From councils to caretakers: the comfort custody battle

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The arrival of a cold snap reliably revives an age-old household debate. Do we crank up the heating, or do we slap on a jumper? More often than not, it is the person paying the energy bill who champions the jumper option. If you are lucky enough to live in a passive house, you might be spared the family drama, because the building fabric is enhanced to a point where occupant behaviour has a smaller impact. If little Tim wants to lounge around in shorts at Christmas, why not?

In hotter climates, the same domestic battle plays out in reverse. During my fieldwork in Sudan, one woman exclaimed, "Can you believe she turns the air conditioning (AC) on and then sleeps under a thick blanket?" A clear pattern emerged. Within the same household, some occupants relied mainly on natural ventilation and used mechanical systems sparingly, which is how mixed-mode buildings are intended to function. Others, however, rarely ventured beyond a handful of air-conditioned cocoons.

You might be thinking, isn't that just typical teenage behaviour? What harm could it really do? The risk is AC dependency. When people are constantly exposed to a very narrow temperature band – say, an unwavering 20C year-round – the body's ability to adapt begins to fade. Thermal comfort, like fitness, is something you can lose if you stop exercising it. The more you shelter yourself from variation, the less capable your body becomes of handling it, reinforcing reliance on artificial systems.

The problem is worst when your cocoon follows you everywhere. I grew up in Saudi Arabia, where daily life involved moving between air-conditioned villas, cars, schools, offices, and malls. I experienced the outdoors the way a fish in an aquarium sees your living room: through a thick sheet of glass, in a tightly controlled environment. It was a textbook worst-case scenario, though my younger self had no complaints.

Given my low thermal tolerance, I became very vocal every summer when we visited family in Khartoum, the capital of Sudan. While my grandma's village had ample opportunities for adaptive behaviours, city folk have limited access to well-shaded yards. We had to use the house in mixed mode simply because there wasn't an AC unit in every room, and you could not run them continuously. Sometimes this was due to power cuts; other times it was down to disapproving glares from your uncle, your aunt, and occasionally your neighbour.

The evaporative coolers we relied on are the Temu version of air conditioning, so temperatures rarely dropped below 30C. To make things worse, evaporative coolers work by increasing humidity to cool dry desert air, so after a while, the space became so humid it felt like you needed gills to breathe. These limitations acted as a built-in deterrent to overconsumption.

This thermal diversity that I unwillingly participated in helps explain why occupants in mixed-mode buildings tend to have a higher thermal tolerance than those in fully air-conditioned spaces, but a lower tolerance than occupants of naturally ventilated buildings.

Mixed-mode buildings sit awkwardly in between. While we have a general sense of their comfort range, the precise boundaries are far harder to define. Designing for mixedmode comfort, particularly in multi-generational homes, often feels like cooking from a recipe with no quantities: something only a seasoned grandmother, or perhaps a seasoned researcher, can reliably pull off.

With each UK summer now described as “record-breaking” and AC becoming more common, it is important to understand not only how buildings perform in heatwaves, but also how people will actually use them.

Well-designed homes, such as passive house buildings, can function effectively in mixed mode. Shaded, well-sized windows can be relied on most of the time. When it becomes too hot outside, occupants can close the windows and rely on low flow rates from mechanical systems, with or without cooling. High insulation levels and low air infiltration further limit heat gains.

The challenge, of course, is behaviour. How do you stop people from turning a house into an oversized fridge? London councils have a few tricks up their sleeve to make up for any lack of surveillance-by-elders. One is the cooling hierarchy, which prioritises small cooling modules attached to mechanical ventilation with heat recovery (MVHR) systems, sometimes called 'temperature lopping' units. Their cooling capacity is intentionally limited, just enough to take the edge off, much like my childhood evaporative coolers. Another approach goes beyond politely “recommending higher setpoints,” which is about as effective as a "drink responsibly" poster in an underground nightclub. Camden Council, for example, makes setpoint limits part of its policy and planning conditions.

Yet the same question remains. How do you, technologically speaking, stop occupants from cranking the dial down to arctic conditions? Do you hide the thermostat behind a painting?

Policing from higher powers, be it governments or grandpas, is not the silver bullet for maintaining comfort without overwhelming power grids. While my working days are spent analysing comfort in the UK (usually involving generous amounts of TM59), my evenings and weekends are dedicated to exploring global thermal comfort through my volunteer work with ARC (Architecture for Resilient Communities). I hope to bring you along as we dive into academic rabbit holes, extract the useful insights, and translate them into something your average Joe, Julius, or Jamal can apply at home. After all, comfort is not just about energy labels and tick boxes. It is about people, and how they live in the spaces we create.