Cal. Civ. Code § 101

  § 101. Requirements for fireproof construction. 1. Every such dwelling
exceeding six stories or seventy-five feet in height shall be fireproof.
No multiple dwelling shall be altered so as to exceed either of such
heights without being made fireproof.
  2. In a fireproof multiple dwelling the walls, floors, roof, stairs
and public halls shall all be fireproof except as provided in
subdivision three. No beams, lintels or other structural members shall
be of wood.  No wood or other inflammable material shall be used in any
of the partitions, furrings or ceilings. For the portion of a multiple
dwelling more than one hundred fifty feet above the curb level, no wood
shall be used except as provided in subdivision three and except for
interior trim of windows.
  3. The foregoing requirements shall not be construed as prohibiting:
  a. Elsewhere than within, or in the openings to, the public halls,
stairs and shafts, the use of wood for sleepers, grounds, nailing
blocks, underflooring, finish flooring, interior doors with their
assemblies and saddles, floor base not more than one foot in height,
picture and wall moulding, shelving, closet and kitchen fixtures,
cupboards, cabinets and wardrobes.
  b. The use of wood for windows and for interior trim and finish backed
solidly against, or filled with, incombustible material when located not
more than one hundred fifty feet above the curb level and elsewhere than
within, or in the openings to, the public halls, stairs and shafts.
  c. The use within apartments of wood for decorative wall panelling,
wainscoting, mantels or other interior finish, and the use in an
entrance hall of wall panelling or wainscoting made of fireproof wood or
other material capable of successfully withstanding standard fire tests
prescribed in the local building code and in a manner approved by the
department.
  d. Where fireproof doors are required, the use for such doors, with
their assemblies and saddles, of material and construction capable of
successfully withstanding a one-hour standard fire test prescribed in
the local building code and in a manner approved by the department.
Should any door required to be fireproof be found to have deteriorated
so that it shall after installation fail to conform to the standard fire
tests prescribed, such door shall be removed by the owner and replaced
by him with a door capable of successfully withstanding such tests.
  4. All materials combustible in their natural state which are
constructed, processed or protected so that they will not support
combustion shall, before being installed in a multiple dwelling for any
of the uses herein specified, be permanently identified by label or
marking with the name of the manufacturer and the year of manufacture in
a manner approved by the department.
  5. When required to be fireproof, any outer wall or any wall or
partition which carries any load in addition to its own weight shall,
unless otherwise in this chapter expressly required, be constructed of
materials capable of successfully withstanding a four-hour standard fire
test prescribed in the local building code and in a manner approved by
the department. When required to be fireproof, any wall or partition
which carries only its own weight, other than an outer wall, shall be
constructed of materials capable of successfully withstanding a one-hour
standard fire test prescribed in the local building code and in a manner
approved by the department.