Islip, NY Accessory Structures: ADU Rules (2026)

New York has no statewide ADU mandate, so accessory dwelling units in Islip are governed entirely by local law - the Town of Islip Accessory Apartments ordinance (Town Code Chapter 68, Article XLVII, beginning at Sec. 68-600). The ordinance permits 'the creation of small apartments within the existing structure of owner-occupied single-family detached dwellings,' and an accessory apartment is defined as 'a dwelling unit which is subordinate to a permitted principal one-family residence use in terms of size, location and appearance, and is located within the principal structure.' No accessory apartment may be located within an accessory structure such as a detached garage or shed. A permit from the Zoning Board of Appeals plus a certificate of occupancy from the Department of Building are required, and an owner holding at least a 50% interest must reside in the principal dwelling. The minimum lot area is 7,500 square feet with a minimum lot width of 75 feet; the apartment may have no more than two bedrooms and a gross floor area of at least 300 square feet but no more than the lesser of 50% or 800 square feet of the principal dwelling's gross floor area. There must be no more than one accessory apartment per lot, at least four off-street parking spaces, and the dwelling must be at least seven years old (for homes receiving a C/O after September 1, 1992). Only one visible front entrance is permitted and no exterior changes that alter the single-family appearance are allowed. The Islip FAQ confirms second kitchens tied to such apartments require special exception approval from the Zoning Board of Appeals after a public hearing and must be renewed every three years (Town Code Secs. 68-600 and 68-419.1).