Written by Tim Gaughan, Urban Edge. Published March 6, 2026. Rules from Portland's ADU zoning page, checked October 2026.
Often, yes. Portland allows accessory dwelling units on most lots with a house, and an existing garage, attached or detached, can be converted into one if it meets the ADU size limits and the building code for a separate dwelling. The difference from a garage bedroom is that an ADU is a home of its own: kitchen, bathroom, sleeping area, its own entrance, and fire separation from the main house if it's attached.
Portland's zoning basics
- Size: an ADU can be up to 75 percent of the house's living area or 800 square feet, whichever is smaller. A 1,000 square foot house allows a 750 square foot ADU.
- How many: one ADU on most residential lots with a house; two in some cases, with only one of them attached.
- Detached ADUs must be 40 feet back from the front lot line or behind the rear wall of the house. An existing detached garage may already meet this, or may not.
- Parking: no extra parking is required for the ADU. If the conversion removes the house's parking space, check the rule in our garage conversion permits guide.
The City also offers a free 15-minute appointment with a planner. Use it before you design.
What makes it a dwelling
| Garage bedroom | Garage ADU |
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| Kitchen | No | Yes |
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| Bathroom | Optional | Yes |
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| Entrance | Through the house is fine | Its own |
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| Fire separation from house | Limited | Required if attached |
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| Utilities | From the house | May need upgrades to water, sewer and electrical |
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| Fees | Building permits | Building permits; system development charges may apply |
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Is converting better than building new?
Converting reuses the foundation, walls and roof, so it can cost less than a new building. But garage slabs, low ceilings and old framing can need more work than expected. If the garage is in poor shape, a new detached ADU may make more sense; our Pool & Guest Houses site covers building new.
Next step
We start with the zoning check and a look at the garage's slab, framing and roof.
Our work is covered by a 2-year workmanship warranty, in writing.
Book a free design consultation or call Tim, (503) 597-8520.