How big can an ADU be in Gresham?
As of October 2026, Gresham's Development Code (Section 10.0110) caps an accessory dwelling at 900 sq ft or 75% of the main house's floor area, whichever is less. The code allows one accessory dwelling per existing single detached house.
What height can a Gresham cottage reach?
It must meet the district's height standard and may not be taller than the main house. In several low-density districts, roof height at the rear setback line is capped at 21 feet.
What setbacks apply to a detached ADU?
- Street side: no closer to the street than the main house.
- Interior side: 5 feet.
- Rear: 10 feet, or 5 feet where the lot backs onto an alley.
An attached unit follows the district's setbacks for a single detached house. The code also lets certain legally existing accessory structures built before June 4, 2026 be converted even if they do not meet these setbacks.
Can I rent a Gresham ADU on Airbnb?
No. Section 10.0110 prohibits short-term rental of an accessory dwelling. Long-term rental is allowed, and the ADU may not be occupied before the main house.
How is a Gresham ADU reviewed?
Through a Type I review, a staff decision by the city's manager. If a design cannot meet the standards, it must also satisfy the code's variance criteria. Lots on an alley take vehicle access from the alley.
Is Gresham's 900 sq ft limit always reachable?
It depends on the house. The 75% rule controls for smaller homes: a 1,000 sq ft house allows a 750 sq ft ADU. The height limit tied to the main house also matters next to a one-story ranch. We run the numbers for your house before design.
Related
As of October 2026. Sources: City of Gresham Development Code Section 10.0100 (Accessory Dwellings, Sections 10.0110 and 10.0120); ORS 197A.425.
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