Home Addition Cost in Seattle (2026): Average Price & Estimate

Home Addition Cost in Seattle

Estimated home addition cost in Seattle

$52,800–$158,400

Roughly about 32% above the national average.

High labor rates and wet-climate detailing raise costs.

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Addition size (square feet)

Addition type

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Based on Seattle, WA pricing.

Estimated cost range

$52,800–$158,400

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An estimate for planning, not a quote. Get written quotes from local pros below.

Estimate, not a quote. Local prices vary by contractor and project. These are 2026 estimates for Seattle, WA. Get written quotes from licensed Seattle contractors before you budget.

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What to know about home addition in Seattle

Soil movement around Seattle is usually modest, but local soil type still drives the right approach.

What affects home addition cost in Seattle

Beyond the local market, the same factors that drive home addition cost everywhere apply in Seattle:

Addition size in square feet.
Type: a bump-out is cheapest, a second-story addition the most expensive.
Whether it includes a kitchen or bathroom (plumbing).
Foundation, framing, roof, and tie-in to the existing structure.

Home Addition cost by addition type in Seattle

These figures are adjusted for Seattle pricing (about 1.32x the national average), so they reflect what local homeowners actually pay.

Estimated home addition cost by addition type in Seattle (2026)

Addition type	Cost in Seattle	Typical total
Bump-out (a few feet)	$106 to $317 /sq ft	About $42,200 to $126,700
Sunroom	$119 to $356 /sq ft	About $47,500 to $142,600
Single room addition	$132 to $396 /sq ft	About $52,800 to $158,400
In-law / suite with bath	$158 to $475 /sq ft	About $63,400 to $190,100
Second-story addition	$185 to $554 /sq ft	About $73,900 to $221,800

Frequently asked questions

How much does home addition cost in Seattle?

In Seattle, WA, home addition typically costs $52,800 to $158,400 in 2026 for a standard project, about 32% above the national average. Your exact price depends on size, materials, and scope.

Why does home addition cost more or less in Seattle?

High labor rates and wet-climate detailing raise costs. Labor rates, permit costs, and local demand are the main reasons Seattle prices differ from the national average.

Do I need a permit for home addition in Seattle?

Most home addition projects require a permit. Requirements vary by city and Washington jurisdiction, so confirm with your local building department. A licensed contractor usually pulls the permit for you.

When is the best time of year for home addition in Seattle?

In Seattle, the mild climate means most projects can run year-round, with only the occasional rainy stretch to plan around.

Is home addition cheaper outside Seattle?

Sometimes. Seattle runs about 32% above the national average. Nearby smaller towns with lower labor costs can come in cheaper, while denser urban areas often cost more. Always compare quotes from contractors who serve your specific area.