Cal. Civ. Code § 149

  § 149. Public halls. 1. Every public hall shall be everywhere at least
three feet in clear width.
  2. Every public hall shall be completely enclosed with fireproof
floor, ceiling and walls, and, in dwellings erected under plans filed in
the department after September first, nineteen hundred fifty-one, such
hall shall be separated from every stair by fireproof partitions or
walls. All doors and their assemblies opening from such hall or stairs
shall be fireproof, with the doors self-closing and without transoms,
except that in a dwelling three stories or less in height occupied by
not more than four families on each story, or in a class A dwelling or
any section thereof two stories or less in height, any such hall which
furnishes access to only one stair need not be separated from such stair
by any partition or door and the walls of a public hall may be
fire-retarded and the floors may be provided with three inches or more
of incombustible deafening materials between the beams instead of being
fireproof.
  3. Except in dwellings three stories or less in height and occupied by
two families or less on every story, and except as provided in
subdivisions four to seven inclusive, every public hall shall have at
least one window opening directly upon a street or upon a lawful yard or
court. There shall be such a window at the end of each such hall and at
right angles to its length, with an additional window in each forty feet
of hall or fraction thereof beyond the first sixty feet from such end
window; or the hall shall have one window opening directly upon a street
or upon a lawful yard or court in every forty feet of its length or
fraction thereof measured from one end of the hall.
  4. When the length of any recess or return off a public hall does not
exceed twice the width of such recess or return, no window shall be
required therein. But whenever the length of a recess or return exceeds
twice its width, there shall be an additional window or windows meeting
the requirements for a separate public hall. No entrance hall shall have
a return or recess which exceeds in length twice its width.
  5. The foregoing provisions of this section with regard to lighting
and ventilation shall not apply to a vestibule or other public hall
which serves as a means of access from one or more apartments opening
thereon to a fire-stair or fire-tower meeting the requirements of
section one hundred forty-four if such vestibule or public hall is
lighted and ventilated as required for fireproof dwellings by sections
thirty-seven and one hundred seven.
  6. The foregoing provisions of this section with regard to lighting
and ventilation shall not apply to that portion of an entrance hall
between the first flight of stairs and the entrance provided the
entrance door contains five square feet or more of glazed surface or
such entrance hall does not extend from the outer entrance of the
dwelling more than sixty feet.
  7. A passenger elevator vestibule not exceeding in length twice the
parallel length of the elevator shaft or shafts opening into it need not
be equipped with a window if it conforms to the requirements of sections
thirty-seven and one hundred seven for public halls in fireproof
multiple dwellings. Every door and its assembly separating such a
vestibule from any public hall connected with a stair, fire-stair or
fire-tower shall be fireproof, with the door self-closing and glazed
with good quality wire glass ten square feet or more in area. No such
door shall be kept open by any device whatever.
  8. Any part of a public hall that is shut off from any other part of
such hall by a door or doors shall be deemed a separate hall.