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The Most Common Flat Roofing Materials

Flat roofing is used in so many different parts of the world that in some cases, they barely resemble each other. Cultural differences equate to differences in architectural style and material choices from one place to another. In fact, there are over a dozen types of flat roofing materials that are used by modern builders. Among these materials we find asphalt, fibreglass, coal-tar and many different types of manufactured rubber and vinyl. We’re going to focus on the 4 most common types of material used to built a strong, functional flat roof in any part of the world.

Asphalt and Coal Tar

Asphalt, or coal tar and gravel, is by far the most common material used to build flat roofs. This material is a by-product of oil, and has a high melting point. The gravel also protects the roof from fire. This type of roof is created by alternating layers of waterproof material with coal tar and gravel, until you have a solid, water resistant platform. Also known as a “built-up-roof,” asphalt flat roofs are durable, inexpensive and fairly attractive. Unfortunately they also produce heavy, toxic fumes during the building process, and are not recommended as a DIY project.

Modified Bitumen

Developed in the 1970s, modified bitumen is actually a modified version of asphalt. Since many of the natural plasticizers found in asphalt and coal tar are lost during the distillation process, developers have found a way to put some of these back in. There are 3 basic additives in use today: attactic polypropylene (APP); styrene-butadiene-styrene (SBS); and styrene ethylene butadiene styrene (SEBS.) The result is a stronger, longer-lasting form of asphalt. Modified bitumen can be applied much more easily than traditional coal tar and gravel roofing, as it is manufactured in adhesive sheets. Homeowners can install this type of roofing material themselves.

Rubber Membrane

The unadulterated type of rubber that is used for flat roofing is called ethylene propylene diene monomer, or EPDM. This option is more expensive to install than modified bitumen or asphalt, but it is more resistant to scrapes and tears. In colder climates, the standard black EPDM is a good choice because it pulls in heat and acts as a good insulator. For the same reason, standard EPDM is not ideal in warmer climates; a lighter-coloured version is available but it is more expensive. Both types of EPDM rubber membrane are durable and resistant to sun damage.


Fibreglass is a popular option for many building jobs, including wall and roof insulation and flat roof structures.  As for the latter, the fibreglass is preformed and then installed over an existing wooden deck. This material is perfect for small-scale roof construction, such as covering bay windows, but less ideal for larger projects due to the number of preformed pieces and joints they would entail. Fibreglass flat roofing materials are relatively inexpensive, durable, and they will never corrode from exposure to the elements.

As with most building projects, the material you choose for your flat roof will generally depend on two things: the climate and your budget. Whatever those are, there is an option for everyone!

 Image courtesy of Wikimedia