Design strategies for truly energy efficient homes in the UK

Considering buildings produce around 40% of all carbon emissions, reaching the UK's current aim of net zero by 2050 will require substantial changes by the property sector - which won't be easy. 38% of homes in the UK were built before 1946. These homes are not only energy inefficient, but are often protected (e.g. listed or in conservation areas), meaning that changes to their appearance are heavily restricted. New builds, on the other hand, present architects with the opportunity to create residences for which their environmental impact has been taken into account from the outset. But, unfortunately, not every firm is equipped with teams well-versed in designing homes that use little energy. There’s no one-size-fits-all solution to the incredible challenge currently facing the British property sector. However, there are several design strategies that every architect, designer and property owner should consider when renovating an older building or creating a new one. Whether by managing glazing ratios and shading systems to keep natural light levels high but comfortable, or by considering options to keep the interior at a comfortable temperature without demanding huge heating, ventilation and air conditioning systems, careful design helps reduce energy use, keeps running costs low and cuts down carbon emissions. Glazing ratios and shading devices Glazing lets in light and heat. But too much of either, at the wrong times, is a problem. Getting more heat from the sun into a cold building in winter is generally a good thing. But a glass tower in a desert can be a disaster from an energy performance perspective. We also see buildings where low sun leads to glare that is uncomfortable, or buildings where lights need to be on much of the time. Striking the right balance between the type of glass used, how much of it makes up a building’s facade, and where it’s going to be placed, is key. Shadow studies and daylight analysis can help architects understand the building context within its environment and shortlist glazing and shading strategies that work in harmony. Material specification The materials selected in new build projects will have a significant impact on their carbon footprint. For instance, concrete has huge levels of embodied carbon. And yet, it can also be used to regulate a building’s temperature, since it heats up and cools down slowly. In contrast, a mass timber structure has much lower embodied carbon – but only if you’re not clear-cutting old-growth forests halfway across the world to supply the timber. Retrofits provide their own challenges. To highlight just one example – depending on the building and its level of protection - adding film to existing windows will be much more cost-effective than swapping the windows for double or triple glazing. But if you’re trying to increase thermal insulation while also cutting out noise from the street, additional glazing might be the only option. Heating, Ventilation and Air Conditioning (HVAC) systems The system specification is the responsibility of a mechanical engineer, but how you design the building will have a major impact on how big your HVAC system needs to be and how hard it needs to work. Many office buildings naturally ventilate. During the day, the occupants and machines warm up the air, which then rises. As the day cools, vents open at the top and bottom of the building. Cold air is drawn in at the bottom, while the warm air leaves via the top. The result is a much lower need for HVAC – leading to lower costs and less floor area eaten up by HVAC equipment. Being realistic about expected occupancy and resisting the urge to over-specify the HVAC system ‘just in case’ can be your friend here. There is plenty of software available which can help both engineers and architects have a good understanding of HVAC needs while in the early design phases. Technology solutions Energy efficient design is not something that can be easily tacked on to a project at the end – it needs to be integral to it from the start. This is where early-stage building performance analysis tools come in handy. Energy, daylight and climate analysis software provides architects with the necessary information to determine the best approach to maximise both a building’s appeal and its sustainability. Professionals are able to test different design ideas for environmental performance (energy use, occupant thermal comfort, use of natural daylighting, optimum HVAC system size, etc.) before the detailed design gets underway. These early insights will help the project stay true to its goals, achieve a good final outcome while also reducing waste. A great example is from Carl Sterner of Sterner Design, now with Sol Design + Consulting. For a new build project in Iowa, USA, Sterner modelled six different home design iterations in SketchUp and analysed them with the Sefaira Daylight Analysis plugin before settling on a selection that not only achieved net zero energy status but also an outstanding annual utility bill of only $24. All the design decisions, combined with passive strategies – such as natural ventilation, optimised building fabric, shading devices – and efficient mechanical systems resulted in construction costs cut in half and a 30% reduction in heating & cooling loads. Working collaboratively In my experience, the best way to get a truly sustainable design outcome is to work collaboratively with your engineer from the earliest phases of the project. Don’t treat the operational performance of a building as ‘the engineer’s problem’. It’s too important and too integral to achieving design goals for the architect to leave it to a group that, historically, is only engaged after conceptual design is locked in. Do your analysis early. Do it often and explore different options while using it. That way, the performance of your building becomes a design input in a much more rigorous way than using rules of thumb. The result will be a better building. Good luck! Byline: Hugh McEvoy, sustainability lead,Trimble

Design strategies for truly energy efficient homes in the UK

Byline: Hugh McEvoy, sustainability lead,Trimble

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