2006 New York Code - Construction Materials And Assembled Elements Of Construction.

 
    §   27-553   Construction   materials   and   assembled   elements  of
  construction.  Except as provided in section 27-555 of this article, the
  dead load shall be the  actual  weight  of  the  building  materials  or
  construction  assemblies to be supported, computed from the unit weights
  given  in  reference  standard  RS  9-1.  Where  unit  weights  are  not
  established  in  reference  standard  RS  9-1, the actual weights may be
  determined by analysis  or  from  data  in  manufacturers'  drawings  or
  catalogs.  Unit  weights  less than those given in reference standard RS
  9-1 may be used only with approval of the commissioner.