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How Long Does a Flat Modified Bitumen Roof Last?

Flat Modified Bitumen Roof

Identification of Modified Bitumen

Just because a roof is classified as a flat roof, that is, a roof with a slope of less the 2:12, does not mean it is a modified bitumen roof. (Important note: a flat roof is not flat, it just has a very low slope).

To properly identify a modified bitumen roof, you can look at the featured image of this post or the pictures below. But, in further detail, a modified bitumen roof is an asphalt material that is rolled on. Typically, the sheets are about two to three feet in width.

The membrane roofing material typically seals using special adhesives or a “hot mop” which is basically a tar and flame.

Life Expectancy of Modified Bitumen

The life expectancy of a modified bitumen roof depends on a multitude of factors, such as, home location, maintenance, and architectural design. However, manufactures suggest the rolled membrane roofing can last up to 20 years. This is simply not true in Florida.

For instance, a home near the beach may experience a lot of wind. On the other hand, a home with lots of surrounding vegetation may require continuous maintenance to ensure vegetation is not on the roof. Lastly, a higher roof slope may shed water easier than a lower sloped roof.

Worn modified bitumen membrane roof

Take a look at this picture above. My guess as a home inspector, without being there, is the roof is about 8 years old. The membrane roof was unprofessionally installed causing ponding in the middle of the roof. This can lead to weight issues and further wear of the roofing material.

At this point, the roof can only last a few more years. In some cases, it may just have to be replaced since four point inspections require the notation of ponding roofs. Insurance companies may then require the roof to be replaced.

worn modified bitumen membrane roof

This is a closer inspection of the same roof. You can see vegetation and the worn asphalt. It would not surprise me if this roof is leaking.

Knowing the information above, how long will my roof last?

It just depends. In Florida, the average lifespan of a modified bitumen membrane roof is 12 years. However, it could be sooner due to the consistent wear, improper install, and lack of maintenance.


Maintaining your roofs can easily extend the life expectancy of all roofing materials. Let’s look into what you can do to properly maintain your roof.

  • Trim all vegetation away from your roof.
  • Sweep all vegetation/leaves off of the roof.
  • Seal, seal, seal. You can use some tar to ensure all edges are sealed down.
  • Repair as needed using other modified bitumen pieces.


There is also the chance you could coat your modified bitumen roofing material. This is done by basically applying an aluminum paint that basically rolls on.

However, this may disqualify you for insurance so just keep this in mind. An inspector will have to call the roof out as coated, and the insurance company may not like that.

Coating a roof can extend the life another 5 years with further maintenance. Here’s a link to an elastomeric paint for coating.

Elastomeric Roof Coating

I would definitely recommend using an elastomeric paint as the paint will expand/contract with the Florida weather.

If you have other questions about your modified bitumen roofing, comment below! You can also check out our other roof guide on shingles.