The UK is increasingly experiencing temperatures beyond historical norms, bringing greater health risks and growing pressure to keep homes, schools and workplaces comfortable. As a result, air conditioning is often seen as the go-to solution. While it provides immediate relief, it also raises an important question: are we addressing the root causes of overheating, or simply managing its symptoms?

The challenge is not cooling itself. The challenge is the demand.

Much of the UK's building stock was never designed for the hotter summers we are now experiencing. As temperatures rise, many buildings require increasing amounts of energy to maintain comfortable conditions, creating a growing reliance on mechanical cooling and placing greater pressure on energy infrastructure.

Air-conditioning systems improve comfort by removing heat from occupied spaces and releasing it elsewhere. While effective, they also increase energy demand and contribute to heat being emitted into the surrounding environment. Across towns and cities, this can create a cycle where more energy is consumed simply to maintain acceptable indoor temperatures. We supplement our infrastructure with solar PV arrays and wind turbines to counteract this demand in an effort to make these cooling installations appear more sustainable. The root cause of the problem is not the resource of energy, but the building itself and its inability to regulate the internal environment.

The result is what could be described as a city of "renewable radiators", where buildings continuously consume energy to regulate internal conditions while releasing excess heat into the urban environment. Adding to the problem, this contributes to the Urban Heat Island Effect, where city centres are often significantly warmer than surrounding rural areas, in cases up to 6°C higher, due to dense development, limited vegetation and concentrated energy use.

The introduction of Part O of the UK Building Regulations reflects growing recognition that overheating has become a fundamental design challenge.

Resilience can no longer be viewed as an optional aspiration. It must become a core performance requirement.

Rather than responding to rising temperatures by continually increasing cooling capacity, we should focus on reducing the need for cooling in the first place. This means placing greater emphasis on building performance through high-quality fabric, effective solar control, appropriate glazing, external shading, airtightness and ventilation.

These measures address overheating at its source. They reduce solar gains, improve thermal stability and help maintain comfortable indoor conditions without excessive reliance on mechanical systems. In buildings designed around these principles, cooling becomes a supplement rather than the primary means of achieving comfort.

The benefits extend well beyond energy efficiency. Buildings that require less energy to heat and cool deliver lower operational costs, improved occupant wellbeing and greater resilience during periods of extreme weather. Reduced demand also eases pressure on energy networks, helping existing infrastructure accommodate future growth more effectively.

This shift in thinking is particularly important because investment decisions too often focus on increasing heating or cooling capacity rather than improving building performance. Yet the most sustainable unit of energy is the one that never needs to be used. Every reduction in demand delivers lasting benefits for affordability, resilience and environmental performance.

A renewed focus on the “Fabric First” approach, or perhaps more appropriately "Fix Fabric First", is therefore essential for both new-build and retrofit projects. Before introducing increasingly complex technologies, we should ensure the building envelope is performing as effectively as possible. Standards such as Passivhaus, EnerPHit and CarbonLite demonstrate what can be achieved when buildings are designed to regulate internal conditions through their fabric and form, dramatically reducing the need for energy-intensive heating and cooling.

To support this transition, policy and investment must look beyond carbon reduction alone and place greater emphasis on resilience, comfort and long-term performance. As the climate continues to change, buildings must be designed not only to minimise emissions but also to remain comfortable, efficient and adaptable in a warmer future.

Ultimately, the most sustainable building is not the one with the most efficient cooling system. It is the one that requires no cooling in the first place. The future of building design is not about fighting the climate with increasingly complex systems. It is about creating buildings that can work with it.