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The 4 Basic Types Of Commercial Flat Roofing

Most people have a basic understanding of residential roofing. They know that most houses have a pitched roof and are covered in asphalt shingles, metal roofing, or even clay tiles in the desert southwest. Commercial flat roofing, however, is another beast entirely. The roofs are flat and the products used to cover the roof look nothing like residential roofing. The following is a basic primer on commercial flat roofing installation and products. 


Like residential roofing, asphalt is a common material used in commercial flat roofing installation. It is available in two main installation methods, including: 

  • Built-Up Roofing — When installing built-up roofing, roofing felt paper and gravel are layered on the roof and liquid tar is applied to the surface with a mop. This process is repeated several times until a thick surface is on the roof. 
  • Modified Bitumen — A variation of built-up roofing is modified bitumen, commonly referred to as mod bit roofing or just MB. Mod bit roofing is several layers of roofing felt and aggregate that are bonded together in a factory, saving time on the job site. The multi-layered sheet is applied to the roof using hot, liquid tar or with a torch. 

Like residential roofing, both built-up roofing and mod bit roofing are durable products.

Single-Ply Membrane

Another option for commercial flat roofing is single-ply membrane. Made from synthetic rubber or vinyl, single-ply membrane comes in wide rolls that cover the roof and are joined together with heat or chemicals at the seams. The main drawback with the single-ply membrane is that is susceptible to damage from the sun's UV rays and changes in temperature.  


Like residential buildings, commercial roofing products are available in metal. While metal panels are not typically used on flat, horizontal roofs, they are well-suited for low-slope roofs. In fact, in commercial applications, metal can be used on roofs with a pitch as low as .25:12. For a point of reference, the average residential roof has a much steeper pitch between 4:12 and 9:12.  

Metal panels used for commercial flat roofing are available in a standing seam or corrugated version. 


While not common, it is possible to have a commercial roof installed that is made up completely of vegetation. After a waterproof membrane is installed, drought-resistant and heat-tolerant plants are added. They add an eco-friendly factor and help cool the surrounding area, often reducing heat islands in urban areas.

Commercial flat roofing installation may be very different in terms of looks and installation, but the basic premise is the same: protect the building.