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DATA_INDEX / COST_PER_SQFT

ADU cost per sqft by city + size

One row per city × size band. Click any cell for the full line-item breakdown.

City400 sqft600 sqft800 sqft1,000 sqft1,200 sqft
Seattle$720–$880$640–$790$580–$720$540–$680$520–$660
Bellevue$778–$950$691–$853$626–$778$583–$734$562–$713
Kirkland$756–$924$672–$830$609–$756$567–$714$546–$693
Redmond$749–$915$666–$822$603–$749$562–$707$541–$686
Tacoma$612–$748$544–$672$493–$612$459–$578$442–$561
Sammamish$756–$924$672–$830$609–$756$567–$714$546–$693
Issaquah$734–$898$653–$806$592–$734$551–$694$530–$673
Renton$670–$818$595–$735$539–$670$502–$632$484–$614
Mercer Island$821–$1003$730–$901$661–$821$616–$775$593–$752
Shoreline$684–$836$608–$751$551–$684$513–$646$494–$627
Everett$648–$792$576–$711$522–$648$486–$612$468–$594
Mukilteo$698–$854$621–$766$563–$698$524–$660$504–$640
Lynnwood$655–$801$582–$719$528–$655$491–$619$473–$601
Edmonds$706–$862$627–$774$568–$706$529–$666$510–$647
Mountlake Terrace$662–$810$589–$727$534–$662$497–$626$478–$607
Mill Creek$691–$845$614–$758$557–$691$518–$653$499–$634
Bothell$698–$854$621–$766$563–$698$524–$660$504–$640
Woodinville$720–$880$640–$790$580–$720$540–$680$520–$660
Burien$648–$792$576–$711$522–$648$486–$612$468–$594
SeaTac$634–$774$563–$695$510–$634$475–$598$458–$581
Tukwila$626–$766$557–$687$505–$626$470–$592$452–$574
Des Moines$655–$801$582–$719$528–$655$491–$619$473–$601
Federal Way$634–$774$563–$695$510–$634$475–$598$458–$581
Kent$634–$774$563–$695$510–$634$475–$598$458–$581
Auburn$619–$757$550–$679$499–$619$464–$585$447–$568
University Place$662–$810$589–$727$534–$662$497–$626$478–$607
Lakewood$605–$739$538–$664$487–$605$454–$571$437–$554
DuPont$662–$810$589–$727$534–$662$497–$626$478–$607
Puyallup$612–$748$544–$672$493–$612$459–$578$442–$561
Lacey$598–$730$531–$656$481–$598$448–$564$432–$548
Tumwater$598–$730$531–$656$481–$598$448–$564$432–$548
Olympia$605–$739$538–$664$487–$605$454–$571$437–$554
FAQ

Cost per square foot — frequently asked

  • Why does cost per square foot vary by ADU size?

    Fixed costs (foundation per linear foot of perimeter, kitchen, bath, MEP terminations, permit fees, mobilization) spread across more square footage as you build bigger. A 380 sq ft studio is $310–$380/sq ft in Seattle 2025; a 950 sq ft two-bedroom is $355–$425/sq ft. Per-sq-ft is lower on smaller units sometimes but only because finish package is thinner — apples-to-oranges.

  • What's included in your $/sqft numbers?

    All-in turn-key cost: site prep, foundation, framing, weather barrier, roofing, windows, MEP rough and finish, insulation, drywall, paint, flooring, cabinets, countertops, standard appliances, bath fixtures, side-sewer connection, electrical service upgrade if needed, permits, plan check, design fees, our overhead and profit. Not included: landscaping, fencing, solar PV, art.

  • How accurate are per-sqft numbers across cities?

    Within ±10% of actual closed-contract values for typical lots. Outliers — steep slope, critical areas, off-grid utilities, premium finishes — can swing 20–35% above the published band. The cost-per-sqft tables are starting points for budgeting; final number always comes from a feasibility study or pre-construction estimate for your specific site.

  • Why is Seattle more expensive than Tacoma?

    Three drivers: (1) higher labor cost (Seattle metro construction wages 12–18% above Tacoma); (2) higher AHJ fees (Seattle plan check ~60% above Tacoma); (3) higher land/site cost (tighter lots mean more site work per sq ft, more carrying cost). Build quality is comparable — we run the same crews. Tacoma is a real cost advantage if your project is there.

  • Do bigger ADUs cost less per square foot?

    Usually yes up to about 900 sq ft, then it flattens. Going from 600 → 800 sq ft typically drops $/sq ft by 6–12%. Going from 800 → 1,000 drops only 2–5% because you start needing a second bedroom plumbing wall and possibly a larger HVAC system. The sweet spot for $/sq ft in 2025 is 800–900 sq ft.

  • Where can I see the underlying data?

    Every cost-per-sqft table on the site cites: (1) median of our closed contracts in the last 12 months, (2) range from 25th–75th percentile, (3) sample size, (4) last refresh date. We do not publish individual project costs without client consent. For a sanity check from a third party, ask any active ADU lender for their current $/sq ft underwriting band — they will line up close to ours.