As we start to mind the weather and put on hats, scarves and sweaters, overheating in our homes is unlikely to be at the front of our minds. Yet that is exactly what we have been discussing since the start of the summer. It is already an issue others have looked at, but judging by our research and the response from colleagues, clients and co-professionals on the topic, it is still a hot topic.

The culmination of our efforts can be found here and the biggest problem we uncovered is we aren’t agreed on how to define what overheating is, never mind on how to then resolve it.

Our research was based on interviews, an independent survey, modelling and recording temperatures in new flats. We focused on London, (the issue is primarily one for flats in cities) but the same issues will apply to any urban area in southern Britain.

Over 80% of Londoners we surveyed said they suffered from overheating in their homes this summer. One in 10 said their homes were uncomfortably hot most of the time and that people’s health and productivity was being affected. Temperature logging in new flats showed temperatures regularly exceeded generally accepted temperature thresholds in this relatively cool summer. Interviews with those living in new flats reinforced the findings and gave them some flavour; the issue is particularly acute in the night in single aspect flats where the side-effect of nearby noisy streets is a real limitation for people trying to open windows. Significantly, we also found over half of people will consider overheating as a factor when looking for a home.

Modelling we ran on a typical project indicated that flats will struggle to avoid overheating without mechanical cooling as temperatures rise in future, even when using other mitigation such as brise soleil and/or solar control glass. Even in flats with good natural ventilation and reasonable measures to reduce overheating there was still a substantial risk of overheating when London’s projected future climate is taken into account.

For our software modelling we used the latest methodology to model overheating risk, CIBSE TM52, but the industry is far from agreed that it is the best way to do it. With the current standards there are a lot of assumptions required regarding occupancy, internal heat generation, window opening, blind use, etc. to the point where even the best consultants will get different results from each other.

Another important issue is the “urban heat island”, where urban areas are hotter than rural areas due to local heat production, less evapotranspiration from plants, and more heat being absorbed by buildings and hard landscaping.

At our event on the topic speakers from the GLA and Notting Hill Housing (NHH) confirmed that this is an issue they are facing from a policy perspective and when dealing with tenants, with NHH also raising the issue of communal systems causing overheating.

In our report we suggest five steps that can be taken to reduce overheating:

1. Develop a robust regulatory overheating analysis method for all new developments where the issue is clearly defined
2. All new housing developments to adhere to a “cooling hierarchy” to minimise need for cooling. 
3. All new buildings to be designed to facilitate retrofitted cooling systems.
4. Measures should be introduced on new developments to reduce the urban heat island. 
5. The “all-electric” city should become a priority – reducing heat production from vehicles and buildings and reducing noise, allowing people to open their windows.

This is an issue of importance to all those working in housing and since the issue of the paper CIBSE have started work on a standard assessment methodology which will be a helpful.

This piece originally appeared in Building magazine.