The threat of overheating in buildings because of the changing climate continues to feature as one of CIBSE’s priority concerns. This summer, I was invited to speak to BBC News about the best ways people can keep cool in their homes.
Top of the list of my recommendations for managing overheating in homes was external shading, followed by effective window-opening strategies, good cross- ventilation, and minimising heat gains from home appliances such as ovens, washing machines and dishwashers.
During the interview, I met Marion Baeli from 10 Design who gave me a tour of her home that she is retrofitting to Passivhaus Standard. She said that ‘whenever we have friends coming around in a heatwave, they think we have air conditioning [here] because the difference is so big between outside and inside [temperatures]’.
Within the retrofit, she has incorporated mechanical ventilation, external shading in her loft conversion, and has plans to install a ceiling fan in one of the main bedrooms. She also wants to incorporate more external shading in other rooms but, in the interim, is hanging dust sheets on the outside of her newly installed tilt-and-turn windows (which provide a large openable area).
Research from University College London has determined that external shading and energy-efficient retrofit measures can reduce heat-related morbidity by up to 52%1 ,depending on weather conditions experienced.
Given that by the mid-century it is estimated there will be around 10,000 deaths related to heat exposure2, passive measures offer a great opportunity to protect people’s comfort, health and wellbeing while simultaneously reducing carbon emissions related to cooling.
The Environmental Audit Committee3 highlighted how in 2022 and 2023 coal-fired power stations were ‘fired up once more’ to meet the UK’s electricity demand for cooling.
This has the potential to undo the good work already done in reducing carbon emissions from the built environment and why it is vital to design buildings to ensure they can adapt to the more frequent, longer, and intense heatwave events we are going to experience in the future.
In my interview with BBC Radio 4’s You and Yours4, I gave myth-busting advice on how to operate windows during heatwaves. I advised against opening them when temperatures were warmer outside than in, and instead opening them when it was cooler outside. This important factor is frequently overlooked and stems from a poor understanding of how to operate our homes during heatwaves.
During the interview, I spoke to two homeowners – Joshua who lives in a new build (pre-Part O) in Bedfordshire, and Hannah who has a poorly insulated Victorian end-terrace in Warwickshire.
Both had overheating issues and were unaware of the role insulation plays in keeping buildings cool in summer. I explained how improving insulation levels helps homes in winter keep the heat in and energy bills low, and helps keep heat out by protecting the thermal environment contained within them – like a vacuum flask.
However, well-insulated homes are susceptible to overheating from increased solar gains through large, glazed areas. If glazing is not well-managed with shading, it can cause a thermal imbalance inside.
The reality is that, in many existing homes, it may be difficult for occupants to keep all rooms comfortable all day so it might be necessary to move around your home using the coolest parts throughout the day.
For example, in my own home, which is east-west facing, I often work downstairs in the west side of my home in the morning, and retreat to the east in the afternoon.
About the author
Dr Zoe De Grussa is research manager at CIBSE
Updates to CIBSE Weather Files and TM59 Design methodology for the assessment of overheating risk in homes will be launched at Build2Perform Live www.build2perform.co.uk
References:
- Comparison of built environment adaptations to heat exposure and mortality during hot weather, West Midlands region, UK (2018) bit.ly/3Xc4bfV
- Health Effects of Climate Change in the UK: state of the evidence 2023 bit.ly/4dsFFNp
- Environmental Audit Committee, Heat resilience and sustainable cooling Fifth Report of Session 2023–24 (2024) https://bit.ly/3Ax0w3z
- You and Yours, BBC Radio 4, bit.ly/3WWQ8JO (Starts at 33:09).