The new spin on tar and gravel, Modified Bitumen flat roofs are the multi-ply version of tar and gravel roofs and can easily last 20-years or more.

Modified Bitumen

Modified bitumen is a material used in membrane flat roof systems that takes the core components of asphalt roofs, mixing them with rubber modifiers and solvents to make a 2-ply flat roof membrane.
Modified bitumen should not be confused with roll roofing for even though it comes in rolls, standard roll roofing is just a paper base with tar and ceramic granules and is adhered with tar. Roll roofing only last up to 5 years whereas modified bitumen lasts up to 20 years.




Modified bitumen shows distinct advantages over previous roofing technology, particularly asphalt and gravel roofs. Modified bitumen seams are as strong as the rest of the material, this means that early leaking is far less common than in asphalt roofing where corners and seams are not as strong. Another advantage to modified bitumen is that it doesn’t need a layer of gravel on top to hold it down like asphalt does. This also means that repairs are easier and finding the root problem of a leak is faster.

The extra modifiers in modified bitumen add weather protection and increase the life expectancy of the product. Other advantages modified bitumen has includes:

Nowadays there is also a variety of modified bitumen that is made with the modifier SBS (Styrene-Butadiene-Styrene) that is a peel and stick variety. Depending on your roof environment we will recommend one or the other.


A disadvantage you should be aware of is that modified bitumen on its own is prone to scuffing. Things like bird droppings, debris and general wear and tear wear down the granular surface of modified bitumen. All this means is if you want to have modified bitumen installed on a roof where there is lots of traffic, you may want to consider getting another protective layer on top like Tufdek. Modified bitumen flat roofs need regular maintenance to last long.