Section 259. Cellar and basement stairs

A cellar or basement stair located
  inside the dwelling shall be entirely enclosed with fireproof walls  and
  be  provided, at all openings, with fireproof doors and assemblies, with
  the doors self-closing, except that in any  dwelling  three  stories  or
  less  in  height,  such  stair  may be enclosed with walls or partitions
  constructed of fire-resistive materials.