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Modified Bitumen Roofing: Pros & Cons

modified bitumen roofing pros and cons

Polymer roofing is a popular choice for many homeowners. These roofs are made of polymers In the world of roofing, there are many different types of materials to choose from.

One such material is Modified Bitumen Roofing (MBR).

It differs from other roofing materials because it is a composite consisting of a polyester fabric and bituminous material which has been modified with various additives.

This article will discuss some pros and cons to help you make your decision about whether or not MBR is right for you.

What is Modified Bitumen Roofing?

Modified-bitumen roofing is a single-ply membrane commonly used in commercial applications for its long life, high reflectivity and wind resistance.

It’s composed of an elastomeric base sheet laminated to a layer of asphalt. Manufacturers add various chemicals like silane to improve adhesion and make the membrane waterproof.

Modified Bitumen Roofing was first engineered in Germany following World War I.

It is a liquid-applied roofing material consisting of a hot asphalt and mineral aggregate mix, which forms a durable membrane when applied at high temperatures.

The combined modification process of the asphalt and mineral aggregate is what gives this roofing a unique look, performance capabilities, and texture.

The Cons of Modified Bitumen Roofing

Although it’s a strong, durable material, modified bitumen roofing has significant disadvantages:

  • Modified-bitumen roofing is not for daily living.
  • Bitumen materials emit noxious fumes that can cause eye and respiratory irritation and nausea, and since they’re petroleum-based, these products are not sustainable.
  • They can also cause discoloration on the roofing surface over time.
  • Modified-bitumen roofing has a high fire hazard.
  • It’s flammable when heated by fire, burns fast and emits toxic fumes that explode in flames, making it easier for the fire to spread.
  • You’ll need specialized equipment for installation.
  • Modified-bitumen roofing is thicker than other roofing materials, so an installer would have to use special machinery with heating devices built in, adding cost and time to the project.
  • Installation can be difficult even for professionals, since modified bitumen is slippery when it’s cold and can be peeled away in sheets.
  • The material is difficult to repair.
  • The membrane doesn’t stick well when repairing small punctures or tears, which results in water leakage.
  • Repairing the material is expensive.
  • Small tears are easy to work with, but bigger punctures or holes require more sophisticated tools, so fixing damages can be costly.
  • Bitumen roofing requires a lot of maintenance.

Although it’s durable in most cases, you’ll have to regularly inspect your rooftop for cracks in the membrane, which can cause leaks.

The Pros of Modified Bitumen Roofing

Despite the cons, modified-bitumen roofing has its benefits:

  • It’s long lasting.
  • Modified bitumen is one of the longest lasting commercial materials on the market today.
    • It can last 20 years or more depending on use and weather conditions like ultraviolet (UV) rays, high winds and extreme temperatures that cause wear and tear.
  • It has a reflective surface.
  • Modified bitumen roofing is highly resistant to heat and sunlight, so it reduces the building’s energy costs because it doesn’t absorb heat like other roof types do.
    • It also helps prevent damage from sun exposure that can result in leaks or cracks over time.
  • The material acts as insulation for your building.
  • Since it’s highly resistant to heat and cold, modified bitumen roofing can keep your building warm in winter and cool in summer – which minimizes the need for energy-consuming heating or cooling systems.
  • It has a long warranty period of 20 years on most products.
    • Because this material is so long lasting, manufacturers offer warranties that cover the product for 20 years or more.
  • Modified bitumen is one of the most durable roofing materials on the market today – making it suitable for harsh conditions like hurricanes and tornadoes where other types fail to provide adequate protection.
Modern Roofing and Decoration of Chimneys. Flexible Bitumen or Slate Shingles

Cost of Modified Bitumen Roofing

Modified bitumen roofing is generally not much more expensive than other types of roofing, however there are certain factors that may increase the total costs.

The following categories will provide a list of factors and whether they increase or decrease the cost:

Surface Preparation – Decreases Cost: Most roofing contractors prepare the roof deck by cleaning existing roofing materials from the surface, repairing any damaged components, and ensuring proper ventilation.

In cases where there is no existing insulation on the roof deck, it is recommended that the roof be prepared with an insulation board like polyisocyanurate.

This will increase the cost of the project, but it will also improve the energy efficiency of the home, resulting in a longer life for your modified bitumen shingles.

Modified Bitumen Roofing – Decreases Cost: Since most homes are currently built with asphalt shingles, applying modified bitumen is the least expensive type of roofing to apply.

Also, since there is no tear off process for this type of roofing system the cost of disposal is also minimal.

However, it’s important to note that most professional companies that install modified bitumen will charge a considerably higher price than asphalt shingle roofers.

Roof Pitch – Increases Cost: Roof pitches greater than 7/12 (or steeper than 4/12) require additional materials and labor, which increase the final cost of the project.

Sometimes modified bitumen is not considered for steep roofs because it doesn’t perform as well in areas with high winds and snowfall.

Adverse Weather – Increases Cost: Rain, snow and high winds will damage roofing materials like any other.

These extraneous factors greatly increase the difficulty of installation and can require additional time and money to complete the work successfully.

Time Frame – Decreases Cost: Since this is a new type of roofing system, more research and development is being completed on it.

This means that there are fewer professionals who can install modified bitumen compared to other types of roofing.

If you speak with a contractor and they do not have experience installing this type of roofing system, then expect a longer installation time and higher labor costs.

Tear Off – Decreases Cost: Since most homes have asphalt shingles as their current roofing system, a tear-off is required for this project.

Tearing off an existing asphalt shingle roof will quickly decrease the cost of installation because you are essentially doing half of the work yourself!

Environmental Impact – Decreases Cost: The modified bitumen process results in less waste since it can be applied as a single ply or as multiple plies, depending on the desired thickness.

Also, since most modified bitumen products are petroleum based they will not biodegrade and must be properly disposed of.

This means that your contractor will have to dispose of the material at an approved landfill and specialized recycling centers which can result in additional costs and time spent on the job.

Installation Time – Decreases Cost: The modified bitumen process is significantly faster than other types of roofing.

Most companies will be able to complete a tear-off and installation in one day, whereas a traditional asphalt shingle roof typically takes 2-3 days to complete. This will lower labor costs and may even result in additional savings.

Is the material safe to use?

Many people are concerned about the safety of using modified bitumen on their roofs. The first thing to note is that the material is made up of a mixture of asphalt and mineral fillers.

All of which have been used for roofing for many years. Modified bitumen was first introduced into Australia in 1978, with no real issues since then.

The concern that people have is that the bitumen will be heated to high temperatures during installation which could potentially release harmful fumes.

To combat this, strict guidelines are in place to ensure the safety of workers and occupants of buildings during installation.

Employees working with modified bitumen must comply with the Occupational Health & Safety Act 2004 (Commonwealth) and also the state regulations.


Modified-bitumen roofing has its pros and cons, but it’s a durable material that can withstand harsh weather conditions.

It provides high reflectivity and insulation for your building – making it an ideal choice if you need protection from the elements.

Roofer installs bitumen roof shingles