It depends on your house. As of October 2026, attached houses and rowhouses are excluded from the ADU rules, and new backyard ADUs are not allowed in LPC historic districts, the Special Bay Ridge District or mapped flood risk areas. Detached and semi-detached one- and two-family homes outside those areas can qualify.
Why can't I build an ADU behind my rowhouse?
The adopted City of Yes rules exclude attached buildings and rowhouses. RPA's September 2025 analysis counted none of the city's attached one- and two-family lots as eligible. Without a side yard, there is also no way to provide the 5-foot Fire Department access path a backyard ADU needs.
What about historic districts?
Brooklyn has many LPC historic districts. In them, new backyard ADUs are not permitted, though HPD's guidebook says an existing structure can be converted. Exterior work in a historic district also needs LPC approval.
Where is flooding a factor?
Neighborhoods along the southern shoreline and Jamaica Bay include mapped flood risk areas. On those lots, basement, cellar and new backyard ADUs are off the table, as of October 2026.
Which Brooklyn homes are good candidates?
- Detached houses with a driveway and a rear garage.
- Semi-detached houses with a side yard of at least 5 feet.
- Houses with full attics or tall basements, outside the flood maps.