How Passivhaus buildings stayed cool during the June heatwave

June 2026 will be remembered for more than broken temperature records. Red heat warnings were issued across parts of England, schools closed as classrooms became too hot to use safely, and conversations about overheating shifted from future climate projections to present-day reality.

Against that backdrop, the Passivhaus Open Days took on an unexpected significance. Some tours were postponed, others scaled back, and a handful cancelled altogether as temperatures climbed. Yet across the UK, lots of visitors still stepped inside Passivhaus and EnerPHit buildings, not to hear theories about climate resilience, but to experience it for themselves. What they found was remarkably consistent.

Buildings designed for tomorrow's climate

While more than 1,000 schools across England and Wales closed during the June heatwave, Buntingford First School in Hertfordshire remained open, as reported by the BBC. Designed to minimise overheating through careful orientation, external shading, ventilation and high-performance building fabric, the school demonstrated that keeping buildings comfortable during extreme weather isn't a matter of luck, it's a matter of design.

Buntingford First School, credit Morgan Sindall Construction

This is what building for the next generation looks like, designed to perform in today's and tomorrow's climate, not yesterday's."

John Gilbert Architects via Linkedin

Stepping inside summer comfort

Across this year's Open Days, visitors toured everything from self-build homes and retrofits to affordable housing, schools and a leisure centre. Whatever the building type, the conversations were strikingly similar. Rather than asking whether Passivhaus worked, visitors wanted to understand how these buildings remained so comfortable while outdoor temperatures climbed into the thirties.

At Wingspan Walk in Haringey, visitors commented on how ordinary comfort felt. Balconies, carefully designed shading and thoughtful layouts helped keep homes comfortable during the heat, while conversations with residents reinforced that Passivhaus is about much more than energy performance.

Passivhaus is not simply an energy standard but a commitment to delivering healthier, more comfortable homes with lower running costs for residents."

Wingspan Walk Open Days attendee via Linkedin

Meanwhile, at Dundashill in Glasgow, 90 affordable Passivhaus homes built on the site of a former whisky distillery, one visitor expected to come away talking about technical details. Instead, it was the residents who made the biggest impression.

"I expected the technical part to be the interesting bit. It wasn't. The interesting bit was talking to the people living there. We talk about Passivhaus as a cost or a standard to hit. The residents talk about it as a flat that's finally warm, comfortable and cheap to run."

Not every stop was residential. At Eclipse Leisure Centre, a tour delayed a fortnight by the heatwave finally went ahead in a comparatively cool 32°C.

“Passivhaus Designer and MEP lead, Jason Fitzsimmon, had really set the bar high for Open Days by hosting a briefing webinar the day before alongside colleagues from contractor Wilmott Dixon. Heavy on the technical details, to the delight of the tour group of all architects, we got an outstanding insight into the complexities of delivering the UK’s first certified combined ‘wet and dry’ sports centre. As well as experiencing the showstopper spaces of the pool hall, sports hall, dance studio and gymnasium, the tour not surprisingly peaked with a lot of time in windowless plant rooms looking at pipes, filters and (well-insulated) ducts. Five stars!”

Mark Elton, Passivhaus Designer, Awen Design

Eclipse Leisure Centre Open Days 2026

The questions everyone was asking

One thing became increasingly clear as the weekend unfolded. This year's visitors weren't just curious about airtightness or certification. They wanted to know how to keep buildings cool.

Hosts across the country reported that questions about overheating came up more often than ever before.

How do you stop solar gain?
Do you still open the windows?
Do you need air conditioning?
What happens during a heatwave?

Get the full picture: explore the Learning Hub's summer comfort resources.

At Parklands EnerPHit, hosts noticed that discussions around overheating strategies dominated conversations in a way they hadn't seen in previous years. "A recurring theme from visitors was the noticeable difference in air quality and comfort levels inside the house. Given the warm weather outside, many commented on how much cooler and fresher the indoor environment felt."

What self-builders are doing differently

For those planning their own projects, the Open Days became an opportunity to see summer comfort in action rather than on paper. At Warkworth in Northumberland, hosts Gilly, Anita, Cath and Geoff welcomed visitors into three self-built Passivhaus homes.

Questions quickly moved beyond energy bills towards practical design decisions.

Why are the internal doorways full height?
How does air move around the house?
Why are some rooms connected by large sliding walls?

These weren't expensive technologies or complicated systems. They were thoughtful design decisions that improve comfort throughout the year while allowing natural ventilation to work effectively during warmer weather.

Two Passive Houses & Godwit House site tours

Visitors also wanted to know about running costs. The answer surprised many. Two of the homes remain in net profit after more than a year of occupation, even after charging an electric vehicle.

Across many of the self-build projects, the same principles appeared again and again:

External shading before mechanical cooling
High-performance insulation and airtightness
Carefully considered glazing
Night-time purge ventilation
Simple, robust design that works with the climate rather than against it

Summer comfort wasn't being achieved through complex technology. It had been designed into the building from the beginning.

Retrofitting for hotter summers

Comfortable buildings aren't limited to new build. Across the country, retrofit projects demonstrated how existing homes can also be transformed to cope with increasingly warm summers.

Architect Paul Testa opened his own retrofit home in Sheffield during one of the hottest periods of June. Reflecting afterwards, he said:

"Retrofit isn't just for winter comfort and reduced energy bills. On one of the hottest June days on record, the outside temperature climbed to well above 30 degrees whilst inside we kept the ground floor to about 25. Retrofit really should be about delight as well as the practical tasks of comfort, performance and health."

The message was echoed elsewhere. Improving insulation, reducing unwanted solar gain, introducing effective shading and developing better ventilation strategies can significantly improve summer comfort as well as winter performance.

As our climate changes, retrofit is no longer simply about reducing heating demand. It is increasingly about creating buildings that remain healthy and comfortable all year round.

Footgate Close, credit HEM Architects

What this summer proved

The science behind Passivhaus hasn't changed. The same building fabric that keeps warmth inside during winter also helps prevent unwanted heat entering during summer. Combined with good orientation, effective shading and appropriate ventilation, these principles create buildings that remain comfortable throughout the year.

What's changed is the weather doing the demonstrating for us. During the June heatwave, visitors didn't simply hear about summer comfort. They experienced it.

The Open Days couldn't have happened at a better time, as we increasingly see the need for much better designed houses which are built to regulate temperatures."

Open Days attendee

Where we go from here

This summer's heat isn't a one-off. It's the climate UK buildings now need to be designed for, and the question facing the sector isn't whether Passivhaus works, but how to deliver it at the pace and scale the country needs.

We'll be continuing this conversation at the UK Passivhaus Conference, returning to London for the first time in almost a decade on 18 November 2026 at the Queen Elizabeth II Centre. With climate resilience at the heart of this year's programme, speakers will explore how we design and retrofit buildings that remain comfortable, healthy and affordable as our climate continues to change.

Can you open your doors?

Passivhaus site visits remain one of the most powerful tools for accelerating understanding and adoption of high-performance building. If you’re working on a certified or in-progress Passivhaus or Passivhaus Retrofit project, we’d love for you to get involved in future editions. Registration for the Winter 2026 Passivhaus Open Days, running 13 - 15 November , will open soon.