We are in the state of a climate emergency, and disruptive climate events will occur more often, and will become more severe. By 2070, the Met Office projects three potential climate scenarios for the UK:
- around 4°C warmer in winter and up to 30% wetter
- around 6°C warmer in summer and up to 60% drier
- hot summer days will become around 7°C warmer
The Met Office also predicts that heatwaves will be more frequent, persistent, and intense. People living in cities will be most affected, as the ‘urban heat island effect’ will amplify the temperatures experienced. Densely populated urban areas can be up to 10-15°C warmer than the countryside1 — a concerning statistic, especially when you consider that, in the next 25 years, it’s likely that more than 80% of European populations will live in cities.
By 2050, the number of heat-related deaths in the UK is projected to rise to 10,000 a year, from around 2,000 per year currently. Overheating also affects mental health, maternal health, and increases risks of injuries and accidents. So, how will patients in hospitals be safe from the effects of overheating?
Hot hospitals
As part of a wider report from Hoare Lea for the UKGBC Climate Resilience Roadmap, analysis showed that many existing UK hospitals will be at severe risk of overheating due to their type, age and design.2 In the optimistic Met Office global warming scenario, this equates to around two weeks every summer when temperatures in the spaces occupied by staff and patients are expected to exceed 28°C. In the more likely, higher emissions warming scenario, this would be up to four weeks. Everyone present would be affected by that, with patients experiencing an uncomfortable environment, and additional health risks tied directly to increased temperatures. It would also affect healthcare staff. Doctors, nurses and healthcare assistants, who already perform difficult and demanding jobs, would need to deal with additional heat-related risks, whilst caring for vulnerable patients. During heatwaves, worker productivity is expected to drop across many industries, but the healthcare sector carries very distinct pressures that don’t allow room for error. Human life is on the line.
Healthcare buildings come in many different forms. They differ from one another in terms of occupancy and use, as well as the geometry of the building and its various properties. Healthcare buildings built after 2000 are mainly purpose-built, with the building properties in line with the Building Regulations issued at the time.
Prior to the year 2000, healthcare buildings were mainly large-scale developments that could be split into two groups: pre-World War II, and post war (which is often represented by a nucleus hospital layout). Modern healthcare buildings (post 2000) typically have large, double-glazed windows, which comprise of many casements, to allow part of the window panels to be permanently closed, and some panels openable for natural ventilation.
Buildings built between 1945 and 1999 tend to be fitted with large windows, which provide a high glazing ratio, and often come with a fixed panel on the bottom of the window, and openable casement at the top half.
In pre-World War II buildings, windows are often arranged in ‘bays’ and are single-glazed, sash openings.
Creating natural ventilation
Window opening restrictors in healthcare buildings, schools, care homes, and public buildings can be a cause of overheating because they restrict natural ventilation. The openings are typically set to be no more than 100 mm for safety reasons, but in many cases, the openings are much less, which compromises air flow. Designers and building owners should consider alternative options, including the provision of high-level opening windows, that fully open.
This issue is particularly acute in new build and post—2000 constructed hospitals, due to them often having higher glazing ratios and lack of thermal mass that can absorb heat. This is particularly prevalent in dense urban areas, with London hospitals most at risk.
Our analysis, based on medium and high emissions climate change projections, show extreme heat impacts several other regions, too, represented in our research by Swindon, Nottingham and Leeds. Lack of sufficient natural ventilation is also a contributing factor for overheating. This is especially common with healthcare building windows, and other ventilation openings, that are restricted to a maximum of 150 mm wide opening. Designed as a safety measure, it does not allow for enough air flow to mitigate rising internal air temperatures. However, it is not always an option for acute and mental health care locations to have wider openings.
Passive cooling measures
The study also showed that incorporating passive design measures can meaningfully lower the overheating risk profile for healthcare buildings. In some cases it reduced the period of overheating risk by a third. This would reduce the number of weeks in summer when temperatures reach 28°C from four to one and a half.
Passive measures, including natural ventilation, represent the first line of defence against overheating. For new hospitals, fixed window solutions are proving popular to improve environmental conditions and infection control. But for older hospitals, one of the simplest and most effective solutions can be allowing larger areas of ventilated openings in window designs, which would allow more air exchange. It would also be a good idea to encourage occupants to not open windows when the outside temperature is higher than the internal one. It would also be advisable to encourage windows to be opened at night to purge the heat.
For older buildings, where refurbishment might be beneficial, adding insulation to the building to improve its thermal performance will help to reduce heat gains, and lower the overheating risk.
Nature-based solutions
In all buildings, using materials that absorb then expel heat, known as exposed thermal mass, help regulate indoor temperatures. Another passive strategy to reduce overheating risk is to use solar shading, either as external shading features, or by using interstitial blinds in the window system. Nature-based solutions can also help reduce overheating risks. Green roofs and green landscaping around healthcare buildings help to reduce surface temperatures. Views of nature also have wellbeing co-benefits and have been shown to help recovery times for hospital patients.
We recommend passive design measures first because they have no operational carbon emissions, and can be incorporated into new designs and refurbishment programmes with relative ease. These measures should be chosen where they will work best, based on location and other design factors such as building orientation and proximity to adjacent buildings. However, healthcare buildings, particularly hospitals and clinics, are very controlled environments. They have many regulations that ensure hygienic environments with clean air. However with this, conflict arises between different design performance metrics and aspirations, including:
- Building regulations: clean, controlled environment, that requires large volumes of mechanical ventilation and filtration systems, to provide healthy and safe environment for patients.
- Reduction in operational energy and carbon: NHS Net Zero Carbon — in order to prevent further degradation of the environment and accelerating global warming, the energy, and associated carbon emissions, required to run healthcare buildings must be drastically reduced. This will, in many cases, require reduction in cooling demand and operating on lower air flow rates.
- Prevention of building overheating and ensuring patient comfort.
Unfortunately, in a lot of the cases, it is extremely difficult to achieve an equilibrium that would satisfy all these requirements. For existing buildings, this is even more challenging, usually resulting in conflict, where only two aspects can be achieved at any time, with one aspect compromised. Regulatory requirements must be met as patient safety is vital. Yet that usually mean that there needs to be a choice between lower energy or higher internal temperatures, particularly in smaller spaces with high occupancy such as waiting rooms, wards, doctors’ offices and staff break rooms.
Conditioning considerations
Considering the tensions between different standards and requirements, as well as the building’s location, active measures such as increased rates of mechanical ventilation or provision of air tempering may be needed. Both solutions would naturally increase the energy demand of the building, and the carbon emissions associated with that. However, they are less energy and carbon intensive than the addition of air conditioning.
Air tempering systems provide ventilation with reduced temperature through a mechanical ventilation unit with heat recovery, and use a fixed cooling capacity coil that operates based on sensors in the room. As occupants of the building do not have control over the air flow rate and temperature of the air provided, the risk of inefficiencies in the system operation due to human error are minimised. This also prevents ‘excessive cooling’, as supply temperature is lowered rather than set to certain targets. For example, with an air tempering system, an internal room temperature would reduce from 28°C to 26°C, but occupants would not be able to cool the room down to 18°C, like they would be able to with an air conditioning system.
Active cooling and air conditioning might be necessary in some healthcare buildings, particularly in urban locations like London. This, however, should be treated as last resort, and a combination of passive design measures with some active measures should be prioritised. This will ensure longevity of the building, and resilience to future climate scenarios, as well as a reduction in operational energy and carbon emissions.
With an already overwhelmed healthcare sector, vulnerable people might increasingly face more difficult conditions. It is particularly concerning because this environmental change does not occur suddenly over a day, week, or even a month — it has been unfolding over the past few decades, and is expected to continue for many more.
Overheating is an increasing problem within our NHS buildings, as reported in the latest NHS Estates Return Information Collection (ERIC).3 Over the past four years, the number of overheating incidents prompting a risk assessment has risen by more than 60% compared with the preceding four-year period. We risk being like the frog in tepid water now, that becomes the frog in hot water later. If the overheating risk in hospital happened immediately, it would have likely already been addressed, but because it was, and still is, happening gradually – we are at risk of acting too late.
Active and passive measures
Our report recommends initially adapting hospitals — where possible and feasible — with passive measures, and adding active measures when and where funding allows. These measures include air tempering and air conditioning. While healthcare buildings are being adapted to improve comfort for patients and staff, we must also work to reduce carbon emissions to prevent further environmental degradation. Implementing urban greening, enhancing air quality, reducing noise and light pollution, and incorporating water features and nature-based landscaping solutions will enable us to fully capitalise on the benefits of passive design measures. Simply put, if the air outside the hospital is cooler, it’s more likely you can open the window to cool it down.
The phrase, ‘take care of the pennies, and the pounds will take care of themselves’ perfectly describes what needs to be done in terms of climate change and climate resilience. Everyone has a small but significant role to contribute to the goal of creating comfortable Net Zero hospitals. We should not wait for perfection but make every action count.
References
1 Mentaschi L, et al. 2022. Global long-term mapping of surface temperature shows intensified intra-city urban heat island extremes. JRC Publications Repository. https://publications.jrc.ec.europa.eu/repository/handle/JRC123644.
2 UK Green Building Council. 2025. UK Climate Resilience Roadmap. https://ukgbc.org/our-work/topics/resilience-roadmap.
3 NHS England. 2023. Estates Returns Information Collection, Summary page and dataset for ERIC 2022/23. https://digital.nhs.uk/data-and-information/publications/statistical/estates-returns-information-collection/england-2022-23.