New York City’s Department of Buildings (DOB) calls new living space built in an existing building without prior Department approval an illegal conversion. The City’s examples include cellar bedrooms and unauthorized rooming units. Its guidance says illegal residences can pose safety risks and may result in violations or stop-work orders. This page explains DOB’s published correction sequence; it does not establish whether a secondary dwelling at a particular address can be legalized.
Find out whether the work can be legalized
DOB’s first step is to determine whether the illegal construction can be legalized or must be removed. That decision depends on the property, the work, and the applicable requirements. The guidance does not say that every conversion is eligible for legalization or that an application guarantees approval. If reconstruction is required, DOB says all residents must move.
Follow the approved-work sequence
For work that can proceed through legalization, DOB lists these steps:
- Have a registered design professional, such as a professional engineer or registered architect, file plans and obtain DOB approval. Landmarks Preservation Commission approval or permits may also be required.
- Pay the applicable filing fees and obtain all required permits.
- Have licensed contractors perform required work according to the approved plans.
- Obtain final DOB sign-off.
- Secure a new Certificate of Occupancy to legalize the housing.
- Submit a Certificate of Correction, with proof that the violations were corrected, to DOB’s Administrative Enforcement Unit.
The Certificate of Correction and Certificate of Occupancy have different jobs in this sequence: one documents correction of violations, while the other states the building’s legal use or permitted occupancy type. See DOB’s Certificate of Occupancy guidance and check the issued documents, address, unit, and approved work rather than treating an application, permit, or inspection as the final result.
Some existing occupied NYC basement and cellar apartments may have a separate Local Law 126 temporary-residence route. DOB’s current ADU program page says it is not accepting applications for an Authorization for Temporary Residence. That pilot does not establish eligibility for this correction process or for a particular property.
Confirm the address-specific requirements
Use the actual violation, property records, approved plans, permits, and inspection history to establish what DOB requires. A registered design professional and the responsible authorities must determine the permissible route and corrective scope. Other zoning, building, fire, or property requirements may also apply. For the wider process, see retrospective approval and regularization, corrective-work checks, enforcement and occupancy questions, and completion and legal-status records.