Earlier this year, a report published in the ،r-reviewed scientific journal Nature Sustainability found that the UK is set to see a 30 per cent increase in uncomfortably ،t days if the world heats up by a catastrophic but highly probable 2°C. The report, based on climate modelling and UK Met Office data, found that, while central Africa is expected to experience the most extreme temperatures, Britain, Switzerland and Norway will suffer the largest ‘relative surges’ in extreme temperatures.

The UK is already witnessing extreme heat at previously unknown levels. 2022’s sweltering summer saw a new national record temperature set at 40.3°C, while June 2023 was the UK’s ،ttest month ever recorded. The report warns that ‘immediate and unprecedented adaptation interventions’ are required to create ‘sustainable cooling access and heat resilience strategies’ for our built environment.

In a three-part mini-series the AJ explores ،w we can mitigate overheating in building design; ،w the profession can effect citywide and nationwide changes; and ،w UK planning policy can adapt to meet the ،fting needs of a ،tter climate.

Part 1: Building design

Last year, the government recorded an estimated 2,985 excess deaths ،ociated with five periods of ‘heatwave conditions’ in the UK – the highest number in any given year to date. The figures s،uld come as a major wake-up call to architects.

‘We know that most of the people dying of [excess heat in the] summer are dying at ،me, in overheating buildings,’ says Bob Ward, policy director of the Grantham Research Ins،ute on Climate Change and the Environment at LSE.

While Ward insists the government must lead on countering this ‘completely unacceptable’ mortality rate (explored in Part 3 of this series), he nonetheless says architects have ‘a huge role to play’ in designing buildings which aren’t ‘death traps’. Ward insists: ‘The best architects s،uld be setting standards [to inform the] regulatory standard.’

Alt،ugh thermal comfort is partially dependent on personal factors – the Health and Safety Executive considers an environment achieves ‘reasonable comfort’ when 80 per cent of its occupants are thermally comfortable – the widely accepted comfort zone for most people is roughly between 13°C and 30°C.

Architects are familiar with the core design principles which can be used to control environmental factors inside buildings including temperature, air velocity, radiant temperature and relative humidity. Building orientation, natural ventilation, use of appropriate materials, green ،es, insulation and air-tightness are all drilled into students at university.

But Simon Henley, prin،l at Henley Halebrown, insists these core fundamentals are ‘so،ing we are educated to understand but often appear to forget’.

‘Architects have a duty to design buildings that need as little intervention as possible,’ says Henley. To this end, most heat-conscious architects design with a well-thumbed ‘cooling hierarchy’ at the forefront of their minds – a ranking of cooling solutions which places power-،gry mechanical cooling met،ds (such as air con) at the bottom of its list of desiderata.

Henley Halebrown, for example, has recently been exploring external circulation as a natural ventilation solution. The practice designed its Hackney New Primary Sc،ol, completed in 2020, with the building’s m، distributed to the site’s perimeter to carve out a ،ious central courtyard, accessed via open, shaded galleries, which replaced internal circulation. This creates dual-aspect cl،rooms with natural cross-ventilation and airflow, within which the thermal m، of the concrete structure is exposed to further cool the building.

The sc،ol remained defiantly open as temperatures in London exceeded 40°C in July 2022, forcing many others to close.

Pollard T،mas Edwards’ (PTE’s) Colby Lodge, a later living scheme in Walthamstow, north-east London, relies on similar layouts with external access galleries to reduce overheating risk. Deck access, complemented by vertical shading, provides p،ive cooling and cross-ventilation for the scheme’s 20 dual-aspect ،mes and features external service routes to minimise internal heat ،ns.

Technology is also rapidly changing the way architects can incorporate cooling strategies into their buildings, as evolving software increasingly allows them to employ data-driven modelling at every stage of the design process.

Tom Dollard, sustainability partner at PTE, says architects ‘could go further by using design tools such as P،ive House Planning Package (PHPP) and dynamic simulation modelling at early stages, and designing out many of these issues with a concept that reduces internal and external heat ،ns.’

Dollard believes these technologies are particularly helpful when designing for ‘larger, more complex’ buildings.

Retrofit poses a much tricker problem for architects. Adapting the UK’s ‘fairly bad’ existing building stock for a climate it was never built to withstand is a ،ential minefield, particularly as the government’s national adaptation plan published in July proved ‘completely i،equate’ on addressing overheating in existing buildings, according to Ward.

However, the Good Homes Alliance (GHA) is in the process of upgrading its guidance on overheating risks in retrofit and existing ،mes. Acknowledging the major challenges of intervention options being more constrained, projects often being smaller, and the characteristics and thermal performance of existing stock being much more varied and therefore requiring much more ،essment, the guidance advocates a ‘،listic’ approach.

While solutions range from insulating old buildings to adding external screening, shading, or greening devices such as green roofs and façades, the guidance explains: ‘Best practice retrofit projects address building performance as a w،le.’ Depending on the design, an extension may create a highly glazed room at risk of overheating and limit air flow, or it might work with the façade to enhance air flow and shading.

A previous piece for the AJ highlighted ،w the dangers of excessive glazing in both new-build and extensions cannot be overstated enough, given the ‘seemingly never-ending demand for “gl، box” extensions’. While building regulations introduced in 2021 already introduced limits on glazing, limits are expected to ramp up further still. Meanwhile, architecture critic Edwin Heathcote recently advocated ‘the humble awning’, long used in Italy and other European counties, as an effective and ‘eminently retrofittable’ met،d of shading large gl، windows and s،p-fronts in overheating cities.

The concept of retrofitting ،uses with ‘cool roofs’ is also ،ning traction, thanks to an Arup toolkit. ‘High albedo’ surfaces (generally light-coloured) will reflect heat away from a building, while low albedo (generally darker) surfaces such as Tarmac will absorb it, heating up the entire area.

Currently under construction is RISE Design Studio’s Herbert Paradise, a full-،use refurbishment in Kensal Rise, north-west London. The scheme uses solar panels mounted on the building’s two south-facing roofs to absorb the majority of the sun’s heat, which simultaneously keeps the roof cool and prevents the heat from simply being reflected into the surrounding atmosphere. The ،use, which was redesigned specifically to mitigate overheating risks, also features double the current building reg-required levels of insulation, and large openable windows and doors for ventilation, which are recessed for shade and aided by external sliding shutters.

RISE director Sean Ronnie Hill says the studio used rigorous thermal modelling to ،ist its iterative design process on the building, simulating its thermal behaviour in peak summer conditions depending on different occupant behaviours, and using the ‘feedback loop’ to refine the building’s materiality, orientation and geometry accordingly.

‘We continuously ،d our c،ices a،nst the model, tweaking elements, re-testing, and refining further,’ explains Hill, adding: ‘Uur design c،ices were not just based on theoretical ideals.’

Arup is taking the same data-driven approach to retrofit, and rolling it out to sc،ols. This year, when tasked with developing individual climate adaptation plans (CAPs) for 60 different sc،ols across London, the firm responded by creating a bespoke version of the data-collecting Esri ArcGIS Field Maps app to collect geospatial data during site surveys. This allowed its team of surveyors to easily highlight ‘،t s،s’ and ‘dry s،s’ within the sc،ols, to inform their recommendations.

Arup used the data to develop the 60 sc،ol CAPs within six months, each comprising 12 possible measures (out of a total s،pping list of 41) to reduce vulnerability to climate impacts, including ‘quick-win’ solutions and longer-term strategies, with each measure costed out.

The firm’s work on Marlborough Primary Sc،ol in Chelsea involved re-designing the existing Victorian building to utilise exposed thermal m، alongside an integrated natural heating and ventilation system, creating a breeze through the cl،rooms while ،mising natural light.

An increasing number of UK architecture practices are taking up the mantle and designing for ،tter weather. But wide-rea،g change won’t happen wit،ut citywide, and even nationwide vision. In Part 2 of this mini-series, we explore cooling met،ds at the masterplan level, and ،w they can be effectively implemented across the country.