Modified Bitumen Roofing System – Anatomy, Benefits, and Installation

Modified bitumen roofing system patch and seam welding

Looking for a durable and high-quality roofing system? Knowing about a modified bitumen roof structure and long-term reliability for residential, commercial, and industrial buildings gives you insight into the value, strength, and longevity these roofing systems offer.

Modified bitumen roofing system professional installation

New Image Roofing Atlanta gathered information defining modified bitumen roofing anatomy, its benefits, and installation details.

Modified Bitumen Roofing System Anatomy

Modified bitumen roofing systems membrane torch down

A modified bitumen roofing system includes several fundamental components that work together to provide superior waterproofing and weather resistance:

Base Sheet – The base sheet is the roofing system’s foundation, providing a stable substrate for the modified bitumen membrane. It is typically fiberglass or polyester reinforcement coated with asphalt or polymer-modified asphalt.

Modified Bitumen Membrane – The modified bitumen membrane is the roofing system’s heart, offering exceptional waterproofing and flexibility. It is an asphalt and rubber or plastic modifier blend, which enhances its elasticity, durability, and resistance to temperature fluctuations.

Surfacing – Modified bitumen membranes may be surfaced with granules, reflective coatings, or a smooth finish to enhance durability, UV resistance, and energy efficiency. Surfacing options vary depending on the roofing project’s requirements and environmental conditions.

Adhesive or Heat Welding – Modified bitumen membranes are typically installed using hot asphalt (hot tar), cold adhesive, or heat welding techniques. Heated asphalt is applied to the substrate and the membrane is rolled out and pressed into place (while heat welding involves using a torch to melt the membrane seams together for a watertight seal).

Flashing and Sealants – Flashing materials like metal, plastic, or modified bitumen strips are used to waterproof roof penetrations, edges, and transitions. Sealants are applied to seams, joints, and penetrations to enhance waterproofing and prevent water intrusion.

Modified Bitumen Roofing System Benefits

Modified bitumen roofing systems waterproofing

Modified bitumen roofing systems offer numerous advantages that make them an attractive choice for various roofing applications:

Durability – Modified bitumen membranes are highly resistant to punctures, tears, and impact damage, making them ideal for high-traffic areas and regions prone to severe weather conditions.

Flexibility – The rubber or plastic modifiers in modified bitumen membranes provide enhanced flexibility and elongation properties, allowing the roofing system to accommodate building movement and temperature fluctuations without cracking or splitting.

Waterproofing – Modified bitumen membranes offer superior waterproofing capabilities, effectively sealing out moisture and preventing water intrusion into the building envelope. This helps protect the roof’s structural integrity and interior spaces from water damage and mold growth.

Energy Efficiency – Reflective coatings and surfacing options can help reduce solar heat absorption and lower cooling costs by maintaining lower roof temperatures. This can result in increased energy efficiency and reduced environmental impact.

Easy Maintenance – Modified bitumen roofing systems are relatively low-maintenance and require minimal upkeep to maintain their performance and appearance. Regular inspections and minor repairs can help prolong the roof’s lifespan and prevent costly damage or deterioration.

Read more about roof upkeep and maintenance plans at

Modified Bitumen Roofing System Installation

Modified bitumen roofing systems material installation

A modified bitumen roofing system installation typically follows these general steps:

Surface/Substrate Preparation – The roof substrate is inspected for damage, cleaned of debris, and repaired as necessary to ensure a smooth and even surface for membrane installation.

Base Sheet Installation – The base sheet is mechanically fastened or adhered to the roof substrate using asphalt or cold adhesive, providing a secure foundation for the modified bitumen membrane.

Membrane Application – The modified bitumen membrane is rolled onto the roof surface and positioned carefully to ensure proper alignment and coverage. The membrane is then adhered to the base sheet using hot asphalt, cold adhesive, or heat welding techniques.

Seam Sealing/Welding – Seams and overlaps in the modified bitumen membrane are sealed using heat welding, adhesive, or liquid sealants to create a watertight barrier against moisture intrusion.

Flashing Installation – Flashing materials are installed around roof penetrations, edges, and transitions to waterproof vulnerable areas and prevent leaks. Flashing components are secured with fasteners or adhesive and sealed with compatible sealants.

Surfacing Application – Depending on the desired finish and performance requirements, the modified bitumen membrane may be surfaced with granules, reflective coatings, or a smooth finish to enhance durability, UV resistance, and energy efficiency.

Final Inspection – Once the roofing system is installed, a final inspection is conducted to ensure all components are correctly installed, seams are sealed, and flashings are secure. Any necessary touch-ups or adjustments are made to ensure the quality and integrity of the roof.

Modified bitumen roofing system post installation inspection

ModBit Roofing Systems

In this article, you discovered how a modified bitumen roofing system is built, its benefits, and how they are installed.

Understanding how a Modbit roof is layered and installed and how it benefits your building helps you make well-informed decisions when seeking a roof-over or replacement.

Unfamiliarity with a roofing system’s assembly and benefits may lead you to install an improper roof on your residential, industrial, or commercial structure.


  New Image Roofing Atlanta

    2020 Howell Mill Rd NW Suite 232
    Atlanta, GA 30318
    (404) 680-0041