EPDM (ethylene propylene diene terpolymer) has been the leading choice for low slope or flat roof applications for the past 40 years. Commonly called “rubber roofing,” EPDM sheets can be manufactured as large as 50’ wide by 200’ long. For most common applications, however, the rolls are manufactured 5’ to 20’ wide and 50’ to 100’ long.
The larger size of the rubber sheets allows for less seaming in the installation and thus less chance of leakage. Where seams are necessary, they are overlapped and then chemically bonded, thus making a functional “single ply” roof. This makes EPDM far more resistant to ponding water or snow common to low pitch roofs.
Rubber roofs can be fully adhered (glued) to a mechanically fastened substrate (usually a specialty insulation board) or ballasted (held down by weight). The fact that mechanical fasteners (nails, staples, and screws) do not puncture the roof surface further enhances their ability to stand up to the tests of time associated with flat roofing.
TPO (Thermoplastic Polyolefin) membrane has been gaining popularity as a flat roofing choice. TPO installation is similar to EPDM installation, with the exception that the seams are robotically heat welded on site, making the seam even stronger than EPDM. TPO is commonly manufactured in white (vs. black for EPDM), making it a more eco-friendly choice as it is Energy Star-compliant with no need for coating after installation.