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27 April 2021

Design Considerations for Dark Coloured Thermoplastic Membranes

TPO Roof 1

Nuralite Waterproofing has over 55 years’ experience as suppliers in the membrane industry. During this time, we have learnt a lot about the technical capabilities of different membrane types, with robustness and durability being the key attributes a client needs to create buildings that provide long term, superior weathertight performance.

We maintain that the lighter the colour the better. This view is supported by the international technical research as well as the photographic evidence from New Zealand projects. Nuralite contends that the membrane colour is a key contributor to high solar loading as the temperature difference between a light and dark membrane is significant.

To illustrate the impact of colour on thermoplastic membranes, Nuralite conducted a simple experiment. Five samples of different coloured membrane were left outside in direct sunlight on a fine Auckland day from 9.30am to 2.30pm. Each hour the membrane temperature was measured.

Testing Samples

Figure 1. Thermoplastic Membranes on test panel.

Figure 2

Figure 2. Test results.

Figure 3

Figure 3. Test results graph.

With an increased temperature we can expect:

  • Greater expansion and contraction causing the substrate and adhesion of the membrane to be stressed.
  • Softening of the membrane, which will decrease puncture resistance and render the membrane more prone to physical damage.
  • Premature exhaustion of anti-aging components such as antioxidants, plasticisers, UV absorbers and heat and light stabilising compounds, and ultimately premature breakdown of the sheet.

The following photos evidence this concerning issue — a dark membrane by an upstand with the coating over the scrim being negligible. These photos are of New Zealand roofs that are less than five years old. The materials had all been used successfully overseas, however they have not performed in these situations in the New Zealand climate.

Figure 4

Figure 4. Membrane blistering from heat from upstand reflection. Material 1.2mm, Age approx. 4 years.

Figure 5

Figure 5. Closeup of membrane in sole of gutter, Material 1.1mm, Age approx. 3 years.

figure 6

Figure 6. Close up, Material 1.2mm, Age approx. 4 years.

Once there is no material above the reinforcing scrim it would be considered that the product has failed and is no longer watertight.

An additional note is that Figures 5 and 6 show the membrane debonding from the substrate. While poor installation may also be a contributor, this can also be caused as a result of the highly heated membrane putting a high load on the adhesive due to thermal movement.

Nuralite recommends that thermoplastic membranes should be installed using light colours such as white or light grey to increase longevity of performance.

View more information on Nuralite, including contact details.
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