Housing and Overheating


Dealing with overheating in UK housing and apartment design is quickly working its way up the list of priorities. I still have difficulty believing that DCLG decided to ignore this in the Housing Standards Review, but they did. Despite the Climate Change Committee report on Climate Change Adaptation stating that :

Many homes, hospitals and care homes are already
at risk of overheating. By the 2040s, half of all summers are expected to be as hot, or
hotter, than in 2003 when tens of thousands of people across Europe died prematurely.
A standard or requirement is needed in order to ensure new homes are built to take
account of the health risks of overheating now and in the future. Cost-effective passive
cooling measures should be adopted rather than relying on air conditioning, which will
be expensive and exacerbate the urban heat island effect.

But meanwhile, other, more responsible organisations are ploughing on regardless. The TSB ran a project called Designing for a future Climate and the outputs are here, for anyone interested in the topic, this is essential reading.

The Zero Carbon Hub have just kicked off a project to look at overheating specifically, and will report back early next year.

But what are practitioners to do now? What is a responsible approach?

I propose the following four steps.

1. Don’t use SAP

2. Carry out simulations, and choose the criteria carefully

3. Don’t believe everything simulations tell you

4. People will adapt, make the buildings ready for adaptation

The Detail


Firstly, lets agree that SAP is an inappropriate tool for providing the answer. Overheating will occur in fairly specific circumstances, caused by a complex mixture of factors and may only occur for a specific set of hours in a particular apartment. For example west facing apartments are likely to overheat in the evenings while east facing apartments in the same building may not overheat or overheat at different times of the day,  and the strategy for dealing with the problem is likely to be different from the east side to the west side. Overheating is elevation specific, not plan specific. SAP is not sophisticated enough to tell us when overheating is likely to happen in time, and therefore is unable to point towards useful strategies for dealing with it. There are a number of other tools on the market capable of analysing the problem such as IES and TAS. These are designed for the purpose and are much more appropriate for this use.

Secondly, we should be carrying out simulations on a regular basis of current apartment schemes to assess whether they overheat using current weather as a minimum, and preferably also assessing them with 2050 and 2080 weather predictions.

The standards to use for testing should be adaptive standards such as EN 15251 or CIBSE TM52 for buildings occupied by able and healthy individuals who will adapt to external temperature and who can control their environment, or who can go for a walk in the shade or go to the swimming pool on hot days.

For buildings where the occupants are young or old both of who have difficulty regulating temperature, and who may not be free or able to move to colder places or unable to close shutters, we should use the more risk averse CIBSE Guide A which sets a temperature level that must not be exceeded for a set number of hours per day.

Thirdly, lets agree that simulations are useful and necessary, but again are only guides to likely scenarios and are not facts. Here is a good illustration of the problems caused by taking simulations at face value.

Whilst working on a recent project we were presented with some analysis of overheating carried out by a well known and respected firm of engineers. Among other sensible suggestions they recommended reducing the size of the windows by 50% to reduce the likelihood of overheating by about 1% for the 2050 high emissions scenario. So, to explain, the suggestion was to reduce the area of glazing by 50% because simulations suggested that this reduced the likelihood of temperature in the apartment exceeding an agreed limit by 1% of the time the apartment was likely to be occupied. 1% of the occupied time for an apartment is about 1% of a year, so lets say 3.5 days in total. To reduce discomfort in 2050 for a three day period, the suggestion was to reduce the quality of life for the remaining 18,250 days. We won’t succeed in adapting to climate change by building buildings that no-one likes or wants to live in.

Fourthly, I believe that we will adapt both our behaviour and our ability to deal with warmer climates. The rate of change is slow enough for many species to migrate ahead of changing climate, so why can’t human beings adapt their behaviour too. Wearing different clothes, travelling at different times, closing shutters before going to work, having a siesta are all cheap ways of adapting to warmer climates. All of this makes simulation difficult. A simulation will assume that people in 205o will be cooking using the same equipment that we are using today, and it will assume that the heat gains from cooking will contribute to overheating. It is likely that people will change their cooking habits in warmer summers to avoid cooking at a time of the day when it contributes to overheating, but a simulation run using one of the currently available tools isn’t able to model changes of behaviour and lifestyle over time.

Our buildings need to be designed to accommodate shutters or blinds on the outside of buildings for those parts that are vulnerable to overheating. It may not be necessary to install them now, but it is likely to be necessary in the future, so design them in now. They are a familiar feature to anyone who has been to southern Europe and everyone understands how to use them immediately.


6 thoughts on “Housing and Overheating

  1. Good blog – thanks Rory! I think of essence is that we can and should be monitoring buildings to see if/when/for how long they overheat; how occupants respond and how this compares to the models used – so real buildings can help validate/fine tune models. The solutions to prevent overheating are quite simple really and include a combination of factors – as you suggest here too – and buildings can be future proofed to adapt – I cover this in The Environmental Design Pocketbook Chapter 2 and Chapter 6 but do find it astonishing this stiff is not more widespread,…Do you happen to know what the latest PII take is (WREN) on future changing climate and our duty to design fit for purpose buildings over the building’s design lifespan? (After all, datasets are easily obtainable from UKCP/Metoffice/Prometheus,and while not gospel, it is the best we have to gain an idea of risk and possible solutions/mitigating circumstances,..)

  2. Thanks Sofie, I don’t think that PII considers this, but it might be a CDM consideration. However I dont want to wait for the lawyers to tell us how to design well!

    • Hi Rory, yes ofcourse we don’t want to wait for law to tell us to design fit for purpose buildings! However, it might help kickstart those into action who are reluctant now? I remember discussions as far back to 2009 and even in my Part 3 further back about force majeur being a grey area with regards to climate change adaptation – i.e. if data exists and reliable evidence suggests the climate is going one way then we cannot claim it was unforseeable if our buildings do not turn out to be fit for their intended purpose and we may well be liable – so it would be a PII issue ( on top of CDM) I guess. Any idea how to find out?

      • The RIBA has its own PII insurance scheme, you could ask them. I think that there would be a statute of limitations on such matters.

  3. Planning to avoid overheating is also difficult where there is no consciousness of the significance of orientation. Current developments ignore orientation effects, mostly going on aesthetics and it’s not possible for a design to work sensibly is these circumstances

  4. Bob, I think that you are simplifying matters somewhat. A development has to meet a great many criteria, and among them are achieving daylight levels, providing an attractive indoor environment, providing value for money for a private buyer who has bought an apartment or house, making the most of available views, wnd so on. Windows are the most important feature in any room, and even if providing a large window will create an overheating problem for some of the time, perhaps the pleasure it gives for the remainder of the year makes it worthwhile?

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