A.Architect and roofing consultant Harrison McCampbell responds: For a variety of marketing reasons, the bids you receive from local roofing contractors may not reflect national averages. Normally, the cost of a fully adhered EPDM roof should be fairly close to the cost of a modified bitumen roof.

EPDM is a butyl-based rubber treated to withstand UV and direct exposure to the sun. An EPDM roof will probably outlast a modified bitumen roof or any other asphalt-based membrane. Asphalt products contain oil, which evaporates, eventually rendering the carrier dry and brittle. Frequent wet-dry cycles will accelerate that process, especially if the wet periods are prolonged. Other factors that can affect the longevity of a roofing membrane include the specific details of insulation, fastening, flashing, lap treatment, and maintenance.