December 6, 2018

Modified Bitumen Roofing & Why It's so Popular for Flat Roofs

A look into the features and long-term advantages of modified bitumen (mod bit) roofing for flat roofs, no matter where you live.

Time to read:
4 Minutes
Written by
Nicholas Capobianco

Many great-looking houses are designed with  flat roofs. Commercial buildings often have flat roofs and, of course, you may have enjoyed a beverage or two on a rooftop deck or café.  This popular style originated in ancient Egypt. As a home or business owner, you probably don’t have the riches of a pharaoh to spend on roof installation or repair, and reasonable cost is one of the advantages you will find with modified bitumen.

The  life expectancy of a flat roof is dependent on many factors. The climate, materials used in the original installation, and proper drainage are all critically important. If ponding (collection of water in a specific place) occurs, the water can seep through and damage the underlying surface. Rot and mold form, and you might not even know until the time comes to repair or replace the roof. Flat roofs can last from as few as 10 years up to as many as 50 years.

Suppose you have a leak. Knowing where it’s coming from is especially difficult in houses with flat roofs. Although you may see a spot on your ceiling, the leak may not be originating directly above that spot. Water seeks the path of least resistance and will simply go where it was easiest to access.

What is “mod bit” or modified bitumen?

When you do your online research or speak to a contractor, you will probably hear the words “modified bitumen.” If you want to sound like a pro, you’ll want to know how to pronounce it. It’s “bit-ew-min” (bīˈt(y)o͞omən) and you can hear someone say it out loud in this YouTube video.

Mod bit roofing (sometimes mod-bit or just MB) is a very common material for flat roof installation and repair. An evolution of traditional asphalt roofing, it is made from asphalt and a variety of rubber modifiers and solvents.  Mod bit can be easily rolled-out on a roof and is extremely durable and relatively fast and easy to install, reducing labor costs and time.

It was first introduced in Europe in the 1960s and became popular in the U.S. in the 1970s, with its primary application on homes and commercial buildings with flat or low-sloping roofs. It remains popular today because of its strength, longevity, and flexibility. Because it comes in rolls, it is simple to transport, install, and (if necessary) repair.

Aside from modified bitumen, other applications for flat roofs include:

  • BUR (built-up roofing), which entails layers of hot tar and gravel. It can be heavy and messy and smelly to install.
  • Rubber membrane roofing, which is often recommended for warm climates. It can cost up to 30% more than other alternatives.
  • PVC roofs, which come in a range of colors and are very durable. They can, however, be  difficult to repair and costly to install.

How is modified bitumen installed?

Mod bit roofing is often  heated with a blow torch as it is rolled out. It can sometimes be applied over an existing tar roof, though we do not recommend it. This “torch-down” method does not give roofers the chance to inspect plywood or insulation for leaks or water-logged (and possibly moldy) areas. It can also make the next install more expensive since the removal process becomes more intense.

Some applications involve “hot mopping” asphalt onto the roof, but newer mod bit applications do not require flames or heat to install. They are known as  cold-applied roof coatings. A mechanically attached base sheet is covered by one or two plies of mod bit membranes. A qualified and experienced roof expert will be able to advise you on the best material, options, and process for your home or commercial building.

Advantages of modified bitumen roof systems

Modified bitumen has many positive features and long-term benefits. New technologies and application systems make it environmentally-friendly and cost-effective.

  1. When installed correctly, modified bitumen roofs have seams as strong as the rest of the roof material. This eliminates most of the leakage concerns around flat roofing systems.
  2. Mod bit is  weather-resistant and can even endure wind and hail. It is very resilient in cold weather and will not easily crack when temperatures fall well below freezing.
  3. An incredibly energy-efficient system, mod bit’s top layer can be treated with “cool roof features” like thermal emission, or the ability to reflect sunlight and release already-absorbed heat. According to  one roofing professional, “this helps reduce your property’s indoor cooling requirements, resulting in lower energy consumption.”
  4. Modified bitumen roofs are also extremely tear-resistant. If you are a homeowner, you may use your roof as a deck. Mod bit will withstand foot traffic.
  5. The newer systems can be patched relatively easily because breaks and leaks are easier to locate.
  6. Mod bit is recyclable, which is better for the environment.

Modified bitumen drawbacks

Every roofing material and process has its shortcomings. Among some of the more common concerns about mod bit are:

  1. The torch method of installation can create fire risks in older homes, where wood may be close to the roof. Again, choosing the right contractor is essential. You can also discuss newer installation methods involving adhesive or hot-air welding.
  2. If proper insulation is not used, mod bit roofs can absorb heat, rather than reflect it.
  3. Scuffing can be a problem if your roof deck gets heavy foot traffic.
  4. The right thickness and treatment of mod bit are essential to its longevity. It is available in 1-ply, which is rare and may not last as long, as well as 2- and 3-ply variations which are much more common, and a bit more costly.
  5. Most materials have a limited warranty (e.g. 30 years). With proper care, a mod bit roof can last up to 20 years.

Final thoughts

An investment in your roof is one of the most critical expenses you will have as a homeowner or business owner. Modified bitumen is one of the most tried, trusted, and true roofing materials—the gold standard in roofing, especially in colder weather areas.

Make sure you choose the right professional who can help you select the proper materials and installation methods for your job, needs, and climate. Ask about installation time, process, and warranties. The right roofer will happily answer your questions and provide you with references and alternatives.

Choosing someone to repair your flat roof is the first—and perhaps most important—step in the process. If you’re looking for roofers with great reviews and insurance, or just curious about installing mod bit on your roof, reach out to Roofr right here on our website! We’ll be glad to help point you in the right direction.

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