Overview
A garage conversion is often the most affordable way to add an ADU to your property. Since the structural shell — foundation, walls, and roof — already exists, you're primarily paying for the interior buildout: insulation, plumbing, electrical, kitchen, bathroom, and finishes.
Under both Seattle's SMC 23.44.041 and Washington's HB 1337, existing legal nonconforming structures can be converted into ADUs even if they don't meet current setback or lot coverage standards. This is a major advantage for older Seattle homes with garages that were built before today's zoning rules.
A typical two-car garage (400–600 sq ft) converts into a comfortable studio or one-bedroom unit. For homeowners on tighter lots — especially in neighborhoods like Capitol Hill, Beacon Hill, Ballard, or West Seattle — a garage conversion may be the most practical ADU option when setback requirements limit new construction.
Our team assesses the structural integrity of your existing garage, designs the interior layout to maximize livability, handles all permitting through Seattle DCI or King County DPER, and manages the conversion from demo through final inspection.
What's Included
- Structural assessment of existing garage
- Interior design optimized for ADU livability
- Full insulation (walls, ceiling, floor) to residential standards
- New plumbing — kitchen, bathroom, and laundry hookups
- Electrical upgrade to support dwelling unit loads
- Egress windows per building code
- Separate entrance with direct street access
- Fire separation between units (if attached garage)
- Change-of-use permit and building permits handled by our team
Explore your options: Already have a basement? Check our basement ADU conversion. Wondering about other conversions? Read ADU vs shed conversion. Want to build new? See our detached ADU construction.
See the full cost breakdown, understand parking requirements, or explore financing options.
Garage conversions are great for house hacking and rental income. Check if your property qualifies with our free feasibility study.
Best neighborhoods for garage conversions: Ballard, Beacon Hill, Greenwood, and Rainier Valley.
Frequently Asked Questions
How much does a garage conversion cost in Seattle?
Garage conversion ADUs in Seattle typically range from $200,000 to $325,000, making them the most affordable ADU type. Total project costs average $500–$600 per square foot including design, permitting, and construction. The exact cost depends on the garage's current condition, size, whether it's attached or detached, and your finish level. A well-maintained detached two-car garage is the ideal starting point.
Can I convert my garage even if it doesn't meet setback requirements?
Yes. Under both HB 1337 and Seattle's code, existing legal nonconforming structures can be converted into ADUs even if they don't meet current setback or lot coverage standards. This is one of the biggest advantages of garage conversions.
What size ADU can I get from a garage conversion?
A standard single-car garage yields about 200–300 sq ft (studio), while a two-car garage yields 400–600 sq ft (one-bedroom). Some oversized garages can produce units up to 800 sq ft. The converted space must include a kitchen, bathroom, sleeping area, and living area to qualify as a dwelling unit.
Do I lose my parking if I convert my garage?
You'll lose covered parking, but if your property is within ½ mile of a transit stop, no replacement parking is required. Seattle's extensive transit network means many properties qualify. Even outside transit zones, you can typically satisfy parking requirements with a driveway space. Our team evaluates this during the feasibility study.
How long does a garage conversion take?
Most garage conversions take 3–6 months from design start to move-in. The permitting phase (6–10 weeks through Seattle DCI) runs concurrent with design, and the physical conversion typically takes 8–12 weeks depending on the scope of work.
