Illegal Conversions in NYC: Vacate Orders, Penalties & How to Legalize
5 min read · Updated 2026-08-13
NYC illegal conversions explained: vacate orders, aggravated conversion penalties, tenant rights, and how to legalize extra units with new filings and a CO.
What Counts as an Illegal Conversion
What is an illegal conversion in NYC?
An illegal conversion is any occupancy of a building that differs from what its Certificate of Occupancy (CO) allows. Common examples include subdividing a single-room-occupancy building, creating apartments in a cellar or basement, converting a garage into living space, or squeezing more dwelling units into a building than the CO permits. Because the CO is the legal document that defines how many units a building may have and how they may be used, any deviation is a violation regardless of whether the space "seems fine." Illegal conversions are dangerous because they often bypass fire-safety, egress, and light-and-air requirements — which is exactly why the City enforces against them aggressively.
How do I know if my building has an illegal conversion?
Compare the actual use of your building to its Certificate of Occupancy (CO), which lists the legal number of units and permitted uses. If there are more apartments than the CO shows, if a cellar or garage is being lived in, or if a single unit has been carved into several, you likely have an illegal conversion. You can look up your CO and DOB records using your property's borough-block-lot (BBL). Warning signs include extra mailboxes or gas meters, multiple kitchens where the CO shows one unit, and rooms rented separately. When in doubt, have an architect review the CO against the physical layout before you rent or buy.
Why are illegal conversions dangerous?
Illegal conversions are hazardous because they usually skip the code requirements that protect occupants. Extra or below-grade units often lack proper egress, fire separations, ceiling height, ventilation, and light and air, so a fire or flood can trap people. Cellar and basement units are especially deadly during flooding, as Hurricane Ida showed in 2021. Beyond life safety, illegal conversions can void insurance coverage and violate mortgage terms, leaving the owner exposed after a loss. The Department of Buildings and HPD treat these conditions seriously and can issue vacate orders that displace occupants immediately. The safety risks — not just the paperwork — are the core reason the City enforces so hard.
Penalties & Enforcement
What are the penalties for an illegal conversion in NYC?
Illegal conversions draw Department of Buildings (DOB) violations and OATH civil penalties, and HPD may take separate enforcement action. Penalties escalate for aggravated or repeat offenses, and converting a one- or two-family home into three or more units carries steeper consequences. In the most serious cases, the City can issue a full vacate order that displaces occupants immediately, or a padlock order for illegal commercial use. On top of fines, an illegal conversion can jeopardize your insurance coverage and violate your mortgage. Because penalties compound and enforcement can be swift, addressing an illegal conversion proactively is far cheaper than waiting for a complaint-driven inspection.
What is an aggravated illegal conversion?
An aggravated illegal conversion is the most serious tier, generally triggered when five or more dwelling units are created illegally. Under Local Law 45 of 2015, this carries a penalty of $15,000 per illegally created unit, and the City can place a lien on the property to secure the amount owed. That means a single aggravated conversion can generate penalties in the tens of thousands of dollars very quickly. Owners who pack many units into a building far beyond what the Certificate of Occupancy allows face this heightened exposure in addition to standard DOB violations, potential vacate orders, and insurance and mortgage risk. The size of these penalties reflects the severe life-safety danger of dense illegal occupancy.
Can the City make tenants leave an illegal apartment?
Yes. When the Department of Buildings or HPD finds an immediately hazardous illegal conversion, the City can issue a vacate order that requires occupants to leave right away, and it can issue padlock orders for illegal commercial use. A vacate order displaces people immediately, which is one reason illegal conversions are so harmful to the very tenants they house. Importantly, the owner — not the tenant — is responsible for the violation, and relocation obligations can attach through HPD. If you own a building facing a vacate order, expect to address both the code conditions and potential responsibilities to displaced occupants, and act quickly to limit the fallout.
Tenant Rights & Legalizing
Do tenants in illegal apartments have rights in NYC?
Yes. Even when a unit is an illegal conversion, tenants retain legal protections. A landlord cannot use "self-help" eviction — such as changing the locks, removing belongings, or shutting off utilities — to force out an occupant, even of an illegal unit; removals must go through the lawful process. If the City issues a vacate order and displaces tenants, relocation obligations can attach through HPD. This means owners cannot simply evict their way out of an illegal-conversion problem, and they may owe duties to the very tenants living in the unlawful space. Tenants who face lockouts or unsafe conditions should contact HPD and 311 for help.
How do I legalize an illegal conversion in NYC?
Legalizing usually starts with an architect or engineer reviewing the building against its Certificate of Occupancy (CO) and the applicable codes and zoning. If the extra units can meet fire-safety, egress, and light-and-air requirements and the zoning permits them, the professional files alteration (Alt) applications with the Department of Buildings, the work is performed and inspected, and ultimately a new or amended CO is issued reflecting the legal layout. Not every conversion can be legalized — zoning, lot size, and physical constraints may make it impossible. For basement and cellar units, a separate legalization pathway may apply in certain pilot districts. Begin with a professional assessment before spending on construction.
Can I legalize a basement apartment created as an illegal conversion?
Possibly, but only through the specific pathway the City has created for below-grade units. Local Law 126 of 2024, the City of Yes for Housing Opportunity changes, and Local Law 127 of 2024 established a legalization program for certain pre-existing basement and cellar apartments in designated BASE pilot community districts, with a 10-year compliance framework. The unit must have existed before April 20, 2024, and owners must apply by April 20, 2029 — though as of August 2026 applications are not yet open pending DOB rules. Outside that pathway, an illegal cellar unit remains illegal. Review both the DOB illegal conversions page and the accessory dwelling unit page to see whether your unit qualifies.