Although most flat roofs have a slight pitch to allow water drainage, any roof angled at less than four inches in twelve is considered a low slope. The two terms are, in essence, the same. While low slope roofs cost less to build — rendering them more desirable for large commercial and industrial buildings — keeping them watertight presents a few challenges. Ancient flat roofs consisted of a support structure topped with clay. Fortunately, we now use more enduring materials to create a weather-proof seal. The following options now protect most flat and low-slope systems. MG Roofing, Inc., offers expert installation of all of these materials and more.
Built-up roofing, commonly known as tar and gravel, employs several layers of reinforcement mesh between thick spreads of bitumen (also known as pitch or tar) topped with a layer of pea gravel to ward off UV rays from the sun. Because sun and chemicals eat away at the bitumen, the thicker the build-up, the better the roof. If well-maintained, they can last upwards of 50 years. However, built-up roofs weigh more than any other system and pose profound burn hazards during installation.
Modified bitumen takes the same basic substance of tar and adds a plasticizing modifier that renders it pliable and much easier to work. Manufactured in rolls, this economical low slope material is thinner and lighter than bitumen build-up and can come with embedded mineral granules for UV protection. Otherwise, this single-ply membrane must be coated with a special film to gain the same defense. Modified bitumen may be the least expensive low slope covering, but it's also the least durable. However, if the roof has sufficient pitch to drain all water quickly, it can last for 20 years or so without a re-application.
PVC and TPO
Polyvinyl chloride (PVC) and thermoplastic polyolefin (TPO) are very similar to each other. Both are, essentially, plastic membranes, served up from rolls and whose seams are heat welded (melted together) for the strongest bond possible. Both hold up well under the sun and resist impacts, punctures and foot traffic. PVC is slightly more flexible, which installation crews like, and can take environmental chemicals, such as restaurant grease and acid rain, better than TPO. On the other hand, TPO can withstand more heat from both the sun and the building interior.
Ethylene propylene diene terpolymer (EPDM) is a synthetic rubber membrane and truly the Cadillac of low slope roof systems. EPDM seams mate with a powerful bonding adhesive. Roofs with ponding issues can last longer without substrate correction with an EPDM cap sheet. The rubber is impervious to water and chemicals. In fact, leach ponds are often lined with EPDM because of its superior impermeability.
All of the membranes have white options for LEEDS points and energy efficiency. Installation methods influence prices and expected lifecycles, so we recommend that you call MG Roofing, Inc. today to schedule a consultation. We'd be happy to discuss which system would best fit your budget and unique commercial low slope roof.