VENTILATION & AIR HANDLING


Heat resilience strategies for social housing


As UK temperatures continue to break records, Andrew Nash examines how overheating in homes is fast becoming a critical health and housing issue – and why a coordinated national response is urgently needed.


Andrew Nash www.nuaire.co.uk


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Divisional manager for Nuaire


ventilated dwellings. Using the TM59 standard, a 2019 government study on overheating in homes showed that out of eight modelled house and flat typologies, not a single one met the acceptable risk criteria for overheating. Apartments are particularly


he years 2024, 2023, 2022 and 2014 are the UK’s warmest years on record, according to the Met Office’s


analysis. In fact, the ten warmest years in the UK since records began in 1884 have all occurred since 2000. The chances of a summer matching the 2022 heat wave in this country could, according to the Met Office, be greater than 50% by 2050.


Overheating impact Hot temperatures are not just uncomfortable, but have serious health implications, especially for older people and those with existing health conditions. High temperatures raise blood pressure and heart rate, impacting the circulatory, nervous, respiratory and renal systems, which can lead to dehydration, heat exhaustion and heatstroke. In extreme cases it can lead to death: the UK Health Security Agency estimates that there were up to 3,712 deaths attributed to heat in summer 2022, the highest number in any given year. Mental health is also impacted by


hot weather as it can exacerbate the symptoms of psychiatric illnesses. Even for those people whose health is not directly affected, hot temperatures often prevent us from getting the sleep we need and therefore have consequences for productivity. The Office for National Statistics estimates that productivity in Great Britain was reduced by an incredible £5.3 billion in 2020 due to heat.


Hotter homes Under the Chartered Institution of Building Services Engineers’ (CIBSE) ‘TM59 Design methodology for the assessment of overheating risk in homes’, overheating is defined as when the internal temperature threshold of 26°C is surpassed for over 3% of the annual occupied hours, for predominantly naturally


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susceptible to overheating, with living rooms and bedrooms being the rooms most affected. Not everyone is impacted by


overheating equally. Low income households and those living in social housing bear the brunt of overheating.


Heating up The Met Office is categorical about the reason behind our increased temperatures: “UK mean temperatures have been shifting over the decades as a result of human-induced climate change”.


But global warming isn’t the entire


story when it comes to increasing temperatures in our homes. Homes built to modern Building Regulations are better insulated and designed to be more airtight and therefore energy efficient. However, this can also lead to raised indoor temperatures. And then there’s the location of our


new build homes, the majority of which are in cities. For many residents in built up urban environments, opening windows to allow cooler air in to their homes is not always an option due to noise, pollution and safety concerns.


Search for solutions There are many ways to reduce heat levels in homes. Urban green spaces can play a key role, with studies showing botanical gardens can cool city air by up to 5°C, and parks and wetlands also lowering temperatures. While such interventions require town planning, housebuilders can help by following Building Regulations, notably Approved Document O, which guides overheating mitigation through measures like optimised glazing, solar shading and natural ventilation. The House of Commons Environmental Audit Committee has called for Part O to cover refurbishments and material changes of use, and for post- occupancy evaluation to assess the real-world performance of installed measures. Part O permits mechanical


Many housing developments have overheating problem areas


cooling only when other methods can’t sufficiently reduce indoor heat, and follows a hierarchy – from acoustic façade vents and mechanical ventilation through to active cooling. Although there has traditionally been a reliance on site-wide air conditioning, mechanical ventilation with heat recovery (MVHR) is a viable alternative. For many new builds, MVHR systems with a third-speed setting can meet the extract ventilation needed to mitigate summer overheating under Part O. Many housing developments have


‘problem’ areas for overheating, such as corner apartments with higher glazing ratios and longer sun exposure. These tend to get hotter than surrounding units. MVHR alone is unlikely to keep temperatures within TM59 limits here, and installing air conditioning in just these apartments isn’t practical due to refrigerant pipework logistics, costs and the need for centralised cooling plant. In such cases, a hybrid cooling system like Nuaire’s MRXBOX offers a viable solution. It integrates with MVHR,


combining heat-exchanger cooling recovery with a DX coil to significantly lower fresh-air supply temperatures. The MVHR targets a comfortable setpoint, using free cooling via bypass when external air is cooler, and cooling recovery when it’s hotter. The cooling module activates automatically as needed.


National strategy The introduction of Part O represents a significant step in recognising overheating as an issue in this country, and providing actionable guidance on how to mitigate it in the design of our homes. However, some types of


development, such as material change of use whereby existing buildings are repurposed as much needed housing, are not covered and their potential risk of overheating has been undiminished by Part O’s introduction. Increasingly, organisations


operating in the housing sector are calling on the government to develop a national strategy on overheating that is more ambitious than the current collection of policy and initiatives, and that introduces urgency into combatting and mitigating overheating. The UK Collaborative Centre for Housing Evidence goes as far to call for a lead Minister for heat resilience to act as a focal point and drive forward coordinated action in this area. Creating and adopting a national


Nuaire’s MRXBOX hybrid cooli ng solution


heat resilience strategy isn’t such a tall order. The government did, after all, sign up to the Global Cooling Pledge initiative at COP28, which has a commitment to produce a national cooling action plan. Ultimately, we will have to wait to see how seriously the government really takes the issue of overheating. ■


EIBI | MAY 2025


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