EXTERNAL ENVELOPE 55 Openings for a net zero future
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
F
rom 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/m2
K – 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
ADF JANUARY 2024
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
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Experts are predicting whole-window U-values could be set at 0.80 W/m2
K for windows in new buildings
K
– a drastic change from the current standard which is 1.6 W/m2
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