Future-Ready Net-Zero Carbon Building Performance & Engineering

The direction of travel for affordable housing is clear. Legislation and policy, including Awaab’s Law and the recently announced Warm Homes Plan, are rightly focused on improving the quality, safety and energy efficiency of affordable homes, whilst tackling fuel poverty and the cost-of-living crisis. Warmer homes should reduce energy bills, improve occupier comfort, support better health outcomes and contribute significantly towards the drive to net zero. However, whilst this ambition is welcome and needed, there is an emerging contradiction – the very measures designed to make homes warmer, more airtight and cheaper to run can also significantly increase the risk of overheating. As climate change brings more frequent and intense heatwaves, overheating is no longer a marginal issue. It is becoming a clear housing risk and even more so for the more vulnerable members of our society. The Warm Homes Plan is fundamentally about enabling people to live affordably in their homes, using modern and renewable technologies to reduce energy consumption and carbon emissions at a time when fuel poverty is rising. That principle is sound. Equally, well-ventilated homes are directly linked to good health and wellbeing. Overheating has a measurable impact on physical and mental health, including sleep quality, metabolic health and productivity. An occupant-centred approach therefore has to underpin the Warm Homes Plan, balancing affordability with health outcomes. The policy’s recognition that passive or active cooling may be required to mitigate overheating is an important acknowledgement that energy efficiency alone is not enough – but it is a complex challenge to address. Why overheating matters – and why it is complex The risk of overheating is surprisingly acute in well-performing homes. Highly insulated, airtight homes – including those built to high specifications and Passivhaus principles – can be vulnerable to excessive internal temperatures if ventilation and heat removal are not carefully designed in at the outset. For residents in affordable housing – including older people and those requiring specialist care – getting this balance wrong has serious consequences. The response to the Warm Homes Plan therefore needs to be right first time, with health and wellbeing underpinned by the appropriate level of technical expertise and correct and ideally regulated execution. The Cooling Hierarchy Well-insulated buildings make absolute sense, but insulation, airtightness and ventilation must be addressed as part of a cohesive energy strategy. Comfort cooling is a more practical solution for reducing temperature. Air conditioning also manages humidity but is energy intensive, maintenance-heavy and costly to run, even when paired with solar. However, there is significant untapped potential in passive measures such as external shading, blinds and shutters – commonplace in warmer climates but still under-utilised in the UK. This is the cooling ‘hierarchy’: 1. Minimise internal heat generation through energy efficient design 2. Reduce the amount of heat entering the home in summer through orientation, shading, fenestration, insulation and green roofs and walls 3. Manage heat within a building through thermal zoning, buffer spaces, exposed internal thermal mass and higher ceilings 4. Passive ventilation 5. Mechanical ventilation 6. Active cooling systems such as air conditioning. The Need for a More Holistic Approach Overheating cannot be considered in isolation. Whole-life carbon, operational emissions from heating systems, materials selection, and long-term maintenance and repair all need to be addressed as part of the transition away from fossil fuels and towards more energy-efficient homes. Ventilation may be key to passive cooling, but real-world constraints quickly emerge. The external acoustic environment matters – homes adjacent to busy roads or railway lines may not be able to rely on opening windows for ventilation without compromising wellbeing. In dense urban areas, background noise can itself become a health issue. Regulatory requirements will also shape the solution. The Building Safety Act requires consideration around fall protection, which may limit window openings through restrictors. Air pollution is another constraint, particularly in city centres. The layout of multi-occupancy housing can severely limit natural cooling strategies. Traditional apartment layouts – with homes on either side of a corridor – make cross-ventilation for cooling extremely difficult, regardless of insulation levels. These inter-relating factors vary widely depending on location, building age and housing typology. Improving thermal performance through additional insulation also introduces the risk of interstitial condensation if ventilation levels are not properly understood. There is no silver bullet or single solution. Designing Building Performance Strategies that Work in Practice The starting point is to treat each building as a whole, rather than a suite of measures to be installed. No single element should be changed without first clarity on how it affects the whole property and its occupants. This requires time, analysis and robust thermal modelling, enabling housing providers to understand, at a systems level, what interventions will deliver the greatest benefit without creating new risks and health hazards such as condensation or overheating. Technology is rapidly advancing. The first ventilation systems with integrated cooling are now available and can be combined with building fabric upgrades and low-energy renewable heating. Where roof orientation allows, solar energy can help offset the additional electrical demand of these cooling systems. But technology alone is not the answer. Occupant profiling is critical. Homes occupied by older or more vulnerable residents, who are likely to remain in the property during the day, need to perform very differently from those properties occupied mainly in the evenings. Overheating in daytime is harder to mitigate than night overheating, and these factors need to inform the performance strategies from the outset. There are significant risks to undertaking blanket upgrades to heating, glazing and insulation without detailed analysis. Homes can take many hours to cool once overheated, and what appears to be a sensible energy upgrade in theory may be hugely detrimental to resident health and wellbeing, increasing risk of non-compliance under Awaab’s Law. There is a delicate balance between resident comfort, health, running costs and carbon emissions, and it cannot be achieved without detailed analysis, modelling and complex calculations. New build affordable homes have more flexibility – window orientation, shading and layout can all be optimised. Retrofit is more challenging. Orientation of roofs or windows cannot be changed; internal insulation reduces room sizes, and the existing interior is someone’s home. The solution will differ from building to building, even across similar typologies. The key is to design for residents – present and future – rather than relying on standardised assumptions. The new legislation rightly raises expectations around building safety, health and affordability, but overheating must be treated as a core risk, not an afterthought. Without a holistic, evidence-led approach, these well-intentioned policies risk poor outcomes for the very people they are designed to help. However, this is also a huge opportunity to increase the affordability, health and resilience of social housing in a changing climate.

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