Knowing what type of flat roofing material is on your building won’t stop your leaks but it will help you make better decisions about maintenance, roof repair, and/or replacing an old flat roof system.


Click here to understand more about your building’s roof will also help you communicate and relate better to potential roofing contractors as you go through the interview process to see which roofing company is a fit for your project.


Most common types of flat roofs:


  1. Bur or Build Up Roofs.


Bur or built-up roofs have been in use for more than 100 years in the United States and are often referred to as tar and gravel roofs. Layers of roofing felt usually three feet wide were stripped in and covered with melted hot tar. Workers would heat the asphalt tar or coal pitch to a liquid in a large kettle then mop it on the roof. After the 2-4 piles or layers, or roofing felt were mopped into place with the tar, the roofs were often covered in aggregate or pea gravel. The small stones or gravel were used to protect the tar from the damaging effects of the sun’s UV rays. How to tell if you have a Built-up roof:


  • Tar and gravel look
  • Small gravel is stuck in the tar
  • Flashings around HVAC curbs and parapet walls are often covered in tar.


  1. Modified Bitumen Roofing


Modified Bitumen is similar to a built-up roof in that it is composed of asphalt rolls usually three-foot-wide but a modified bitumen roof is usually only made of two piles or layers, a base sheet, and a cap sheet. Modified bitumen can be installed in four basic ways: 1) hot-applied with hot tar, 2) cold-applied solvent-based adhesive that does not require the use of heat, 3) torched down with an open flame that melts the two sheets together, or 4) peel and stick base and cap sheets that self adhere once a release tape is removed. The cap sheet or top layer usually looks granulated similar to the granules on a shingle roof and often is light gray in color. How to tell if you have a modified bitumen roof:


  • Seams in the roof every three feet.
  • Granulated look to the top layer that resembles the granules on an asphalt shingle (Note: Modified Bitumen roofs are sometimes coated with an elastomeric roof coating but you should still be able to see the seams or rolls in the roof and also the granules.) 


  1. EPDM Rubber Roof


Rubber roofs are fairly easy to recognize and are installed in two basic ways: 1) Ballasted or weighted down with large river stone or 2) Adhered or glued down. Rubber roofs that are adhered are easy to spot, they are black in color and usually stretched tight over an insulation board or fiberboard.


Rubber roofs that are ballasted are being held down and in place with the use of ballast or large stones on top of the sheets of roofing. These roofs are covered in rock similar to a built-up roof but the stones are usually larger and they are not stuck to the roof with tar. If you gently move the stone away you will be able to expose the rubber membrane. How to tell if you have a rubber roof:                    


  • Rubber can easily be seen
  • Rocks or stones can be moved to expose the rubber membrane
  • You will also be able to see the rubber around the HVAC curbs, parapet walls, and other flashings. 


  1. Spray Polyurethane Foam Roof


A spray foam roof begins with a layer of high-density polyurethane foam sprayed from a wand or sprayer. The foam is then coated with some type of waterproofing elastomeric topcoat. This topcoat is often reflective gray or white in color. How to tell if you have a spray foam roof:


  • A degraded topcoat will expose the polyurethane foam.
  • Since the foam is sprayed on from a wand you can usually identify the spray pattern the applicator used during installation.


  1. Thermoplastic membranes PVC or TPO


Thermoplastic roofing membrane is single layers of material usually white or gray but can be found in other colors. These membranes can be either adhered to, similar to an EPDM rubber roof, or mechanically attached with screws and plates. From a distance, PVC and TPO membranes are hard to distinguish but will most often be white or light color. How to tell if you have a PVC or TPO roofing membrane:


  • Light color or white roof
  • Tight look overbuilding, looks like white rubber roofing


These are not the only types of flat roofing systems you will find in Indiana, but they are the most common that are found.