Any contractor or roofing company who has been in business any length of time and done commercial work is familiar with modified bitumen. The classic replacement to old style BUR (built up roof) systems, the easiest way to recognize if a modified bitumen (mod bit) roof is being put on is whether or not the installer has a blow-torch in their hand.
Currently, Infinite Roofing no longer installs Modified Bitumen roofs, in favor of using either EPDM, TPO or PVC options, however we’ve assembled this page for your research in making your decision on what the best flat roof system is for you.
What is Modified Bitumen?
Modified Bitumen is a kind of asphalt product. Usually the asphalt comes in rolls and is “rolled out” over the top of the roofing substrate / deck using a blow-torch. It was one of the first replacements to Built Up Roof systems that dominated low slope or flat roofs in the early 20th century.
TPO Roofing, known as an energy star rated eco-friendly flat roofing option.
EPDM Roofing Systems are an economical install without disturbing day to day business.
PVC Roofing is popular for being heat reflective, lightweight, & eco-friendly
See an overview of our commercial roofing service options and comparisons.
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See an overview of our industrial roofing service options and comparisons.
What is the life expectancy of a modified bitumen roof?
Mod bit roofs last upwards of 20 years, sometimes even longer with proper maintenance and have a very long and established track record in the roofing industry. Modified bitumen is well known for it’s durability and strength and is one of the reasons why this style of flat roofing has withstood the test of time.
However, due to the difficulty of installation, most modified bitumen roofs don’t actually last this long and end up with a 10 to 15 year life span. In fact, the installation skill required for mod bit is often so high, and so hard to consistently do from job site to job site that it can be difficult to guarantee a total life span, especially if the roof surface itself is tricky to work around.
Plus, the requirement for a blow-torch and the possibility of a building fire from the use of it on the roof during installation often requires that the building not be occupied during the process.
EPDM vs. Modified Bitumen
Modified bitumen can usually take more abuse than EPDM but comes at a higher degree of error when it comes to installation. Plus Modified bitumen does not stand up to ponding water (stagnant water that does not properly drain off the roof) very well.
EPDM on the other hand has an easier install and is generally very reliable as a roofing system and stands up to ponding water very well. However, EPDM’s durability as a material is less than Modified bitumen.
Cost wise, generally mod bit is cheaper than EPDM.
TPO vs. Modified Bitumen
For mod bit see the above listed characteristics in “EPDM vs. Modified Bitumen.” TPO for comparison comes in single ply roofing systems and is often considered to be the “green” choice. The biggest thing to know about TPO in this case, is that often TPO can be installed over an older mod bit roof, and that one of the things to pay attention to during a TPO installation is how the seams are installed and to make sure the contractor is installing them properly.
The reason to make sure TPO is installed properly is that one of the most common causes of early failure is wind getting underneath the non-sealed middle areas of the sheets (as the seams seal the TPO sheets to the deck around the edges rather than across the whole surface) and causing catastrophic failure of the system.
However, assuming proper installation this is not a problem to worry about and otherwise TPO has been found to be very resistant to tears, chemical spills and grease while being UV resistant and being energy star rated for it’s energy saving properties.
Modified Bitumen Pros
At the top of the list, modified bitumen is extremely durable and lasts for a long time. Most traditional asphalt roofing systems experience problems after 10 years and start requiring more frequent maintenance and even replacement after this lifetime, but modified bitumen roofs have been known to last 20 years without needing much maintenance or attention at all.
Especially well known for extremely good waterproofing properties in addition to its durability, it also has had the benefit of having a variety of different methods of installation, although usually a hot processing technique is used in order to get the longest-lasting durability.
Also, mod bit is well known for it’s performance in extremely cold weather. The material was designed to remain flexible (not crack) even when temperatures fall well below freezing.
Modified Bitumen Cons
Mod bit usually requires heated installation and as a result is a fire hazard during the process, especially if the building has a wood structure or has wood decking or components around the roof itself.
Additionally, because of the way the surface is applied during installation, it’s difficult to detect where a leak is coming, leading to a costlier repair process. Also, because the installation process is so difficult and skill dependent, the average roof will really only see a shelf life of 10-15 years, despite the material itself being rated to last much, much longer than that.
Which leads to another problem: even though the roof itself is no longer serviceable after the 10-15 year mark, the material is still mostly intact and when torn off and put into a landfill, takes an extremely long time to decompose, making it not an exactly ‘green’ option for roofing, especially compared to more modern rubber roof options that both last as long or longer and are 100% recyclable.
During installation there’s often a very distinct smell coming from the modified bitumen, which can lead neighbors and customers to complain about the odor, and addition due to the fire hazard of installation, most of the time it’s not recommended to keep the business open during the application process, whether for basic safety or insurance purposes.
Does Infinite Roofing offer Modified Bitumen services?
For years we offered a mod bit service for installation and even repair, however we’ve recently moved away from offering Modified Bitumen roof replacement as a service. Primarily for the above listed “cons” and because customers have started to be more aware and favor more environmentally friendly options, such as TPO, EPDM and PVC over the classic mod bit. Either way, we hope the information above will help you compare different roofing options so you can select the best one for your situation.
To learn more about the dangers associated with modified bitumen torch down roofing and why we recommend against it, please visit this link: