New York Consolidated Laws, Multiple Dwelling Law - MDW § 151. Spaces under stairs

1. It shall be unlawful to have a closet of any kind under any public stair.

2. The space beneath every stair from the foot of the stair to a point where the soffit is four feet or more above the floor shall be entirely enclosed with unpierced fire-retarded partitions.  Such enclosure beneath a flight of public stairs leading from the entrance story to the story next above shall be fireproof.

3. Any unenclosed portion of the space beneath a flight of public stairs leading from the entrance story to the story next above shall be left entirely open and kept clear and free from encumbrance.