Composite Decks in Seattle

Five local firms publish their own numbers, and the spread says a lot about what each one includes:

• A Kirkland builder: $28–$45 per square foot installed
• A Puget Sound builder: $35–$65
• A Bothell builder: $40–$75
• An Eastside builder: $60–$110
• A Snohomish County builder: $70–$95, with framing, decking, railing and stairs included

The middle of that spread is where the table above lands. As a worked example, a 300 square foot Trex deck with aluminum railings usually lands in the $14,000 to $22,000 range. Eastside pricing is similar from town to town, including Bellevue and Redmond. The Seattle deck cost guide ranks everything else that moves the total.

It comes down to upkeep. A cedar deck wants restaining every two to three years at $6–10 per sq ft, and a sanding, staining and sealing cycle runs roughly $1,200 to $1,800, every 18 to 24 months. Composite boards skip that work, so the gap narrows over time. If the upfront number matters more, read the cedar and pressure-treated deck guide.

A pressure-treated wood frame, which runs $3,500 – $7,000 on a typical Seattle build with 2x8 joists and 6x6 posts. The frame is where a deck lasts or fails: the ledger board plus flashing adds $400 – $1,200, a detail builders here call non-negotiable in this climate. Butyl joist tape adds about ~$200 per deck.

Seattle's own rules apply to the frame too. The city requires a minimum live load design of 60 pounds per square foot, and a ledger must be connected so the deck will not pull away from the house during an earthquake. The Seattle deck permit guide covers the rest.

Cable rail adds $80–$150 per linear foot around Seattle and glass panels $150–$300, which is why railings often surprise people. An Everett-area builder prices composite railings at $120 - 150 per linear foot with labor and materials. Glass guardrails in Seattle have special code requirements, and the city notes you may need a structural engineer to design one.

The product line, the frame, the ledger flashing, railings and stairs, removal and who pulls the permit, each as its own line:

• The decking product line and color, and the fastening method
• Frame lumber, joist spacing and whether joist tape is included
• Ledger attachment and flashing at the house wall
• Railing type and linear feet, stairs and landings
• Removal of the old deck, if there is one
• Who applies for the permit and whether the fee is in the price

The checklist for choosing a deck builder explains how to check a company's Washington registration before you sign.