South Portland, Maine Accessory Dwelling Unit (ADU) Rules

City Acceptance Rating: 7/10
last updated 3/08/2023

SOUTH PORTLAND ADU RULES — UPDATE 3/2/23

What you need to know about South Portland:

South Portland allows both attached and detached ADUs (oversized tiny homes), but they have extensive design guidelines and pay special attention to preserving the character of neighborhoods.

We expect the permitting process in South Portland to be reasonably quick. The rules are fair and reasonable and compliance is determined by the building department.

Type of Permit Required:

ADUs permit applications are approved by the Code Enforcement Officer. South Portland does not require ADUs to be reviewed at a public hearing or by additional planning staff.

The ADU application requires an existing conditions survey plan (mortgage inspection survey). This inspection requirement may be waived if you are converting existing space within your home such as the attic or basement.

This existing conditions plan must be used to create a scaled version site plan of the proposed changes to the property to accommodate the ADU. This site plan does not need to be “stamped” by the licensed surveyor.

Other Rules in South Portland:

Only one ADU is allowed per lot
Owner occupancy is required
Attached and detached ADUs are allowed
ADUs can be added to single-family homes as well as multi-unit structures with up to 3 dwelling units
ADUs may not be used for short-term rentals. The existing primary units also cannot be used for short-term rentals after an ADU is added
If a zoning district does not have a maximum coverage ratio, 25% shall be the maximum building coverage
When built on a single-family home, the ADU and single-family home must be held in the same ownership and cannot be sold separately
The ADU’s exterior design must be compatible with the existing architecture. We recommend reading the detailed notes on design regarding entrances and roofs from the bylaw.
The combination of the ADU’s interior layout, position on the property, and landscaping features must preserve the privacy of the neighbors.
A walking path at least 3’ wide must be provided from the nearest public right of way to the ADU. Parking areas do not count as walkways, however, an additional 3’ wide walkway can be positioned adjacent to the driveway.
No additional parking is required for ADU

The ADUs size must be:

On parcels less than 10,890 SF the ADU must be 800 SF or 90% of the primary dwelling living area, whichever is smaller
On parcels greater than 10,890 SF the ADU must be 1,200SF or 90% of the primary dwelling living area, whichever is smaller
The ADU must be at least 190SF
New buildings created (detached or attached) cannot exceed a footprint of 800 SF

Non conforming structures can be converted into an ADU, under certain circumstances:

The nonconformity cannot be increased
The height can only be increased to make a roof compliant with the building code
No 2nd story windows can be within a setback unless set to the roof (skylights)
An ADU cannot be located within 12 feet of an inhabited structure on an adjacent property
Structures within 12’ of existing inhabited structures cannot be converted into an ADU