ADU Rules: Gresham vs Portland
How do adu rules rules compare between Gresham, OR and Portland, OR?
Portland has fewer restrictions than Gresham.
Gresham, OR
Multnomah County
Gresham allows accessory dwelling units (ADUs) in residential zones per Oregon state law (HB 2001). One ADU is permitted per lot. ADUs must meet development code standards for size, setbacks, and parking.
View full Gresham rules →Portland, OR
Multnomah County
Portland allows accessory dwelling units (ADUs) on every single-dwelling residential lot under PCC 33.205. ADUs can be attached, internal (basement/attic conversion), or detached and may be up to 75% of the primary dwelling's living area or 800 sq ft, whichever is greater. No additional parking is required, no owner-occupancy is required, and System Development Charges are waived under PCC Title 17.13.
View full Portland rules →Key Facts Comparison
| Fact | Gresham | Portland |
|---|---|---|
| Allowed | One per single-family lot | - |
| Size | Up to 800 sq ft typically | - |
| Types | Attached or detached | - |
| State Law | Oregon HB 2001 | - |
| Code | - | PCC 33.205 (Accessory Dwelling Units) |
| Size Limit | - | Greater of 800 sq ft or 75% of main dwelling |
| Detached Height | - | 20 ft (more under RIP standards) |
| Parking Required | - | None |
| Owner Occupancy | - | Not required (removed 2017) |
| SDC Waiver | - | PCC 17.13 — SDCs waived |
Highlighted rows indicate differences between cities.
Gresham FAQ
Can I build an ADU in Gresham?
Yes. Oregon law requires cities to allow one ADU per single-family lot. Building permits are required.
How big can an ADU be in Gresham?
Typically up to 800 square feet, subject to the Development Code standards for the zone.
Portland FAQ
How big can my Portland ADU be?
Under PCC 33.205.040, the greater of 800 square feet or 75% of the primary dwelling's living area. So a 1,200 sq ft house allows an ADU up to 900 sq ft; a 2,000 sq ft house allows up to 1,500 sq ft.
Do I need extra parking for a Portland ADU?
No. PCC 33.205 explicitly requires no additional off-street parking for ADUs, regardless of the underlying zone. This was a deliberate choice to reduce barriers and is reinforced by Oregon state law.
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