ADU & DADU Construction in Seattle & the Puget Sound
Love Construction offers accessory dwelling unit (ADU) and detached ADU (DADU) construction services throughout Seattle and the broader Puget Sound region. A notable aspect of their approach is that they build these units to Passive House standards — meaning super-insulated, airtight construction designed for very low energy use.
Seattle's zoning rules are relatively accommodating for ADU projects, allowing both an attached ADU and a detached ADU on most single-family lots, which means up to three dwelling units on a single property. DADUs can be up to 1,000 square feet. Love Construction handles all zoning research and permitting as part of their process.
Planning Costs and Timelines
For homeowners considering an ADU project in Seattle, it helps to understand the general cost ranges and timelines involved:
- Attached ADUs (basement conversions, garage conversions): typically range from $85,000 to $280,000, depending on the existing structure and scope of work.
- Detached ADUs / backyard cottages: typically range from $175,000 to $550,000, depending on size, site access, utility work, and finishes.
- Design and permitting: generally 3 to 9 months.
- Construction: typically 8 to 18 months depending on project type.
Attached ADUs tend to cost less because they make use of existing structure. Detached ADUs require a separate foundation, roof, utilities, and site work, which adds to both cost and timeline.
Love Construction's ADU and DADU services include:
- Detached ADUs 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
Their Construction Process
Love Construction follows a structured process for ADU and DADU projects:
- Site & Zoning Review: They evaluate the property for ADU feasibility, reviewing zoning requirements, setbacks, lot coverage limits, and utility connections.
- Design & Energy Modeling: The ADU is designed to maximize livable space within the allowed footprint while targeting Passive House energy performance.
- Permitting: They manage all City of Seattle permits, including building, mechanical, electrical, and plumbing, navigating ADU-specific requirements.
- Passive House Construction: Their crew builds with attention to airtightness and insulation consistent with Passive House standards.
- Testing & Handover: Blower door testing and energy performance verification are completed before handover. The project comes with a 5-year labor warranty.
A well-built Passive House ADU in Seattle's climate can result in total heating and cooling costs under $20 per month. Some clients also add a small solar array to reach Net Zero energy performance. Love Construction provides ADU and DADU construction services throughout Seattle and the Puget Sound area, including King County jurisdictions such as Bellevue, Kirkland, Renton, and SeaTac.
