Built-Up Roofing (BUR)
Built-up roofing (BUR) is one of the oldest options for material for flat roofs or roofs that are very low in pitch. BUR systems are constructed with several layers of roofing felt impregnated with asphalt that’s applied hot. The felt is applied in overlapping layers to make a barrier two to four layers thick, then a layer of finely crushed stone is embedded in hot tar over the highest to make a really durable and impenetrable roof.
BUR roofs typically cost $2.50 to $5 per sq ft, installed. Industry surveys show that a properly installed BUR roof can last 20 to 30 years.