By Wojciech Brozyna – MD of Aluprof UK
Around a third of all our energy use in the UK is used in our homes. With the majority of this energy used in heating, this equates to about forty MTOE (million tonnes of oil equivalent) used every year. The UK Government have some ambitious plans to cut energy usage by 2050 in many sectors. Glasgow will be hosting the 26th UN Climate Change Conference of the Parties (COP26), from 31 October to 12 November 2021 and the UK is striving to take a global lead to drastically cut carbon emissions.
The last change to our legislative window U-values for new homes was implemented in Approved Document, Part L in 2013. Little has changed since then, but, that is all set to change following the Government’s recent Future Homes Standard Consultation. The updated Part L will likely be finalised and released at the end of 2021 to be introduced into legislation early in 2022. This will likely mean the introduction of window systems having to meet a lower U-value of 1.2 W/m2K (in England) for the ‘notional’ building and the possible introduction of triple glazing. Following this change, it is likely that Part L will be further revised in 2025, possibly taking window U-values down to 0.8 W/m2K. The changes are the result of the Government mission to achieving net-zero carbon by 2050 and ensuring that new homes are built to be “zero-carbon ready” as the National Electricity Grid decarbonises.
With the introduction of revised air tightness requirement, down from the limiting value of 10 m³/h.m² at 50Pa to 8 m³/h.m² at 50Pa (with 5.0 m3/h.m2 at 50Pa for the notional building) using the ‘blower door’ test method or a new ‘Pulse’ test method, our building structures are likely to become even more airtight. It is suggested that a house achieving an airtightness of 5 m³/h.m² will use 40% less energy on space heating than a house built to 2013 standards of 10 m³/h.m². With stricter airtightness, this calls into question how we can retain heat in our buildings in winter whilst maintaining healthy indoor air quality for well-being with controllable natural ventilation.
Will the change in thermal requirements in Part L and the revised guidance in Approved Document L Volume 1 change the material of choice for specifiers? Probably not, as both of the predominant materials chosen for new construction, aluminium and PVC, can achieve the U-values required, albeit they will be thicker, more thermally efficient and may carry triple or quadruple glazing, consequently products will become more expensive. Balancing this increased cost will be increased product quality which is likely to offer products an increased in-use life, possibly up to twice the current life expectancy.
There are three areas of carbon emissions we have to remember; the production and installation of a product, what the product can save (or use) during its useful life and what value it has at its end of life, or how it can be reused or recycled. Reducing the rate of replacement will significantly reduce carbon. In the future, we may be required to prove a carbon payback if a lesser performing product is to be replaced with a newer carbon saving product. Aluminium has proven its almost 100% recycling ability with no loss of structural strength, however, with long life comes the shortage of end of life recycling and currently, we can only supply up to 50% of the global demand for the material. Product recycling and sustainability are crucial if we are to ensure cyclical ‘cradle to cradle’ material resources in the future. Specifying aluminium will ensure its continued use for generations to come. 75% of all aluminium ever produced since 1880, when it became commercially viable, is still in use today.
There will likely be a move to adopting differing designs of windows and doors in the future to make the most of high insulation glazing, such as reducing sightlines to a minimum. This may mean a move to sliding systems for large glazed opening doors and the adoption of tilt turn window systems. Will this herald a move away from the UK’s love of the outward opening ‘casement’ window?
What does seem to be missing in this rapid move towards increasing thermal efficiency and airtightness in our future builds is the need for air ventilation, particularly in our homes. This is crucial for our well-being and continued health. We know that sealing up a small dwelling will eventually lead to condensation appearing on the coolest elements in the room, sometimes a wall or an abutment with a ceiling, where dampness can turn quickly into unhealthy mould growth. This is particularly relevant in social housing where occupants may be reluctant to ventilate due to the cost incurred in reheating. It, therefore, seems logical for future legislation to include mechanical ventilation with efficient heat recovery, or indeed cooling of incoming fresh air depending on the time of year.
Another issue that we do need to attend to as an industry is the robust detailing of interfaces between windows and doors and the building structure. Cold bridges often decrease the claimed efficiencies within a building construction that can reduce the effectiveness in use of a designed build by up to 50% of its claimed thermal efficiency. As an industry, should we be doing more to incorporate or encourage the specification of interface designs that reduce cold bridging to an absolute minimum?
Here at Aluprof we already have an approved range of high-efficiency windows, doors and curtain walls which all meet Passivhaus accreditation. As a member of the Passivhaus Trust in the UK we are supplying systems for new and refurbishment properties whilst working closely with the trust regarding installation. In each of our technical manuals, we show how our products can be installed to ensure the minimum of cold bridging. Our team of engineers are also on hand to work with architects and designers to help detail thermally efficient interfaces for Aluprof windows and doors into any structure.