Building homes for a heating planet

This summer the Pacific Northwest was hit by one of the most severe and sustained heatwaves in history. The “heat dome”, which settled over California, Oregon, Washington and British Columbia, broke temperature records in the region.

July was Earth’s hottest month since records began. Europe has recorded its highest temperature in history (48.8C in Sicily). Data from the World Meteorological Organization shows that 2011 to 2020 was the warmest decade on record in a long-term upwards trend. The annual number of days reaching 50C around the planet has nearly doubled since the 1980s, from 14 to 26.

Earlier this month, more than 200 international medical journals published a joint statement warning that “climate change is the greatest threat to global public health”. Worldwide, every year, people are dying of heat exhaustion in their homes. In England alone there were more than 2,500 heat-related deaths during three heatwaves in 2020, the highest number since data started to be collected in 2003, according to Public Health England.

The homes we live in could change this. When the Pacific Northwest was sweltering under the heat dome, one ordinary looking home in “cold climate” British Columbia, where temperatures soared to 46C, stayed 20C cooler inside — and it doesn’t have air-conditioning.

Yet many new homes — especially in the UK, where active cooling is rare — are proving less able to cope with heat than older ones. Resorting to air-
conditioning exacerbates the problem, pumping warm air into the streets, compounding the urban heat island effect and adding to greenhouse gas emissions. According to the International Energy Agency, international sales of air-conditioning units nearly quadrupled between 1990 and 2016. The power consumed by the world’s 1.6bn units annually is more than all the electricity used in Africa, it says.

“Ever since we started depending on fossil fuel for heating and cooling, we’ve been building houses with disregard to the climate,” says Eleni Myrivili, chief heat and resilience officer for the city of Athens, where temperatures reached 45C this summer. “We’ve lost centuries of wisdom that taught us about thick insulating walls, small windows, shading and tall deciduous trees to the south and west where heat beats harder and about whitewashing surfaces in the spring to reflect the summer heat.”

Paradoxically, turning to the past may be one way we could face the homebuilding challenges of the future. The ancient architecture of the Iranian desert, the tall windcatchers and cooling channels of mountain water in the World Heritage city of Yazd and even the tents of desert nomads are an inspiration for architect Sue Roaf, Emeritus Professor of architectural engineering at Edinburgh’s Heriot-Watt University.

Roaf also points to multistorey palaces — haveli — in the Indian subcontinent. Despite daytime temperatures in the high 30s, interiors remain comfortable thanks to shady courtyards and “thermal mass” of bricks and marble. Thermal mass is the ability of materials to slowly absorb heat energy, acting as a “heat sink”. 

It was this vernacular architecture that inspired the design of Roaf’s 25-year old home, the Oxford Eco-House. Thermal mass of internal walls moderates the temperature indoors. There is cross-and-stack ventilation, with no windows on the western side where low afternoon sun is hottest. A porch provides an airlock, a barrier to minimise hot air entering. There is thick insulation. Trees and deciduous climbers provide shade. On hot days, Roaf opens windows on the north-facing side to draw in cool air, and keeps the triple-glazed windows on the south side shut.

“It’s like setting sails on a boat,” she says, “you have to learn how to operate your home to keep it cool.” Roaf will soon install new external shading. “I’m planning for when we get a heat dome.”

“By the time today’s [new] buildings are built we’ll be in an even warmer world. We need to be designing for survival; for when the power goes off.”

Roaf takes issue with architects who specify sealed windows, intending buil­dings to be air-conditioned. “Architects have sold their souls to the heating, ventilation and air-conditioning industry. They need to take back control and be great climatic designers of the future.”

Unfortunately not everyone can enjoy breezes. “In urban areas, noise, pollution and security concerns mean people don’t necessarily want to open windows,” says Michael Swainson, principal engineer at the Building Research Establishment (BRE) and chair of a government-appointed working group reviewing a proposed new building regulation on overheating in dwellings for England, the first time overheating in dwellings has been addressed.

The draft guidance, currently under review, includes measures such as limits to glazed areas. “In this country, everyone seems to want big windows with views,” says Swainson. “That’s fine but it also leads to overheating.”

Overheating happens when more heat enters a building than can leave, says Swainson. It can be prevented with simple measures: small windows or shading to limit heat coming in, and open windows or mechanical ventilation to allow it to escape. In warmer countries, such measures have long been common practice. “In Italy and France people shut out the sun with external shutters, leaving windows open for any breeze,” he says.

With, as yet, no legal requirement to prevent overheating, new homes in the UK are proving particularly prone. The Ministry of Housing, Community and Local Government’s English Housing report 2019-20 found that “residents in more recently built homes were more likely to report overheating than those in older homes.”

Climate change aside, the main reasons for overheating in new homes are inappropriate design and cost. “There are lots of single-sided shoebox size flats being built and nightmare conversions of offices to flats. [Likewise] building in enough thermal mass to moderate temperature is expensive. We’ve moved to lightweight construction. Thermal mass also takes a long time to cool so you need to leave windows open all night,” says Swainson.

Potential overheating is a case of “buyer beware”, he says. In England, renters have recourse to the Housing Health and Safety Rating System. An environmental health officer can direct a landlord to take action if a home is above 25C for long periods.

As for homeowners, Roaf has some ideas. “We’re never going to retrofit every property in the next 20 years — and people can’t afford that anyway — but for a couple of thousand pounds you can build a ‘cool corner’,” she says. A cool corner would be on the side of a property that receives the least sunshine; the ceiling should be insulated, and any carpet taken up to reveal cool concrete or floorboards with gaps for air to circulate. Outside, walls and windows should be shaded with vegetation or dark-coloured hessian awning that absorbs and dissipates heat. Permeable blinds can be sprayed with water. Likewise, the ground outside can be dampened after sunset to aid evaporative cooling. Awnings should be retracted at night to allow cooler air to enter.

But it is the poorest of the world, already living in some of the hottest regions, who are most susceptible to climate change. Ashden, a UK-based climate change charity, is funding projects from Asia to Latin America, developing affordable cooling solutions that don’t add to greenhouse gas emissions.

In Medellín, Colombia, Ashden is helping to plant thousands of trees on the city’s streets to provide shade. In India, cBalance, an employee-owned social enterprise working to combat the effects of climate change, is helping poor families in informal housing to transform tin-roofed homes that become life-threateningly hot. Measures such as moveable rooftop foil screens to reflect the sun’s heat, green roofs and interior walls of recycled plastic bottles filled with water to provide thermal mass are all being trialled.

In Egypt, architectural practice ECOnsult, founded by Sarah El Battouty, has received funding to scale up lessons learned from its accommodation for 138 employees on a farm in the western desert oasis of Bahareya. Here, where temperatures reach 50C, interiors maintain 19C-26C, says ECOnsult. Cooling is achieved with shading, natural ventilation, interior thermal mass and solar-powered ceiling fans.

Further south, another architect inspired by vernacular architecture is Paul Marais, director of South African practice, Simply Sustainable. He has designed two properties of rammed earth in Botswana, where daytime summer temperatures reach into the 40s but nights are cool. Crucially, the embodied carbon of rammed earth is far lower than that of concrete.

In summer, the homes, which don’t have air-conditioning, maintain an average daytime temperature of 26C, “within the comfort range for Botswana”, says Marais. “Thick, shaded rammed earth walls create cavelike spaces, keeping indoor temperatures constant by drawing out excess heat energy.” A pool next to the main house provides evaporative cooling. The family pets approve. “The dogs that used to sleep under a big tree during the hottest part of the day now choose to sleep inside the house next to the rammed earth wall that has the pool outside.”

And the house that stayed cool under British Columbia’s heat dome? Valemount Passivhus, Laura Keil and Andru McCracken’s 180 sq m home in the village of Valemount, is surrounded by snow-capped mountains for 10 months of the year. Built to international Passivhaus standards, it was designed to cope with winter lows of -40C but summer highs of just 25C. Heating bills are minimal but there is no active cooling.

Yet this summer, the 50cm thick insulation and air-tightness — usually meant to keep out extreme cold — effectively kept the heat out. Judicious management was needed. Windows and doors were shut tight by day. McCracken erected external window shades. Remarkably, for the first three days the house maintained a comfortable 23C, though it eventually rose to 26C. “Not comfortable, but bearable,” says McCracken, especially compared with 46C outside. Unlike other Valemount residents who sought refuge in air-conditioned municipal buildings, McCracken and Keil rode out the heat dome at home. 

Lessons are being learned. “New homes are now being modelled based on Earth’s temperature increasing 2C in the next two decades [even in cold climate BC],” says the architect of Valemount Passivhus, Vincent Siu. Active cooling such as low energy hydronic cooling — piped cold water — is being specified. Such low energy cooling can be powered by a home’s solar panels. 

Heatwaves are not the only climate chaos we will have to endure. Our homes will experience more wind and torrential rains. Cities need to cope with increasing inundation. Thai architect Kotchakorn Voraakhom has designed a new 4.5-hectare park in Bangkok. She describes Centenary Park in Chulalongkorn University as “a crack in the concrete jungle”. Built up to a three degree slope, it contains artificial wetlands, underground cisterns and an area intended to flood. It can hold more than 1.5 Olympic swimming pools of water, saving surrounding homes.

As for temperatures, the warming Arctic has also been implicated in harsh winter spells due to stretching of the polar vortex. Homes in regions that usually experience mild winters will have to cope with extreme cold as experienced in Texas in February when the biggest freeze for 70 years resulted in the electricity grid failing, leaving hundreds of thousands without power or heat.

“The extreme weather we have been experiencing this year is a taster of what happens with a global average temperature increase of 1.1C above the preindustrial level,” says Dr Oksana Tarasova, head of atmospheric and environment research at WMO.

Imagine what 2C would be like.

Follow @FTProperty on Twitter or @ft_houseandhome on Instagram to find out about our latest stories first