The City of Portland’s single-dwelling zones govern the types of housing permitted in our neighborhoods.
The variety of housing options in Portland’s neighborhoods includes
- multiple accessory dwelling units (ADUs)
- cottage clusters (a detached housing option)
Required standards in the Zoning Code include adopted limits on the size and scale of residential development.
Residential infill options: more flexibility for how you use lots
In zones R2.5, R5, R7, R10 and R20, the residential infill options add flexibility to what you build by:
- Increasing the number of units you can build on each lot
- Increasing the number of allowable configurations on lots
- Removing off-street parking requirement in single-dwelling zones
- Allowing detached housing developments called cottage clusters
Limits to building size
Floor area ratio (FAR)
A requirement to measure each building’s floor area ratio on the lot limits the size of buildings.
- Floor area ratio and how it might affect your project
- How to calculate floor area in single-dwelling zones
Height limits also determine how tall a building is allowed to be.
Find out if your lot can have more units
A duplex is allowed on all single-dwelling zoned lots where a primary structure is allowed, with the exception of the RF (Residential Farm Forest) zone.
Residential infill option housing types are not allowed in lots in the z overlay on the zoning map. Lots in the z overlay have flooding, landslides, environmental zoning, or wildfire hazard.
See Portland City Code 33.418, Constrained Sites Overlay Zone for a complete list of the constraints that require application of the z overlay.
You cannot build more than two units on lots that are on unmaintained streets, unless they have frontage on a dedicated pedestrian or bike connection that leads to a maintained street.
Minimum lot size requirements
The minimum lot size for most housing options is shown below:
- Zone R2.5: 1,500 square feet
- Zone R5: 3,000 square feet
- Zone R7: 4,200 square feet
- Zone R10: 6,000 square feet
- Zone R20: 12,000 square feet
Cottage cluster development
Cottage clusters are groups of relatively small homes oriented around a shared common space such as a courtyard or garden.
A cottage cluster is defined as a group of three to 16 detached dwelling units on one lot with a footprint of less than 900 square feet each.
This type of development option is allowed in most zones that allow residential development. Cottage clusters are allowed in the RM1, R2.5, R5, R7, and R10 zones (see Zoning Code sections 33.110.265.G and 33.120.270.G).
Not allowed: The common outdoor spaces may not include projections from individual units, such as eaves, bay windows, and patios.
For new construction with three or more units on the site, including ADUs, one building must be visitable. Visitability standards include:
- A no-step, barrier-free main entrance
- A bathroom and small living area accessible to the main entrance
- 32-inch-wide internal doors between the entrance, the bathroom and the living area for wheelchair accessibility
Middle Housing Land Division (MHLD)
Land divisions for middle housing will allow certain specific development types (e.g. a fourplex or cottage cluster) to be divided into separate lots at the same time that building permits under review for the development.
Middle Housing Land Divisions are processed through an expedited process and are subject to clear and objective standards.
Learn more about Middle Housing Land Divisions and how they apply to certain types of residential developments.
Residential infill options for a property with an existing house
Zoning rules allow more dwelling units to be added to existing houses and duplexes.
Before considering adding units to an existing structure, you should schedule a 15-minute appointment with a building code reviewer.
Resources on conversions and adding dwelling units:
We can answer questions about the residential infill options.
Book a free 15-minute appointment with a city planner or call the General Inquiries phone number to discuss your questions.
For a deeper discussion about the residential infill options, set up an Early Assistance meeting.
More information about zoning changes in single-dwelling zones
For more information about the zoning code changes and how they affect certain types of residential development, please visit the web pages for each of these legislative planning projects:
Video recordings: Lunch and Learns
Lunch and Learn videos recorded when both projects were adopted explain the changes:
Questions and answers from the Residential Infill Projects are also available.