Cal. Civ. Code § 213

  § 213. Lighting and ventilation of rooms. 1. No tenement, its lot or
any room, public hall or stairs therein shall be so altered as to have
its light or ventilation diminished in any way not approved by the
department.
  2. In every tenement erected after April twelfth, nineteen hundred
one, every stair hall, public hall and living room and at least one
water-closet compartment or bathroom containing a water-closet in each
apartment, shall have at least one window opening directly upon a street
or upon a lawful yard or court existing on April eighteenth, nineteen
hundred twenty-nine. Such window shall be so located as to properly
light all portions of such hall, room or compartment. Every part of an
apartment of three rooms or less in such a tenement shall be within
eighteen feet of a street or yard or have a window opening upon a lawful
inner or outer court existing on April eighteenth, nineteen hundred
twenty-nine. When a room in a tenement opens upon an inner court on a
lot line and less than ten feet wide from the lot line to the opposite
wall of the dwelling, such room shall be provided with a sash window
communicating with another room in the same apartment. Such window shall
contain at least ten square feet of glazed surface and be made so as to
open readily.
  3. No room in any old-law tenement shall be occupied for living
purposes unless it meets the conditions in one of the following
paragraphs:
  a. Such room has a window opening directly upon a street, or upon a
yard at least four feet in depth, or above the roof of an adjoining
building, or upon a court or shaft at least twenty square feet in area
open to the sky.
  b. Such room is located on the top story and is adequately lighted by
a ventilating skylight opening directly to the outer air.
  c. Such room has a sash window opening directly into an immediately
adjoining room in the same apartment which latter room opens directly on
a street or yard at least four feet in depth. Such window shall have a
vertically sliding pulley-hung sash not less than three feet by five
feet, except that when it is impossible to construct a window of such
size, the department may permit such window to be narrower. Both halves
of the sash shall be made so as to open readily, and the lower half
shall be glazed with translucent glass, or with obscure wire glass if
the department shall so require. So far as possible such window shall be
in line with windows in outer rooms opening on a street or yard, so as
to afford a maximum of light and ventilation.
  d. Such room has an alcove opening, of no less dimension than required
for such a sash window, to such an adjoining room, in addition to the
usual door openings.
  4. In every existing tenement the department, in addition to the
requirements of subdivision four of section eighty, may, as often as it
deems necessary, require the walls and ceilings of every room that does
not open directly on a street to be kalsomined or painted white to
improve the lighting of such room.
  5. Notwithstanding anything in this section to the contrary, no room
in any old-law tenement in an apartment which is vacant on June
thirtieth, nineteen hundred sixty, or thereafter becomes vacant, and, on
and after June thirtieth, nineteen hundred seventy no room in any
old-law tenement shall be used for living purposes unless such room
shall have a window opening directly upon the street, or upon a yard not
less than four feet deep, or above the roof of an adjoining building, or
upon a court or shaft of not less than twenty square feet in area, open
to the sky without roof or skylight, unless such room is located on the
top floor and is adequately lighted and ventilated by a skylight opening
directly to the outer air.
  An alcove shall be deemed to comply with the requirements of this
subdivision if (1) it opens directly into an immediately adjoining room
in the same apartment, and (2) such adjoining room opens directly on a
street or yard, and (3) a single unbroken open space occupies at least
sixty per centum of the area of the vertical plane between the alcove
and such adjoining room. The required open space between any such alcove
and an adjoining room through which it receives light and ventilation
shall not be obstructed by any curtain, portiere, fixed or movable
partition or other contrivance or device.