Section 27-350. Ceiling construction

Ceilings that are to be suspended below
  floor or roof construction by means of a framing system shall consist of
  supporting  hangers,  carrying  channels and a supporting grid complying
  with reference standard RS 5-16 or shall  have  supporting  hangers  and
  carrying  channels and a supporting grid that can be demonstrated to the
  satisfaction of the commissioner to be of strength adequate  to  support
  the  ceiling  material.  The  hangers  and  supporting  grid shall be of
  noncombustible materials. In buildings of construction group  II,  every
  other  hanger supported from wood members shall be attached by a through
  bolt or clinched through nail.  Where,  in  table  3-4,  floor  or  roof
  construction  is  required  to  have a fire-resistance rating, a ceiling
  having  no  fire-resistance  rating   may   be   suspended   below   the
  fire-resistance construction.
    (a)  Luminous  ceilings.  For  the purpose of this section, a luminous
  ceiling shall  be  defined  as  a  ceiling  consisting  of  translucent,
  louvered,   egg-crated,   mesh,   or  similar  light-diffusing  material
  suspended from the ceiling or structural framework. A suspended  ceiling
  containing  less  than  twenty  square  feet  of  translucent, louvered,
  egg-crated, mesh, or similar material in any one hundred square feet  of
  ceiling  area  shall  not be considered a luminous ceiling, and shall be
  constructed and installed in accordance  with  department  of  buildings
  requirements for lighting fixtures. Luminous ceilings shall, in addition
  to  the requirements of this section, conform to all of the requirements
  of section 27-348 of this article for interior finish.
    (1) LUMINOUS CEILINGS OF NONCOMBUSTIBLE  MATERIAL.  Luminous  ceilings
  constructed  of glass and/or metal or other noncombustible materials may
  be used in any location.
    a. Glass used in  luminous  ceilings,  unless  it  is  wire  glass  or
  heat-resistant  glass  as specified below, shall not weigh more than two
  psf, nor shall any pane be larger than eight square  feet  in  area.  If
  glass  used  in luminous ceilings is wire glass, or is heat resistant by
  reason of having a maximum coefficient of expansion of 36 x 10-7 in. per
  in. per degree C, the glass may be of any weight and any  size,  limited
  only by considerations of structural safety.
    b.   Luminous  ceilings  installed  below  sprinkler  heads  shall  be
  constructed of a type of noncombustible  louver,  mesh,  or  other  open
  material that will not impede the flow of water from the sprinkler heads
  over  the  intended  area  of  coverage.  The  luminous ceiling shall be
  constructed so as to provide access to all heads and valves.
    (2) LUMINOUS  CEILINGS  OF  COMBUSTIBLE  MATERIAL.  Luminous  ceilings
  constructed of combustible materials shall not be installed in:
    a. Any exit or corridor.
    b.  Any  room  classified  in  occupancy  group H, or any room leading
  therefrom as defined in note b of table 5-4.
    c. Any room in which the net floor area per occupant is twenty  square
  feet  or  less,  or  any  room leading therefrom as defined in note b of
  table 5-4.
    d. Luminous ceilings constructed elsewhere than in the  spaces  listed
  in  subparagraphs  a, b, and c above shall be exempt from the provisions
  of section 27-348 of this article, provided that:
    1. The panels of such ceilings are of slow-burning plastic;
    2. The panels  are  installed  above  or  below  sprinklers  that  are
  constructed in accordance with the provisions of subchapter seventeen of
  this chapter;
    3.  No individual plastic panel exceeds ten feet in maximum dimension.
  Where installed below sprinkler heads, the plastic shall be  a  material
  that  will  fall  from  its  mounting  at a temperature at least fifteen
  degrees lower than the temperature at  which  the  sprinkler  heads  are

  designed  to  operate or are constructed of open material which will not
  impede the flow of water from the  sprinkler  heads.  Luminous  ceilings
  shall  be  installed  so  as  to  provide  ready access to all heads and
  valves.
    (b)  Suspension  of new ceilings below existing suspended ceilings. In
  construction group I a new ceiling may be suspended below not more  than
  one  existing suspended ceiling and shall be supported directly from the
  ceiling carrying channels adjacent to the hangers. In construction group
  II, an existing suspended ceiling shall be completely removed  before  a
  new ceiling may be suspended.