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

In south London, a 1960s ex-council house is defying the summer heat, remaining remarkably cool despite external temperatures reaching 35C, all without the aid of air conditioning. The homeowner, Marion Baeli, an architect, has spent over a decade adapting her home to cope with increasingly warmer British summers, which are predicted to reach 40C.

Baeli compares her home's performance to a well-insulated flask, emphasizing the importance of sealing it against the elements. During a recent heatwave, her house was 10C cooler than the outside temperature. She attributes this comfort to the Passivhaus standard, an international building certification developed in Germany about 35 years ago. This standard aims to maintain a constant internal temperature year-round by creating a highly sealed building envelope.

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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.

The retrofit process involved several key stages. Initially, draughty windows and poor insulation were addressed through insulating shared walls, flooring, and the roof. The work also focused on eliminating "thermal bridges" – areas where heat can easily transfer. Later, cavity brick walls were replaced with "thinner, super-insulated" timber-framed walls, and new triple-glazed windows were installed to further slow heat transfer. Crucially, the house was made airtight, necessitating a ventilation system to ensure a constant supply of fresh air.

These comprehensive measures work in tandem to prevent drastic temperature fluctuations, significantly reducing energy use. Baeli reports that in winter, a single radiator is now sufficient to heat her entire four-bedroom home across three floors, a testament to the effectiveness of the insulation and airtightness achieved through the Passivhaus principles.

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