What will your ADU actually cost?
Move the sliders to estimate the real, all-in cost of building a detached ADU (DADU) or custom home in the Greater Seattle area — design, permitting, site work and construction together. Built on the same honest 2026 numbers we use on real projects.
Real numbers, no lowball games.
This is an all-in estimate for planning. The exact figure for your property comes from a feasibility study of your specific lot — but this gets you honestly in the ballpark in seconds.
Estimate only. Your real number depends on your specific lot, design and finishes — we confirm it with a Pre-Construction Planning feasibility study.
Where the dollars actually go.
A believable ADU estimate has to include all three of these — the advertised “per square foot” number almost always hides the first two, and that's exactly where budgets blow up on a real Seattle lot.
Design & Permitting (Soft Costs)
Architecture, engineering, permits, geotech
Site Development & Difficult Lots
Slopes, ECAs, utilities, grading, retaining walls
Actual Construction (Hard Costs)
Foundation through finishes
Want the full picture on Seattle ADU pricing? Read our guide on how much a DADU costs in Seattle, see our realistic all-in cost breakdown, or browse ready-to-build floor plans.
“From the beginning I felt professionalism and trust — DIGS navigated the permit process seamlessly.”
The honest answers.
How much does it cost to build a DADU in Seattle?
Most detached ADUs (DADUs) in the Greater Seattle area run about $375,000 to $600,000+ all-in, or roughly $350–$600+ per square foot. That figure includes design, permitting, site development and construction — not just the stripped-down "cost per square foot" that ignores everything below grade. Your number depends on size, finish level and how difficult your lot is to build on.
Why is the DIGS calculator higher than the $200–$300/sq ft I see elsewhere?
Because those numbers are usually hard construction costs only. On a real Pacific Northwest lot you also pay for design and permitting (about 10–15%) and site development — slopes, Environmental Critical Areas, utilities, grading and retaining walls — which can add 15–30%+. Our calculator shows the honest all-in cost so you can budget with facts, not surprises.
What makes an ADU cost more or less?
The three biggest levers are size (square footage), finish level (standard vs. premium vs. luxury materials and fixtures), and site conditions. A flat, simple lot with utilities nearby is far cheaper to develop than a steep lot with critical areas or long utility runs.
Does the estimate include permits and site work?
Yes. The calculator bundles design & permitting (soft costs), site development, and construction (hard costs) into one all-in range — the same three categories DIGS breaks out on every real project.
How do I get an exact price for my lot?
The calculator gives you a realistic range; the exact number comes from a Pre-Construction Planning feasibility study, where we research your zoning, setbacks, Environmental Critical Areas, utilities and soils and hand you a firm starting price for your specific property.
Serving Seattle, King & Snohomish County · (206) 900-6072
Price your ADU for real.
Tell us about your lot and your goals. Eric follows up personally — the same person from the first call through final inspection. No pressure, no obligation.
- Owner-led — 35+ years, 100+ homes built
- Clear, line-item pricing · no hidden fees
- Serving Seattle, King & Snohomish County