Section 27-327. Ceilings

(a)  Ceilings  that  contribute  to the required
  fire-resistance rating of a floor or roof assembly shall  be  continuous
  between  exterior  walls,  vertical  fire  divisions,  fire separations,
  corridor partitions or any other partitions having  at  least  the  same
  fire-resistance  rating  as  the ceiling. All such fire-rated partitions
  shall be constructed as set forth in section 27-340 or  subdivision  (a)
  of  section  27-341,  as  appropriate.  The  concealed  space above such
  ceiling shall be firestopped into areas  not  exceeding  three  thousand
  square  feet  with materials listed in section 27-345 of this subchapter
  for the full  height  of  the  concealed  space.  Access  to  each  such
  concealed  space may be through one or more openings, not exceeding nine
  square feet and protected by self-closing opening protectives having the
  fire-protection rating required by table 5-3.
    (1) Firestopping shall not be required where  the  structural  members
  within  the  concealed  space  are individually protected with materials
  having the required fire-resistance rating, or where the ceiling is  not
  an essential part of the fire-resistive assembly; nor shall firestopping
  be  required  where  a concealed space is sprinklered in accordance with
  the construction requirements of subchapter seventeen of this chapter.
    (b) Electrical and other openings in ceilings.  Ceilings  required  to
  have   a   fire-resistance   rating   may   be  pierced  to  accommodate
  noncombustible electric outlet boxes or recessed  lighting  fixtures  if
  the  aggregate  area  of  such  openings  does not exceed sixteen square
  inches in each ninety square feet of ceiling  area  and  the  electrical
  outlet  boxes  or recessed lighting fixtures are constructed of steel at
  least  .022  inches  thick  and   sealed   tightly   at   the   ceiling.
  Noncombustible  pipes,  ducts,  and  additional  or larger electrical or
  other service facilities may pierce ceilings that are required to have a
  fire-resistance rating only when the type of ceiling to be used has been
  tested with  such  types  of  facilities  installed  in  place  and  the
  proportionate  area  of  openings for such facilities to be installed in
  the ceiling does not exceed the proportionate area of such  openings  in
  the  assembly tested, and provided no opening is larger than that in the
  assembly tested. Protection for such  openings  shall  be  the  same  as
  provided  in  the  test.  Duct openings installed in accordance with the
  foregoing  shall  be  protected  by  fire  dampers  complying  with  the
  requirements of subchapter thirteen of this chapter.