uPVC Stability in New Zealand UV light

When talking with people interested in our product, they love the insulating properties of uPVC, the integrated fly screens, and the cost. The next question often asked is about uPVC stability in the harsher New Zealand sun.

There may be hearsay or an anecdotal account of some other uPVC product (most often cladding) that was installed 20-30 years ago and just didn’t stand up to the test of time.

Though this old and anecdotal comparison is true, it is entirely a result of where those uPVC materials from: Europe. Europe has much less UV than NZ and therefore doesn’t need to have the same levels of protection against UV that NZ does. The main reason for the differing levels of UV is because of how far each region is away from the equator. Regions that are closer to the equator have more direct sunlight and UV light than areas that are further from the equator. England starts at 50° away from the equator. NZ goes from 35-45° from the equator. Therefore NZ is expected to have more UV than England, and that bears out in anecdotal evidence from 30+ years ago.

However, there are many regions that are even closer to the equator and have higher UV exposure than NZ. This includes all of the southern US states. Hawaii starts at 19° and other southern states start at 25°. This is much closer to the equator than NZ.

Below are some facts based upon scientific research. The references (#) to the articles are at the bottom of this document.

  • “UV dose is a strong function of latitude.” (1)
  • Neither the UV-A nor UV-B wavelengths which are attributed to damaging plastics is large in NZ compared with other locations. (1)
  • “Data shows that the annual doses of UV in New Zealand are significantly less than at sites within 30° to 35° of the equator, a region that represents more than half of the global surface area” (1)
  • Peak UV Index values of 14 are similar to those measured in Boulder, Colorado.  (2) [FYI, Boulder is in the middle of the US]
  • The peak UV Index value for Hawaii is ~20 @ 19° N. (2) [note that this is 50% higher than max NZ UV levels]
  • “Compared with equatorial regions, our [NZ] UV is not particularly strong – contrary to anecdotal evidence”. (2)
  • It has been suggested that material damage by UV is accelerated under high temperatures, however compared with tropical sites, temperatures in NZ are relatively low.  (1)
  • “Related to the ‘high’ UV-levels in NZ, these are NOT due to NZ being under the Antartic ozone hole. Each spring, when the Antartic Ozone hole is near its peak, there are even some parts of Antartica that are not under the ‘hole’, not to mention NZ which is some 3000 km further north. NZ is under a ridge of high ozone during ozone-hole period, having ozone levels near to the highest worldwide during Austral Spring.” (3)
  • NZ requires a minimum amount of titanium dioxide acting as sunscreen of 8 pph to protect uPVC products from prolonged NZ UV exposure. (4)


Many New Zealanders equate anecdotal evidence that the UV exposure in NZ is greater than UV exposure in Europe, and equate that the sun in stronger in NZ than anywhere else. Many also falsely attribute higher NZ compared to Europe as due to the ozone hole. Actual data from NZ experts doesn’t reflect either of these. The largest contributor to UV exposure is latitude.

NZ has UV levels similar to Boulder, CO which is about the middle latitude of the US. All of the southern US states are within 35° of the equator and get similar or more UV exposure than NZ.

To stand up to higher levels of UV, uPVC products require a different formulation that has a much higher concentration of ‘sunscreen’. ThermaScreen products exceed this requirement AND have 40+ years of installed experience in locations with even higher UV exposure than NZ to validate their extended product lifetime.


(1)  Materials-Damaging UV Radiation in New Zealand: Comparison with Other Locations: Michael Kotkamp, Richard McKenzie, Hisako Shiona from NIWA,  Steve Rhodes from Bureau of Meteorology in Melbourne Australia, Patrick Disterhoft from NOAA, and Germar Bernhard from Biospherical Instruments

(2)  Where on Earth Has the Highest UV?: J. Ben Liley and Richard L. McKenzie; NZ National Institute of Water and Atmospheric Research (NIWA)

(3)  What’s Happening to Ozone in This Part of the World?: Richard Querel from the NZ National Institute of Water and Atmospheric Research (NIWA)

(4) NZ tests EN 12608 and EN153