Overheating is back in the news [1]. As the UK faces potential heatwaves, it is an apt time to look at some figures. In this blog we’ll look at Met Office Projections, the difference between regions and what can you do to reduce overheating in your homes and buildings.
Before that though, it is worth remembering that although sunny days are always welcome, prolonged and intense heatwaves, can and do, cause health problems and affect the supply of our food, water and thermal comfort.
Met Office Projections
The Met Office carries out a series of climate projections, where they examine how climate change will impact rainfall, wind speeds, temperatures etc [2]. A range of scenarios can be examined to give various outputs. For this blog we’ve looked at the summer temperature increase in a central projection and a bad case projection. The central projection is a case where the world slowly reduces CO2 emissions and manages to limit global warming to around 20 degrees Celsius. The second scenario is where emissions are not reduced nearly as quickly and the anticipated effects are worse.
Regional
Knowing how much regional summer temperatures increase is one thing. The next step is to add the increases to historical summer temperatures. Also, an allowance has to be made for how much temperatures inside the home increase compared to external temperatures during a heatwave. Both these bits of data are available in an older version of energy efficiency calculations necessary for the satisfaction of building regulations [3]. The same methodology indicates that if the average internal temperature is above 20.5 degrees Celsius then there is a risk of overheating in that home.
Putting all that together, the chart below indicates which regions have the higher risk of overheating homes.
In the central projection scenario, the regions from the Midlands southwards seem to be at increased risk, but those north of that divide don’t have the same increased risk. In a bad case scenario only northern parts of Scotland seem to be comfortable.
How hot your local area becomes is only one risk factor for overheating in a home. Other risk factors are: presence of communal heating; being a flat; built since 2000; in an urban heat island; not being able to ventilate by opening windows.
What can you do:
We will all have to consider the risks to our safety from overheating now and even more in the near future. This is especially so if the home has 3 or more of the six risk factors listed above. So what can we do about it?
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- Reduce CO2 emissions – this won’t necessarily reduce some overheating risk, but it will certainly help you do your bit for reducing the worst risks of overheating.
- Part O for new build homes – if you are involved in building new homes, then adhere to the recent Part O additions to building regulations both in spirit and in compliance. Treat them as a basic minimum standard rather than “comply and forget”.
- Cavity wall insulation can reduce overheating – as well as reducing heat loss in winter, there is anecdotal evidence that it also helps keeps the home cool in the summer. Plus, this action reduces carbon emissions from a home in the winter.
- External shading – this can have a significant impact on reducing internal temperatures. Shading can come from external shutters as well as Brise Soleil. Deciduous trees can also provide summer shading plus doubling up as providing a little bit of biodiversity. In winter when they shed their leaves, they will still allow winter sun in.
- Adequate ventilation – being able to extract warm air from the home also helps a great deal.
- White walls and surrounding green areas – there is some advice that white walls tend to reflect the worst of the summer heat, but this may not be as effective as external shading and adequate ventilation. Green spaces around the home can also reduce temperature a bit, but not as dramatically as other measures. It’s still a great idea for lost of green spaces around homes for other reasons – help reduce flood risk, increase biodiversity, recreational value and cleaner air.
- Adapt – you can get great advice for keeping cool in the summer from the British Red Cross [4]. It can range from reducing internal heat gains to knowing which widows and curtains to shut at which time of day.
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If you manage a portfolio of homes and want to examine overheating, other climate risks or indeed reducing carbon emissions, please be in touch on [email protected]
[1] https://www.bbc.co.uk/weather/articles/cly13d9eeq0o
[2] https://www.metoffice.gov.uk/research/approach/collaboration/ukcp
[3] Appendix P of SAP 9.93. The overheating calculations have now been superseded by Appendix O in building regulations
Picture from Met Office projection output