Flat roofs with a low slope — or roofs that rise less than 4 inches over a 12-inch run — require special systems to prevent water leakage. You want the best roof system for your building, no matter if it is protecting a large industrial building or your home. Low-slope roofs can now be re-covered or built with any of the four main materials: TPO, EPDM, PVC, or Modified Bitumen. Built-Up is losing popularity.
TPO
Thermoplastic Polyolefin (or olefinic thermoplastic elastomer), a relatively new roofing material, is a single-ply sheeting that has many outstanding qualities. The seams can be welded by heat to increase durability because they are made of plastic. TPO in white is a good choice for high temperatures and direct sunlight on your roof. It has a higher reflectivity than other colors and can keep the interior cooler than dark shades. It withstands weather changes and offers flexibility — as well as building settlement and thermal expansion/contraction. TPO has a tough hide that resists punctures. It is also resistant to moderate hail, although it is not impervious.
PVC
Polyvinyl Chloride, (PVC), was the dominant single sheet roofing product before TPO. PVC has similar characteristics to TPO and is a great replacement to gravel and tar roofing systems (also known as BUR or built-up roofing). It is also flexible and can be heat-welded, so it has an upper hand over TPO. For restaurants with a venting system, PVC is a good membrane roof covering.
EPDM
Ethylene Propylene Derne Terpolymer (EPDM) is a modified rubber material that brings many outstanding qualities to any flat roofing system. EPDM is extremely flexible and can withstand years of heat/cold cycles as well as differential settling without any difficulty if it is adhered to. EPDM is chemically inert and can withstand almost any chemical. This is actually similar to the material used to line retention ponds and leach pits. EPDM is available in white as well, despite being the most popular color. EPDM is the most resilient single-ply membrane. EPDM is a rubber product that can easily resist punctures in normal conditions. However, boot soles that are gravel-embedded can cause EPDM to fail so it might not be able to work where heavy foot traffic will occur.
Modified bitumen
Modified bitumen (also referred to as Atactic Polypropylene or APP) is another single sheeting material, is an asphalt product that is more cost-efficient compared to rubber membranes and plastics. It can also last longer than rubber membranes as long as it doesn’t accumulate water.
There are two options: using a torch, where crews melt the back and roll it out, or using a peel-and-stick self-adhering membrane, the most economical option, but it will also require more frequent replacement. Mod bit is available in many colors so that you can match your pitched roof’s tiles with a sloping cover.
Built-up roofing
Gravel and tar roofing (also referred to as built-up) has been a reliable option for more than a century. It consists of reinforced felt or scrim layers that are bonded to liquid hot asphalt and then covered by pea gravel to protect from UV. It has been used as a roofing system and is hail-proof. However, BUR does require the use of a kettle to dissolve the asphalt which is very risky. In addition, built-up is a great option for large roofs with low slopes. It’s cost-effective and lasts longer than single-ply materials.