N.Y.C. Admin. Code § BC 1209: Section BC 1209: Access to Unoccupied Spaces

1209.1 Crawl spaces.

Crawl spaces shall be provided with not fewer than one access opening that shall be not less than 18 inches by 24 inches (457.2 mm by 609.6 mm). All crawl spaces shall have a minimum clear height of 18 inches (457.2 mm).

1209.2 Attic spaces.

An opening not less than 20 inches by 30 inches (508 mm by 762 mm) shall be provided to any attic area having a clear height of over 30 inches (762 mm). Clear headroom of not less than 30 inches (762 mm) shall be provided in the attic space at or above the access opening.

1209.3 Mechanical appliances.

Access to mechanical appliances installed in under-floor areas, in attic spaces and on roofs or elevated structures shall be in accordance with the New York City Mechanical Code.