No Flame, No Claim

PVC is composed of two basic components: chlorine derived from common salt, and ethylene derived from natural gas. By taking these two components and adding other components, PVC can be made rigid, flexible or semi-flexible. This is why PVC is considered one of the most versatile plastic materials.

PVC considered PVC is considered a “single-ply” roofing system. This is because the system only requires a single layer of membrane to keep the roof watertight. Other systems, such as an asphalt-based “built-up” roof system (BUR), involve multiple layers of asphalt-soaked felt to make up the system.

Both PVC and TPO can be mechanically attached (using plates and screws) or adhered to the roof substrate. Unlike PVC however, TPO membranes do not adhere readily, especially with water-based adhesives. They also have higher coefficients of expansion and contraction resulting in much greater movement through temperature cycles. Whereas adhered PVC roofs have performed exceptionally well over decades, the properties previously mentioned create challenges when adhering TPO.

PVC’s overlapping seams are “hot-air welded” together to prevent water from penetrating the building. Once welded together, the seams are one of the strongest parts of the system and do not break down over time like other roofing systems that use glues, double-sided tape or asphalt to bond their seams.

While PVC and TPO are both in the thermoplastic, single-ply roofing family, they are very different in their base chemical composition and physical properties. They are also not compatible with each other. PVC has been used as a roofing material since the 1960s and has over 50 years of proven performance

Aside from the different chemistries used to create the membranes, PVC and TPO have other important differences worth mentioning. TPO manufacturers are still continuing to modify their formulations to try and achieve the required level of performance, while PVC has been performing very well for over 50 years. PVC membrane’s resistance to fire performance is significantly greater than TPO membranes, as evidenced in the video below. Another important difference is TPO’s sheet flexibility. TPOs are much stiffer than PVC, making them harder for contractors to work with. This is especially important when having to flash penetrations or any other detail work, possibly leading to areas not being watertight, and when working in colder weather. For a complete list of the differences between TPO and PVC, click on the link to download the Sikaplan Versus TPO infographic below.

There are many reasons why building owners choose to trust a proven PVC roof membrane over a TPO membrane. One of the most important reasons is that most, if not all, TPO manufacturers are on their third or fourth formulation of the membrane, while PVC boasts 50+ years of real-world performance. For a roofing contractor, however, the reasons they prefer to install PVC over TPO have a lot to do with them being able to give you a water-tight system.

In general, PVC is a much easier membrane for the contractors to work with, even in cold temperatures. TPO membranes are stiffer, making sheet handling and detailing more difficult, especially in cold weather. If the membrane is challenging to work with and a contractor needs to flash penetrations or a wall/curb, it increases the risk of an improper application.

TPO also requires all cut edges of the membrane to be sealed from water migration, and seams are much more sensitive to probing. All of this leads to extra time, money and an increased potential for mistakes. When TPOs fail prematurely, contractors run the risk of tarnishing their reputation. No contractor wants to get a call that the roof they installed has failed. No matter what the reason, all parties involved usually take the blame.