How this 1960s ex-council house is managing to stay cool without air con

A terraced house with light grey brick walls, a series of windows on the upper floor, two windows and a yellow door on the ground. There is a garden path and bushes on the side

Image source, BBC/Kevin ChurchByMiho TanakaSenior climate and science journalist

Published3 minutes ago

After five heatwaves and plenty of advice on how to stay safe in what is set to become the UK's hottest summer on record, many people continue to find it a challenge to stay cool - particularly in their homes.

This is perhaps no surprise. More than half of homes, external in the UK are already at risk of overheating and at current rates of climate change this will rise to 92% by 2050 if we do not adapt.

But in south London, on a 35C day, one 1960s ex-council house, with no air-conditioning is managing to stay remarkably cool.

Marion Baeli's home is one of many across the UK being adapted for warmer - maybe even 40C - British summers.

A woman in a blue long sleeved top sits on a stool at her kitchen counter. On the counter is a vase with some small pink flowers. The background is blurred but some plants on the windowsill are visible behind her, and behind her right should is a glass window set into the wall.

Image source, BBC/Kevin ChurchImage caption,

Marion Baeli has been adapting her home over more than a decade to cope with rising heat

As well as being the homeowner, Baeli is an architect - and she compares her house to a well-insulated flask.

"You wouldn't put holes in your flask if you wanted to keep the ice in. You'd close the cap and make sure it is firmly twisted on. It's the same in this house."

When the BBC visit Baeli on the hottest day of this summer's fourth heatwave, her house is 10C cooler than outside.

"It feels like you have air-conditioning [inside the house] but you haven't. This is the beauty of the Passivhaus standard," she explains.

Passivhaus is an international building standard that was developed around 35 years ago in Germany. The concept is simple: design your home to keep the temperature constant at all times, by effectively sealing it against the elements.

It is estimated, external they consume up to 90% less energy than typical houses.

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Figure caption,

The homes being adapted to cope with 40C British summers

When the Baeli family moved in 10 years ago, their house had draughty PVC double-glazed windows with little insulation - they struggled to keep warm in the winter and overheated in the summer.

The most disruptive part of the retrofit work was carried out first, and included the insulation of shared walls, flooring and the roof.

The work also focused on getting rid of "thermal bridges" - which are parts of the home where heat is exchanged rapidly, such as where the insulation is broken up between rafters in your home.

Two years later, during the second phase of the works some cavity brick walls were replaced with "thinner, super-insulated" timber-framed walls, while new triple-glazed windows were installed to slow down the transfer of heat from outside.

With the house now air-tight, a ventilation system went in to ensure that the air inside the house was kept constantly fresh.

Diagram showing a cross-section of a Passivhaus home showing high insulation, airtight construction, high-performance windows, minimal thermal bridging, and a heat-recovery ventilation system that brings in fresh air and removes exhaust air efficiently.

All of these measures work to prevent the temperature fluctuating inside the house - in winter and summer - so much less energy is used.

In the colder months, one radiator is now sufficient to heat Baeli's entire four-bedroom home over three floor she says, because heat is now not being lost.

Baeli estimates energy demand in her retrofitted house has gone down by 88%, giving her a yearly saving of nearly £750 on her bills.

The cost of retrofitting your home

But the Passivhaus Trust - for which Baeli is a non-executive director - acknowledges retrofitting your home to this standard is "expensive".

The total cost of the work Baeli carried out on her house was around £80,000, not including any additional costs for architectural work.

The most expensive purchase, she calculates, were the windows at £30,000, while one of the cheapest measures was making the whole house airtight, which cost £5,000.

Baeli says, like most people, she could not fund everything at once and decided to carry out the work in stages over ten years to spread the cost.

Although the house does prevent heat entering the home, it does need cooler air to start with.

As well as closing the windows and curtains during the day, Baeli says you need to ensure that "the sun doesn't hit the glass and create the glasshouse effect - to stop your home from overheating".

Outside in her garden she shows us dust sheets which have been hung up to cover the windows.

But if outdoor temperatures do not fall at night, as happened once during the June heatwave this summer, Baeli's house can remain hot. On that June evening, the nighttime temperatures was 27C so the house temperature remained at 27C, the highest Baeli has ever recorded in her home.

If such tropical nights occur again in the future, she says she might need to use air conditioning for a limited time to cool the house and then the Passivhaus measures can maintain that temperature.

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A composite image showing two pictures of the back of a house during the night (right) and during the day (left). The house has wooden panels across the top and two windows, on the ground floor of the house is a large glass patio door. In the day picture it is covered by a sheet, in the night picture this is pulled back and the door and windows are open. In the day picture part of the garden with a white table and chairs, and pink flowered foliage can be seen

Image source, Marion Baeli/BBCImage caption,

Marion Baeli covers all the windows of her home during the day and opens them at night

Including Passivhaus measures in a building's initial design is much cheaper than trying to add them retrospectively.

According to the Passivhaus Trust, the additional construction cost associated with building to the standard range from 2% extra for flats to 5% for a semi-detached house.

In March, the Future Homes Standard will come into force which will set higher building and energy performance requirements for new homes in England - taking the regulations closer to the Passivhaus standards.

In Scotland, consultations for a new set of building regulations "to deliver an equivalent to the Passivhaus standard" are ongoing, and the new guidelines could be published later next year.

Meanwhile, one of the country's largest housebuilders, Barratt Redrow has decided to build a block of affordable and private flats in west London to the standard - complete with heat pumps to heat and cool the properties.

Oliver Novakovic, the company's technical and innovation director, explains that the 900-apartment Bollo Lane development is an experiment to "future-proof" the company and stay ahead of "continually increasing" regulations, even though it will cost more to apply the standard.

Around 1% of all new homes in the country are now built to the voluntary standard, and the Passivhaus Trust estimates this could grow to 10% in the next decade.

But building these types of new homes can be challenging. In April, City of York Council struggled to attract interest from construction firms to build 315 homes to the standard due to market conditions and the complexity of building to such specifications.

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Even if new Passivhaus homes can be constructed, it is estimated that 80% of the UK housing stock in 2050 already exists today, so millions of homes will have to be retrofitted to cope with the rising heat.

There was a previous government support system to help those in low-income households install insulation and other measures, but after reports of botched work it will close later this year. The date when the replacement scheme will begin has not been announced.

Jay Morton, incoming President Elect of the Royal Institute of British Architects, told BBC Radio 4's Rare Earth programme that cost can be a barrier for many homeowners, but that even implementing half these measures can make a significant difference.

"You won't necessarily be able to insulate every single wall," Morton says, "but by even doing the 50% best is actually massive in terms of energy bills."

For those in homes which are not built to the Passivhaus standard, Baeli offers one simple piece of advice - shade your windows.

"It doesn't need to be sophisticated," she says, "whatever you can do, just absolutely shade your windows and you will definitely feel the difference in the summer months."