ADU Construction in Seattle, WA

An ADU is any accessory dwelling unit added to a residential property, while a DADU is specifically a detached structure built separately from the main home. Seattle allows both types, and under current rules you can build one of each on the same lot in Bellevue, Kirkland, and across the greater Seattle area.

Most single-family residential lots in Seattle and surrounding cities like Redmond and Sammamish now qualify for at least one ADU under Washington State's HB 1337. Factors like lot size, slope, existing structures, and proximity to environmentally critical areas still affect what is buildable on your specific parcel.

Yes, adding an ADU increases your assessed property value, which raises your annual tax bill, but only the ADU itself gets a new value assigned, not your existing home. In King County, the combined levy rate typically runs between $10 and $12 per $1,000 of assessed value, so the increase is a fixed annual cost to weigh against rental income or added equity.

Skipping a thorough site feasibility review before committing to a design is one of the most costly mistakes Seattle homeowners make. Lot conditions like steep grades, existing easements, or proximity to shorelines or environmentally critical areas can require design changes mid-project, which drives up cost and delays the build.

Building an ADU permanently increases your property tax bill, requires navigating Seattle Department of Construction and Inspections permitting, and demands careful coordination of trades, utilities, and site conditions. Homeowners who underestimate the planning complexity often face budget overruns, which is why detailed upfront coordination matters on every project.

Yes, we build ADUs and DADUs throughout Seattle, Bellevue, Mercer Island, Kirkland, Redmond, Issaquah, Sammamish, Woodinville, Bothell, Kenmore, Bainbridge Island, Clyde Hill, Gig Harbor, Fox Island, Poulsbo, and Maple Valley. Each project is managed with the same hands-on approach regardless of location.