A Closer Look at Modified Bitumen in Commercial Roofs

/ / Bitumen Roofs, roof, Uncategorized

Find out why modified bitumen remains so popular in commercial roofs especially in harsh climates such as New Orleans.

With a long proven track record of offering protection against outside elements, modified bitumen membrane systems are the ideal solution for commercial roofs. MB, or modified bitumen, is an asphalt-based roofing system that is quite similar to a built-up roof (BUR). Like BUR, modified bitumen roofing systems are ideal for flat, low slope roof structures.

Modified bitumen roofing membranes were first engineered and manufactured in the 1960s and have been used in the southern United States since the mid-1970s. Today, two specific systems are used in commercial applications. These modified bitumen systems include:

  • APP (Atactic Polypropylene) – This type of system uses a heat torch technique for application.
  • SBS (Styrene Butadiene Styrene) – This system is typically installed using cold adhesives or hot asphalts.

Both APP and SBS roofing systems are often reinforced using polyester or fiberglass. They offer significant advantages over other available roofing systems that include:

  • Factory Manufactured – Both SBS and APP roofing materials are produced in rolls at a factory, to ensure quality control.
  • Better Temperature Reaction Control – Both of these systems are ideally suited for the reaction of expansion and contraction caused by temperature changes.
  • Various Available Finishes – The modified bitumen roof system is available in a variety of surface finishes that can increase oxidation resistance, and protect against damaging UV rays.

A Build Up of Five Components

A modified bitumen roof system has a composition of five key components that are often assembled in a variety of combinations. These include:

  • Insulation – The modified bitumen roof system can be designed with the specific “R” value. The insulation provides the roof system’s stable substrate.
  • Modified Bitumen Membranes – This membrane sheet is fabricated in the factory. It is made up of co-polymer modified bitumen that has been reinforced with fiberglass, polyester, or some type of composite carrier.
  • Modified Base Plies/Sheets – The modified base ply is usually positioned underneath the modified bitumen top ply.
  • Adhesive – The adhesive properties of the roofing system can be either applied hot or cold with specific binding agents and waterproofing material.
  • Surfacing – With a wide selection of available surfacing materials, it provides protection against UV rays. It also acts as a weatherproof surface that is applied either in the field or at the factory.

In addition to the five key components on a built-up modified bitumen roof system, flashing is also a key component. It provides significant waterproofing around the perimeter of the roof, along projections, and under equipment.


There are specific features to a modified bitumen roof that make it a far better choice than other available roofing applications. These features include:

  • Proven adhesive can save on application errors and additional labor on-site
  • Factory-applied surfacing meets insurance requirements and building codes
  • Resistance to fire
  • Polymer-modified asphalt construction that is highly resistant to splitting and thermal shock
  • High tensile strength composite with heavy reinforcement adds exceptional toughness and strength
  • Multiple system options are available to ensure durability and performance. Options can be fully customized.

Routine Inspections Are Necessity

To ensure longevity of the product, it is important to maintain a quality coating on the modified bitumen. The asphalt product can quickly age due to the many combined effects of water, UV rays, heat, along with expansion and contraction.

When the modified bitumen is properly installed, and the coating is well maintained, the structure owner can expect longevity of the roof system. The success or failure rate of a modified bitumen roof system is no different from any other roof. Any small defect that is left to its own devices can quickly fail the entire system. However, with proper inspection, and quick response to repair, the modified bitumen roof can last for decades.

Additional Resources:

  • Click here to learn more about our roofing maintenance services.
  • Click here to learn more about modified bitumen roofing.