34 THE CLIMATE CHALLENGE


elderly, it has broader wellbeing effects on the population at large, including through sleep deprivation. The EAC says economic costs from overheating are likely to “run into the billions.”


Overheating is the accumulation of warmth within a building to the extent where it causes discomfort to the occupants. Until Part O of the Building Regulations came into effect in 2022, there was no requirement for the explicit assessment of overheating to be considered in a home’s design. Consequently, there are thousands of homes built relatively recently with increased levels of insulation and airtightness to keep them warm in winter (in compliance with Part L), but which may be at increased risk of overheating in summer.


Alongside increased external temperatures, factors that can contribute to overheating include: solar gains from unshaded windows, heat from people and equipment and, in communal apartments, heat from uninsulated domestic hot water pipework in communal areas. There is also the increasing problem of the urban heat island effect.


The type of home most likely to be affected by overheating are apartment buildings in city centres with windows on only one elevation which faces south, east or west, particularly if there is no opportunity for cross ventilation. Occupant behaviour can also make overheating worse. In the UK people often leave windows open to increase ventilation throughout the day, even when the outdoor temperature is higher than indoors whereas in the Mediterranean occupants are used to closing windows (and shutters) to keep heat out at the warmest time of the day.


As the climate warms, overheating WWW.HBDONLINE.CO.UK


issues are set to increase. Research has shown that by 2050, passive measures such as thermal mass and night-time ventilation may not be effective in providing sufficient thermal comfort in homes and active cooling systems, such as air conditioning, may be necessary in some locations in the UK.


Currently less than 3% of dwellings have air conditioning, but this figure is epected to grow significantly, particularly as the number of people using their home as their main place of work is increasing. The International Energy Agency says that record-breaking temperatures feed the demand for air conditioning which in turn results in surges in demand for electricity – risking a vicious cycle of increased greenhouse gas emissions that in turn make the world even hotter. The cost of running air conditioning is also expected to lead to a doubling of electricity bills for homeowners.


he definition of overheating in Approved Document O of the Building Regulations is based on the Chartered Institution of Building Services Engineers (CIBSE) document TM59. The Approved Document outlines two methods for achieving the performance targets: a simplified method and the more thorough dynamic thermal modelling method embodied in CIBSE TM59. The Building Regulations apply to new-build homes, but four out of five homes that will eist in  are already built, meaning that the scale of retrofitting reuired for eisting homes to protect them from overheating is vast. Overheating is exacerbated by excess solar radiation. Modelling shows that external shading is highly effective protection against solar gains because it stops sunlight reaching a window. Overhangs, for example, can be


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