Looking after Schoolchildren during Heatwaves: Background Information

People's perceptions of temperature inside buildings vary depending on a range of factors. These include the age, sex, health, activity level, metabolic rate, and clothing of the occupants, the temperature of surfaces within a room, as well the conditions of the air within the room (for example, temperature, speed, humidity and turbulence intensity).

Reducing overheating in existing buildings, without the use of air conditioning, relies on a combination of reducing the amount of heat transferred into (or gained by) the building and increasing the rate of removal of the heat already in the building using ventilation and absorption by the building fabric. The impact of heatwaves on indoor temperatures may also be reduced by modifying occupant behaviour and periods of building use.

Building-related measures during heatwaves

During periods of hot weather, including heatwaves, all unwanted heat gains by the building should be minimised during the day and night to allow the building’s internal air structure to cool down whenever possible. It is important that the heating system for the whole building is turned off during the heatwave, but the domestic hot water system should remain in operation as normal.

Building-related measures to reduce the impact of heatwaves fall into the following categories.

Reduction of casual gains – keep the use of electric lighting to a minimum during heatwaves. All electrical equipment, including computers, monitors and printers should be switched off when not in use and should not be left in ‘standby mode’.
Reduction of solar gains - awnings and other forms of external solar shading can be fitted to classrooms to prevent heat from the sun penetrating the room. These can be temporary measures for summer use or permanently installed. Solar shading should not restrict ventilation or window openings. Providing external shading prevents both the direct sunlight from entering and heating up the classroom, whereas internal blinds allow the heat into the classroom and often prevent the windows from being opened wide enough to allow for summertime ventilation.
Increase of daytime ventilation rate, if the external temperature is close to or less than internal temperatures –- all windows, other natural ventilation devices and internal doors should be fully opened in rooms as permitted by health and safety regulations. This helps the natural ventilation to remove heat and increases internal air movement. However, fire and smoke control strategies should not be compromised by inappropriate opening of fire doors.
Increased night-time ventilation rate to cool the internal structure of the building and its contents – windows, openings provided for the purpose of ventilation and internal doors should be left open overnight in a secure manner. If this is not possible for security reasons, it should be considered whether they can be opened in the morning, as early as possible before teaching begins.

As many as possible of these measures should be used. In addition, certain further temporary measures are available as a last resort, although these have energy, financial, carbon dioxide emission consequences, as well as their own localised thermal comfort and noise implications.

Increased air speeds using oscillating mechanical fans – such fans are themselves heat sources, so should be used cautiously.
Use of temporary local room air conditioners or dehumidifiers – exhaust heat from such units should be removed to the outside of the building using temporary ducts; free-standing units without such ducts should not be used as their net effect is to heat the room further.

Occupant- and management-related measures during heatwaves

There are several occupant- and management-related measures which can help to reduce the effects of heatwaves. As many as possible of these measures should be used. These include the following.

All staff and students should be encouraged to wear appropriate summer clothing. Comfort in summer is improved by suitable summertime clothing. At present, many schools have the same uniform throughout the year.
Drinking water should be provided throughout the day.
General activity levels (and hence metabolic rate) should be reduced whenever practical. This could include, for example, cancelling sports lessons during periods of very high external temperature.
Exposure to direct sunlight should be minimised during periods of highest solar intensity, including during break times.
School start and finish times could be re-arranged to avoid teaching during periods of very high external temperature.
Use classrooms or other spaces which are less likely to overheat in preference to those that do, and adjust the layout of teaching spaces to avoid direct solar exposure of the occupants.

Looking after Schoolchildren and those in Early Years settings during Heatwaves:Guidance for Teachers and Other Professionals is also available.

Last reviewed: 17 August 2009