§ 148. Public stairs. 1. Every stair, fire-stair and fire-tower shall,
except as otherwise provided in subdivisions three and four of this
section and section one hundred forty-nine, be constructed as provided
for fire-stairs in sections one hundred two and one hundred five for
fireproof dwellings.

2. Every stair, fire-stair and fire-tower shall be at least three feet
in clear width throughout, and at all floor levels shall have landings
at least three feet six inches in clear width.

3. Every stair, fire-stair and fire-tower shall be completely
separated from every other stair, fire-stair and fire-tower and from
every public hall and shaft by fireproof walls, with fireproof doors and
assemblies, with the doors self-closing and without transoms, at all
openings, except that in dwellings two stories or less in height such
walls may be fire-retarded on both sides in lieu of being fireproof. The
doors giving access to such stairs shall not be held open by any device
whatever.

4. Except in the case of an interior enclosed stair separated from and
directly accessible to the public hall by a self-closing fireproof door
and except as provided in subdivision five, there shall be provided to
light and ventilate every stair at every story a window or windows
opening on a street, court, yard or space above a setback. At least one
such window shall be at least two feet six inches wide and five feet
high unless it opens on a street, in which case its minimum height shall
be four feet. The aggregate area of such window or windows at each story
shall be at least eighteen square feet. On the top story a ventilating
skylight may be substituted for a window. At the entrance story or at
the roof level a sash door, such as described in section thirty-five,
opening to the outer air may be substituted for such window.

5. In a dwelling occupied by two families or less on every story:

a. If such dwelling is three stories or less in height, there may be
provided for any stair, in lieu of windows, a stairwell sixteen inches
or more in clear width extending from the entrance story to the roof.

b. If such dwelling is a class A dwelling and is two stories or less
in height, there may be provided for any stair, in lieu of windows, a
stairwell six inches or more in clear width. For the purposes of this
paragraph a section of a class A multiple dwelling may be deemed a
separate multiple dwelling.

c. If such dwelling is two stories in height and has no public hall on
the first story, no stairwell or stair windows need be provided.