2026 Puget Sound ADU cost report
Real $/sqft by city · No $250 headlines
We pulled the closing costs on every ADU and major remodel Golden State permitted in the last 24 months and normalized them to per-square-foot ranges by city, build type, and finish tier. This is what construction actually costs in the Puget Sound right now — not the number a salesperson quotes you on a discovery call.
$/sqft by city — hard cost only
Ranges reflect mid-tier finishes on a typical 600–900 sqft DADU or a 1,200–1,800 sqft interior remodel. Add 14–22% for soft costs (design, permits, geotech, surveys).
| City | County | Detached ADU | Garage Conv. | Attached / AADU | Permit + Tap Fees | Notes |
|---|---|---|---|---|---|---|
| Seattle | King | $330–$380 | $230–$300 | $285–$345 | $9k–$22k | SDCI design review surcharge on larger lots; sewer cap fees in older neighborhoods. |
| Bellevue | King | $335–$380 | $235–$305 | $290–$350 | $11k–$26k | LUC R-rated zoning slows review when lot coverage > 35%. |
| Kirkland | King | $330–$375 | $230–$295 | $285–$340 | $8k–$20k | DADU encouraged; tree retention drives site work cost on sloped lots. |
| Redmond | King | $330–$378 | $230–$298 | $285–$345 | $9k–$21k | Faster review than Seattle; geotech often required east of 148th. |
| Sammamish | King | $340–$380 | $240–$305 | $290–$350 | $10k–$24k | Critical-areas overlays add $4k–$12k in studies. |
| Tacoma | Pierce | $330–$360 | $220–$285 | $275–$330 | $6k–$15k | Lowest fee schedule on the I-5 corridor; sewer side-sewer rebuilds common. |
| Puyallup | Pierce | $330–$358 | $215–$280 | $270–$325 | $5k–$13k | School impact fees apply to net new bedrooms. |
| Everett | Snohomish | $330–$365 | $225–$290 | $278–$335 | $7k–$17k | Snohomish PUD service upgrades 200A common on older lots. |
| Lynnwood | Snohomish | $330–$370 | $228–$292 | $280–$338 | $7k–$18k | Stormwater detention triggers above 2,000 sqft of new impervious. |
| Olympia | Thurston | $330–$355 | $215–$280 | $270–$325 | $5k–$13k | Thurston County wells/septic add scope on unincorporated parcels. |
What actually moves the number
Crane vs. all-hand framing swings detached ADU labor by $18–$35/sqft.
Stem wall vs. monolithic slab differs $9–$14/sqft; pin piles add $14k–$28k where required.
Side-sewer reroute and meter upsize commonly $8k–$22k in Seattle and Tacoma.
Heat-pump + envelope upgrades add ~$6–$11/sqft over 2018 baseline.
Builder-grade vs. mid-tier finishes swings $22–$40/sqft on a 700 sqft DADU.
Discretionary review in Seattle/Bellevue adds 4–9 weeks of carry cost.
Methodology
- Sample: 41 permitted Golden State projects closed 2023-08 → 2025-11 across King, Pierce, Snohomish, Thurston.
- Hard costs only in $/sqft columns. Soft costs (design, permits, geotech, surveys, utility connection) shown separately.
- Garage conversion $/sqft reflects net new conditioned area, not raw garage footprint.
- All numbers exclude site demolition over $8k, retaining walls > 4 ft, and accessory site features (patios, fences, irrigation).
Press and researchers may cite this report freely with attribution to Golden State ADU Builders — 2026 Puget Sound ADU Cost Report. For the raw permit list, email office@golden-adu.com.
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