ADU rules in Islip, NY — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Islip allows accessory apartments through its Accessory Apartment Permit program under Town Code Chapter 68, Article XXIII. One ADU per owner-occupied single-family home is permitted with an annual renewable permit from the Building Division.
The owner must live on-site, the ADU cannot exceed 650 sq ft or 35 percent of the main dwelling, and only one additional off-street parking space is required. Minimum lot size is generally 10,000 sq ft. The unit must have separate egress, smoke/CO alarms, and pass a Fire Marshal inspection. Permits are renewed annually and transfer with sale only if the new owner continues owner-occupancy. Illegal basement or garage apartments are a major enforcement target.
Illegal ADU: $1,000-$5,000 per day, vacate orders, and criminal housing charges. Permit denial for outstanding code violations.
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