PVC vs TPO

As the most trusted thermoplastic membrane manufacturer in the world, Sika is dedicated to educating its customers about the differences between PVC and U.S. manufactured TPO systems*. 

Take a few minutes to learn the differences between these similar, but not equal, membranes and the issues that plague U.S. manufactured TPO systems.

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

TPO stands for “thermoplastic polyolefins.”

Thermoplastic polyolefins (TPO) are in the thermoplastic elastomer family.  TPO membranes are made from ethylene propylene rubber (a synthetic elastomer) and polypropylene (a thermoplastic polymer) which is then polymerized (bonded together using chemicals). Filler materials are then added to create the finished roofing membrane.

TPOs have been used as a roofing material since the early to mid-1990s and billions of square feet have been installed on roofs across the United States since then.  While this may sound impressive, it’s no secret that U.S. manufactured TPO roof membranes have gone through numerous formulation changes due to premature failure, as mentioned in John Manville’s Dr. Kimberly Deaton-Tokarski’s RCI workshop presentation (summary below).  Those changes continue today as they try to find a formula to provide a durable membrane. 

While TPO and PVC are both in the thermoplastic, single-ply family, they are very different in their base chemical composition. TPO is made of ethylene propylene rubber and polypropylene, while PVC, also commonly known as vinyl, is composed of ethylene and chlorine. Petroleum or natural gas is processed to produce ethylene, and chlorine is derived from salt.  Both TPO and PVC look similar but PVC has been used as a roofing material since the 1960s, while TPO roofs started to be used in the 1990s.  PVC 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. As mentioned above, U.S. 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.  

Fire performance is also a concern with TPO membranes. As you can see from the video below, even fire-resistant TPOs do not perform as well as PVC membranes. 

Another important difference is TPO’s sheet flexibility. TPOs are much stiffer than PVC making it 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. 

Over the past 20 years, TPO has grown to become one of the most commonly used single-ply roof membranes in the US thanks in large part to its low price point.  It is hard to say exactly why a customer would purchase a TPO membrane.  Most facility managers or building owners don’t have time to do the research on every product being used in their building, so they trust the General Contractor or the Roofing Contractor to choose a roofing system given the budget. If a contractor perceives TPO to be a membrane just like PVC but at a lower cost, then it sounds like an easy decision.   Unfortunately, it only takes a few years after the job is complete for them to realize that initial cost is much less important than life-cycle cost (the cost of the roof over the life of it on their roof).  Choosing a membrane with a history of proven performance will be much less expensive for the owner over time.

In certain instances in the U.S. , TPO’s initial cost can be less expensive than PVC. But this is only true when looking at initial installation costs and not the cost over the life of the roofing system. PVC’s are documented to last longer than U.S. manufactured TPO membranes who are still experiencing premature failures. As noted in the chart below created from RS Means data, if you compare the life cycle costs of a Sarnafil roof estimated to last 35+ years versus a TPO roof lasting 20 years, PVC is the less expensive choice.  And with recent advances in PVC membranes and adhesive technology, the gap between TPO and PVC’s in initial costs have all but disappeared.  Installing a Sikaplan Adhered System using Single-Step Membrane Adhesive is now the same if not cheaper in initial price.

The latest formulations of  U.S. manufactured TPO membranes* have relatively few years of “real world” exposure, so their resistance to heat, UV and general weathering is still unknown. As mentioned previously in the history of TPO’s section, early generations of TPO membranes had many performance issues, which led to changes in their formulations. One of the most common problems was TPO failing in hot climates or when exposed to increased UV.

The following are excerpts from various design grades, presentations, articles, etc. of customers/organizations who have used TPO roofing membranes and are concerned about their performance.

TPO Membranes: Why Performance Matters

Presented by Rene Dupuis and Helene Hardy Pierce at the 2015 International Roofing Expo

• Throughout 2013 and early 2014, Structural Research, Inc. (SRI), a well-known and highly respected laboratory that has done testing with UL, NRCA, and MRCA, independently obtained various rolls (a total of 45 in all) of all of the major TPO brands
  
• SRI conducted a variety of ASTM physical property testing including thickness above scrim and weld strength which showed that the four TPO brands exhibit relatively similar performance on these tests. It wasn’t until accelerated aging using heat aging, weathering, and weight loss tests — the tests most closely associated with long-term membrane performance — were conducted that the various TPOs exhibited significant differences.
• When looking at many physical properties such as thickness above scrim and weld strength, the four TPOs are quite similar. However, there are big differences in accelerated aging.
  
• In the overall thickness test of the 60 mil TPO membranes, the average thickness of each product was 55-57 mils.

_{*A word of caution: U.S. manufactured TPO is not comparable with European TPO known as high quality Flexible Polyolefin (FPO). Developed in 1989, Sika’s FPO manufactured in Europe is established as a premium technology and offers a unique double reinforcement for both dimensional stability and tensile strength. A few American roof membrane manufacturers introduced their own TPO technology in the 1990’s based on low cost ingredients and sold it against Sika Sarnafil’s popular, time proven PVC membranes developed in the 1960’s. This low quality TPO approach in the U.S. led to a well-documented history of premature failures and ongoing formulation changes. The two different types of TPO membrane products may create confusion for intercontinental customers. Sika’s recommendation is to always base material decisions on the long-term performance history of the company and product. Follow the advice of the well-respected roofing expert Carl Cash from engineering firm Simpson, Gumpertz & Heger who said, “the only rational procedure for selecting a roofing system is its past performance on the roof in the same climate as the new project.”}