Southampton, NY Accessory Structures: ADU Rules (2026)

Article IIA of the Zoning Code, adopted in 1992 and amended most recently in 2019, governs accessory apartments in the unincorporated hamlets of the Town of Southampton, from Hampton Bays to Flanders. An applicant applies to the Town Building Department the same way as for any other building permit under § 330-11.1A, and pays the fee schedule under § 123-12 of the Town Code for any structural alteration. Under § 330-11.2, the owner or owners of the lot must reside in either the principal dwelling or the accessory apartment as their domicile, and no other co-owner may hold a larger ownership share than the owner-occupant, with a narrow exemption for lots held by the Southampton Housing Authority.

The lot must carry only one dwelling unit at the time of application, and no more than one accessory apartment is permitted per lot. Minimum lot area is 30,000 square feet, dropping to 20,000 square feet where the apartment sits in a census-designated place with population density under 500 people per square mile; nonconforming lots can qualify at 80% of the district minimum, never below those floors. The apartment itself must run at least 400 square feet and cannot exceed 35% of the principal dwelling's floor area or 1,000 square feet, with an efficiency-unit carve-out down to 220 square feet for occupancy by no more than two people.

No accessory apartment may hold more than two conventional bedrooms, and at least one off-street parking space is required for a studio or one-bedroom unit, two for a two-bedroom unit. Upon permit issuance, the Town extinguishes one Town-owned development right in the school district where the apartment sits, and no permit issues without that extinguishment.