Modified Bitumen

What is Modified Bitumen?

Modified Bitumen products are time-proven systems that have been around for decades due to their reliable performance. A modified bitumen roof is usually composed of an insulation layer, one or more base layers, and a cap sheet with embedded granules.

Modified bitumen is the most common low slope roofing system found on older roofs. Modified bitumen is installed in 3′ rolls, either torch applied using flame heat to weld the cap sheet to the base sheet(s) or self-adhering using factory applied adhesives on the various components.


  • Some of the best long-term fire resistance because of the integrated glass fibers used in the manufacturing
  •   Ease of installation
  •   Adaptability


  •   Lack of flexibility in cold weather conditions
  •   More seams (because of the narrow rolls) creates more potential for leaks
  •   Use of open flame torch down installation increases the risk of fire during installation
  •   Lacks U.V. protection found on other products leading to premature weathering.

When Should I Consider Modified Bitumen?

Modified bitumen roofs may be best suited for compatibility with other existing roofs. A mod bit roof may initially be less expensive than other options but given its shorter lifespan is not usually the best value proposition.

The Installation Process

A variety of installation options are available including a hot mop, torch/heat weld, cold applied, and self- adhered to fit many different types of roofing challenges


Warranties are available up to 20 years, although, in the Southwest, a 10-year lifespan is more likely for a modified bitumen roof.