How many NYC properties can have an ADU?
Fewer than many owners expect. The Regional Plan Association estimated in September 2025 that about 68,000 of the city's roughly 565,400 one- and two-family lots, about 12 percent, are eligible for an ADU under the adopted rules.
Why are so many lots excluded?
RPA found three main barriers, which overlap:
- Building type. Attached houses and rowhouses are excluded, which rules out about 53 percent of one- and two-family lots.
- Dimensions. Lot line distances, the 5-foot access path and yard rules eliminate many more.
- Ownership. The owner must live on the lot at initial occupancy.
By building type, RPA counted about 29 percent of detached homes and about 9 percent of semi-detached homes as eligible, and none of the attached homes.
What changes from one borough to the next?
- Flood maps. Shoreline neighborhoods in all four boroughs include DEP flood risk areas, where basement, cellar and new backyard ADUs are not allowed.
- Contextual districts. R1-2A, R2A and R3A districts block backyard ADUs outside the Greater Transit Zone. We check whether your lot is in one.
- Historic districts. LPC districts block new backyard ADUs, though existing structures can be converted.
Do you work in Manhattan?
Rarely. Manhattan has very few one- and two-family homes of the kind the ADU rules cover. If you own one, send your address and we will tell you whether we can help.