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adu & home addition cost calculator
Estimate ADU, DADU, and home-addition costs across Seattle, the Eastside, and Snohomish County. Configure project type, size, site conditions, and financing to see live construction cost ranges, rental-income projections, and break-even timelines based on 2025–2026 Puget Sound data.
Evercrest's ADU cost calculator gives Seattle and Puget Sound homeowners a fast, realistic starting point for the cost of a detached backyard cottage (DADU), an attached ADU, or a home addition. Set the project type, square footage, site conditions, and finish level, and the tool returns a live construction cost range plus rental-income and break-even projections built on 2025–2026 King and Snohomish County data.
Every lot and design is different, so treat the result as a planning range, not a quote. Real costs move with site access, foundation and utility work, permits, and how custom your finishes are — smaller units often cost more per square foot because kitchen, bath, design, and permit costs are largely fixed. Eastside cities like Bellevue and Kirkland typically run somewhat higher than the regional average.
When you're ready to turn an estimate into a real plan, request a free ADU feasibility review — we check your lot's zoning, sizing, and placement — or a fixed-price quote from Evercrest LLC, a licensed, bonded, and insured Seattle general contractor.
frequently asked questions
How much does it cost to build an ADU in Seattle?+
Most detached ADUs (DADUs) in the Seattle area run roughly $125,000–$350,000, with a typical two-bedroom DADU around $320,000, depending on size, site conditions, and finishes. Use the calculator for a range tuned to your project, then book a free feasibility review for an exact figure.
How accurate is this calculator?+
It's a planning-grade estimate based on recent Puget Sound project data — great for budgeting and comparing scenarios. Your exact, fixed price comes from a free Evercrest consultation once we've reviewed your lot and design.
Can I build an ADU on my lot?+
Most single-family lots in Seattle and King County now allow at least one ADU, but setbacks, lot size, and utilities vary by property. Request a free ADU feasibility review and we'll confirm exactly what your lot allows.