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Modified Bitumen Roofing System

Modified bitumen roof membranes have been around longer than you would expect. Since about 1975, these roofing membranes have been used successfully in the United States and Canada. Now it is considered to be one of the most popular commercial roofing systems in North America.

This type of roofing membrane is also very versatile. Both residential and commercial buildings with modified bitumen roofs are taking advantage of their flat or low-sloped roofs by turning them into decks, rooftop gardens, and patios.

What is a Modified Bitumen Roof?

A modified bitumen roof (MBR) is commonly known as a “torch-down” roof. This type of roof is an ideal solution for those with flat roofs and low-sloping roofing systems. It creates a durable surface through applied layers of fiberglass-based asphalt sheeting. What makes it different from other roofing systems is that the seams are usually melted together, which helps stop leaks.

The MBR is closely related to the built-up-roof (BUR), which is also ideal for buildings with low-sloped roofs or flat roofs. MBR systems can be installed through the torch-application method or “hot-mopped” like BUR. The difference is that the MBR system can be applied with “cold-process” adhesives while BUR cannot.Bitumen-Roofing

The MBR rolls can be manufactured with a release paper that uses a special combination of polymers which modify the underside of the modified bitumen sheets. Having the release paper helps eliminate the risks that come with the use of torches and hot-asphalt to make them free from volatile organic chemical (VOC) fumes during and after application.

The MBR system has been influenced by one of two additive types: atactic polypropylene (APP) and styrene-butadiene-styrene (SBS). Modified bitumen APP and modified bitumen SBS are created from asphalt modified with one or more polymers or solvents. This modification provides flexibility, impact resistance, and strength.

The difference between the two is that modified bitumen APP can be torch applied while modified bitumen SBS can be applied by torch, hot-mopping, or cold-applied adhesives. Always consult a professional to figure whether APP or SBS modified bitumen works for your flat or low-sloped roof.

Modified Bitumen Roof Pros & Cons

As with every new commercial roofing project, one must weigh the pros and cons to help determine what type of roofing material works best for their project.


  • MBR has a proven track record of performance, durability, and strength.
  • Decreases the event of cracks, damage, and other issues from weather elements.
  • There is a broad range of application methods.
  • The light-colored mineral surface and waterproofing characteristics help regulate fluctuating temperatures and climates inside and outside.
  • The roof can be installed flame-free and volatile-organic-chemical-free (VOC).
  • Competitive life-cycle cost.
  • Many MBR systems have long-term warranties available.
  • Able to withstand high roof traffic.
  • The redundancy of layers reduces the chance of a leak.
  • Highly adaptable to meet any penetration or flashing detail.


  • High cost due to 2-5 ply’s, which require labor and materials for installation.
  • Asphalt based roofs rely on gravel or granules for protection from the sun since, without them, these types of roofs crack and break apart.
  • Mop-down installation methods are extremely unsafe for workers.
  • Asphalt products do not last as long as they used to.
  • MBR is much heavier than a single-ply roof system.
  • Very few contractors still have the required equipment to install this type of roof.
  • Not environmentally friendly to remove.
  • Not as scuff- or tear-resistant as other commercial roofing membranes.

Modified Bitumen Roof Cost

Modified bitumen roofs can be expensive to install, but it can lower energy costs for a commercial building. This helps balance the life-cycle cost. Getting the peak performance from your roof depends on the quality of the installation, so make sure you choose a roofing contractor experienced in modified bitumen roofing.Bitumen-Roofing

You want to make sure that the roof is installed with the appropriate R-value. R-value is the measure of thermal resistance, so the higher the R-value is, the greater the insulating effectiveness. This adds to the overall cost of the new roof.

It is important to put in high-quality insulation to make sure you will not be wasting money on the heating and cooling costs. The temperature will also fluctuate inside your home without it. This is a cost designed to save money on energy costs in the long run.

The location of your roof, as well as the complexity of the installation, can make the costs add up. An often-overlooked cost is the price to strip and dispose of the existing roof before the actual installation of the new modified bitumen roof.

Elevated Roofing has your experts for a complete run-down on the cost of your commercial roofing project.

Modified Bitumen Roof Installation

Installing a modified bitumen roof involves preparation steps before the roof is applied. The materials themselves need to be stored properly to keep out moisture so the materials remain at the correct flexibility.

Before applying the MBR, the actual ambient temperature is important to improve the quality of the installation, and the roof needs to be dry, smooth, and free of dirt and other loose material. Each section of the roof has to be completed before the end of the workday to ensure that nothing is left exposed overnight. MBR systems are created using a five-layer combination of roofing elements.

  1. Insulation is used for thermal resistance to create temperature stability for the roof.
  2. Modified base sheets or plies are required layers for MBR systems after the insulation.
  3. Modified bitumen membranes are factory-fabricated sheet membranes made of co-polymer reinforced with polyester or fiberglass, which is the next layer.
  4. An adhesive made from waterproofing materials with a bonding agent applied hot or cold is used for the next layer.
  5. For the final layer, surfacing provides UV protection and weathering resistance.

MBR systems can be installed by heat-welding (torching), hot-asphalt cold-process adhesives, or self-adhesives.

  • Hot-asphalt is mopping down the roofing asphalt before rolling out the modified bitumen.
  • Heat-welding (torching) is the method of melting the asphalt so it can flow into the substrate.
  • Cold-process adhesives can be applied at ambient temperature and are free from VOC. 
  • Self-adhesives are often used for doing the roof oneself. This peel-and-stick method starts the same as heat-welding but is free from VOC.

UV radiation can lead to surface cracking on your newly applied MBR. Applying a field-applied coating made from aluminum-pigmented asphalt, asphalt emulsion, or acrylic can help keep your commercial roof from cracking.Bitumen-Roofing

Modified Bitumen Roof Repair

Any type of built-up roof is expensive to repair. The typical flat roof repair can cost $350 – $400 on the low end. It involves locating the source of the leak then patching the seams or the holes. It really depends on how severe the damage is and the type of material installed for the overall cost.

These types of roofs are very difficult and expensive to fix, even with high-quality MBR installers. With flat and low-sloped roofs, it can be very difficult to find the source of the leak. So, it is imperative to use knowledgeable and experienced MBR contractors who have the know-how to repair the damage.

UV protective coating helps to keep modified bitumen roofs from aging too fast, but that does have a time limit. Getting a re-coating adds to the longevity of an MBR system. The re-coating helps to eliminate waste and improve the durability of your commercial roof. Re-coating occurring more frequently than every 15-years is not recommended.

There are signs that the modified bitumen on your commercial roof is getting really old and may be in need of replacing sooner rather than later. Look out for for the following:

  • Thinning and blistering
  • Cracking
  • Flaking
  • Contractions or pulling
  • Slice marks
  • Grease and dirt build-up that can’t easily be removed

If these things happen, contact us at Elevated Roofing to discuss what your next steps should be.

Modified Bitumen Roof Lifespan

Modified bitumen roof systems have a competitive life-cycle cost due to how much money it can save you in the long run with internal energy costs. This type of roof is known for having a long service life, being dependable, and having exceptional waterproofing.

Overall they can last about 10-20 years. Actual longevity depends on the quality of the installer and materials. The experts at Elevated Roofing are the ones to call if you have an MBR that needs to be repaired. With the application of a reflective coating, getting necessary repairs, and cleaning, you can get more life out of your MBR system.

When it comes to getting a modified bitumen roof for your commercial roof project, make sure to talk to Elevated Roofing to get the work done right the first time.

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