Garage conversions, Seattle and the Eastside
What a Garage Conversion Costs in Seattle
$45,000 for a garage turned into an office, up to $180,000 for a full ADU with a kitchen and bathroom. The space already has walls, a roof and a slab, which is why this is one of the cheapest ways to add a legal room.
The first feasibility check is free and usually takes about a day.
Free feasibility check
Send the address and what you have in mind. David replies within one business day with what the site and the code are likely to allow.
- 1996Licensed architect since 1996
- 1992AIA member since 1992
- 20 to 30Projects designed each year
- 3Masonry Excellence Awards, commercial projects
- AIAAIA · NCARB · Washington licensed
Why it is cheap, and why it is not free
The shell is there. The code work is not.
A garage already has a foundation, walls and a roof, so a conversion skips the most expensive parts of an addition. That is why it is one of the most cost effective ways to add square footage to a Seattle home.
What it does not have is anything the building code expects of a room people live in. The conversion changes the occupancy from U, utility, to R-3, residential, and that one change is what triggers the insulation, heating, electrical and sometimes structural work.
Most of the budget goes there, not into finishes. Knowing which of those triggers apply to your garage is what turns a range into a number.
Estimate
Estimate your garage conversion
Pick what the garage is becoming and its size. The result always sits inside the range this page publishes for that conversion, so the estimator never quotes something the page does not already stand behind.
Planning range for design, permits and construction, not a quote. The architecture fee on a garage conversion typically runs $8,000 to $20,000. Structural surprises in the slab or the walls are what push a project to the top of its range. Call David on 425 753 6452 about your own garage.
Projects
Selected work
Real houses, real constraints. Photographs and drawings from the practice.
The numbers
Garage conversion cost, Seattle 2026
Every figure here matches the other cost pages on this site. The ADU cost guide has the detached and attached options in full.
| Conversion | Typical cost |
|---|---|
| Garage to office or bonus room | $45,000 to $85,000 |
| Garage to bedroom | $55,000 to $100,000 |
| Garage to ADU, with kitchen and bathroom | $80,000 to $180,000 |
| Architecture fee | $8,000 to $20,000 |
Design, permits and construction for a typical attached garage. The ADU range matches the ADU cost guide on this site. A detached garage becoming a backyard cottage is priced as a DADU.
Permits
What the code asks for, and why
Garage conversions in Seattle always need a building permit, usually with electrical, plumbing and mechanical permits alongside it. The occupancy change from U to R-3 is what brings the rest of the code in.
- Insulation. Walls to R-21 minimum and the ceiling or floor above to R-38 minimum, with continuous insulation in most configurations under the current energy code. Garages are usually uninsulated, so this is a large part of the work.
- The garage door. Normally replaced with a wall, often with windows, which is where the room starts to look like part of the house.
- Egress. A room used for sleeping needs an egress window with at least 5.7 sq ft of net clear opening. If the garage is below grade, basement rules apply instead.
- Fire separation. The wall and ceiling between garage and house must keep at least half inch gypsum board while the space is a garage. Once the occupancy changes, that separation can go, which is how the room opens into the house.
- Heating and electrical. Code compliant heat and circuits for a habitable room.
Going further
Garage to ADU
Converting an attached garage into an ADU adds a kitchen, a separate entrance and energy code compliance for the whole unit. That is what moves it from the $45,000 end of this page to the $80,000 to $180,000 range.
A detached garage usually becomes a DADU, a backyard cottage. Seattle allows two ADUs per lot, a detached cottage plus an attached or internal unit, with DADUs up to 1,000 sq ft and no owner occupancy requirement. Setbacks, height and lot coverage limits still apply, and land use review can apply once it becomes a dwelling unit.
If the aim is rental income or a family member living separately, run the ADU numbers before settling on a bonus room. The extra cost buys a legal second unit.
Timeline
How long it takes
Plan on roughly 2 to 4 weeks of design, 6 to 12 weeks of permitting and 8 to 16 weeks of construction, which is about 4 to 8 months end to end. City review time is the part that varies most, and Seattle’s is longer than most of the Eastside’s.
Questions
Garage conversions, answered
Not answered here? Call David, most calls are answered the same day.
How much does a garage conversion cost in Seattle?
A garage turned into an office or bonus room typically runs $45,000 to $85,000, a bedroom $55,000 to $100,000, and a full ADU with a kitchen and bathroom $80,000 to $180,000. The architecture fee typically runs $8,000 to $20,000.
Do I need a permit to convert my garage?
Yes. A conversion always needs a building permit in Seattle, and usually electrical, plumbing and mechanical permits too, because the occupancy changes from utility to residential. If it becomes an ADU, land use review may also apply.
Is a garage conversion worth it?
For most Seattle homeowners, yes. It adds legal living space at a lower cost per foot than a ground up addition, and as an ADU it can earn rental income. The trade offs are losing covered parking and the code work the occupancy change triggers.
Can I convert a detached garage?
Yes. A detached garage usually becomes a DADU, or backyard cottage. Seattle allows DADUs up to 1,000 sq ft, subject to setbacks, height and lot coverage limits.
Can the converted garage be a bedroom?
Yes, if it has an egress window with at least 5.7 sq ft of net clear opening, plus the insulation, heating and electrical a habitable room needs.
How long does a garage conversion take?
Roughly 2 to 4 weeks of design, 6 to 12 weeks of permitting and 8 to 16 weeks of construction, so about 4 to 8 months in total depending on scope and city review.
Will it add value to my home?
Done well and permitted, yes. Added legal living space and, for an ADU, rental income both raise appraised value. Unpermitted conversions do the opposite and cause problems at resale.
Keep reading
The rest of the picture
- ADU cost guide, Seattle and the EastsideAttached, detached and garage ADUs, with its own estimator
- ADU and DADU designWhat the design work involves and what each city allows
- Seattle DADU rulesWhat Seattle allows for a backyard cottage
- Home addition costWhen the space you need will not fit in the garage
- Architect fees in SeattleWhat the design work costs, with a calculator
- Seattle residential architectSDCI permit tracks and what they mean for timing
Keep reading
Related guides
ADU Architect in Seattle, WA Backyard Cottages & Garage Conversions
ADU architect in Seattle, WA. Piper Cole Architects designs and permits backyard cottages and garage conversions across the city.
ADU Cost Guide: Seattle Eastside 2026
What an ADU really costs in Kirkland, Bellevue, Redmond and Sammamish, by type, with an estimator and city permit fees. Call David on 425 753 6452.
Seattle ADU Permit Timeline 2026: What to Expect
How long does it really take to permit an ADU in Seattle in 2026? Phase-by-phase timeline with realistic numbers from Piper Cole Architects in Kirkland.
Next step
Find out what your garage can become
Whether it can be a bedroom or an ADU depends on the slab, the walls, the ceiling height and the lot, and all of that is answerable in one conversation. Call David Meade directly. The first feasibility check is free and usually takes about a day.
Free feasibility check
Send the address and what you have in mind. David replies within one business day with what the site and the code are likely to allow.