Performance of PVC vs TPO Roofing Membranes PVC Flat Roofing Material — cool single ply roofing

Performance of PVC vs TPO Roofing Membranes PVC Flat Roofing Material - cool single ply roofing

In the current single ply roofing market, the two most popular options are thermoplastic membranes PVC and TPO. PVC has been successfully used in commercial and residential roofing since the 1960s, while PVC is a newcomer, and has been around since early 1990s. TPO is being touted as the more improved and cheaper version of PVC, and as a result has been steadily gaining in popularity. However, the reality is that when it actually comes down to longevity and performance, PVC has a long proven track record of performance, which TPO lacks. If you are on the fence whether to go for a PVC or a TPO membrane, learn more about these membranes similarities, as well as important differences, to help you make the right decision for your home or business.

SIMILARITIES BETWEEN TPO AND PVC

There is actually only a few similarities between TPO and PVC membranes:

- Thermoplastic

- Have heat-weldable seams

- Energy Star Rated for cool reflective properties, and are energy saving

- Typically light color (white or gray)

- Can be installed fully adhered, mechanically attached or ballasted

- Highly resistant to fire

DIFFERENCES BETWEEN TPO AND PVC

It is the differences between TPO and PVC that need to be carefully analyzed, as they ultimately determine each roofs performance, and longevity.

PRODUCT COMPOSITION

The most significant difference between TPO and PVC is their chemical composition.

PVC (polyvinyl chloride) is made up of ethylene and chlorine. Petroleum or natural gas is processed to produce ethelyne, and chlorine is derived from salt. PVC sheets contain plasticizers, stabilizers, ultra-violet light inhibitors, biocides and polyester or fiberglass reinforcement, all of which contribute to the membranes flexibility and durability.

TPO (thermoplastic olefin) is a blend of  polypropylene and ethylene propylene polymers, which is usually reinforced with polyester. TPO sheets contain colorant, flame retardants, UV absorbers and other substances that make TPO flexible and resistant to the elements.

Performance of PVC vs TPO Roofing Membranes PVC Flat Roofing Material - cool single ply roofing

DURABILITY, LONGEVITY AND PERFORMANCE

In theory, TPO membranes are supposed to be more durable and long lasting that PVC, because there are no plasticizers in chemical make up of TPO. Because PVC membranes contain these plasticizers, overtime they arguably break down and migrate to the surface area of the top layer over time, which ultimately leads to the membranes shrinkage and tears.

However, in practice the situation is very different. PVC membranes have a proven track record of performance. Membranes that have been installed on commercial rooftops over 30 years ago are still there today. These membranes have been able to withstand a wide range of weather conditions, temperature variation, ponding water, remaining completely watertight and in tact. The original formulation that has first been developed in Europe in the 1960s is still followed today with little changes, and it works. Moreover, PVC membranes are manufactured in accordance with strict ASTM standards that have been developed for PVC membranes decades ago.

By contrast, the fairly short existence of TPO membranes in the US is marred with numerous documented roof failures and product recalls. The reason is simple: the original formulation that was also developed in Europe, has been tampered with and altered many times by numerous US manufacturers to lower the cost of manufacturing. Unfortunately, by trying to cut corners and save money, TPO membranes have taken a major hit in terms of performance and longevity. Over the course of their existence, there have already been at least 3 new generations of TPO, all with slightly different chemical compositions. The newest TPO membranes are less than 5 years old and there is no data to support how low they will last.

In particular, TPO roofing membranes are known to go through accelerated weathering when subjected to high thermal or solar loading. This issue has been documented on numerous TPO membranes in Southern states that get a lot of heat and sun throughout the year. As a result, the MRCA committee issued TPO Advisory detailing the problems and made a recommendation to roofing contractors to install a product that has a proven track record of withstanding the loading.

Another significant issue is that for many years there have been no clear ASTM standards for TPO, and only in recently these standards have been developed (however, they too continue to be revised and improved). Overall, while it may be the case that the composition of TPO may in fact be superior to PVC when the manufacturers get it right, currently the formulation is still being experimented on.

Ultimately, you have to decide whether you want to pay more money for a time tested PVC membrane, or save money and take a chance with a TPO membrane, hoping that you get a formulation that will be durable and long lasting.

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