ADU Construction & DADU Design-Build in Seattle & the Puget Sound
ADU construction for attached units, detached ADUs and backyard cottages in Seattle and the Puget Sound, with design-build delivery and Passive House performance available.
Seattle & Puget Sound ADU Construction
We carry attached ADU construction and detached DADU projects from early site and zoning review through design, permitting, construction, testing and handover. For a plain-language explanation of the terms and the practical differences between attached and detached units, read our ADU vs DADU guide for Washington homeowners.
- Feasibility: property, zoning, setback, lot-coverage and utility review.
- Design and permits: livability planning, energy modeling and permit coordination.
- Construction: high-performance building, testing and move-in-ready handover.
About Our ADU & DADU Construction Services
Seattle’s ADU-friendly zoning makes it one of the best cities in the country for backyard cottages and Detached Accessory Dwelling Units (DADUs). We build ADUs to Passive House standards, super-insulated, airtight, and incredibly efficient, so your rental unit, guest house, or aging-in-place suite costs almost nothing to heat and cool. These small, efficient buildings are the perfect canvas for Passive House construction: manageable budgets, incredible performance, and they pay for themselves through rental income.
- Detached ADUs (DADUs) and backyard cottages up to 1,000 sq ft
- Attached ADUs including basement conversions and garage conversions
- Passive House performance with ultra-low energy costs
- Full kitchens, bathrooms, and living spaces designed for independent living
- Aging-in-place design with accessible features and single-floor layouts
- Rental-ready finishes with separate entrances and utilities
Our ADU & DADU Construction Process
Site & Zoning Review
We evaluate your property for ADU feasibility, review zoning requirements, setbacks, lot coverage limits, and utility connections.
Design & Energy Modeling
We design your ADU to maximize livability within the allowed footprint while achieving Passive House energy performance.
Permitting
We handle all City of Seattle permits, including building, mechanical, electrical, and plumbing. We navigate the ADU-specific requirements.
Passive House Construction
Our crew builds your ADU with the same precision and attention to airtightness and insulation as our full-size Passive House projects.
Testing & Handover
Blower door testing, energy performance verification, and complete walkthrough. We hand over a move-in ready space with your 5-year labor warranty.
ADU & DADU Construction Service Areas
We provide adu & dadu construction services throughout Seattle & the Puget Sound. Click on a location to learn more about our services in your area.
Frequently Asked Questions
Do you build both attached ADUs and detached backyard cottages?
Yes. Our ADU/DADU construction services include attached units such as basement and garage conversions as well as detached backyard cottages. If you are still deciding which format fits your property, start with our ADU vs DADU comparison guide.
How much does an ADU cost to build in Seattle?
ADU costs in Seattle vary by type. Attached ADUs often range from $85,000-$280,000 depending on the existing basement, garage, or addition scope. New DADUs commonly range from $175,000-$550,000 depending on size, site access, utility work, finishes, and whether Passive House performance is included.
How long does ADU construction take in Seattle or King County?
Attached ADUs commonly take 8-12 months from contract to certificate of occupancy. New DADUs often take 12-18 months because they require separate foundation, utility, structural, permit, and inspection work. City review time varies by Seattle, SeaTac, Bellevue, Kirkland, Renton, and other King County jurisdictions.
Can we handle ADU zoning review and permitting?
Yes. We review the property for ADU feasibility, zoning requirements, setbacks, lot coverage and utility connections, then coordinate the building, mechanical, electrical and plumbing permits required for the project.
Can a Passive House ADU really have near-zero energy costs?
Yes. A well-built Passive House ADU in Seattle’s mild climate can have total heating and cooling costs under $20/month. Many of our ADU clients add a small solar array to achieve true Net Zero.
Ready for Your ADU & DADU Construction Project?
Contact Love Construction today for a free consultation.