Basement and cellar apartments in NYC: legality and risks

A basement apartment in NYC is legal only if the Department of Buildings has approved it for living, which shows up on the building's certificate of occupancy. HPD's rule is that a cellar in a one- or two-family house can never be lawfully rented as things stand; the city's new accessory dwelling unit laws create narrow, DOB-approved exceptions that don't cover existing illegal units. Many below-ground units are rented anyway, so check before you sign. Illegal units carry real fire and flood dangers and can be emptied by a city vacate order.

You don't lose basic rights by living in one. Your landlord still can't lock you out, and the city provides relocation help if it orders you out. Here's how to tell what you're looking at and what to do.

Basement or cellar? The difference that matters

HPD uses a simple height test. A basement is a story partly below curb level with at least half its height above the curb. A cellar has more than half its height below curb level. Stand outside, find the curb in front of the building and compare: if most of the room's height is below the curb, you're looking at a cellar.

HPD's rules for renting a basement in a one-family house also say the yard can't be higher than six inches below a required window's sill, walls must be damp- and water-proofed if soil conditions require, and rooms must meet Housing Maintenance Code size minimums. In a two-family house, a basement can't be rented if doing so would turn the building into a multiple dwelling that needs a new certificate of occupancy. For buildings of every size, HPD's rule is the same: basements and cellars can never be lawfully rented unless they meet minimum light, air, sanitation and exit standards and have DOB approval.

How to check a certificate of occupancy

A certificate of occupancy (CO) states a building's legal use and type of permitted occupancy. No one may legally occupy a building without a CO or temporary CO, unless it's an older building exempt from needing one. If the CO for a two-family house lists two apartments on the first and second floors and nothing residential in the basement, a basement apartment is not legal.

1. 1

   Get the exact address and block/lot

   Search the address on Roofy's building lookup. The building page shows the BBL, building class, unit count, year built and DOB record.
2. 2

   Open the CO on the DOB site

   For COs issued before March 1, 2021, search the address in the Buildings Information System (BIS) and choose “View Certificates of Occupancy.” For later ones, use the DOB NOW public portal and choose “Certificate of Occupancy.”
3. 3

   Read the basement or cellar line

   Look at the row for the basement or cellar. Uses like “storage,” “boiler room” or “accessory” mean no one may live there. Count the dwelling units the CO allows and compare with the doorbells.
4. 4

   If there is no CO

   Buildings put up before 1938 aren't required to have one unless later alterations changed their use, exits or occupancy. The owner can request a Letter of No Objection from DOB to show legal use. See how to read a CO.
5. 5

   Look for red flags in the record

   DOB complaints about illegal conversions, "work without a permit" violations or an HPD vacate order are strong signs. See DOB complaints explained.

The flood danger is real

When the remnants of Hurricane Ida hit in September 2021, 13 New Yorkers died. The City Comptroller reported that 11 of them drowned in mostly unregulated basement apartments in Queens and Brooklyn. Flash flooding from heavy rain can fill a below-grade room in minutes, and a unit with one exit and barred windows is a trap.

• Sign up for alerts. At nyc.gov/notify, subscribe to Notify NYC and choose the basement apartments option to join the Basement Alert Group, which sends targeted warnings about life-threatening weather.
• Move up early. NYC Emergency Management advises basement residents to move to a higher floor when it rains, without waiting for water to reach the unit. Arrange this with upstairs neighbors in advance.
• Check your flood risk at floodhelpny.org, and keep valuables off the floor.
• Insurance: ask your insurer whether your renters policy covers flood damage before a storm, not after. See flood insurance in NYC.

Your rights if the apartment is illegal

• No lockouts. If you've lived there 30 days or more, or have a lease, the owner can't remove you by force, by changing the locks or by cutting utilities. Only a court order or a government vacate order can. Violations carry civil penalties of $1,000 to $10,000. See illegal lockouts.
• Habitability. Every residential lease, written or oral, includes the warranty of habitability, and it can't be waived.
• Rent in multiple dwellings. In a building that legally counts as a multiple dwelling (three or more families) and is occupied without the required certificate, the Multiple Dwelling Law bars the owner from recovering rent for that period or evicting for nonpayment of it. This rule doesn't reach one- and two-family houses, where most basement units are. Talk to a tenant lawyer before you stop paying anything.
• Relocation help. If the city issues a vacate order, HPD says occupants can receive relocation services, and the owner is billed for the cost. See vacate orders explained and help after displacement.
• Free legal help. If you're sued in Housing Court, you may qualify for a free lawyer under Right to Counsel.

The legalization pilot (not open yet)

Local Law 126 of 2024 created a pilot to bring some existing basement and cellar units in one- and two-family homes up to code. It covers only certain community districts: Bronx 9, 10, 11 and 12; Brooklyn 4, 10, 11 and 17; Manhattan 2, 3, 9, 10, 11 and 12; and Queens 2. Units in high-risk flood areas (FEMA Special Flood Hazard Areas, Coastal Flood Risk Areas and DEP's 10-year rainfall flood risk area) are excluded. Separately, since April 2026 DOB has accepted applications for newly built cellar ADUs in one-family homes under Local Law 80 of 2026; that is a construction path, not a way to legalize an existing rental.

1. Before April 20, 2024

   Unit must already exist

   Only basement and cellar units in place before this date can enroll.

2. December 2024

   Local Laws 126 and 127 enacted

   Passed alongside City of Yes for Housing Opportunity.

3. November 10, 2025

   Rules proposed

   DOB and HPD propose an Authorization for Temporary Residence (ATR) that would let tenants stay while owners make upgrades over ten years, with a right to return after construction.

4. Pending

   Applications open when rules are final

   DOB says pilot and ATR applications are not being accepted until its rules are promulgated.

5. April 20, 2029

   Owner application deadline

Until an owner has an ATR or an amended CO, a unit in the pilot area is still unpermitted. Ask the owner directly whether they plan to enroll, and read ADUs in NYC for the homeowner side.