Tackling Overheating in our Homes

This summer saw some extreme temperatures in London so we’ve asked Project Architect, Joe Scragg, to reflect on his experiences of tackling overheating in our homes and others:

Thursday 25th August 2022

The rain has returned and summer feels as if it’s drawing to a close, and it’s not often that I’m glad to see the back of it. But then again, it’s not often that we experience a summer like we’ve had in the UK, one of; extreme droughts, temperatures exceeding 40°C, wildfires, crop failures and camping-out inside on the sunny days. It feels unprecedented in my lifetime but my parents will be quick to remind me of the sticky summers of 1990, 1995 and 2003, none of which I can remember of course…

So unprecedented maybe not, but the annual UK state of the climate report which is published to analyse how the UK’s climate has changed compared with historical averages would suggest we’re only heading in one direction. The report shows that 9 of the 10 warmest days in the UK since 1900 have been since 1990.

So, in a changing climate what can we do with our habitats to keep them habitable? Every household will have their own techniques for keeping cool through heatwaves; from blowing a fan across a damp towel for a rudimentary evaporative cooling effect, opening sash windows top AND bottom so that the cooler incoming air effectively flushes the warm buoyant air out of a room, drawing curtains through the hottest parts of the day and so on. These are great ways of mitigating heat that has already entered a building, however, as climate conscious architects, we are most interested in ways to design buildings that effectively and passively keep our clients cool through hottest days of summer (and subsequently snug through the freeze of winter).

I live in a Victorian end of terrace maisonette in North London, it’s split across two floors with an upper ground floor and a lower ground floor. The upper ground floor like many buildings of this era has solid masonry walls with no insulation measuring 220mm in depth and it is made lovely and bright through large exposed sash windows. In contrast the lower ground floor has 500mm solid masonry walls that are set within the ground to create a basement and paired with smaller window openings. Behaviourally we found ourselves migrating downstairs in the hottest period of this summer, however, friends without this luxury were unfortunately turning to AC units. This nicely illustrates a design challenge that we seek to address in our projects. Our basement provides a space that 1. is well insulated (albeit from soil…), 2.has high thermal mass in its 500mm deep masonry walls and 3. has small window openings on the parts of the building most exposed to direct sun. Designing buildings that can effectively function without the use of AC is essential if we are to exist in a changing climate. It’s clear that an over reliance on carbon intensive technologies such as AC will only create a negative feedback loop where we become hooked on the very thing that’s harming us through its emissions.

So to summarise those three important factors:

• Insulation – A well-insulated building should work to prevent heat loss or heat gain between two spaces that have different temperatures – indoors and outdoors for example. Insulation can help reduce heat loss during the winter months but also prevent over heating in summer. This means that there will be less of a reliance on AC to cool it and less fuel required to warm it.

• Thermal mass – Spaces like a basement often have ‘high thermal mass’ and this relates to the ability of the thick solid masonry walls to absorb, store and release heat. Materials such as concrete, bricks and stone all have high thermal mass, where as materials like timber, steel and carpet have low thermal mass. This summer it took a long time for the fabric of my basement to warm up and release it internally which created some respite for us on the hottest days.

• Windows – Lots of our clients come to us hoping to achieve a naturally bright and airy building. That impulse is both understandable and achievable without risking overheating. Again, with the example of my basement it contains windows located on walls that weren’t exposed to direct sunlight unlike the oversized sash windows on the floor above. Generally speaking it is always best to avoid large expanses of glazing exposed to the southern midday su.

The beautifully simple aspect of these simple measures is that they will keep you comfortable at both extremes of our seasons and will mean that your fuels bill come down in line with your carbon footprint and hopefully signal a brighter (and cooler) future.

In the meantime, it’s pouring in London and autumn is nearly here meaning my cat seems more inclined to spend time with me which is always a plus.

Joe Scragg, Project Architect, Collective Works