General Information 

An Accessory Dwelling Unit ("ADU") is a second dwelling unit, subordinate 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 ADU's in 2016 in a limited geographical area, then allowed them citywide in 2018. (Click here for the 2016 ordinance. Click here for the 2018 ordinance.) In 2022, amendments to the ADU ordinance were adopted lowering barriers to the addition of ADU's. (Click here for the 2022 ordinance.) Key changes in 2022 included:

  • Removing the lot size minimum for construction of a detached ADU;
  • Removing the owner-occupancy requirement; and
  • Changing the maximum size from 800 square feet to 75% of the floor area of the principal unit.

Accessory Dwelling Units

Standards and Conditions

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. The following standards and conditions must be met in order to establish an ADU:

  • Only one accessory unit is allowed on a lot.
  • No more than one household is allowed in both the principal unit and the accessory unit together. A household is six (6) 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.
  • The maximum size of a detached ADU is 75% of the floor area of the principal unit;
  • The maximum height of an ADU in RL-RM2 residential districts is the lesser of 25 feet or the height of the principal structure.
  • All other requirements for an accessory structure must be met, including location and setback. 
  • If the accessory dwelling unit is located within the principal unit, the principal structure must be at least 1,000 square feet. If the principal building has more than one story and was built before 9/14/2016, the maximum floor area of an accessory dwelling unit may be equal to that of the first floor, but shall be less than or equal to 50% of the total floor area of the building.
  • There must be a sidewalk from the street to the primary entrance of the accessory unit.
  • An accessory unit on the upper floors of the principal building shall have an interior stairway to the primary entrance of the accessory unit. Secondary stairways may be located on the exterior, but not on the front of the building.
  • 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. 

Last Edited: March 1, 2023