Pros and Cons of Asphalt Based Systems vs Single Ply

November 08, 2012

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Modified Bitumen: For those new to the roofing industry, the name "modified bitumen" generally describes reinforcing sheets of glass fiber, polyester, and/or polyethylene that have been factory coated into roll roofing.









  • SBS-modified bitumen sheet products have been used successfully in the United States since 1975.  However, during the past several years, there has been a noticeable increase in the number of reports of blistering associated with mop-applied SBS-modified bitumen roof systems.
  • A roof membrane that combines the multi-layer benefits of a built-up roof.
  • Perhaps the greatest advantage to modified bitumen is their versatility.  These products can be torched, mopped, or cold applied, depending on the limitations of the project.
  • They are also an excellent material for repairing existing bituminous roofs.


  • A minimum of two plies-base and cap sheet should be used for modified bitumen (increases labor costs).
  • The roof surface has to have positive drainage.
  • An additional ply of modified bitumen cap material is needed at the inside and outside corners of base flashings (increases labor costs).
  • Many critical steps in the application of these products: one is that  you must ensure a proper adhesion of laps seams  at the sides and the ends of the sheets.
  • Proper asphalt temperature during application and skilled torching techniques are critical to modified bitumen performance.
  • Most cases a hot kettle is needed- can be very messy and has a bad odor.
  • Modified bitumen is Not well suited to application in ponding water conditions.  Furthermore, their effectiveness is limited in recover situations where latent moisture in the original roof system generally exists.
  • Today less than 30 percent of the roofs now being installed are modified bitumen roofs.  Certainly, the cost of petroleum and the difficulty of finding skilled laborers willing to work with hot asphalt are major factors.

Single Ply (TPO): Thermoplastic Olefin membrane is based on polymers defined by ASTM D 5538.  A thermoplastic Elastomeric is a diverse family of rubber-like materials that, unlike conventional thermo set rubbers, can be reprocessed and recycled like thermoplastic materials.  Thermoplastic polyolefin's are in the thermoplastic Elastomeric family and are commonly called TPO in the single-ply roofing industry.










  • Single Ply roofs have the advantage of using both less material and labor, and, in many regards, they are tougher and more flexible than the asphalt and pitch roofs that preceded them.
  • Properly welded seams on a weld-able TPO membrane are stronger than the membrane itself and unlikely to give problems in the future.
  • A White Single Ply roof system's strong advantage in hot climates is its reflectivity. This helps to reduce urban heat islands and lower energy costs.
  • The TPO single-ply roofing market has grown to hundreds of millions of square feet annually with TPO membrane comprising the fastest growing segment of the U.S. single-ply roofing industry.
  • Hot-air weld seams are easier and cleaner than adhesive-based seams.Material is not as heavy and is easier to handle than multi-ply membranes.
  • Lower cost than some other hot-air welded membranes.
  • Mechanically fastened systems work well in re-cover applications.
  • Non-reinforced membrane is easy to form for detailing.
  • Stiff membrane that does not relax well.
  • Noticeable changes in color and texture of membrane over time.
  • Perception that because it is thinner than Asphalt based systems they are not as puncture resistant.