Ask House Spouse · Exterior & Weatherproofing · Decks & Outdoor Structures
What does it cost to replace a deck in the Seattle area?
Short answer
A full deck replacement in the Seattle area typically costs between $80 and $200+ per square foot. For a common 400 sq. ft. deck, this means a pressure-treated wood deck might cost $32,000-$50,000, while a high-end composite deck could exceed $80,000. The final price hinges on materials, railing style, foundation condition, and permit requirements.
Key Cost Factors in a Deck Replacement
Several major factors influence the final cost of a new deck. The choice of decking material is the largest variable: pressure-treated wood is the most affordable, cedar offers a natural look at a mid-range price, and composite materials (like Trex or TimberTech) are the most expensive upfront but offer low maintenance. The condition of the existing foundation is another critical factor. If footings are sound and properly located, they may be reusable, saving significant cost. Finally, the complexity of stairs, railing style (wood, metal, cable), and any added features like built-in benches or lighting will impact the total price.
Repair or Replace: Making the Right Call
Deciding whether to repair or replace your deck comes down to the condition of its underlying structure. If the main posts, beams, and joists are solid, and only a few surface boards are worn, repairs are a viable option. However, if you find rot in the main support posts or, most critically, in the ledger board that secures the deck to your home, a full replacement is almost always necessary for safety. Widespread rot in the joist system also points toward replacement, as piecemeal repairs become impractical and less cost-effective.
The Deck Replacement Process
A professional deck replacement follows a clear process. It begins with a structural assessment and design phase, followed by securing necessary permits from your local municipality. Next is the demolition and removal of the old deck. Then, we construct the new frame, ensuring the ledger board is properly flashed and attached to the house structure. After the frame is approved by a city inspector, the decking, stairs, and railings are installed. The project concludes with a final inspection to ensure every aspect meets current building codes.
Why the Ledger Board is So Critical
In the rainy Pacific Northwest, the single most common point of failure for a deck is the ledger board. This is the piece of lumber that attaches the deck directly to your house. If not installed with proper metal flashing, water runs behind it, rotting both the ledger and the house's framing. Modern codes require very specific bolting patterns and weatherproofing techniques that were often overlooked in older construction. Any sign of softness, sagging, or a gap at the ledger board is a major red flag that warrants immediate professional inspection.
Why it happens
Decks in the Pacific Northwest have a finite lifespan due to our relentless moisture. The primary cause for replacement is wood rot, which compromises the structural integrity of posts, joists, and especially the ledger board where the deck attaches to the house. Over time, fasteners corrode, boards warp and split, and railings become loose. Furthermore, building codes evolve; a deck built 20 years ago may no longer meet today's stringent safety standards for railings, stairs, and structural connections, necessitating a full replacement rather than a simple repair.
How to diagnose it
- 1Probe for rot. Use a screwdriver to press firmly on posts, stair stringers, and the ledger board. If the wood is soft or spongy, rot is present.
- 2Check for stability. Vigorously shake the railings. They should feel solid with no give. Walk across the deck and feel for excessive bounce or springiness.
- 3Inspect the ledger board. Look where the deck attaches to the house. There should be no gap, and you should see proper flashing designed to keep water out.
- 4Examine the structure from below. Look for dark stains, moss, or fungal growth on the joists and beams, which are all signs of water intrusion.
- 5Look for corroded fasteners. Check if screws, bolts, and joist hangers are rusted, as this can indicate a loss of structural strength.
- 6Assess the decking surface. Look for widespread cupping, deep splits, or boards that are deteriorating and holding moisture.
DIY vs. professional
DIY-friendly if…
DIY is appropriate for staining, sealing, or replacing a few individual deck boards on a deck that is otherwise structurally sound.
Call a pro when…
A full deck replacement is a major construction project that requires a licensed general contractor for structural framing, code compliance, and permitting.
Cost expectations
$32,000–$80,000typical WA labor + materials
For a 400 sq. ft. (20'x20') deck. Low end represents pressure-treated wood; high end represents composite materials, new footings, and complex railings.
Every House Spouse job is quoted in writing before we start. 12-month workmanship warranty included.
What we see on Home Health Assessments
Roughly 71% of homes older than 8 years show one or more failed caulk joints letting water into wall assemblies.
Caught early on assessment: $220–$750 · Left until failure: $1,200–$8,500
A Home Health Assessment includes a detailed inspection of your deck's structure, from the footings and posts to the ledger board connection and railings. We identify rot, fastener corrosion, and code compliance issues to give you a clear picture of its remaining lifespan and safety.
How the Home Health Assessment worksServices we'd bring to this job
Where we handle this
We answer this question on real Home Health Assessments across Snohomish and King County.