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

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 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 beat the heat.

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

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 they consume up to 90% less energy than typical houses.

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 constantly kept fresh.

These measures work to prevent the temperature fluctuating inside the house – in winter and summer – so less energy is used.

In the colder months, one radiator is now sufficient to heat Baeli’s four-bedroom home over three floor she says, because heat is 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.

Baeli’s priciest 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.

She says, like most people, she could not pay for everything at once and so 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.