Koppers Coal Tar Built-Up Roofing Systems for Dead Level and Low Slope Roof Designs Select from the following: Tarred Organic Membrane - Aggregate Surface Specifications Specification No. 220-4 (4-ply) Specification No. 210-4 (4-ply) Tar-Glas Membrane - Aggregate Surface Specifications Specification No. 220-4 GP (4-ply) Specification No. 210-4 GP (4-ply) Specification No. 920-4  (4-ply) Specification No. 420-4  (4-ply) Specification No. 910-4 (4-ply) Specification No. 410-4 (4-ply)  Return to Application Considerations and Specifications