TPO, PVC and Modified Bitumen

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TPO stands for thermoplastic polyolefin, a single-ply roofing membrane that covers the surface of the roof. The name is a bit misleading, because rather than being a plastic, TPO is actually one of a few different types of rubber, usually a blend of polypropylene and ethylene-propylene rubber. or most residential applications, TPO membranes come in two thicknesses options: 45 mils (.045″) or 60 mils (.060″). The width and length of the membrane can vary depending on the manufacturer, with a typical TPO membrane roll being 6 to 6.5 ft. wide and 100 ft. long. Other membrane thicknesses and widths are also available depending on the manufacturer, including a 3 feet-wide rolls for the edges of the roof. Commercial grade TPO membranes may have a thicknesses of up to 80 mils (.080″) and may come in up to 12 feet-wide rolls. The flexibility of the membrane makes it highly resistant to tears, punctures and impact damage. This flexibility also allows for a building’s movement and setting, without compromising the roof’s performance.

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PVC roof material is composed of two layers of PVC with a polyester reinforcement scrim in between. The top ply contains additives that make the membrane UV resistant. The top layer also contains the plasticizers that make the sheet flexible. The bottom ply is black PVC and also contains plasticizers for flexibility. On the roofing contractor’s side, PVC roof membranes are really great to work with. They’re incredibly flexible, which is great for the installation process, and they have a great track record for longevity and performance.

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Modified Bitumen

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Modifiers are added to standard roofing asphalt to replace plasticizers removed during the distillation process. Bitumen is reinforced with fiberglass or polyester fiber matting in order to increase durability and strength.
The two most common types are SBS and APP. The use of SBS (styrene-butadiene-styrene) increases the flexibility of the membrane and allows it to have stronger expansion and contraction capabilities. APP (attactic polypropylene) increases the aging ability of the roof system. A standard SBS modified bitumen roof system is a two-ply system applied in rolls that overlap the edge of the previous roll.