Base Sheet When a base sheet is substituted for the first ply it shall be non-perforated. The base sheet shall be embedded in a solid mopping of steep asphalt followed by thorough brooming to eliminate air pockets, wrinkles, fishmouths, buckles, etc. The remaining plies of felt shall be solidly mopped with coal tar in accordance with the specification, and completed the same day. When specifying the Base Sheet as an alternate for the first ply, use the designation BS as a subscript to the specification number. When base sheets are mechanically fastened in high wind areas, specify the use of discs to be used with the fasteners, 2" (51mm) dia. min. or as required with type of fastener. Refer to the FMRC Approval Guide for specific requirements. NOTE: If Koppers Asphalt Coated Base Sheet is used for the first ply of the roofing specification, it must not be left exposed or used as a work surface or temporary roof prior to roof completion. Good roofing practice dictates that the total roofing membrane be completed the same day. Base sheets manufactured with holes or perforations for venting purposes shall not be used in Koppers Built-Up Roofing Specifications. Koppers Glass Base Sheets should be unrolled and allowed to relax approximately 30 minutes prior to application. Care should be taken when unrolling felts in cold weather. When mechanically attaching the base sheet, tack the front end and pull the remaining base sheet taut. Apply fasteners 9 inches (229mm) on center along the laps and stagger nail along two rows down the center portion of each sheet 9 inches (229mm) on center (approximately 100 fasteners per 100 square feet) (9.3m2). As the fastening progresses down the length of the base sheet, keep pulling the sheet taut and permanently fasten as specified. (Dimensions are approximate). In high wind areas use fasteners with discs, 2" (51mm) minimum diameter, or as required with type of fastener. Refer to FMRC Approval Guide for specific requirements.  Return to Application Considerations and Specifications