Passivhaus Perspectives: Passivhaus and a warming climate

The last few years have seen a panoply of heat records broken worldwide, and in particular, on the continent from which the Passivhaus Standard emerged more than 30 years ago. Europe is one of the fastest warming areas in the world, at twice the global average, and this is translating into increasingly frequent extreme heat. An estimated 35,000 excess deaths occurred during 2026 alone, with higher numbers reported for 2022-2024 and of course widespread ecological and economic impacts.

Passivhaus Perspectives: Joel Callow, Beyond Carbon, Sept 2026 2026

"Climate resilience should become a core part of the process of delivering the best buildings in the world. The basis in fundamental physics is already there; what's missing is a really challenging overheating standard that makes us ready for 2070 and beyond."

Dr Joel Callow, Founding Director, Beyond Carbon

So, it is getting hotter, which will come as no surprise to anyone remotely interested in our global climate. What does this mean for a low-energy building standard with its first buildings completed in 1990-1991? That year the global climate was around 0.45°C warmer than the historic baseline (1951-1980) and the CO₂ concentration averaged 354 parts per million. For 2025, those figures are 1.19°C and 426ppm respectively. A changed world and a changed climate.

2026 The warmest summer for western Europe - image credit CS3 Bulletin

C3S Bulletin PR 202608 - warmest summer for western Europe

Beyond Carbon recently merged with PHT member Delta Q to become a single Passivhaus Trust Patron member and one of the largest Passivhaus consultancies in the UK. Ultimately, we’ve increased capacity to deliver the buildings the climate crisis demands. But, we regularly encounter project stakeholders who mistakenly think Passivhaus windows can’t be opened, or that mechanical cooling is banned. Some claim that Passivhaus makes overheating worse, or that at least it is not relevant in the UK now that we have to consider overheating so carefully.

Building physics gets it right

What hasn’t changed since 1990 is building physics. Thankfully, heat is still heat, and heat transfer still occur in the same ways. The data and science that Wolfgang Feist and colleagues built on as they set up the Passive House Institut (PHI) in Darmstadt in 1996 is unchanged. How we apply the rules of physics to the complex challengesof first designing, then constructing, then operating buildings is a different question.

I’ll confess that for much of my earlier career I focused too much on winter heating efficiency and associated carbon emissions and didn’t give as much thought to overheating and summer thermal comfort as perhaps I should have. This probably mirrors the industry at large in the UK to some extent, and it is notable that the first UK regulation to govern overheating only arrived in 2022 in the form of Part O. For the last 10-15 years however, I have been more concerned about overheating than any other single built environment issue.

To establish if Passivhaus is helping or hindering efforts to avoid overheating we need to separate out poor practice and design from the standards used by designers. It is difficult but not impossible to design a Passivhaus that overheats – for example by gaming the winter heat demand by having large south-facing windows. The standard has built-in safeguards including an overheating check and an expert Certifier reviewing the work of the design and construction teams.

We need to recognise that both Passivhaus and the UKs nationally recognised CIBSE TM59 methodology for evaluation of overheating risk are based on agreed climate files and that even the most skilled practitioners are limited to the available files. Both standards default to present-day climates very unlike those expected in 2070, but CIBSE offers the advantage of future files being optionally available, albeit at considerable cost to users. Passivhaus Trust guidance issued in 2023, directs complex Passivhaus projects in the UK to TM59 or TM52 to supplement overheating assessment. The Passivhaus Trust & CIBSE are collaborating on active cooling research, due to be published next year.

The big question

However, our question here is whether or not the standard is fundamentally misaligned with a warming climate, not whether a single project could apply the standard poorly and overheat. I have two answers to this key question:

No. The UK climate continues to be dominated in most buildings most of the time by the energy required to maintain winter comfort. While summer comfort energy will increase as buildings require mechanical cooling, there is no basis for concluding that winter heating no longer matters or is subordinate to cooling.
No, but the current overheating checks within the standard are limited in scope and no longer aligned with the warmer climate extremes we are now experiencing in Europe. In the UK we use guidance from the UK Certifiers Circle to navigate dynamic thermal modelling to ensure summer comfort. This works when applied by experienced designers, but the integral checks should be updated to suit our new and emerging climate here in the UK and elsewhere.

A recent paper by researchers at the University of Oxford evaluated exactly this issue for the recently completed Schwarzman Centre for the Humanities which is certified to the Passivhaus standard. They tested the models used for the design of the building under a wide variety of climate futures through to the 2070s. They concluded that to ensure Passivhaus was ready for future climates, complex dynamic simulations should be standard for complex buildings, tested against the best available high temperature climate files. They also note a prediction of ~20% reduction in heat energy by 2070 for their case study, not enough to offset the increased cooling energy required at that point, nor enough to cease to focus on heating demand reduction as a design priority.

Bollo Lane by Barratt London

AAM, Bollo Lane, image credit Barratt London

When Beyond Carbon evaluated one of our recent Passivhaus projects, we found that the energy and comfort optimal g-value for glazing for the building will have dropped from 0.50 today to 0.35 in 2050 when the next replacement cycle for glazing occurs. But Passivhaus still outperforms at that point, just with different glazing.

The best designers today already test buildings extensively against future climate, but at present it is effectively optional, and is certainly not yet central to the process of Passivhaus Certification. Passivhaus helps designers of UK buildings focus on the underlying physics and my view is that climate resilience should become a core part of the process of delivering the best buildings in the world. The basis in fundamental physics is already there: careful building envelope optimisation, high-performance components, and the much vaunted genuine ‘golden thread’ of quality that construction is currently seeking.

What is missing is a really challenging overheating standard that makes us ready for 2070 and beyond. At Beyond Carbon we will continue to push the limits on climate resilience in UK Passivhaus design, but let’s sort the doubters once and for all, ensuring it is only possible to design a climate resilient Passivhaus Certified project.

Pick up the resilience to heatwaves conversation with Joel and other speakers at this year's UK Passivhaus Conference 18 November 2026, at the QEII Centre in London and online.

UK Passivhaus Conference 2026