16 CONTEXT 182 : DECEMBER 2024 JONATHAN TAYLOR Sustainable heating for listed buildings The problem of how to reduce the approximately 17 per cent of the UK’s carbon emissions produced by space heating and cooling of buildings needs to be approached intelligently. It is now generally accepted that most traditionally constructed buildings are unsuited to the high levels of insulation required to meet current building regulations. Some improvements are clearly practical and necessary in the vast majority of cases, with minimal harm to their character and significance, but many listed buildings will have to look at other avenues for reducing their carbon emissions if these buildings are to play their part in achieving a reduction of 43 per cent by 2030 and net zero by 2050.These can include low- and zero-carbon heating technology and better management of heat. Insulation is not the only solution. The problem with insulation The best place for insulation is on the outside of a structure. Placed here heat from the inside keeps the fabric warm in winter, minimising the chance of condensation and promoting faster drying should any moisture find its way into the structure. Failing to get this right can lead to mould growth, decay and loss of the original material’s insulation value due to the higher thermal conductivity of a damp structure. Placed on the outside, the insulation also protects the walls from external heat so they remain cooler in the summer, and their mass helps to moderate temperature fluctuations. The downside is that external insulation changes the appearance of historic buildings dramatically by obscuring surface textures and details and by changing the size and proportion of features like window openings and eaves. Major alterations may also be required to the roof, eaves and windowsill details to protect external insulation from the rain. On buildings which are important historically or aesthetically, insulation is more usually applied to the interior face of external walls and inside the roof space. Here perhaps the biggest drawback is that it makes everything on the outer side colder and more prone to condensation, including roof and wall structures, for example, so the insulation needs to be highly permeable. It is also less efficient, as cold bridging will occur wherever cross walls connect with the outer wall through the insulation. Research published by Historic England in 2020 (Understanding Carbon in the Historic Environment) showed that a sensitively retrofitted Victorian terrace home might not be able to compete with a new-build equivalent if only the day-to-day carbon cost of heating were taken into consideration. However, when the carbon expended in all aspects of their current retrofit Adding insulation to the external walls of a listed building is rarely simple and risks trapping moisture.
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