Yes, in many cases. As of October 2026, HPD's ADU guidebook says garage conversions are not considered rear-yard ADUs under NYC zoning and follow separate rules, because the structure already exists. Existing garages may be converted or rebuilt even in some places where new backyard ADUs are restricted, though extra review may apply.
Why does it matter that the garage already exists?
DOB defines a backyard ADU as a structure developed after December 5, 2024. An older garage is not one, so the conversion follows the rules for existing structures, which HPD links to Zoning Resolution section 54-53. In practice, that can matter in two places where new cottages are blocked:
- Historic districts: HPD says new rear-yard ADUs are not permitted in LPC historic districts unless an existing structure is converted. Exterior work there still needs LPC review.
- Flood zones: a converted or rebuilt garage may be permitted if it is elevated to the design flood elevation.
Can I build the ADU on top of the garage?
Yes. When parking stays on the ground floor, the ADU above it can be up to two stories and 25 feet, according to HPD and DOB guidance as of October 2026. That keeps the parking space and adds a unit, on lots where the side yard and lot line rules allow it.
What does a city garage usually need?
- A structural check of the slab, walls and roof, which on older garages are often minimal.
- Insulation, a new floor build-up and windows where the overhead door was.
- Fire-rated walls near lot lines and a full sprinkler system.
- New water, sewer and electrical lines from the house.
- The 5-foot Fire Department access path from the street.
Do I lose required parking?
The City of Yes rules do not require a parking space for the ADU itself. Converting a garage removes a space from the main house, so we check how the zoning treats your existing parking before you commit.