The roughness of the section. 
   Namespace:   Autodesk.Revit.DB.Mechanical  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2013 
Syntax
Remarks
 In one section, all section members have same roughness. Default unit is Decimal feet. For Duct, unit type is UT_HVAC_Roughness. For Pipe, unit type is UT_Piping_Roughness