N.Y.C. Admin. Code § 27-321: § 27-321 Use of combustibles.

The use of combustible component materials in units or assemblies shall be limited to construction group II, except as hereinafter expressly permitted in construction group I. Combustible aggregates may be integrated with other materials to form a noncombustible material provided that the entire mixture, in the form in which it is to be used in construction, meets the requirement of this code for noncombustibility.