For several years, housing providers have had to balance major demands relating to building safety, decarbonisation, asset management, damp and mould, and the long-term condition of ageing homes. Increasingly, however, another issue is demanding attention alongside them: overheating. As extreme heat becomes more common and impacts residents’ health and wellbeing, housing providers are being forced to rethink how homes are designed, retrofitted, managed and occupied.

A recent roundtable convened by CIOB in collaboration with the Chartered Institute of Housing (CIH) and the National Housing Federation (NHF) brought together social housing providers, developers, consultants and sector representatives to discuss how organisations are responding. Held under the Chatham House Rule, the discussion revealed a sector that increasingly recognises overheating as a significant risk but is still developing its response.

The issue sits within a wider policy context. Climate projections suggest that periods of extreme heat will become more frequent and more intense across the UK. Evidence from recent heatwaves has highlighted links between high temperatures and increased illness and mortality, particularly among older people and those with existing health conditions. 

The policy response is evolving. England introduced Part O of the Building Regulations and Approved Document O to address overheating in new homes. Other UK nations are taking different approaches and are at different stages of development. At the same time, overheating intersects with wider agendas around retrofit, net zero, building safety, public health and climate adaptation.

What emerged from the roundtable was a clear sense that overheating is no longer being viewed as a distant future problem. For many housing providers, it has become a clear and present operational challenge.

A risk that extends across entire portfolios

A striking feature of the discussion was the extent to which organisations are beginning to assess overheating systematically across their homes.

Several participants described using ‘archetype’ modelling to understand how different categories of homes are likely to perform under current and future climate conditions. Rather than assessing individual properties, organisations are grouping homes with similar characteristics and modelling their likely behaviour under projected future weather scenarios.

This approach is helping landlords identify which parts of their portfolio are most vulnerable and where limited investment resources should be targeted.

Some organisations have already reached sobering conclusions. One participant reported projections suggesting that almost all their homes could experience overheating by 2050. Others described overheating as a formal strategic risk that now sits alongside more established concerns such as building safety and asset condition.

The discussion also highlighted concerns about resident vulnerability. Older people, those with long-term health conditions, and residents with limited ability to adapt their homes or behaviour were repeatedly identified as groups at particular risk. Later-living schemes emerged as an area of immediate concern, with some organisations already introducing temporary cooling measures in communal areas during hot weather.

One participant contrasted overheating with flooding. Whereas flood risk is often concentrated in specific locations, overheating has the potential to affect almost every housing provider and almost every part of the country. That raises important questions about scale, prioritisation and preparedness.

When decarbonisation and adaptation collide

The discussion highlighted the way that overheating interacts with decarbonisation. Many contributors described previous situations where measures intended to improve energy performance resulted in unforeseen negative consequences for how buildings behaved during hot weather. Nobody questioned the importance of reducing carbon emissions. However, participants repeatedly stressed that homes must perform well in summer as well as winter.

One participant described a retrofit project where insulation measures introduced to meet energy performance targets subsequently increased overheating risk, requiring solar-control film to be added to windows as a post-completion corrective measure. Another noted that homes undergoing whole-house retrofit programmes were becoming measurably warmer as a result of improvements to fabric performance without any strategy for cooling when thermal comfort thresholds were breached in warm weather.

Underlying these examples was a broader concern that policy, funding and assessment systems can sometimes focus heavily on reducing heating demand while paying insufficient attention to summer performance.

The discussion repeatedly returned to building physics. Thermal mass, ventilation, solar gain, orientation and insulation strategies all influence how homes behave during hot weather. Participants argued that two homes with similar energy performance certificates may perform very differently in practice depending on, for example, whether they have internal or external wall insulation.

Rather than presenting decarbonisation and overheating as competing objectives, contributors generally saw them as interconnected. The challenge, they suggested, is to ensure that climate mitigation and adaptation are considered together rather than as separate workstreams.

The complexity of existing homes

Although new-build housing featured prominently in the discussion, participants repeatedly emphasised that the greatest challenge lies within existing homes.

The diversity of social housing homes makes simple solutions difficult. Participants described managing everything from early twentieth-century non-traditional homes and solid-wall properties to high-rise towers, later-living schemes and relatively recent apartment developments.

Many organisations are dealing with housing that is 50, 75 or even 100 years old. Others highlighted the challenges that may be posed by historic system-built homes, conservation constraints, mixed-tenure estates and buildings where extensive retrofit work is technically possible but financially difficult to justify. One participant described effective retrofit costs exceeding £100,000 per dwelling in some cases because of underlying construction issues.

Building safety obligations add a further layer of complexity, with organisations already balancing major investment requirements associated with fire safety, structural remediation and decarbonisation. Overheating therefore enters a crowded field of competing priorities. This creates an asset-management challenge as much as a technical one. The question is therefore about how finite resources should be allocated across highly varied housing homes facing multiple demands.

The importance of getting design decisions right

If existing homes present the greatest challenge, participants were clear that overheating is often easiest to address at the beginning of a project and most expensive to address later.

Several participants described instances where overheating assessments had been undertaken late in the design process, leaving mechanical systems as the only viable solution. They had learnt from the experience, bringing overheating considerations into subsequent projects much earlier and focusing on passive factors such as window design, orientation, shading and ventilation from the outset.

Passivhaus principles featured prominently in the discussion. Participants argued that many of the design decisions associated with Passivhaus could also reduce overheating risk while delivering wider health and wellbeing benefits.

There was also criticism of design features perceived to contribute unnecessarily to overheating. Floor-to-ceiling glazing was repeatedly mentioned, particularly in apartment developments. Participants argued that extensive glazing can increase solar gain while providing limited practical benefit for residents. One described how 30-degree outdoor heat sent temperatures soaring to 48 degrees in a flat with floor-to-ceiling glazing, forcing its residents to retreat to a hotel.

At the same time, contributors acknowledged that achieving good outcomes is not always straightforward. Acoustic constraints, security requirements, fire safety considerations and planning expectations can all affect the viability of natural ventilation and other passive measures.

The implication was clear: overheating is often the result of decisions made long before anyone checks compliance. Yet making the right design decisions is only part of the challenge.

The contractor challenge: protecting intent through delivery

Participants also reflected on what they need from contractors and the wider supply chain. A recurring concern was the gap that can open up between design intent and what is ultimately delivered on site. Several participants reported monitoring contractors more closely than they had in the past, particularly on projects where specific thermal and environmental performance requirements are one of the intended outcomes.

Contributors highlighted the risk that overheating measures can be diluted through value engineering or lost amid the complexity of modern housing projects. Building safety requirements, energy performance targets, ventilation strategies and overheating mitigation measures must all be delivered simultaneously, often through extensive supply chains involving multiple subcontractors.

Participants argued that this places a premium on clear employer's requirements, early engagement with sustainability specialists and effective quality assurance during construction. Addressing overheating, they suggested, is as much a delivery challenge as it is a design challenge.

From passive measures to active cooling

Participants were clear that there is no single solution to overheating. They described a broad range of interventions, many of them relatively simple. External shading, solar-control films on windows, reflective coatings, improved ventilation, careful use of thermal mass, tree planting and green infrastructure all featured in the conversation. The broad consensus was that passive measures should be considered first wherever possible.

Several participants spoke openly about the potential role of active cooling. In particular, air-to-air heat pumps were highlighted for their ability to provide both heating and cooling, their relatively high efficiency and their potential suitability for certain housing types – including homes currently relying on electric storage heating. Early pilot projects were reported to have generated positive feedback from residents.

Participants also discussed ‘cool rooms’ or ‘comfort spaces’ fitted with active cooling solutions within communal facilities, particularly in housing designed for older residents. Acknowledged as far from ideal, these solutions nonetheless reflected a growing recognition that mechanical cooling systems may become necessary in parts of the housing stock, especially for vulnerable residents during periods of extreme heat.

In that sense, the conversation suggested a shift in thinking. Cooling is no longer being treated as taboo. Instead, it was being discussed as one component within a wider strategy for maintaining safe and healthy homes. The key is to reduce cooling demand first, then deliver cooling as efficiently and cleanly as possible, so that decarbonisation goals can also be met.

People matter as much as technology

One of the strongest themes throughout the roundtable was that technology alone will not solve overheating. Again and again, participants returned to the role of residents.

Several described situations where homes did not perform as intended because the assumptions built into design models failed to account for the diverse ways that people use and live in their homes. Examples included windows being opened during the hottest parts of the day, ventilation systems not being understood, and monitoring equipment being removed because residents did not trust its purpose. 

This reinforced the importance of communication and trust. Residents need clear, practical advice about how to keep homes cool and how building systems are designed to operate. Equally, housing providers need to recognise that technical solutions must account for the way people live.

Participants also questioned whether information is most effective when it comes directly from landlords. Trusted family members, neighbours and community networks may have an equally important role in shaping behaviour during periods of extreme heat. The challenge, therefore, is social and behavioural as well as technical.

A sector still learning

Another recurring theme was the need for better evidence, with participants discussing monitoring technologies, post-occupancy evaluation and building performance data. 

Several participants expressed frustration that housing organisations continue to run similar pilot projects and gather similar evidence independently, often repeating work that has already been done elsewhere.

Calls for greater collaboration, open data and wider dissemination of lessons learned surfaced repeatedly throughout the discussion. As one participant remarked, "It’s not a win unless we’re all winning."

There was also recognition that collecting data creates new responsibilities. Monitoring systems only have value if organisations have the capacity and thought-through strategy to interpret the information and act on it. 

Bridging the gap between policy and practice

Participants broadly supported the direction of travel on overheating. However, they also highlighted areas where regulation, guidance and funding mechanisms are struggling to keep pace with operational reality.

The discussion touched on Approved Document O, TM59 modelling, future weather files, acoustic constraints, heat networks and accreditation requirements for emerging technologies – especially air-to-air heat pumps. Contributors highlighted examples where funding programmes and technical standards appeared to be working towards different objectives or operating on different assumptions.

Several participants argued that future regulations need to reflect how buildings perform in practice rather than relying solely on compliance exercises. Others emphasised the importance of updating modelling assumptions to reflect the climate conditions that buildings are likely to experience over their lifetime rather than conditions from the recent past.

The underlying message was not a call for less regulation. It was a call for better alignment between policy goals, funding criteria, technical standards and real-world outcomes. Indeed, some participants argued that the sector should engage more proactively in policy formation and make a stronger evidence-based case for climate adaptation and decarbonisation measures.

A challenge that is becoming operational

The roundtable revealed a sector in transition. Only a few years ago, overheating was often discussed as a future climate risk. Today, housing providers are beginning to treat it as a present operational issue that affects asset management, resident wellbeing, development decisions, retrofit programmes and long-term investment planning.

The discussion also demonstrated that overheating cannot be considered in isolation. Efforts to decarbonise homes, improve energy efficiency and adapt to a changing climate are increasingly converging within the same buildings and often within the same projects.

The challenge now is ensuring that homes designed to cope with colder winters and lower carbon emissions are equally capable of remaining safe, healthy and comfortable for their residents during hotter summers.