As overheating becomes an increasing challenge, Stuart Dantzic of Caribbean argues that architects should put passive measures such as external shading ahead of mechanical cooling.

The Environmental Investigation Agency’s recent report, UK Cooling Policy in a Warming World, should prompt serious questions about how we approach overheating in buildings.

The report calls for a National Cooling Action Plan that prioritises passive measures, including shading, before mechanical cooling. I believe that principle deserves greater attention from everyone involved in building design. As we know only too well by now, the UK is experiencing hotter summers and more frequent periods of extreme heat while increasingly well-insulated and airtight buildings can be vulnerable to overheating if solar gains and ventilation have not been properly considered.

The obvious response is to increase cooling capacity. But that treats the heat after it has entered the building. A better approach is to prevent as much of that heat entering in the first place.

For architects, this is where solar shading becomes particularly important. Large areas of glazing can transform a building, bringing daylight into interiors, providing views and contributing to the architectural character of a facade. They can also allow substantial solar radiation into the building, particularly when glazing is exposed to strong sunlight.

Once solar radiation has passed through the glass, the resulting heat becomes part of the building’s internal heat load. Removing it later requires energy. External shading addresses the problem before that happens by intercepting solar radiation outside the glazing and reducing the amount of heat reaching the glass.

This is an important distinction. Shading does not work like an air-conditioning system, lowering temperature by mechanical means. Its value is in reducing solar heat gain and helping to limit the conditions that lead to overheating.

The principle is reflected in the Cooling Ladder highlighted by the European Solar-Shading Organisation. Its approach places prevention and measures to reduce heat entering the building ahead of passive methods of removing heat, with active cooling further down the hierarchy. Solar shading is identified as one of the measures that can help prevent solar heat gain.

That is a logical sequence. We would not normally specify a heating system without first considering insulation and the performance of the building envelope, so overheating deserves the same level
of thought.

The evidence for giving shading greater consideration is also growing. Research commissioned by the British Blind and Shutter Association examined overheating in a block of London flats. In the study, rooms without shading reached a maximum ‘feels like’ temperature of 47.5°C, while rooms fitted with external blinds reached 28°C.

Those figures relate to the specific building and conditions of the study, so they should not be treated as universal performance guarantees. They do, however, demonstrate the potential difference that effective solar control can make.

For architects, the implication is significant. Solar control needs to be considered alongside glazing specification, orientation, ventilation and the wider performance of the building envelope. It should form part of the design response to solar exposure rather than being left until the end of the project.

Dynamic shading also deserves consideration. Movable systems can respond to changing solar conditions, allowing shading to be deployed when solar gain is problematic and retracted when daylight or useful solar gains are desirable. Automated control can further improve performance by responding to solar radiation and internal conditions.

This makes shading part of the building’s environmental strategy rather than simply a product applied to the facade. It also reinforces the importance of considering shading early, because the relationship between glazing, solar control, daylight, glare and ventilation is too fundamental to be resolved effectively as an afterthought.

The same thinking needs to extend beyond new-build projects. The EIA is clear that the UK needs to address overheating in existing buildings as well as future development. Retrofitting passive measures can be more challenging where the original facade, window design or planning constraints limit the available options, but shading should still be considered wherever significant solar gain is contributing to overheating.

The EIA also warns that an unmanaged expansion of mechanical cooling could increase energy demand, emissions and inequality in access to comfortable indoor temperatures. Mechanical cooling will
have a role in many buildings, but the question is whether it should be the first response to overheating.

I believe the EIA report gives the industry an opportunity to reconsider that hierarchy. Architects already balance daylight against glare, glazing against solar gain and openness against thermal performance. As summers become hotter, overheating needs to sit firmly within that conversation.

External shading is not a substitute for good building design, ventilation or mechanical systems where they are genuinely required. It is one of the tools that can help make the whole building work better, and it needs to be considered early enough to influence the design.

If we are serious about creating buildings that remain comfortable as the climate changes, preventing excessive heat gain should come before finding ever more energy-intensive ways of removing it.

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Stuart Dantzic is MD at Caribbean Blinds