Overheating in schools.

Written by Emily Martin

As carbon emissions continue to cause the earth’s temperature to rise, the UK is set to experience hotter and hotter summers. The UKCP18 predicts that a rise of 2°C in global average temperature would not only cause a similar increase in our average annual temperature across the whole UK, but could also cause summers in the South-East of England to be a further 3-4°C warmer. Higher levels of global warming are likely to yield even more extreme results.

Many buildings within the UK were built during the previous century, and therefore were designed with its historically cooler climate in mind. This means they are optimised to retain heat with little facilitation for ventilation and cooling so are now at a high risk of overheating, particularly during the multiple prolonged heat waves that are now expected to become a regular summer occurrence. With the continuing increase in annual days with extremely high temperatures this dissonance is only going to become more pronounced in the coming decades.

Newer buildings, however, are often no better at coping with extreme high temperatures. One of the key contributors to climate change is our ever-increasing energy consumption, so understandably there is a lot of pressure on making buildings as energy efficient as possible; this is often done by minimising the need for heating in the cooler months, as keeping homes warm in the winter has always been the main topic of concern. Unfortunately, improvements in air tightness and insulation within newer buildings means that they continue to trap heat in the summer and cause uncomfortably high temperatures. The lack of awareness and attention given to these issues is something that Shade the UK would like to change.

Why do schools overheat?

For a variety of reasons, schools are often at a higher risk of falling victim to higher indoor temperatures than other similar spaces, like offices. Many schools at least partially occupy an older building designed to thrive in the previously lower summer temperatures. They are also made up of lots of smaller rooms, unlike more commonly open-plan office areas, so there is a lack of ventilation and airflow throughout the entirety of the building. This is amplified by the fact that classroom doors may often need to be kept closed to avoid disturbance to other areas of the building through noise.

Classrooms generally need to hold large numbers of students in a small area and are at their full capacity for most of the time they are occupied, which can also contribute to a warmer environment. An increase in IT equipment used in schools may be having an effect also, as devices like computers can emit a noticeable amount of heat when in large numbers.

Often schools have large windows to allow adequate light into the building. Depending on their orientation these windows may contribute hugely to solar gain, as heat from the sun moves through them far more easily than it does solid walls. In some cases, it may also be necessary that these windows remain closed, restricting ventilation to the room. This may be done to avoid noise or air pollution in particularly urban environments with proximity to roads with heavy traffic.

What are the effects of overheating in schools?

Overheating within buildings is often assessed with respect to thermal comfort, but health and productivity of occupants can also be useful indicators as to whether a space is functioning at the correct temperature. Thermal comfort can depend on a variety of environmental factors as well as air temperature, such as air speed and humidity, but is also very dependent on the circumstances of the individuals occupying the space. Things like age, clothing and activity can influence how well an individual functions at a given temperature.

Universally understood impacts of a workspace that is too warm include, reduced productivity and a lack of focus; this can have a negative impact on the speed of learning in students of all ages but may be the most concerning for older students preparing for and undertaking exams, as these are often in the summer when the conditions are at their worst. In younger students, teachers often note that children become lethargic and widely complain that they feel unwell when they occupy overheating classrooms during heatwaves, and that a dip in ability to complete simple academic tasks is observed.

Studies have shown that children function differently enough that the temperature they require for thermal comfort may be multiple degrees lower than that of adults. This means that teachers may not be aware that students are experiencing uncomfortably high temperatures. Children may also be less aware of when and how to behaviourally regulate their temperature, making them a more vulnerable group and therefore a particular concern of Shade the UK.

What can we do?

There are a wide variety of changes that can be made to existing buildings to reduce overheating, and these options will greatly vary in price and extremity. While it is possible to change the temperature of a building through retrofits, it is key that we thoroughly implement overheating mitigation measures into future developments, especially schools, from the very beginning, and look at adding cooling elements into general refurbishments. When doing this it is essential to remember that even if a school is not overheating now, rising temperatures and increased instances of heatwaves may mean that it will in the near future unless preventative action takes place. Current methodologies used for school planning projects include TM52, informing those planning the building on the limits of thermal comfort, and BB101, a document produced by the UK government specifically to give guidance on overheating and air quality in schools.

External shading devices may be one of the easiest measures to implement across a large building like a school; this is an effective change as buildings often take on most solar gain through windows, especially those that have facades east/south/west facing as they remain in direct sunlight all day. External shade is more effective at reducing building temperature than internal shades like blinds as they prevent the heat from even entering a building and creating a source of heat inside the room.

Retrofitting a cool roof to a school building could make a big difference to internal temperature, as schools often take up a large area with most of the roof surface heating up all day in direct sunlight. Cool roofs involve using a highly reflective coating or material to reduce the amount of solar heat absorbed through the roof and trapped within the building; this does mean, however, that heating costs in winter may be increased.

An alternative to this is a green roof, which comes with the added benefits of improved drainage and increased local biodiversity. It can also act as an urban green space in cities, and therefore help reduce the urban heat island effect’s impact on the building. The leaves of the plants will shade the building’s roof and reflect light away from it, but the plants themselves will also cool the air around the building through their process of evapotranspiration. Green roofs have the greatest effect when combined with green walls, for as high a level of surface plant coverage as possible – you can also apply green roofs with solar panels!

Adding more green spaces around the school will generally provide a wide range of benefits to those using the space; this includes improved mood and mental wellbeing, as well as potentially providing more exciting play areas for younger children. While they are a long-term improvement tactic, planting deciduous trees in proximity to a building is effective as they will provide shade from the sun in the summer when they have leaves, but will block far less solar gain when it is needed in the winter. Vines and smaller shrubs can be implemented much quicker and can provide shading when planted near walls, while also allowing them ventilation.

The behaviour of people within a space and the actions they take to improve the conditions within buildings can also make a huge difference to problems with temperature. It is important that the windows in a room are accessible and easy to use for teachers and other adults in authority within the school building, and that education is provided on how best to implement cooling measures to maximise effectiveness.

While these natural cooling methods are very useful, a 2018 study used modelling to provide evidence for the fact that mechanical cooling will soon become a necessity in a school environment. The study looked at three different forms of ventilation: natural, mechanical and a mixture of the two, and assessed their impact on reducing overheating in an average school in both current and future (2050) UK climates. It was found that when only using natural ventilation only the modelled school in London would already be overheating, and the problem would be considerably worse by 2050. Fully mechanical ventilation would obviously be capable of preventing overheating in all scenarios, but so was a mixture of natural and mechanical; this shows the importance of still implementing and fine-tuning natural ventilation measures, as this hybrid option uses far less energy than mechanical alone and therefore is in keeping with carbon reduction goals and efforts to prevent increased warming.

Overall, overheating in schools is becoming an ever more pressing issue, and one that Shade the UK is highly intent on bringing awareness to due its negative impacts on vulnerable groups. Children are often unable to keep themselves safe in higher temperatures and this therefore puts them at risk; this issue is set to become far worse with continually increasing temperatures and instances of heatwaves, so it is imperative that preventative measures are taken now, and overheating prevention becomes fully implemented in future builds and refurbishments.