Aluminium Fenestration News


With less than a month to go until the new Part L standards come into force, Reynaers Aluminium UK Ltd, is once again reassuring fabricators and installers that its full range of window systems and products are fully compliant and future ready.

The changes, which come into play on June 15th, are part of the Government’s wider push to achieve zero-net carbon emissions by 2050 and will improve the thermal and energy efficiency performance of our homes and commercial buildings.

“Home energy use accounts for more than 25 per cent of the UK’s carbon emissions and therefore is a major contribution to climate change,” explains John McComb, Technical Services Director for Reynaers.

“A typical house loses around 10 per cent of its heat through the windows. Therefore, increasing the thermal efficiency standards of windows and doors in new and existing houses, as well as in commercial buildings, will significantly reduce heat loss and have a direct impact on reducing carbon emissions and nudge us closer to achieving these net-zero target.

“The new standards are a just a steppingstone in lieu of much bigger changes which will become law in 2025.  From June any new houses or commercial buildings must be fitted with windows and doors that produce 31 per cent less emissions than those installed today. Whereas after 2025 they will need to emit 75 per cent less carbon.

“As a manufacturer of aluminium window and door systems, we’ve been analysing our entire range of products over the last 12 to 18 months to ensure they comply with the new standards.”

There are typically three ways in which manufacturers can show that their products and systems comply – U-values, hot box testing and BFRC ratings. The most common ways to demonstrate the requirements as detailed with Part L 2022 are typically provided via either a U-value calculation or BFRC window or door energy rating (WER/DER).


A U-Value is the measure of the overall rate of heat transfer through a particular section of construction – in this case windows and doors.

In other words, a U-value is used to measure how well or badly a component transmits heat from the inside to the outside. The slower or more difficult it is for heat to transfer through the component, the lower the U-value. This means that as a manufacturer we are looking for our products to have a lower U-value. The lower the U-value the better.

BFRC window/door rating scheme

The BFRC is a subsidiary of the Glass and Glazing Federation. Its window energy rating scheme is based on a traffic light system and gives each window and door product a rating from A++ to E for energy efficiency.  Bandings are the result of a complex calculation which considers a standard size window, standard building occupancy and average climate solutions. An A++ rating indicates the highest level of energy efficiency with E demonstrating the lowest and gives an overall indication of how energy efficient the window is and how much air it will allow to penetrate a building. The BFRC rating can be used to demonstrate building regulation compliance for replacement windows.

From June all windows or doors installed in new dwellings or buildings must have a­­­­­­ U-value rating of 1.6 – a significant drop of 0.4 from the previous standard. New windows installed into commercial buildings required a U-value of 1.6 OR notably, compliance can be shown by having a WER of Band B or better. In the case of new commercial buildings, high usage entrance doors must have a U-value of 3.0.

However, any replacement windows installed into existing buildings are required to demonstrate a U-value rating of 1.4 (down from 1.6) OR notably, a Band B WER. Similarly, replacement doors with >60% internal glazing must have a U-value of 1.4 or Band C WER.

Keeping ahead of the regulations

Over the past year Reynaers has been rigorously benchmarking its existing and planned new products to ensure they comply with the updated standards.  This has involved detailed FEA  analysis using specific thermal modelling software to calculate the thermal performance and U-value. Reynaers is also working towards gaining full BFRC (British Fenestration Rating Council) approval status to ensure its customers have the utmost confidence in their purchasing decision that our products and systems are fully compliant with Part L 2022.

Some of the company’s most popular products are already well ahead in terms of their thermal efficient properties, giving fabricators and installers confidence when embarking on new and replacement projects.

The SL68, slimline window has a U-value rating of 1.4 and a Band A energy rating so can be used in all cases with absolute reassurance. While the CF68, one of our best-selling folding doors, has a U-value rating of 1.43 and Band B energy rating so can be used in all new and replacement situations. Indeed, some of our products, such as the MasterPatio system, already exceed the current requirements with a U-value of 1.39 and energy rating of Band B, again providing fabricators and specifiers with the reassurance that the products are fully compliant and more than fit for purpose.

John concludes: “We’ve been ready for the new standards now for some time. However due to the scope of the changes to Part L that will be imposed in 2025, we will inevitably see a significant change in the way windows and doors are manufactured and will likely be the stimulus for the biggest change to construction methods in recent history.”

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