Converting an attached garage to living space is one of the most cost-effective ways to add square footage to a Seattle home. Here is what the process requires.
Permit Requirements
Garage-to-living-space conversions in Seattle always require a building permit. The conversion changes the occupancy type of the space (from U — utility — to R-3 residential), which triggers code requirements for insulation, heating, electrical, and sometimes structural work.
Insulation Requirements
Garage spaces are typically uninsulated. Conversion requires insulating the walls (R-21 minimum), ceiling/floor above (R-38 minimum), and the garage door opening (typically replaced with a wall with windows). Current energy code requires continuous insulation in most configurations.
Egress
If the converted space will be used as a sleeping room (bedroom), an egress window is required — minimum 5.7 sq ft net clear opening. If the garage is below grade, see basement conversion requirements.
Fire Separation
The wall and ceiling between the garage and the house must maintain a minimum 1/2″ gypsum board fire separation. If this separation is being removed as part of the conversion (opening the space to the rest of the house), it can be eliminated entirely once the occupancy change is complete.
ADU Garage Conversion
Converting an attached garage to an ADU adds kitchen requirements, a separate entrance, and energy code compliance for the full ADU unit. See our ADU service: ADU Design.
Costs in Seattle (2026)
- Basic garage-to-office conversion: $45,000-$85,000
- Garage-to-bedroom conversion: $55,000-$100,000
- Garage-to-ADU conversion: $90,000-$180,000
- Architect fees: $8,000-$20,000
Piper Cole Architects designs garage conversions throughout Seattle and the Eastside. Free consultation — call 425-753-6452.
Ready to Start Your Project?
Piper Cole Architects offers a free initial consultation for all project types — residential, commercial, ADU, and renovation. No obligation. Based in Kirkland, WA. Serving the entire Seattle metro area since 2000.