Accessory dwelling unit (ADU) zoning requirements

• In RF through R2.5 Zones: One ADU on a lot with a primary structure must meet the minimum lot sizes in Section 33.110.202.
• Different minimum lot sizes apply when
  • An ADU is proposed with an attached house.
    • "Attached" means the ADU and house share a common wall.
  • More than one ADU is allowed on a lot

You can have one ADU on sites with a house, attached house, or manufactured home. 

RF through R2.5 zones:

• The sites must meet minimum lot size requirements.
• Reference: Table 205-1 Minimum Lot Size Requirements

R20 through R2.5 zones:

• Allowed: One ADU on a site with a duplex (two units in one detached structure) if the site:
  • Has frontage on a City-maintained street.
  • Meets minimum lot size requirements.
    • Reference: Table 205-2 Minimum Lot Size Requirements.
  • Is not in the overlay zone, Constrained Sites ("z").

Multi-dwelling, commercial, and central employment (EX) zones:

• One ADU is allowed with a duplex. This holds, regardless of site size and whether the City maintains the street.

Note: The ADU must be detached from the duplex.

R20 through R2.5 zones:

• Allowed: Two ADUs on a site with a house, attached house, or manufactured home if the site:
  • Has frontage on a City-maintained street.
  • Meets minimum lot size requirements.
    • Reference: Table 205-2 Minimum Lot Size Requirements.
  • Is not in the overlay zone, Constrained Sites ("z").
• Only one ADU can be attached to the house or another ADU.
• Multiple ADUs are not allowed on sites with a duplex.

Multi-dwelling, commercial, and central employment (EX) zones:

• Two ADUs are allowed on sites with a house, an attached house, or a manufactured home. This applies regardless of site size or street frontage.
• Only one ADU can be attached to the house or another ADU.

ADUs cannot be built with other development types, including:

• Floating homes
• Triplexes
• Fourplexes
• Cottage clusters
• Multi-dwelling structures

The maximum size for an ADU is 75% of the living area of the main structure or 800 square feet, whichever is smaller.

Example: If a house has 1,000 square feet of living area after these exclusions, the ADU can be 750 square feet. For a house with 2,500 square feet, the ADU is limited to 800 square feet.

This limit does not apply if the ADU is in the basement of a primary structure that is at least five years old.

Living area - do NOT include the following:

• Thickness of the exterior walls.
• Garage areas.
• Basement areas with a ceiling height of less than 6 feet 8 inches.
• Areas where the floor-to-ceiling height is less than 5 feet or is not accessible by a stairway.

• Maximum height is 20 feet outside the required setbacks.
• Inside required setbacks, the maximum height is 15 feet.

• The building coverage of a detached ADU cannot exceed that of the primary structure.
• All detached accessory structures must not cover more than 20% of the site.

Detached ADUs must be set back 40 feet from the front lot line. Or, located behind the rear wall of the main structure.

For detached ADUs taller than 15 feet, the following exterior standards apply:

• Visually match the primary structure:
  • Finish materials: match the house or be on the list of approved finished materials
  • Roof pitch: match the house or be at least 6/12
  • Trim: match the house or be 3.5 inches
  • Eaves: match the house or be at least one foot
  • Window orientation: match the house or be square or vertical
• Approved finished materials can be either:
  • wood
  • composite boards
  • vinyl
  • aluminum
• All siding materials must be in a shingle pattern.
  • If not, siding must be horizontal clapboard or shiplap pattern with boards 6 inches or less wide.
    • Shiplap pattern is when boards overlap each other.

References

• Single-dwelling zones
  • Section 33.110.245 Detached and Connected Accessory Structures
• Multi-dwelling, commercial, and central employment (EX) zones
  • Section 33.120.280 Detached Accessory Structures

Note: Historic designations (33.445) may have extra design requirements. ADUs in historic areas must meet the Community Design Standards (33.218). If they can't, they must pass a Historic Resource review.

Floor area limits apply in all zones except RF.

In R10 and R20 zones, these limits apply only to lots smaller than 10,000 square feet.

In R7 through R2.5 zones, extra floor area is allowed for each proposed ADU.

No extra on-site parking is needed for an ADU.

For two ADUs on a lot with a house or one ADU on a lot with a duplex, at least one unit must allow for visitors in wheelchairs.

• Zero-step access and entrances
• Bathrooms
• Living area
• Doors

Reference: Development Standards requirements for accessory dwelling units, Subsection 33.205.040.C.5.

If ADU development standards are not met, you'll need an Adjustment Review. This review follows the guidelines in Zoning Code Chapter 33.805.

Key points about the Adjustment Review:

• It is a discretionary land use review.
• It takes approximately 8 to 10 weeks to process.
• Approval or denial is based on the criteria in Chapter 33.805.
• There is no guarantee of approval.

Reference: Adjustment Reviews

You can use ADUs as Type A accessory short-term rentals. Chapter 33.207 of the Portland Zoning Code outlines the details.

Important points about Type A rentals:

• They allow renting out up to two bedrooms.
• Guests can stay for less than 30 consecutive days.

You need proper permitting to rent an ADU as a Type A unit. Get the correct documentation before listing your space. Keep in mind that:

• SDC waiver granted during the construction of the ADU? If yes, you cannot rent out bedrooms in the ADU as short-term rentals for 10 years.

You can use ADUs as Type B accessory short-term rentals. You must follow the rules in subsection 33.815.040.B.1 of the Portland Zoning Code.

Important points about Type B rentals:

• 3 to 5 bedrooms can be rented to guests.
• SDC waiver granted during the construction of the ADU? If yes, you cannot rent out bedrooms in the ADU as short-term rentals for 10 years.