what is a built-up roof with modified cap sheet
What is a Roofing Cap Sheet. Used in low slope roofing such as built-up roofing (BUR) or modified bitumen roofing, a cap sheet is used to create a water-tight surface. Constant exposure to wind and weather can cause a BUR roof to become brittle and crack, then water can seep into the cracks, eventually working into the interior of the building.