title: "Cedar vs. Pressure-Treated: How a Seattle Homeowner Made the 10-Year Call" description: "A Seattle homeowner pricing a 16×12 deck used the deck and lumber calculators to compare PT and cedar side by side. The numbers confirmed cedar cost 30% more upfront — but would likely outlast PT by a decade in the Pacific Northwest." client: "Homeowner in Seattle, WA" project: "16×12 pressure-treated deck addition" calcUsed: ["deck", "lumber"] outcome: "Chose western red cedar over PT after a clear cost-per-year comparison" date: "2024-11"

Cedar vs. Pressure-Treated: How a Seattle Homeowner Made the 10-Year Call

When a homeowner in the Eastlake neighborhood of Seattle started pricing a deck addition off their back door, the contractor they consulted gave them the standard advice: go with pressure-treated (PT) lumber, it's cheaper and it holds up fine. What the contractor didn't offer was a side-by-side number comparison. That's what the homeowner decided to build herself.

The project: a 16×12 foot deck, ground level, attached to the back of a 1940s craftsman. Enough room for an outdoor dining set and a couple of chairs. Seattle's famously wet climate — over 150 days of measurable rainfall per year — made the lumber choice feel like a real decision rather than a default.

Building the Comparison

The homeowner opened the Deck Calculator and entered the project dimensions. The deck would use 5/4×6 boards at 16-foot lengths, 16" OC joists. The calculator returned the board count: 26 decking boards, 13 joists, and 5 posts.

She then ran those board counts through the Lumber Calculator twice — once priced at her local lumber yard's current PT rate, once at their western red cedar rate.

| Material | PT (Southern Yellow Pine) | Western Red Cedar | |---|---|---| | Decking boards (26 × 16 ft) | $624 | $842 | | Joists (13 × 12 ft, 2×8) | $211 | $286 | | Posts (5 × 4×4 × 8 ft) | $89 | $121 | | Total lumber cost | $924 | $1,249 | | Difference | — | +$325 (35% more) |

The PT option was $325 less upfront. That number sounds clear-cut until you run the lifespan math.

The 10-Year Calculation

PT lumber in the Pacific Northwest carries a meaningful asterisk. The chemical preservatives protect against rot, but PT boards also check (crack) and warp more aggressively than cedar as they dry out after installation. In Seattle's damp climate, that means boards that look rough in 5–7 years and typically need replacement or full resurfacing in 10–12 years.

Western red cedar, by contrast, contains natural oils — thujaplicins — that resist rot and insect damage without chemical treatment. In Pacific Northwest conditions, a well-sealed cedar deck typically performs for 20–25 years with periodic cleaning and re-sealing every 3–4 years.

Run that lifespan difference through a simple cost-per-year table:

| Option | Upfront Cost | Expected Lifespan | Cost Per Year | |---|---|---|---| | Pressure-treated | $924 | 10–12 years | $77–$92/yr | | Western red cedar | $1,249 | 20–25 years | $50–$62/yr |

On a per-year basis, cedar is the less expensive option — by roughly $25–$30 a year — despite costing more upfront. The homeowner also factored in that PT replacement in 10 years would involve both new lumber costs and the labor to demo and rebuild, making the true lifecycle cost comparison even more favorable to cedar.

The Decision

She went with western red cedar.

The full material order — decking, joists, posts, joist hangers, decking screws, and flashing — came to $1,640 including hardware. She hired a neighbor with framing experience to help for two weekends; total labor was her own time plus one paid day.

The deck was completed in mid-November, just before Seattle's winter rains set in. She applied a penetrating oil sealer rated for naturally rot-resistant species, which is a better choice for cedar than film-forming sealers that can trap moisture beneath the surface.

What This Project Teaches

The upfront number is not the right number. For a long-lived outdoor structure, cost-per-year almost always tells a different story than sticker price. Running the same board count through the lumber calculator twice — at different material prices — made a $325 difference visible as a 20+ year decision rather than a one-weekend decision.

Regional climate changes the math. PT lumber is a perfectly reasonable choice in dry climates where freeze-thaw and constant moisture aren't factors. In the Pacific Northwest, that calculus shifts. What's right in Phoenix may not be right in Seattle.

Know your quantities before you compare prices. Getting an accurate board count first — not a rough guess — meant the homeowner was comparing apples to apples across two lumber yards and two species. Both the deck calculator board count and the lumber cost calculation were based on the same inputs.

Use the Deck Calculator to get your board count, then price that count in the Lumber Calculator at the rates your local yard quotes. The comparison takes less than five minutes and gives you something real to base a long-term decision on.