Built-Up Roofs (BUR) are composed of alternating layers of re-enforced membrane and bitumen. The number of layers used determines how many plies it has, as in "four plies". The surface is usually aggregate, but glass fiber, aluminum coating, or hot asphalt may be applied.
Energy efficient as it adds insulation
More layers mean better waterproofing
Creates a more rigid platform for mechanical systems
Fire resistant
Low maintenance
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