Section 27-338. Roof structures

(a) Construction of penthouses. Enclosure
  walls of penthouses shall comply  with  the  requirements  for  exterior
  walls  of  table 3-4 for the construction class of the building on which
  they are erected. Roofs of penthouses shall comply with the requirements
  for roof construction of table 3-4 and section 27-337 of article five of
  subchapter six of this chapter.
    (b) Construction of  bulkheads.  Bulkheads  shall  be  constructed  of
  noncombustible  materials  having  a  one  hour  fire-resistance rating,
  except that in  buildings  of  construction  class  II-E,  they  may  be
  constructed  of  combustible materials having a one hour fire-resistance
  rating.
    (c)  Scuttles.  Scuttles  shall  be  constructed   of   noncombustible
  materials,  or  of  combustible materials covered on the top, sides, and
  edges with noncombustible materials.
    (d) Skylights. For the purposes of this section, the  term  "skylight"
  shall  be  construed  to  include  the sash, frames, and glazing of roof
  monitors and sawtooth roofs.
    (1) SASH AND FRAMES. Skylights that are inclined at  less  than  sixty
  degrees  to  the  horizontal on all buildings of other than construction
  classes II-D and  II-E,  shall  have  sash  and  frames  constructed  of
  noncombustible  materials,  and  their glazing shall be as prescribed in
  paragraph two of  this  subdivision.  Skylights  that  are  inclined  at
  greater  than sixty degrees to the horizontal shall have sash and frames
  constructed as required for windows,  and  their  glazing  shall  be  as
  required  for windows. Glass, glass blocks, or plastic used in skylights
  shall be designed and constructed to withstand the same  live  loads  as
  required for roofs plus any concentrated live loads required herein.
    (2)  GLAZING. a. Skylights over stairways and shafts. Skylights placed
  over stairways and shafts shall be glazed with plain glass not more than
  one-eighth  inch  thick  or   unreinforced   plastic   not   more   than
  three-sixteenths of an inch thick.
    b.  Skylights over other spaces. Skylights in all locations other than
  over stairways and shafts shall be glazed with  one-quarter  inch  wired
  glass, plain glass, glass block, or plastic of material and installation
  complying with subparagraph c of this paragraph.
    c.  Plastic.  Plastic  used  for  the  glazing of skylights other than
  skylights over stairways and shafts shall be slow burning  plastic.  The
  aggregate  area  of  skylight  openings,  other  than over stairways and
  shafts, shall not exceed thirty-nine per cent of the floor area  of  any
  room or space sheltered by the roof in which they are located. The edges
  of   plastic,   if  exposed,  shall  be  protected  by  metal  or  other
  noncombustible material. Skylights in which plastic is used, if on roofs
  having a pitch of twenty degrees to the horizontal  or  less,  shall  be
  constructed in accordance with the following:
    1.  The  area  within the curbs of each skylight shall not exceed five
  square feet, except that this area may be of any size, limited  only  by
  other  provisions  of  this  section,if  the opening is protected on all
  sides by a noncombustible railing thirty-six inches in height  complying
  with  the  provisions  of  section 27-558 of article three of subchapter
  nine of this chapter for railings; or the skylight  is  subdivided  into
  areas  of  five  square  feet  or less by noncombustible muntins or bars
  capable of supporting a live load of three hundred pounds at any  point;
  or a noncombustible screen or grid capable of supporting a load of three
  hundred  pounds  over  any  one foot by two foot area as provided above,
  integral with, or not more than three feet below the skylight, with  the
  wire or bars spaced into areas of five square feet or less (if above the
  roof, the wires shall be of corrosion resistive metal).

    2.  There  shall  be  a  minimum  clear distance of three feet between
  skylights.
    (3)  Separation  of skylights from structures. There shall be at least
  ten feet between a plain glass or plastic skylight and  any  door  in  a
  stair  bulkhead located above the roof in which the skylight is located,
  and at least ten feet between such a skylight and  any  opening  in  any
  roof structure or other wall above the roof not equipped with an opening
  protective. On buildings up to one hundred feet in height there shall be
  at  least  ten  feet  from  such  a  skylight  to the outside face of an
  exterior wall facing on a frontage space.
    (4) SCREENS.  Plain  glass  skylights  shall  be  protected  on  their
  underside  by  noncombustible  screens  having  a  mesh not smaller than
  three-quarters of an inch by three-quarters of an inch nor  larger  than
  one  inch by one inch of at least No. 12 B.&S. gauge wires. The screen
  shall be installed tight against the roof opening or  shall  project  on
  all  sides  for  a  distance of not less than the distance of the screen
  below the glass, and shall be of such material and construction so as to
  support a load of three hundred pounds over any one  foot  by  two  foot
  area. The provisions for wire glass or screen protection shall not apply
  to glass block skylights.
    (e)  Greenhouses.  Greenhouses  on  the  roofs of buildings other than
  buildings of construction class II-D or II-E  shall  be  constructed  of
  noncombustible  framework  and shall be glazed with plain or wire glass,
  or slow burning plastic. The floors of greenhouses shall be  constructed
  at  least  as  required  for  roof  construction  in  table  3-4 for the
  construction class of the building on which it is located.
    (f) Construction of sloping roofs. Roofs having a slope of  more  than
  sixty  degrees to the horizontal shall be constructed of material having
  the same fire-resistance rating as required for an exterior  non-bearing
  wall  of  the  building  of  which it is a part. When the slope is sixty
  degrees or less to the horizontal, the sloping roof shall be constructed
  as required for the roof of the building. Where  the  back  of  a  false
  mansard  is  exposed  to  the  outdoors,  the back shall be covered with
  noncombustible material or with roof coverings as required for the  roof
  of the building.
    (g)   Dormers.  Roofs  of  dormers  shall  be  of  the  same  type  of
  construction and have roof covering of the same class  as  required  for
  the roof of the building on which they are located. The walls of dormers
  shall be constructed of materials having the same fire resistance rating
  as required for non-bearing exterior walls of the building on which they
  are  located;  except  that  in  buildings of construction classes II-A,
  II-B, II-C, and II-D,  the  walls  may  be  constructed  of  combustible
  framing  provided that the outside face of the framing is protected with
  noncombustible sheathing and the  aggregate  area  of  all  such  dormer
  walls, including openings therein, does not exceed twenty percent of the
  roof area.
    (h) Water tanks.
    (1)  SUPPORTS. All water tanks placed in or on a building and having a
  capacity of more  than  five  hundred  gallons  shall  be  supported  on
  noncombustible  walls  or  framing. When such tank is located within the
  building, above the lowest story, its framing shall be fire protected as
  required for columns supporting one floor or the tank shall  be  located
  within  a  room  or  space  that  is enclosed with construction having a
  fire-resistance rating equivalent to that  otherwise  required  for  the
  protection of the framing.
    (i)   Cooling   towers.   Cooling   towers  shall  be  constructed  of
  noncombustible materials, except as follows:

    (1) Outside the fire districts,  when  located  on  a  building  three
  stories or forty feet in height or less of construction group I, cooling
  towers may be constructed of combustible materials provided they are not
  more than fifteen feet high and do not exceed seven hundred fifty square
  feet in area.
    (2)  Outside  the  fire  districts, when located on the ground and not
  exceeding three stories or forty feet in height  or  one  thousand  five
  hundred  square  feet  in  area,  cooling  towers  may be constructed of
  combustible material provided they are  protected  by  a  noncombustible
  screen,  fence, or wall at least twenty feet from the tower and at least
  seven feet high.
    (3) Filling and drift eliminators may be of combustible  materials  if
  the  towers  are  provided with automatic sprinkler protection complying
  with the construction provisions of subchapter seventeen.
    (4) Filling and drift eliminators  may  be  of  combustible  materials
  where  the  towers are not provided with automatic sprinkler protection,
  provided all of the following conditions are met:
    a. The cooling tower is constructed of noncombustible material;
    b. The cooling tower is located on a building  in  construction  group
  I-A or I-B;
    c.  The cooling tower and filling and drift eliminators are located at
  least thirty feet away from any windows or fresh air intakes  which  are
  at  an  elevation  above the roof on which the cooling tower is located,
  whether in the same building or in an adjoining building;
    d. The cooling tower is located not less than fifteen  feet  from  the
  nearest lot line; and
    e.  The  cooling  tower  is  located  not  less than ten feet from any
  chimney, except that the distance shall be not  less  than  twenty  feet
  from a chimney venting products of combustion other than from gas or oil
  fired appliances, whether on the same building or an adjoining building.
    (5)  In no event shall cooling towers or filling and drift eliminators
  be constructed of materials that contain asbestos.
    (j) Miscellaneous roof structures. The following roof  structures  may
  be  constructed  of  combustible  material if less than twelve feet high
  above the roof: antenna  supports;  flagpoles;  clothes  drying  frames;
  duckboarding or platforms that do not cover more than twenty per cent of
  the roof area at that level.