Code: Basement (building space definition)
Description: (Basement) is a story of a building that is partly below street level but has at least half of its clear height above curb level, which is what legally separates it from a cellar. In NYC, the rules for what you can use a basement for — including whether it can be occupied or rented — depend on the building type, ceiling height, ventilation, egress, and what the Certificate of Occupancy says. It is not a cellar.
Practical Meaning: As a homeowner, you need to know if your basement is legally occupiable or rentable — this depends on ceiling height (minimum 7 ft), windows, waterproofing, and your Certificate of Occupancy. Using a basement as a living space without DOB approval is considered an illegal conversion and can lead to violations, fines, and required removal of the space.
Where You May See It: In your Certificate of Occupancy (which states whether the basement is a legal story and how it may be used), in DOB inspection reports, HPD notices about illegal occupancy, and in violation letters when basement space is used without proper approval. In your house.
Why It Matters: If you rent or occupy a basement that does not meet NYC legal requirements, you risk DOB and HPD violations, fines, forced tenant relocation, and costly required work to either bring the space into compliance or remove the illegal use. Misidentifying a cellar as a basement — or vice versa — is a common and serious mistake that can affect your CO, resale, and financing.
Source: Illegal Basement – IQarius Guide