The UK Government has proposed the Future Homes Standard to ensure new homes built from 2025 will produce 75-80% less carbon. Chris Armes from Liniar Design & Development offers advice on choosing windows and doors for low carbon development projects which will meet the standard
From 2025, new residential and non-domestic buildings will need to be much more energy efficient, producing significantly less CO2 emissions than current standards permit. Within the fenestration industry, U-values are widely used as a measure of window energy efficiency, with a lower U-value meaning better thermal performance.
Details on the regulations are still unknown, but experts are predicting whole-window U-values could be set at 0.80 W/m2K – a drastic change from the current standard of 1.6 for windows in new buildings. Additionally, replacement element requirements (including windows and doors) in existing buildings are also being looked at in terms of energy performance, with the industry waiting in anticipation for an update. Consequently, refurbishment projects will inevitably be required to adhere to more stringent energy efficiency regulations over time.
Whole-window U-values add together heat loss through all major components of a window – the frame, glazing, and spacer bars – and it’s important to consider the performance of each element to avoid reliance on cost-prohibitive add-ons. When a supplier claims a low U-value, it’s advisable to check how this is achieved. For example, is it through a combination of highly efficient components, or is the performance reliant on an expensive, non-standard element such as quadruple glazing or Krypton-filled glazing units?
Considering how a window or door achieves its U-value will help ensure you choose products that deliver the required results in a cost-effective way, making it easier for developers to stay within budget.
Innovations in window technology
PVCu has emerged as a highly insulative, thermally efficient material since the 1980s, making it a popular choice for window frames. While the imminent stricter energy efficiency standards will push the limits of PVCu’s former performance capabilities, British companies have been designing innovative new products, supporting the push to net zero, with products already available and being utilised in projects nationwide.
A major benefit of PVCu frames is the ability to exploit one of nature’s best insulators – air! By using a multi-chambered design, PVCu window frames trap air inside, creating a thermal barrier that reduces heat transfer and improves energy efficiency. Crucially, the deeper the window and the more chambers inside the frame, or profile, the better the energy performance it can achieve. Furthermore, PVCu is fully recyclable at the end of its useful life and means whole life carbon reductions on top of energy savings.
Over the years, a depth of 70 mm has become the standard width for domestic PVCu window profiles. However, the industry has now seen the development of 90 mm deep multi-chambered window systems, such as a Liniar range which is capable of a 0.66 U-value with triple glazing, using standard Argon-filled panes of glass. This particular system also offers a retrofit solution, which is ideal for refurbishment projects where 70 mm windows are being removed.
PVCu windows delivering this level of energy efficiency are not only Future Homes Standard-ready, but are also entering the range of being Passivhaus certified – an energy efficiency specification becoming increasingly mainstream in the face of imminent regulatory changes and a move towards net zero communities and low carbon homes.
The Passivhaus standard
Passivhaus is a set of eco-friendly, performance-based design criteria which ensure compliant buildings achieve a superior energy performance standard. Rigorous design and construction methods integrate the five principles of robust windows, high-quality insulation, airtightness, heat recovery ventilation, and the elimination of thermal bridges (areas in a structure that allow excessive heat transfer in or out).
In 2022, Mansfield District Council commissioned four ultra-low energy homes for social housing rental with the aim of achieving Passivhaus accreditation. Mansfield council is proactive in its green agenda, with a target to halve emissions by 2030 and reach net zero by 2050. Passivhaus-certified windows must achieve U-values no greater than 0.80 W/m2K. Liniar’s 90 mm system was specified for the Saundby Avenue project, which went on to successfully achieve Passivhaus accreditation – the first buildings of their kind to be developed for social housing.
Noise reduction benefits of deeper PVCu profiles
Another benefit of choosing windows made using deeper PVCu profiles is that when combined with triple-glazed units they can offer enhanced noise reduction. This is particularly beneficial for architects and specifiers developing properties in urban areas or other locations where noise pollution may be an issue. A comparable 70 mm window reduces external noise by 33 decibels (dB) compared to a triple-glazed, 90 mm frame’s 42 dB.
Preparing for a net zero future
As energy-efficient housing takes centre stage and regulations continue to tighten, architects and specifiers must have access to innovative products that can help to future-proof their developments.
British-designed PVCu window systems capable of meeting more stringent energy efficient standards are beginning to enter the market. Nevertheless, manufacturers must be clear about how products are achieving their energy performance so that specifiers can make well-informed decisions and choose the most cost-effective solutions for their projects.
Chris Armes is director of Liniar Design & Development