A garage apartment, an ADU built above a garage, is one of the most efficient ways to add living space in Seattle. It combines two functions in one structure and works well on lots where ground space is tight. Here is what you need to know.
The Garage Apartment Concept
A garage apartment places a full living unit on the second floor above a one or two-car garage. The garage serves the main house or the ADU tenant; the apartment above is a complete dwelling with kitchen, bathroom, and living space.
New Construction vs. Adding Above an Existing Garage
- New garage with apartment: Designed from scratch with proper structure to carry the upper floor. Cleaner and often more cost-effective.
- Adding above an existing garage: Possible if the existing foundation and walls can carry the new load, but often the existing garage was not built for it, requiring reinforcement.
Planning a project?
Wondering what an ADU on your lot would cost?
Send David the address and a few lines about what you want. The first feasibility check is free and usually takes about a day: what the site and the code are likely to allow, and what to check first.
Architect since 1996, member of the AIA and NCARB. Three Masonry Excellence Awards for commercial projects; the Carr residence was featured in Above The Lake and Lux magazines.
Seattle Rules
A garage apartment is regulated as a DADU. It counts toward the 1,000 sq ft DADU limit (the garage level is typically exempt as parking). Height limit is 24 feet, which accommodates garage plus apartment.
Cost (2026)
- New garage with apartment above: $250,000 to $420,000
- Apartment added above existing garage: $180,000 to $320,000
- Architect fees: $22,000 to $38,000
See our detached garage design guide and ADU service.
Authoritative sources
Regulatory requirements referenced in this guide are set by the official agencies below. Rules change, always confirm current requirements with the source:
