Guy Hubble, joint managing director at RegaLead, warns that the UK fenestration industry could be sleepwalking into colour trouble…

It’s now spring and the warmer weather sees the return of an age-old problem. Heat expansion can be a real issue for many homeowners as some windows and doors become difficult to open and close.

But there’s far more to it than just a rise in temperature and it all boils down to colour.

The huge growth of coloured windows and doors, moving away from traditional white or woodgrain, has been great for our market, but there is a serious downside. Remember the problem of warping rosewood PVC panels several years ago?

While this was bad for the industry, due to lower volumes, the problem was on a tiny scale compared with the hundreds of thousands of coloured doors we now have in the market.

You can’t fight physics

The threat we are now facing is, at its root, basic physics. Put into simple terms, the darker the colour, the higher the absorption of incident sunlight (Solar Heat Gain) which is converted into heat (Heat Build Up). The higher the Heat Build Up (HBU), the higher the material expansion rate, which ultimately affects the product’s integrity and stability. White, cream, and lighter colours are less affected by this as the titanium dioxide present in them reflects more of the incoming energy and the infrared waves that do the damage.

The problem is made even worse in cases where different substrates with different expansion rates are housed together – for example, a black GRP composite product in a white PVC frame.

The different rates of expansion under temperature changes can lead to a serious product failure, even to the point where hardware slippages mean doors won’t lock or open.

Time for some reflectance

The percentage of irradiated energy that is reflected by an object is called Total Solar Reflectance (TSR). The effectiveness of this can also be expressed in terms of HBU, which shows the rise in temperature above the ambient.

The tests we carried out showed that a standard white UK window profile has a reflectance of around 88% and HBU of between 20°C and 22°C. However, a black coated surface has a reflectance of just 5%, with 95% being absorbed by the object, and a HBU 44°C above ambient temperature.

While some substrates, such as wood, are not significantly affected by temperatures of up to 700°C, this is a far different story with PVC-U and can cause critical damage such as softening, deforming, and changes to the mechanical properties of the substrate.

Keep cool with IRR pigments

Some fabricators attempt to counter this problem with metal reinforcement, but while this helps, it only deals with the effects of the issue rather than the issue itself. In order to prevent the problem in the first place, the solar reflectance of coloured windows and doors needs to be raised.

Thanks to our experience in the North American markets, where Infra-Red Reflective (IRR) paints are now commonplace, and based on our extensive laboratory testing, we have developed a range of ‘Cool Colours’ to complement our existing range.

Cool Colours uses specialised IRR pigments, substantially reducing any HBU and countering the problem of heat expansion with dark colours. The IRR pigments reflect 44% of the infrared wavelength and the HBU is only marginally above that of standard white profile.

In testing, the HBU of white PVC-U profile was 22.33°C. With the IRR black paint under the same conditions, the HBU was 24.91°C. In contrast, with standard black paint, the HBU was 42.22°C – more than enough to warp a frame.

Don’t sweat it

The demand for coloured windows and doors is only going to continue to grow, and with each successive summer setting record temperatures in the UK, this issue needs to be tackled now.

Prevention is always better than a cure.