Overview

An Accessory Dwelling Unit ("ADU") is a secondary dwelling unit to a principal one-family dwelling, within or attached to a one-family dwelling or in a detached accessory building on the same zoning lot.

Saint Paul first allowed ADUs in 2016 in a limited geographical area, then allowed them citywide in 2018. In 2022, the requirement that the property owner live in either the principal dwelling unit or the ADU and the lot size minimum for construction of a detached ADUs were removed, and in 2023, Ordinance 23-43 lowered more barriers to constructing ADUs. Key changes in 2023 included:

  • Allowing 2 ADUs for each one-family dwelling on a lot
  • Changing the maximum unit size to 800 sf or 75% of the area of the principal dwelling, whichever is greater
  • Changing the maximum height for ADUs in a detached accessory building to be 25’ regardless of the height of the principal dwelling

Regulations regarding accessory dwelling units are found in Section 65.913 of the Zoning Code. Regulations regarding all accessory buildings and uses are found in Section 63.501 of the Zoning Code. Applicable regulations are summarized below.

Definition

A dwelling unit that is secondary to a principal one-family dwelling, within or attached to the one-family dwelling or in a detached accessory building on the same zoning lot.

Zoning Districts That Permit ADUs

Number of ADUs Permitted on a Lot 

(See Sec. 65.913(a))

Two ADUs are permitted for each one-family dwelling on a lot.

Example: If there are two one-family dwellings on a lot, there can be a maximum of four ADUs on the lot, two for each one-family dwelling.

Attached and Detached ADUs 

(See Sec. 65.913(a))

ADUs are only permitted when there is an associated one-family dwelling on the same lot. ADUs can be within or attached (see Interior Attached ADUs and Attached ADU in the image below) to the one-family dwelling or in a detached accessory building that could include a garage.

There can be other housing types, such as a duplex, on the same lot as the one-family dwelling(s) and ADU(s).

If there are two ADUs for one-family dwelling, at least one of the ADUs must be detached from the one-family dwelling. EXCEPTION: both accessory dwelling units may be attached to the one-family dwelling if at least 50% of the floor area of an existing principal residential structure on the zoning lot is retained.

Accessory Dwelling Units

Unit Occupancy 

(See Sec. 65.913(c))

The combined occupancy of the one-family dwelling unit and associated ADUs cannot exceed the number of occupants as specified in the definition of Household (Sec. 60.209). A household is six or fewer adults, together with the minors in their care. (For example, if four adults occupy the principal dwelling unit, only two adults may occupy the ADU.) Click here for additional notes on occupancy limits on a residential property.

Maximum Unit Size 

(See Sec. 65.913(d))

The maximum floor area of each accessory unit is 800 square feet or 75% of the floor area of the associated principal dwelling unit, whichever is greater. Floor area (Sec. 60.207) is the sum of the horizontal areas of each floor of a building, measured from the interior faces of the exterior walls or from the centerline of walls separating two buildings.

Ownership 

(See Sec. 65.913(f))

ADUs cannot be sold separately from the associated principal dwelling unit, and may not be a separate tax parcel.

Applicable Zoning District Standards

  • Lot Area Minimum (per principal unit): Zoning district (RL-H2) standard does not apply; ADUs are not principal units and are not counted in this calculation.
     
  • Floor Area Ratio Maximum: Zoning district (RM1-RM2) standard applies for attached ADUs in RM1-RM2. Detached accessory structures are not included in this calculation, per the definition of floor area in Sec. 60.207.
     
  • Lot Width Minimum: Zoning district (RL-H2) standard applies to the lot.
     
  • Maximum Number of Principal Units Per Lot: Zoning district (RL-H2) standard does not apply; ADUs are not principal units and are not counted in this calculation.
     
  • Building Height Maximum: Zoning district (RL-RM2) standard applies to ADUs that are attached to a principal building. For ADUs that are in a detached accessory building, the maximum height for accessory buildings containing a dwelling unit is 25 feet. See Sec. 63.501 (d).
     
  • Minimum Yard Setbacks: Zoning district (RL-RM2) standard applies to ADUs that are attached to a principal building. For ADUs that are in a detached accessory building, the setback standards for accessory buildings (Sec. 63.501 (b)) apply.
     
  • Maximum Lot Coverage for All Buildings: Zoning district (RL-H2) standard applies to all buildings, including principal and accessory.

Access and Entrances Requirements

(See Sec. 65.913(e))

  • A walkway must be provided from an abutting public street to the primary entrance of the accessory dwelling unit.
     
  • Upper floor units within the principal structure must have interior stairway access to the primary entrance of the unit. Secondary stairways required for fire safety may be located on the exterior of the side or rear of the building, but are not allowed on the front of the building.
     
  • Exterior stairways must be built of durable materials that match the finish of the principal structure or accessory building to which they are attached. Raw or unfinished lumber is not permitted.

Principal Units and Accessory Dwelling Units

Principal units are located in main (principal) buildings (see Sec. 60.214). ADUs are only permitted when there is an associated one-family dwelling on the same lot, and can be attached to a one-family dwelling or in a detached accessory building (see Sec. 65.913). Consider these characteristics when deciding to add a principal unit or ADU.

Characteristics

Principal Unit

ADU

Principal Unit with Associated ADU

Counts towards the district’s lot area minimum (per principal unit) and the maximum number of principal units per lot

Yes

No

Yes

Considered secondary to a principal one-family dwelling

No

Yes

No

Size-limited by ADU maximum floor area and height

No

Yes

No

Limited in occupancy by the definition of household with the associated principal unit

No

Yes

Yes

Can be sold separately or be on a separate tax parcel

Yes

No

No

Compliance with Other Regulations

(See Sec. 65.913(b))

Compliance with other city, local, regional, state and federal regulations is required. Pursuant to section 60.109 of the Zoning Code, all accessory dwelling units must comply with city, local, regional, state and federal regulations.

All building code requirements for the accessory unit must be met and a building permit must be obtained for the change of use and/or construction work.  

Sewer and Water Connections

Sewer and water connection requirements are regulated by the State Plumbing Code. Specifically, Section 311.1 states that “every building shall have its own independent water and sewer connection except that a group of buildings may be connected to one or more sewer manholes on the premises that are constructed to standards set by the Authority Having Jurisdiction.”

Detached ADUs are in a different building from the main (principal) unit and would therefore require separate water and sewer connections that is not connected through the existing principal unit’s existing water and sewer connections. To be permitted to connect utilities through the principal unit, the property owner must request an alternate to the Plumbing Code. Submission is required by the Master Plumber of the shop that will be performing the work or a Minnesota-licensed Engineer; approvals are on a case-by-case basis.

See the information sheets below for more details:

What’s required to submit a building permit?

  • Certified signed survey
  • Civil plans with utilities
  • ADU floor plans and elevations
  • Floor plans of associated single-family dwelling to verify unit size based on the definition of floor area (Sec. 60.207)

Last Edited: March 6, 2024