Section 27-561. Roof loads

Roofs and marquees shall be designed for wind,
  live, and other loads as prescribed in subdivisions (a) through  (d)  of
  this  section. It may be assumed that maximum wind load occurs with zero
  live load and that maximum live load occurs with  zero  wind  load.  For
  dwellings  an exception is made for awnings, canopies, and patio covers,
  which may be designed for a  live  load  of  twenty  psf  of  horizontal
  projection.
    (a) Live load. Minimum design live loads shall be as follows:
    (1)  For roofs with slopes up to and including twenty degrees from the
  horizontal, thirty psf of horizontal projection.
    (2) For roofs  with  slopes  greater  than  twenty  degrees  from  the
  horizontal,  thirty psf of horizontal projection, reduced by one psf for
  each degree of slope in excess of twenty degrees.
    (3) For valleys, live loadings  shall  be  increased  to  provide  for
  accumulations  of  snow.  The loading intensity shall be assumed to vary
  from forty-five psf at the low point to fifteen psf at the ridge.
    (4) For roofs having curved or pyramidal  shapes,  the  proposed  live
  load  shall  be  established  by  the  architect or engineer, subject to
  approval by the commissioner.
    (b) Wind load. The provisions of section 27-569  of  article  five  of
  this subchapter shall apply.
    (c)  Concentrated  loads. The provisions of subdivision (b) of section
  27-557 of this article shall apply.
    (d) Special loads.
    (1) When used for purposes such as promenades, assembly areas, or roof
  gardens, design shall be  made  for  live  loads  corresponding  to  the
  particular  usage, as indicated in reference standard RS 9-2. Such loads
  shall be considered as nonconcurrent with the wind load or with the live
  load specified in subdivision (a) of this section. The design  live  and
  wind  loads  for roofs, as specified elsewhere in this subchapter, shall
  be deemed to provide for incidental use of the roof of a building by the
  occupants thereof.
    (2) Where roofs are intended for the ponding of water, the roof  shall
  be  designed for the maximum possible depth of water which may be ponded
  thereon as determined by the relative levels of roof deck  and  overflow
  weirs  or  scuppers.  Such  load  need  not  be  considered as occurring
  simultaneously with wind or live load.
    (3) Girders and roof trusses (other than  joists)  over  garage  areas
  regularly  utilized  for  the  repair of vehicles and over manufacturing
  floors or storage floors used for commercical purposes shall be  capable
  of  supporting,  in  addition  to  the  specified live and wind loads, a
  concentrated live load of two thousand pounds applied at any lower chord
  panel point for trusses, and at  any  point  of  the  lower  flange  for
  girders.
    (4)  Where  roofs  are landscaped, the uniform design live load on the
  landscaped portions shall be thirty psf. The weight of  the  landscaping
  materials  shall be considered as dead load and shall be computed on the
  basis of saturation of the earth. The areas adjacant to  the  landscaped
  portions   shall  be  considered  as  assembly  areas,  unless  specific
  provision is made to prevent such use.
    (5) Where equipment is placed on roofs, the design shall  provide  for
  the support of such equipment.