A flat roof system built up from multiple layers of asphalt and felt, topped with gravel — the classic commercial flat roof.
A traditional flat or low-slope roofing system consisting of multiple alternating layers of bitumen (asphalt or coal tar) and reinforcing fabrics (felts or plies), topped with aggregate surfacing or a cap sheet. BUR systems have been used for over 100 years and are valued for their durability, redundancy, and resistance to foot traffic. They are installed by moppers or mechanical applicators that spread hot bitumen between layers.
The 1960s warehouse had a 4-ply BUR system that was still performing adequately after 50 years, requiring only localized repairs.
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