NRCA Research on the Performance of TPO roofs in the US – Guide For Roofing Contractors

Currently, there is a big marketing campaign extolling the virtues of TPO roof membranes over its two direct competitors in the single ply roofing market EPDM and PVC. The ease of installation, potential benefits of the membranes and its attractive economical price are leading many roofing contractors to begin working with TPO roofing membranes. Check out our comparison of TPO roofing vs EPDM rubber.

In fact, according to NRCA’s 2000-2001 Annual Market Survey, TPO membranes were used in 9.5 % of all low-slope roofing projects in 2000, totaling about $970 million in installed costs. Despite TPO’s steady growth, the truth is that this membrane is one of the newest products in the roofing market, first entering the US market in the early 1990’s, and it is still going through experimental stages in terms of its final product composition. The initial years of TPO’s performance in the US have been rocky to say the least, with numerous product failures shortly after installation, consequent recalls and further modifications of the chemical composition of the membranes.

TPO’s less than desirable performance in the field was drawing attention and concern to such an extent that in 2000, NRCA”s Technical Operations Committee, with support from NRCA’s Executive Committee, authorized an extensive study of TPO roof membranes currently available in the United States. The major goal of this research study was to determine the exact chemical composition as well as physical characteristics of various TPO membranes from different US manufacturers, so that based on this information TPO’s long term performance in the field could be evaluated with greater precision. For the purposes of the study, 9 product samples representing products from 6 different US manufacturers were analyzed without identifying the products’ manufacturers or brand names.



The summary of NRCA’s findings provided below is revealing about TPO’s actual vs marketed durability and performance. It is important information for roofing contractors to be aware of when deciding whether or not to install TPO membranes for their clients.

Summary of TPO Study Results

Chemical Composition NRCA deemed it necessary to conduct an in depth chemical composition analysis of each sample TPO membrane. There were 3 types of analyses conducted: dynamic mechanical analysis, fourier transform infrared spectroscopy analysis, and scanning electron microscopic analysis.

These tests served a dual purpose:

1. to establish a baseline of data for evaluating and comparing present and future TPO membranes.
2. to determine the exact composition of each membrane so as to better understand how different components may affect the membranes durability and performance.

The most significant finding was that a number of sampled membranes contained certain chemical additives such as bromine compounds, that were used as fire retardants. It was determined that these chemical compounds may actually have an adverse affect on the membranes’ physical properties after accelerated aging. As a result of these findings, a number of TPO manufacturers has switched to other types of fire-retardant additives.

Thickness

NRCA found the different thickness of all 9 membranes to be within an acceptable range. It was noted that on 6 of the products the actual thickness was slightly less than the value indicated on the packaging by the manufacturers.

Water Absorption

Tests revealed significant variations in the water absorption capabilities of the 9 different TPO membranes. NRCA deemed this to be a concerning finding since this makes the membrane’s actual field performance questionable in the long run.



Dimensional Stability

Dimensional stability of the 9 samples was expressed as percentages of dimensional change after conditioning for six hours at 158 F (70 C). Overall, the values of all except one membrane were comparable to other single ply roofing membranes. One TPO membrane showed a concerning value for dimensional change.

Brittleness

According to the results, values of tested membranes’ brittleness points range from -27 F (-33 C) to -62 F (-52 C). NRCA deemed 5 out 9 membranes to be potentially problematic based on these results, as they all showed brittleness points greater than -50 F (-46 C). It is likely that this may negatively affect TPO membrane’s performance in the field. However, it is not possible to precisely determine what these adverse effects may be, and is something that will only become clear over time.

Breaking Strength

All membranes were tested for breaking strength at three different points in time: 1. as-received condition. 2. after 7 days of heat aging. 3. after 28 days of heat aging. The results for all but 1 membrane were within the range of acceptable by NRCA, staying the same or increasing slightly during seven-day conditioning, then decreasing slightly during 28-day conditioning. However, one TPO membrane showed a significant decrease in breaking strength after being heat conditioned both for the first and second time as compared to its initial condition. This significant difference is concerning as it is not clear how this may negatively impact the membrane’s long term performance in the field.

Tearing Resistance

All 9 TPO membranes were tested for tearing resistance at three different points in time: 1. as received condition. 2. after 7 days of heat aging. 3. after 28 days of heat aging. The NRCA was generally concerned with results as 6 out of 9 membranes showed significant changes in the tearing resistance values after both first and second stages of conditioning. Again, it is not clear how these result will translate into the membrane’s long term performance and durability, but it is a red flag for potential problems.

Recommendations for roofing contractors.

It is clear that despite previous issues and failures in the field, TPO roofing membranes are here to stay and will in fact continue to grow in popularity both in residential and commercial roofing in the US. Particularly, the price difference between more reputable PVC membranes and TPO, often makes contractors who are looking for a bargain to choose TPO, without fully considering the potential adverse consequences. NRCA’s research clearly sites a number of areas where TPO’s long term performance in the field was called into question. If you are a roofing contractor seriously considering working with TPO membranes, it is important for you do a lot of research on the membrane and manufacturer you are planning to work with, so that you do not end up putting your reputation on the line by installing a low quality roofing product. Make sure that you have got all of the points bellow covered before you commit to a TPO membrane.

-You need to make sure that you are working with a manufacturer who has been producing TPO roofs for a relatively long time, i.e. at least 10 years.

-You should only be installing a TPO membrane that meets the ASTM standards for single ply roofing membranes.

-Request from the manufacturer and closely evaluate the previous performance data of a particular TPO roofing membrane.

-Request and evaluate product data, such as important performance factors discussed in this article both for the membrane’s initial condition and after tests for accelerated weathering.

– When making your final decision, keep in mind that all TPO membranes that have been installed so far across the US are relatively young, some are not even 3 years old. Therefore, there is currently no reliable data about their long-term performance in the field.

TPO vs EPDM Rubber roofing – singly-ply roofs comparison.

Are you looking for a quality, energy efficient solution for a low slope roof and are not sure whether to go for TPO or EPDM roofing membranes? It can be difficult to distinguish between the two products as both are single ply roofing membranes. However, there are important differences that you need to be aware of to figure out which roofing membrane is right for you. When making your decision consider such factors as cost, longevity, durability, maintenance, ease of installation and energy efficiency. To learn more information about how TPO and EPDM stack up against one another, refer to our comparative guide.

Cost

EPDM roofs are the most economical choice for single ply roofing membranes. TPO roofing membranes are more expensive than EPDM. Regardless of which membrane you choose, it is better to spend more money and ivest into a thicker membrane. Both EPDM and TPO roofs perform better and last longer if they are thicker.

Longevity

By far the most important aspect that will determine the longevity of a single ply roofing membrane is the method by which the overlapping seams have been attached together. Permanently attached seams are the safest solution, and improper attachment can be the cause of 99% of leaks.



It is difficult to determine the longevity of TPO roofing membranes for a couple of reasons. First, this is a fairly new roofing product, there are no TPO membranes in the US today that are older than 15 years. Second, TPO membranes continue to be an experimental products- they are all in their 2nd, 3rd and in some
cases 4th generation of formulations, so it is not possible to definitively say how low any of these will last. Moreover, many TPO products have been pulled off the market in the past both for seam and material failures.

Durability

An EPDM rubber roof has a solid reputation for durability. Made of rubber compound, EPDM roofs have been on the market for decades- having properly tapered seams and detailed flashings, an EPDM roof will last up to 25 years. It is recognized in the industry as a dependable roofing material that offers resistance against ultraviolet light, ozone, oxidants and severe weather conditions. An EPDM membrane will also preform better than TPO in colder climates.

TPO seam strength is 3 to 4 times that of EPDM adhesive and tape seams.TPO membranes are manufactured to be as durable as EPDM. However, because there are continuous changes and improvements to the formulation, different TPO membranes perform differently. TPO is known to respond poorly to ponding water (it splits and cracks) and also does not have strong resistance to heat and solar overload.



Maintenance

In the beginning of its service life, a properly installed EPDM membrane will not require much maintenance. However, unlike TPO ( which has hot-air welded seams) an EPDM’s seams are treated with an adhesive, making them ultimately vulnerable to coming apart. This means that in the long run an EPDM roof will require maintenance to keep in tact. Be aware that EPDM responds very poorly to any kind of solvents and oils. Therefore, you should not use cleaners or conditioners that contain petroleum solvents, harsh abrasives or Citric based cleaners as these may cause irreparable damage to an EPDM membrane.

TPO membranes are not as easy to maintain as EPDM roofing membranes. In general, it is problematic to weld new materials to a TPO membrane, because as compounds age they loose their pliability and their subsequent thermoplastic capabilities. Consequently, to effectively heat weld new material to an old membrane may require an an “activator” similar to hypalon to seal repairs.

Ease of Installation

An EPDM rubber roof is easier and faster to install than a TPO roofing mebrane. EPDM requires no special equipment for installation while TPO needs to be hot air welded. This makes installing a TPO roofing membrane a more complex and costly process that also requires specialized knowledge. While a beginner roofer contractor will most likely be able to properly install an EPDM membrane, you should only hire an experienced contractor to install a TPO roof. Improper installation will invariably cause leaks and will require costly repairs or replacement.

Energy Efficiency

TPO membranes have become an increasingly popular single ply roofing choice because they offer energy efficiency. White TPO membranes are considered to be a “cool” roofing technology, but other colors of TPO are also formulated to have sun reflective properties. With a TPO roof, it is possible to save money of cooling costs of both residential and commercial properties because by reflecting solar heat, a TPO roof is able to maintain a cooler thermal balance inside the space, reducing the need for additional air conditioning. Energy efficiency makes TPO roofs particularly popular in hot sunny regions that get a lot of cooling days.

While EPDM roofing membranes are also available in white and will offer better reflective properties than darker colored EPDM, and EPDM roof will not offer the same level of energy and financial savings as a TPO roof.

Alternatives to both TPO and EPDM:

Although both EPDM and TPO roofs are widely used in commercial flat roofing, there is another product worth mentioning here – it is PVC roofing. PVC roofs have been around almost as long as rubbers, and much longer than TPO. In fact TPO was created to be a cheaper alternative to PVC (to provide all the benefits of PVC, such as cool roof surface, hot air welded seams, etc), while offering just a slightly higher price than EPDM rubber. However with lower price, come issues of quality. Without going into much details (its a topic for an entire separate article, which we will post shortly), TPO has still unproven track record, and has had its share of material / weld failures, and major reformulation by the manufacturers, to fix the problems of first few generations.

PVC roofs on the other hand, have been installed installed in US for 35+ years with only one major issue which was isolated to a specific membrane type made by a specific manufacturer (Trocal), which is no longer in business. Other than that, PVC roofs (such as IB Roof) have great performance, no leaks when installed properly, by certified contractors, and are very easy to repair, even when they are 30+ year old (see video above).