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

After five heatwaves and numerous proposals on how to stay safe during what is regarded as the UK’s hottest summer on record, many people continue to search for ways to keep cool, particularly in their own homes. In south London, on a day when the temperature reached 35°C, a 1960s former council house without any air‑conditioning remains remarkably cool. Marion Baeli’s property is one of many across the UK being adapted for warmer conditions, potentially reaching 40°C in future British summers. As the homeowner and an architect, Baeli likens her house to a well‑insulated flask. “You wouldn't enactment holes successful your flask if you wanted to support the crystal in. You'd adjacent the headdress and marque definite it is firmly twisted on. It's the aforesaid successful this house,” she says. When the BBC visited Baeli during the hottest day of this summer’s fourth heatwave, the interior of her home was 10 °C cooler than outside. “It feels similar you person air-conditioning [inside the house] but you haven't. This is the quality of the Passivhaus standard,” she explains. Passivhaus is an international building standard developed roughly 35 years ago in Germany. Its principle is simple: design a dwelling to keep indoor temperature steady at all times by effectively sealing it against the elements. It is estimated that such buildings consume up to 90 % less energy than typical houses. When the Baeli family moved in ten years ago, the house had draughty PVC double‑glazed windows with minimal insulation; it struggled to stay warm in winter and overheated in summer. The most disruptive part of the retrofit was carried out first, involving insulation of shared walls, the floor and the roof. The work also focused on eliminating “thermal bridges”—points where heat is transferred quickly, such as where insulation is interrupted between rafters. Two years later, during the second phase, some cavity brick walls were replaced with thinner, super‑insulated timber‑framed walls, and new triple‑glazed windows were installed to slow the transfer of heat from outside. Once the house became airtight, a ventilation strategy was introduced to keep the indoor air continuously fresh. All of these measures aim to prevent indoor temperature fluctuations in both winter and summer, thereby reducing energy use. In the colder months, a single radiator is now sufficient to heat Baeli’s four‑bedroom home across three levels, she says, because heat is no longer being lost. Baeli estimates that energy demand in her retrofitted home has fallen by 88 %, saving her roughly £750 a year on bills. The Passivhaus Trust, for which Baeli serves as a non‑executive director, acknowledges that retrofitting to this standard is “expensive”. The total cost of the work Baeli undertook on her house was about £80,000, not including any additional fees for architectural services. She calculates that the most expensive item was the windows at £30,000, while one of the cheapest measures—making the whole house airtight—cost £5,000. Baeli says, like most people, she could not afford to pay everything at once and chose to carry out the work in stages over ten years to spread the expense. Although the house prevents heat from entering, it still requires cooler air to begin with. As well as closing windows and curtains during the day, Baeli advises that you must ensure “the prima doesn't deed the solid and make the glasshouse effect - to halt your location from overheating”. Outside her garden she displays sheets that have been hung up to shade the windows. If nighttime temperatures do not drop—as happened during the June heatwave this summer—the interior can remain hot. On that June evening the night‑time temperature was 27 °C, so the indoor temperature stayed at 27 °C, the highest Baeli has ever recorded in her home. Should such tropical nights recur in the future, she says she might need to use air‑conditioning for a limited period to cool the house, after which the Passivhaus measures could maintain that temperature. Incorporating Passivhaus features into a building’s original design is far cheaper than adding them later. According to the Passivhaus Trust, the extra construction cost associated with meeting the standard ranges from 2 % more for flats to 5 % more for a semi‑detached house. In March the Future Homes Standard will come into force, which will impose higher building and energy performance requirements for new homes in England, bringing regulations closer to Passivhaus levels. In Scotland, consultations on a new set of building regulations “to present an equivalent to the Passivhaus standard” are ongoing