Section 27-507. Use of combustible materials

(a) General.  In all signs
  required  to  be  constructed  of  noncombustible  materials  under  the
  provisions  of  this  code,  wood  or  other  materials  of  combustible
  characteristics similar to wood may  be  used  for  moldings,  cappings,
  trim,  nailing  blocks,  letters, latticing, and other purely ornamental
  features.
    (b) Slow-burning plastics.  Slow-burning plastics may be used in  sign
  construction subject to the following conditions and requirements.
    (1)  If  all  parts of the sign other than the letters and decorations
  are made from noncombustible materials,  the  display  surface  or  sign
  facing  may  be  made  of  slow-burning  plastic,  or may be occupied or
  covered  by  letters  and  decorations  made  from,   or   faced   with,
  slow-burning  plastics  not  exceeding  a total area calculated from the
  values given in tables 7-2 and 7-3.
 
      Table 7-2  Ground Signs and Wall Signs (Noncombustible Materials)
 
  Area of Facing or Display           Area Occupied or Covered by plastics
  Surface 150 sq. ft. or less         100 per cent of display surface area
 
  Over 150 sq. ft., but not over      150 sq. ft. plus 50 per cent of the
    2,000 sq. ft.                       difference between 150 sq. ft.
                                        and the area of the display
                                        surface
 
  Over 2,000 sq. ft.                  Not over 1,050 sq. ft. without
                                        permission of the commissioner
 
         Table 7-3  Roof Signs, Projecting Signs, and Marquee Signs
                         (Noncombustible Materials)
 
  Area of Facing or Display Surface   Area Occupied or Covered by Plastics
  150 sq. ft. or less                   100 per cent of display surface
  Over 150 sq. ft. but not over         area 150 sq. ft. plus 25 per cent
    2,000 sq. ft.                       of the difference between 150 sq.
                                        ft. and the area of the display
                                        surface.
 
  Over 2,000 sq. ft.                  Not more than 575 sq. ft. without
                                        permission of the commissioner
 
    (2) If combustible materials are permitted in the framework, moldings,
  cappings, trim, nailing blocks, latticing or other parts  of  the  sign,
  the display surface or sign facing may be occupied or covered by letters
  and  decorations  made  from  or  faced  with  slow-burning plastics not
  exceeding a total area calculated from the values given  in  tables  7-4
  and 7-5.
 
       Table 7-4  Ground Signs and Wall Signs (Combustible Materials)
 
  Area of Facing or Display Surface  Area Occupied or Covered by Plastics
  300 sq. ft. or less                 50 per cent of display surface area
  Over 300 sq. ft. but not over       150 sq. ft. plus 25 per cent
    2,000 sq. ft.                       of the difference between 150 sq.
                                        ft. and the total area of the
                                        display surface
 
  Over 2,000 sq. ft.                  Not over 575 sq. ft. without

                                        permission of the commissioner
 
                Table 7-5  Roof Signs (Combustible Materials)
 
  Area of Facing or Display Surface   Area Occupied or Covered by Plastics
  1,000 sq. ft. or less               25 per cent of display surface area
  Over 1,000 sq. ft. but not over     250 sq. ft. plus 10 per cent of the
    2,000 sq. ft.                       difference between 1,000 sq. ft.
                                        and the total area
                                        of the display surface
 
  Over 2,000 sq. ft.                  Not more than 350 sq. ft. without
                                        special permission of the
                                        commissioner