Is overheating something your homes are actually prepared for? As UK summers get hotter, keeping tenants cool and comfortable is fast becoming as pressing a concern as damp and mould – with real consequences for health, wellbeing and building performance, whether you’re a landlord, housing provider or resident.
This podcast, recorded with the Chartered Institute of Housing (CIH), features our Managing Director, Jack Allen, in conversation with CIH policy manager Matthew Scott, covering the human cost of overheating, who’s most at risk and why, and the practical steps that can be taken to address it – across both existing homes and new builds.
In this podcast, you’ll learn:
- Why overheating has become a serious health risk, not just a comfort issue
- Which building types – and which residents – are most vulnerable, and why
- Where Part O succeeds and where it still falls genuinely short
- Practical mitigation options for both existing homes and new builds
- How PAS 2035 and Passivhaus both offer a route to tackling overheating
🎧 Listen to the podcast:
Why Overheating is a Growing Crisis
The podcast covered several crucial aspects of the overheating problem, moving beyond simple temperature readings to look at what’s actually driving the risk:
The Alarming Human Cost
Matthew and Jack cited a stark figure: 4,500 excess deaths recorded during the 2022 heatwave alone. Recent research cited in the discussion suggests it’s set to get worse still – with as much as 90% of UK housing stock projected to suffer from overheating by the 2030s. Beyond fatalities, overheating severely affects mental health, sleep, and overall productivity, making homes uncomfortable and unhealthy living spaces.
Identifying Building Vulnerabilities
Certain building types are inherently more susceptible to overheating. The discussion pinpointed:
- High-rise flats: Often exposed to more solar gain due to less shading, and prone to the “stack effect” where warm air rises, making upper floors significantly hotter. Many also run communal heating systems year-round for hot water – if these aren’t properly insulated, they can end up acting like a central heating system that never switches off.
- Single-aspect properties: Lacking the cross-ventilation needed to purge hot air, particularly on the still, windless days that tend to accompany the hottest weather.
- Extensive glazing: While offering views, large south- or west-facing windows can become heat traps without adequate shading.
- Urban Heat Islands: Cities are typically around 2°C warmer than surrounding rural areas, but this can reach as much as 10°C on a hot summer’s day – all that concrete and tarmac radiating heat back out, long after the sun’s gone down.
It’s also not just a London problem. While the South East sees the highest solar radiance, the discussion noted genuine overheating risk in south- or west-facing apartments as far afield as Wales – geography alone doesn’t rule a property out.
Who’s Actually Most at Risk
Overheating risk isn’t just about the building – it’s just as much about who lives in it. Older residents with reduced mobility often can’t simply leave a hot flat to cool off elsewhere, and existing cardiovascular or respiratory conditions can be seriously exacerbated by heat stress. The impact isn’t only physical: sleep disruption, reduced concentration and mental health strain all follow from a home that won’t cool down – including, as the podcast highlighted, children trying to study for GCSEs in a bedroom that won’t drop below 28°C. Because the worst-affected housing tends to be denser, cheaper social and private rented stock with the least choice attached to it, the health burden of overheating falls disproportionately on lower socioeconomic groups.
Our ‘Whole Life Cycle’ Approach
At Building Energy Experts, our guiding principle is that energy performance needs to be considered at every phase of a building’s life. The podcast underscored this philosophy, from initial planning (asking if a building is even necessary, or if repurposing an existing structure is more sustainable) to material choices (e.g. timber vs. carbon-intensive concrete), operational performance, and eventual end-of-life recycling. Climate change demands a holistic view that moves beyond isolated design decisions.
Navigating Part O: Strengths and Limitations
Part O of the Building Regulations is a welcome step, setting technical definitions for overheating (not exceeding 28°C for more than 1% of occupied hours in normal rooms). But the discussion was candid about how far it currently falls short in practice:
- It only applies to new-build. The vast majority of existing UK homes – the ones actually experiencing today’s overheating problems – sit entirely outside its scope.
- It doesn’t mandate shading. Compliance can be achieved by adjusting a window’s G-value or adding mechanical ventilation, without a scheme ever genuinely engaging with passive design.
- There’s no verification that specified measures actually get installed. The only sustainability-related test consistently enforced on new-build is the air test – nobody checks, as standard, that the overheating mitigation specified at planning stage has actually made it onto site.
- Planning friction discourages the best fix. External shading is the most effective way to stop solar gain reaching a building, but retrofitting it onto an already-consented scheme often means reopening a lengthy planning process – and some conservation officers reject shading outright as “not in keeping” with an area, despite shutters and awnings having been the historical norm on British buildings for centuries.
That combination of gaps and friction is part of why some developers reach for mechanical cooling instead of a passive fix – it’s simpler to install, and doesn’t carry the same planning risk, even where it isn’t the most sustainable answer.
For guidance that goes beyond the base compliance check, CIBSE (the Chartered Institution of Building Services Engineers) publishes the technical modelling methodology – TM59 – that underpins genuine overheating risk assessment, rather than a design that simply clears the regulatory bar.
Practical Solutions for Overheating Mitigation
The conversation set out practical strategies for both existing and new properties.
Overheating mitigation for existing homes:
Start with resident engagement – questionnaires and direct conversation reveal how a home is actually being used, alongside any monitoring data available. Blue-green infrastructure helps at a microclimatic scale: green roofs and walls, and even fast-growing deciduous trees like birch, which shade a building in summer while still letting winter sun through. Continuous mechanical ventilation keeps air moving without relying on residents leaving windows open overnight – often unrealistic given security concerns – and has the added benefit of tackling condensation and mould. External shading (shutters, overhangs, brise soleil) remains the most effective single measure, and can be modelled accurately in advance of installation; setting a window back slightly into its reveal adds shading while also reducing thermal bridging, solving two problems at once.
Fire-safety recladding presents a genuinely overlooked opportunity here. Buildings currently being recladded to remove dangerous cladding could have shading devices designed into the new façade at the same time – but because extending beyond a building’s existing envelope typically triggers a fresh planning application, this is very often skipped. Given most local authorities have declared a climate emergency, there’s a reasonable argument this already carries some legal weight, not just a “nice to have.”
Heritage restrictions add a further wrinkle, since the standard external shading fixes aren’t always available. We’ve seen this constraint play out directly on period properties in London, where a listed building’s protected windows and façade ruled out the usual passive toolkit entirely:
Where sensor data already exists – increasingly a requirement under Warm Homes Wave 3‘s monitoring and evaluation rules – it’s worth checking directly whether any properties are breaching CIBSE’s thermal comfort thresholds, and treating that as a priority to address rather than a data point to file away.
Overheating mitigation for new builds:
Prioritise thoughtful orientation, design for effective cross-ventilation, manage glazing ratios, and integrate advanced ventilation systems like Mechanical Ventilation with Heat Recovery (MVHR) from the outset – increasingly important as airtightness requirements tighten further under the Future Homes Standard.
The PAS 2035 Opportunity
Retrofitting properties presents a significant chance to address overheating. The current wave of PAS 2035 requires a proper ventilation assessment – tested with a calibrated anemometer or balometer, not assumed – before any measure affecting the building’s fabric can go ahead, precisely to avoid retrofit work inadvertently making overheating worse. An archetypal approach helps at scale too: grouping large property portfolios into a manageable number of archetypes, then using overheating risk assessments on the highest-risk examples of each to work through where a genuine problem exists, without needing to test every single property individually.
Embracing the Passivhaus Standard
The podcast concluded with an exploration of Passivhaus, a rigorous building standard developed in Germany around 30 years ago. Jack explained how Passivhaus homes require minimal heating thanks to exceptional airtightness, a highly insulated fabric and MVHR systems that recover around 90% of the heat from extracted air. Shading is designed in deliberately too – positioned to block high summer sun while still letting in the lower winter sun, so the same design principle helps a home stay warm in winter and cool in summer.
Jack pointed to a real-world example from his own work: an air test on a Passivhaus Premium property in the Cotswolds, later featured on Grand Designs, which produces around four times more energy than it uses. It isn’t only a one-off luxury build approach, either – Exeter has been delivering social housing to Passivhaus standard for several years, with a marked improvement in both resident health and heating costs. Done properly, it’s a powerful standard; done as insulation and airtight windows alone, without the shading, ventilation and certification that make it work as a system, it can just as easily create an airtight home with too much solar gain and not enough ventilation to cope.
Q&A Highlights
Closing out the discussion, Matthew asked Jack the practical question a lot of listeners were likely thinking: if you’re a housing provider and want to start tackling overheating tomorrow morning, where do you begin? Jack’s answer:
Get to grips with your building stock and how it performs. Conduct risk assessments. Explore different funding options. Collaborate with experts to implement effective solutions. And advocate for stronger building regulations, and support any initiatives that prioritise resident wellbeing.
— Jack Allen, Managing Director & Founder, Building Energy Experts
If you’d like to go deeper on this, we also run a specialised Part O Overheating CPD session covering compliance pathways and practical design strategies for housing developers, architects and housing professionals – learn more and book here.
What’s Next?
Overheating is a solvable problem – but only if it’s designed for from the outset, in existing stock as well as new build.
We carry out overheating risk assessments and Part O compliance calculations for new-build and existing homes across the UK.
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