Modified Bitumen Roof System “Mod-Bit”

Completed Modified

Modified Bitumen Roof Systems have been installed since the mid 1970’s. A Modified Bitumen Roof System is typically installed with 1-3 ply’s, and comes in a wide variety of colors. There are many ways to install a modified bitumen roof, but the four most common methods are cold applied (liquid adhesives), torch applied (torch with open flame), hot applied (hot asphalt) and self adhered (adhesives built into the sheet).

CertainTeed Flintlastic Color OptionsModified Bitumen Systems are typically seen as the next generation of asphaltic or pitch based Built Up Roofs (BUR). It carries many of the same strengths as a traditional BUR roof system, while the modified bitumen installation can be completed in a much safer and less expensive method.

At Chaffee Roofing, we typically install self adhered modified bitumen roof systems due to their safe and effective installation technique. Self adhered modified bitumen roof systems are similar to fully adhered single ply roofs, in that the entire system is adhered to the freshly installed insulation, or the next ply.

Self Adhered modified bitumen roof installations are completed by:

  1. Fastening the rigid polyisocyanurate insulation (The Roofing Process – Insulation Installation – Polyisocyanurate) to the steel deck.
  2. Then, on the first ply, which is called the plybase, the backing paper is peeled off. Then the plybase is placed over the rigid insulation, and then rolled in.
  3. Now that the plybase is fully installed, each additional ply, known as the midply, is installed directly over the last ply. If it is only a two-ply system, this step is skipped.
  4. Finally, the last ply, known as the capsheet, is installed in the same manner, with the cap sheet being rolled into the midply.
 Step 1  Plybase installed  Peal and Stick  Cap Sheet Rolled in

 Step 1

 Step 2

 Step 3

 Step 4

Detail work is completed in the same fashion, with all details being completed 2-5 times based on the number of plys in the system.

Benefits of an Modified Bitumen Roof

Some of the benefits of Modified Bitumen Roof Systems are:

  • Proven system that has been installed for over 40 years.
  • Proven performance of asphalt, which is known to go the distance.
  • Strongest puncture resistance of any roofing system.
  • Available in a wide variety of colors with little to no quantity restrictions.

Drawbacks of an Modified Bitumen Roof

Modified Bitumen Roof systems have a few disadvantages, which are:

  • 1 ply modified bitumen roof systems have not shown any long term success.
  • Very high cost if there are 2-3 ply’s that require labor and materials to install.
  • Asphaltic based roofs rely on granules for protection from the sun. Without granules, Asphalt based roofs crack and break apart.
  • If granules are not included with your modified roof system (known as a smooth surface mod-bit), the materials must be coated with aluminum roof coating or the surface will show accelerated aging. Typically, periodic recoating will be required.
  • Modified Bitumen roof systems age prematurely if used on roofs that hold any water.
  • Some installation methods, such as torch down, are very unsafe and pose a major risk to your building.

Please note that Chaffee Roofing will not install any 1 ply modified bitumen roof system and will not use any open flame torch application methods.

Modified Bitumen Roof systems are a great option for roof systems that have heavy foot traffic or increased likelihood for punctures. Mod-Bit roofs are also great for any roof system that requires a certain color that is unavailable in a single ply membrane.