Underwriters Laboratories Classification For Koppers Coal Tar Built-Up Roof Systems Combustible decks Koppers coal tar BUR systems are classified as Class A on combustible decks with KOP-R Insulation and all other UL Classified insulations of approved thicknesses when specified with gravel surfaced Tarred Felt or Tar-Glas felt roofing systems. Non-Combustible Decks Koppers coal tar BUR systems are classified as Class A on all UL Classified insulations of approved thicknesses when specified with a gravel surfaced Tarred Felt or Tar-Glas felt roofing system.  Return to Product Compliance and Approvals