides — eliminates the maintenance cycle entirely. No re-sealing, no re-staining, no moss treatment. The polymer shell resists moisture absorption, which is what causes the rot and degradation that ends cedar and PT surface decks in PNW conditions.
The cost premium is real: a composite surface deck in Seattle runs $22,000–$40,000 installed, compared to $15,000–$28,000 for cedar. But many homeowners, once they calculate 20 years of maintenance cost and potential resurfacing, find the gap narrower than it looks on the initial quote.
For homeowners who want zero maintenance, PVC decking — no wood fiber content at all — takes it a step further. Our [composite decking page](/composite-decking) and [PVC decking page](/pvc-decking) cover how these materials perform specifically in King County's 38 inches of annual rain. Our [composite vs. cedar 10-year comparison](/blog/composite-vs-cedar-decking-seattle) runs the full ownership math if you want to dig into the numbers.
What We Recommend for King County Homeowners
**For most Seattle projects:** A PT substructure (frame, posts, joists) with a capped composite surface is the standard we recommend. The frame gets the material built for ground contact and structural longevity; the surface gets the material that handles decades of PNW rain without a maintenance schedule.
**If you prefer natural wood:** Western red cedar is a better surface choice than PT in almost every Seattle application. Use clear vertical-grain cedar, commit to the 1–2 year maintenance cycle, and it will look excellent for 15–20 years. Factor $400–$600 per year in maintenance into your budget.
**PT surface decking:** Best suited for budget-constrained projects where upfront cost is the primary driver, with the understanding that resurfacing is likely within 10–15 years in King County conditions. We specify PT surface boards only when the homeowner understands the maintenance requirements and the likely replacement cycle.
Preventing early failure on any wood deck starts with proper rot prevention — our [deck rot prevention guide](/blog/deck-rot-prevention-seattle) covers the specific conditions in Seattle that accelerate wood degradation and how we build against them.
---
The right material for your Seattle deck depends on your budget, maintenance tolerance, and how long you plan to stay in the home. We'll walk through the honest math with you — no upsell, no pressure. Call The Seattle Decking Company at **(425) 675-6259** or [request a free estimate](/contact) to get a real quote for your specific project.