Your Ultimate Guide to Modified Bitumen Roofing Systems

Modified Bitumen (mod bit) roofing systems have emerged as a reliable and efficient solution for commercial properties with flat or low-slope roofs. Since its introduction in the 1960s, mod bit has gained popularity as a cost-effective alternative to traditional Built-Up Roofing (BUR) systems. In this guide, we will explore the key aspects of mod bit roofing, from its components to installation and contractor selection.

Understanding Modified Bitumen Roofing System

Modified Bitumen was developed to improve upon built-up roofing systems. This hybrid material combines asphalt membranes with polymerized rubber or plastic and reinforced with fiberglass, resulting in a sturdy yet flexible roofing material. The mod bit system offers several advantages that make it a go-to choice for many applications:

  • Suited for various applications: The mod bit system is versatile enough for commercial, industrial, and residential roofing.
  • Multi-layer protection: Mod bit roofing typically comprises two or more layers, providing enhanced durability.
  • Weather-resistant: This roofing solution excels in various climates, including harsh conditions like South Florida weather.

Benefits of Modified Bitumen Roofing

Mod bit roofing has become a popular choice due to several reasons:

  • High Tensile Strength: Mod bit is celebrated for its resistance to punctures and tears resulting from storm damage, wind-driven debris, and foot traffic.
  • Waterproofing: Mod bit provides excellent waterproofing protection, particularly when multi-ply systems are installed.
  • Energy Efficiency: With high UV resistance, mod bit systems help reduce energy costs significantly.

Modified Bitumen Roofing System Installation

The Installation Process

Two primary methods are used for installing a mod bit roof:

  1. Peel-and-stick: This cost-saving method is generally less reliable than professionally installed torch-down systems.
  2. Torch-down: A professional technique that involves heating the roofing layers until they adhere directly to the underlay. This method creates a consistently sealed defense against water penetration and UV rays.

Selecting the Right Modified Bitumen Membrane

Choosing between Atactic Polypropylene (APP) and Styrene-Butadiene-Styrene (SBS) membranes is a critical decision:

  • APP Membranes: APP membranes have a plastic-like quality due to atactic polypropylene, enhancing UV ray protection and promoting effective water runoff.
  • SBS Membranes: SBS membranes maintain greater elasticity and flexibility thanks to their synthetic rubber composition, making them versatile for various installation methods.

Considerations with Modified Bitumen

While mod bit roofing offers many benefits, it’s essential to consider a few aspects:

  • Lifespan: With an average life expectancy of about 20 years, its lifespan is relatively shorter than some other materials.
  • Heat Absorption: Dark-colored mod bit membranes can absorb more heat, potentially increasing indoor temperatures.
  • Installation Drawbacks: The installation of mod bit roofing can produce a strong odor and potentially harmful fumes, especially with torch-applied mod bit.

Modified Bitumen Roofing System

Choosing the Right Modified Bitumen Roofing Contractor

Enlisting an experienced commercial roofing contractor is essential for the technical nature of installing a mod bit roofing system. Here are some factors to consider:

  • Licensed, bonded, and insured in your state.
  • Specific training and certification from manufacturers.
  • Experience in managing staged roofing projects requiring simultaneous tear-off and installation.


Opting for a modified bitumen roofing system is not just a choice; it’s a sound investment in your property’s longevity and protection. By understanding its components, the benefits, the installation process, and the importance of choosing the right contractor, you can ensure a high return on this investment for years to come. Armed with this engaging and comprehensive guide, you can confidently move forward with your commercial roofing project.

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