Where are ADUs allowed:

The town of Southampton allows Accessory Apartments only on lots that conform to current district area and dimensional regulations. Lot size needs to be more than 30,000 square feet unless “…accessory apartment is located within a Town boundary area defined as a "census-designated place" (CDP) where the density measures less than 500 people per square mile according to the ten-year data published by the United States Census Bureau; in such case, the lot shall not be less than 20,000 square feet.”

If your lot is nonconforming, you may still be eligible for an accessory apartment. If your lot is nonconforming, the following criteria apply:

“A nonconforming lot may be eligible for an accessory apartment, provided that the lot area is not less than 80% of the required lot area for the applicable zone district, but in no case less than 30,000 square feet unless the lot is located in a CDP that meets the above-referenced density requirement; then the nonconforming lot shall be not less than 20,000 square feet. All other dimensional nonconformities shall not be less than 70% of the required setback or lot width. A lot with a nonconformity of a greater degree shall not be eligible for an accessory apartment under this article. “

Types of ADUs:

Attached, Detached, or Converted ADUs are permitted in Southampton.

Parking:

At least one additional off-street parking space shall be provided for an accessory apartment which is a studio or one-bedroom, and two off-street parking spaces for accessory apartments having two bedrooms, on the lot for the accessory apartment, and such space(s) shall not be located in the required minimum front yard and shall be adequately screened with landscape plantings, which shall include evergreen shrubs, not less than three feet in height at the time of installation.

Size:

The accessory apartment shall be a minimum of 400 square feet, and it shall not exceed 35% of the total floor area of the principal dwelling to a maximum of 1,000 square feet on the lot to which the accessory apartment is to be added.

For example:

• If your main home’s floor area is 2500 square feet, your ADU can be as large as 875 square feet.

• If your main home’s floor area is 2857 square feet or larger, the maximum size of your ADU will be limited to 1,000 square feet.

If an accessory apartment is to be constructed in an accessory structure, all habitable living space in that structure will count toward the maximum square footage of the accessory structure.

The accessory apartment shall contain no more than two conventional bedrooms.

Rental Use:

Renting of Accessory Apartments in Southampton is permitted as long as the regulations around renting are met:

“ …at the time of application for a rental permit, or at the time of renewal of the permit, the owner shall provide a fully executed lease agreement or other documentation that demonstrates that the rent does not exceed the annual fair market rent (FMR) for Suffolk County as established by the Department of Housing and Urban Development (HUD) and that the tenant’s income meets the standards established for low-moderate income or middle income as defined under Chapter 216 of the Town Code”

Other Requirements:

Owner occupancy is required. The owner or owners of the lot upon which the accessory apartment is located shall reside within the principal dwelling or the accessory apartment and said dwelling or apartment shall be considered the owner's domicile or principal place of abode.