Future sustainable cities

By Wojciech Brozyna, managing director of Aluprof UK.

Around a third of all our energy use in the UK is used in our homes and, since most of this energy is used in heating, this is equal to about forty million tonnes of oil every year.

The last change to our legislative window U-values for new homes was implemented in Approved Document Part L in 2013. Following the government’s recent Future Homes Standard Consultation. The updated Part L will likely be 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 1.2W/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 0.8W/m2K. The changes are the result of the government’s mission to achieve net-zero carbon by 2050, and ensuring that new homes are built to be ‘zero-carbon ready’ as the National Grid decarbonises its electricity supply.

With the introduction of a revised air tightness requirement of 8m³/h.m², our building structures are likely to become even more airtight. It is suggested that a house achieving an airtightness of 5m³/h.m² will use 40% less energy on space heating than a house built to 2013 standards of 10m³/h.m².

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 PVCU – can achieve the U-values required, albeit thicker, more thermally efficient, and may carry triple or quadruple glazing. They will also become more expensive. Balancing this increased cost will be increased product quality, resulting in 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 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.

What does seem to be missing in this move towards increased thermal efficiency and airtightness 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. Therefore, it 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 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. Should we be doing more to encourage the specification of interface designs that reduce cold bridging?

Aluprof already has 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 while working with the trust regarding installation. In each of our technical manuals, we show how our products can be installed to ensure the reduction 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.