The Green Register loading now

Ways to Stay Cool in Future Heatwaves

Over the last week or so I have seen a lot of ‘tips and tricks’ for staying cool in the heat. Everything from shutting all windows and curtains/ blinds before 10am, putting bowls of ice under off-the-shelf fans to freezing hot water bottles to rest your legs on at night and whilst this may placate our immediate discomfort, overheating is a very real problem that is only going to get more prevalent and requires a more permanent solution for heat waves to come. It is a significant aspect in retrofit design and installation for year-round comfort and health.

There has been extensive talk from central and local governments about decarbonising our housing stock and meeting our climate targets, resulting in government initiatives and funded schemes for technologies such as heat pumps, or boiler replacements, or once upon a time, feed in tariffs for microgeneration. Whilst these are all nice-to-haves none of them address the core issues we have with our housing stock and these issues will be exacerbated as global summer temperatures rise.

Overheating is not something we look at very often in the UK because we don’t often think about it being too warm, but the past seven years have been the warmest years on record, and 2022 is set to meet them or beat them for global average surface temperature (1) and it is likely that that trend will continue. Perhaps it is time to start looking at keeping our buildings cooler in the summer as well as warm in the winter. 

Tips and Tricks aside, staying cool is not too difficult, provided we plan for it and work accordingly. Insulating ourselves against extreme temperatures is a very familiar process – it’s just that we normally look at staying warm rather than staying cool – though the process is the same.  Passivhaus design principles look at both the heating and cooling demand of a building and show us that creating a consistent airtight, insulated layer around your building makes it much easier to control and stabilise the comfort temperature within; whether you need to warm up with the heating ticking on for a few minutes, or cool down with a quick burst from an AC (or similar) unit. 

We need to start looking at insulation as temperature stabilisation through all the seasons rather than just staying warm in winter. Retrofitting insulation in our houses effectively provides a more consistent temperature across the year, reducing huge energy demands for heating OR cooling, but has to go hand-in-hand with ventilation and shade.

Once our buildings are insulated and airtight, controlling the temperature can become much easier – Mechanical Ventilation with Heat Recovery (MVHR) works for both heating and cooling. For cooling, the heat from warm air coming in from outside is transferred to the cool air that is removed from the building, leaving us with cooler fresh air coming in.

Historically we have spent a lot of time and energy designing buildings to have large south facing glazing to maximise our solar gains and provide us with as much free warmth as possible but as we enter the realm of overheating this becomes more detrimental and requires more thought. The majority of overheating risk in UK properties is due to solar gain through large south facing glazing.(2)  Large windows and doors that let in the sun have always been something I personally enjoy, but as I sit in a room that is 30℃ before noon I can see the need for some more thought around solar gain. South facing glazing is always going to be beneficial to us in the cooler months, so we just need to resolve overheating issues in warmer months and there are many ways of doing this. 

Passivhaus principles also calculate and deal with overheating by analysing measures for shade. Use of controllable or permanent shade is the primary method for limiting solar gain – be it external blinds or angled fins that only shadow the windows when the sun is at a particular angle. However I have seen other methods, from the highest of high tech to the simplest symbiosis. 

‘Solar Glazing’ combines photovoltaics and glass where the PV cells are laminated between the two panes (3). I have also seen this done with a sensor that detects how warm it is internally and lowers solar panels over the windows to both provide shade, and electricity though in practice it made the building very dark internally. 

My personal favourite method of reducing solar gain in the summer was one I first discovered at the home of our very own Lucy Pedler, who has the space for a wonderful glazed-roof veranda with a grape vine growing throughout. In the winter the vine is bare and so the sun pours into the house, but in the summer there is so much foliage it’s a consistently cool, shaded place to sit, and a wonderful use of greenery to both benefit the building, and improve biodiversity- if you have the space.

greenery used to prevent summer solar gain
Shaded glazing using greenery

It is a harder beast to tackle in tower blocks or flats which have no cross-ventilation (if they are on one side of a tall building – much like the one I am sat in) but we need to prepare ourselves to do that work, or at least finds ways of mimicking it either through heat shields that can be put in the window (like those you might see in a car or van) or through heavy curtains that block incoming sunlight. It is no doubt harder to retrofit external shading to tower blocks, but it could be done, and I would expect it to need to be done to meet carbon targets. 

Another solution for this would be to have a closed system with PV’s directly powering air conditioning units, with the output on the AC increasing as the intensity of sunlight increases, and this is something that I have looked into in the past, but there has just not been the market for it in the UK. 

Heat pumps can also be used for cooling, so in theory it’s a good solution, but their efficiency relies on good building fabric, and in the UK we have around 25 million homes that still need retrofitting to a decent standard before heat pumps can be effective. I am all for heat pump installation, but I am wary of the magic bullet approach that the central government seems to be pushing.

If we can solve the overheating problem through improving building fabric and providing shade, we inherently improve our housing stock by comfort, carbon and climate standards. More stable internal temperatures means less requirement for heating and cooling. Reducing the heating load of our housing stock in the UK is the single biggest impact we can have on our carbon emissions (4). 

We can further impact our carbon footprint by improving internal temperature stability  through having cooler showers – we have a tendency to stay in a warmer shower for longer when it is cold at home so by improving the internal temperature we can reduce our water consumption – and water usage is another big factor in our climate challenge. 

If I can leave you with one message from this article, I want it to be this:
Our current heatwave, July 2022 is not an anomaly. It is indicative of the changes we will see to our global climate. I am convinced we will see more of these warmer temperatures. Being proactive in dealing with issues like this is far more beneficial than being reactive, so let’s start looking at the fabric and controllable shading of our buildings and improving that, before we rush for an off the shelf AC unit in summer, and a fan heater in winter. 

Thank you for taking the time to read my thoughts. For more information, please take a look at the webinars and training that the Green Register has coming up here:

We are running a session on building physics in October that will look at the fabric of buildings and how different retrofit measures interact with each other –

We have some retrofit case studies coming up –

And we have a session in November on sustainable water usage where you can find out more about just how important our water usage is –

I am always keen to discuss further, so please do get in touch with us.

Warmest regards,

Seb Keightley

  1. World meteorological organisation, The State of the Global Climate 2021
  2. Green Building store MVHR usage for cooling
  1. I.


  1. UK average household CO2 emissions