Estimating additions and ADUs in Seattle, WA
Prices for additions and ADUs in Seattle, WA, how they compare with the national median and what to know when bidding here, for remodeling contractors.
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Room addition prices in Seattle
Q4 2026 pricing. Ranges are rounded to the nearest $50, or $100 from $5,000 up.
1 story over a basement
$54,700 to $359,800
150 to 1,000 square feet
National median: $45,700 to $302,100.
2 story over a basement
$82,600 to $549,500
150 to 1,000 square feet
National median: $69,300 to $464,400.
How Seattle compares
Across the work in the cost data, Seattle prices run 16% above the national median.
More work in Seattle
- Kitchen remodelsCabinets, countertops, appliances and finishes.
- Bathroom remodelsTile, fixtures, vanities and plumbing rough-ins.
- GaragesOne and two car garages, framed and sided.
- Decks and porchesFraming, decking, railings and stairs.
- PaintingInterior and exterior, by surface area and substrate.
- Electrical workService upgrades, rough-ins, fixtures and finish work.
- All of Seattle, WAEvery category, against the national median.
- Additions and ADUs nationallyNational ranges, cost drivers and the estimate's structure.
Estimate additions and ADUs with Seattle prices
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