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.