DADUSeattleWA.com · Free educational tool
Explore a Backyard Cottage Budget
Change the size, site conditions and construction choices to explore a planning budget.
Estimated Project Cost
$465,000 – $700,000
Starting configuration: New one-story backyard cottage, 750 sq. ft., standard finishes. Figures are project planning estimates, not binding quotes.
Pricing basis: October 2026. Version 2026.10.1.
How the planning range is calculated
Estimates use the published construction rates, project minimums, selected allowances, planning/design fees, applicable modeled sales tax and a separate contingency. Actual costs depend on the property and project scope.
Included in construction: Standard kitchen and first bathroom, normal labor, ordinary building systems, typical overhead/profit and structure appropriate to the selected project type are included in the base rate. Special conditions and owner-paid fees appear separately.
Not necessarily included: Land purchase, financing, major hidden conditions, unforeseen geotechnical work, extraordinary utility infrastructure, future price increases and unknown site-specific agency requirements may not be priced.
Source status: Published editorial planning rates; not contractor bids or official fee schedules. Editorial review: 2026-10-27; pricing version 2026.10.1.
Seattle permit amounts are planning allowances. Refer to Seattle SDCI for applicable official fees. Seattle permit fee guidance.
Frequently asked questions
Does this calculator confirm my project will be permitted?
No. Seattle zoning, building, fire and utility requirements depend on the specific site and design. Use Seattle SDCI guidance for permit and eligibility information.
Why does the estimated budget change with size?
Construction changes with area but fixed design, review and infrastructure costs do not scale evenly. The model also applies minimum construction amounts to small projects.
Are these current contractor bids?
No. These are independent budgeting estimates calculated from the listed rates and options, not contractor bids or official City of Seattle fees.
Learn why costs change
- Understanding site work costsLearn why slope and equipment access change project scope.
- Utility connection expensesExplore utility runs, infrastructure and service connections.
- Building shape and design costsRead about one-story, two-story and complex layouts.
- Interior finish allowancesSee how flooring, cabinets and other finishes affect the budget.
- What a DADU estimate includesUnderstand common budget categories and exclusions.
This is an independent educational estimate, not a contractor quote, zoning approval, legal advice or official fee calculation. Unknown subsurface, structural and utility conditions can exceed the displayed range.