Alex Hill from Whitecode Consulting looks at fabric-based approaches to balancing thermal performance and comfort in UK school buildings, in the context of a range of challenges
We are currently experiencing unprecedented levels of heat in the UK, and British buildings are not designed to accommodate this. According to official sources, Western Europe’s 2022 heatwave may have caused 20,000 excess deaths. In England and Wales 3,271 excess deaths were recorded from the start of June to the 7 September (Office for National Statistics), this is 6.2% higher than the five-year average with Covid-19 deaths excluded.
The government’s introduction of new overheating regulations should warn the industry of the severity of this issue, and suggests that the industry needs to change its approach. Commercial buildings must comply with CIBSE’s TM59 to reduce overheating. For domestic dwellings, all previous regulations on overheating have been brought together into Approved Document O, to highlight the importance in the design of limiting solar gains through windows and providing adequate opening areas to remove excess heat.
Matters are made worse by the fact that we are facing a climate emergency. In 2022, our highest temperature was 40.3°C which exceeded the previous record of 38.7°C. We have now arrived at the point where the purpose of energy efficiency is to drive down heating costs and we are looking to mechanical cooling to deal with our overheating problem, which should not be the first port of call.
These temperatures we have faced are comparable to a Spanish summer. The Spanish prevent overheating by keeping doors and windows shut to keep out hot air in the middle of the day, shutting blinds and utilising mechanical cooling in the evening to lower inside temperatures. We are experiencing temperatures that you expect from Spain, and yet we are not adjusting our architecture to accommodate this.
The Spanish approach to preventing overheating
In the UK it is imperative that we design the building in a way that is sympathetic to the higher temperatures that we have been experiencing in our recent summers. Spanish designers consider high temperatures in building design. Their buildings feature hard ceramic floors and hard concrete ceilings to reduce the heat. Moreover, ‘persianas’ or exterior shutters, used as an external shading solution are commonplace.
This Spanish approach to keeping buildings cool would be an excellent start to dealing with our overheating problem and meeting the relevant standards. It is pertinent to start having a discussion within the built environment about exterior shading for buildings and moveable shutters that you often see on Spanish apartment buildings, as these features could be the solution to the British overheating problem.
Preventing overheating in schools
Schools generally have a lower heating demand than other types of buildings. Typically, schools need to be warmed in the mornings before the pupils arrive. As human heat output contributes to building temperatures, we should consider that a class of 30 pupils would contribute approximately 4.5 KWh of heat energy to the building. Therefore, in a well-insulated building less heating is required throughout the day, and good ventilation to counteract the effect of human heat output is critical for large periods of the year. Although term time does not usually coincide with the UK’s hottest temperatures, there have been occasions in May where temperatures have been excessive, making it difficult for students to learn.
Often, schools expand their sites with the addition of a series of boxy, lightweight classrooms which are low cost. This design is often implemented due to budgetary reasons but we as designers could be doing more. Sometimes this is done due to limited budgets but capital infrastructure cost bears little consequence when we consider overheating and the associated operational costs of having a mechanical cooling system running constantly due to poor building design.
Unfortunately, schools rarely receive enough capital investment. We need only look at the current state of the education sector where schools are losing teachers as they cannot afford to pay both energy bills and teachers’ salaries. Having exposed concrete soffits as increased thermal mass, exterior shading to keep the building cool, and securely opening windows at night to cool the building are the best strategies to deal with overheating in schools.
What’s the solution?
If the government goes ahead with the gas boiler ban for new builds, will this ban extend to the retrofit market? If so, will hydrogen energy become the replacement? Ostensibly, there hasn’t been enough investment in hydrogen energy or incentives from the government to make this viable. As a result, we are likely to see a lag where purchasers are going to potentially face a ban on gas boilers, without a real alternative to consider, other than heat pumps.
We must also look to fabric improvements as this can greatly affect occupant comfort. Consider glazing for example, which can contribute to overheating. We must first get the building fabric right and then maximise natural ventilation. Then, and only then, should we apply mechanical means to solve the risk of overheating that could not be designed out by fabric first and natural solutions. We must begin designing our buildings in a way which is sympathetic to heat. Architecturally, in the UK we are keen on buildings with low ceiling heights, and small compartments which overheat
very easily.
In addition to Spanish building design, the built environment sector could refer to Victorian buildings, as architects of the time designed structures which were excellent at preventing overheating. Consider any Victorian building with its high ceilings, spacious interiors and top-opening windows that allow for single-sided ventilation in a room.
Given the current climate crisis, it is imperative that we adapt our current approach to building design, and we must start solving these problems that are all too often characteristic of modern British buildings.
Alex Hill is managing director at Whitecode Consulting