The Ancient Wisdom of Passive Cooling
It was not the postcard-worthy aesthetics that prompted Greek islanders to first drench their cliffside-carved homes, churches, and pathways in a thick layer of pearly white paint. Much like wearing a white tunic on a hot sunny day, painting your house a shade of reflective white is a fine way to keep an ancient island cool, bouncing some of the sun’s heat back into space instead of absorbing it into the structure of the buildings themselves. Before air conditioning existed, people in warmer areas of the world often built with similar techniques in mind: Iran’s picturesque badgirs have helped desert dwellers stay cool for millennia, for example, and in the tropics, Malaysians have long engineered their homes to avoid floods and let a breeze in. Many homes and cities in Europe are still living as they have for centuries, relying largely on their thick shutters, ventilated courtyards, and other strategies to encourage shade and airflow. But after a deadly heat wave tore through western Europe last month, killing at least, it has become increasingly clear that old-world buildings are not cooling enough on their own for our rapidly warming climate.
After a heat wave pulsed over the eastern U.S., a nation of AC aficionados faces the inverse of this problem. Since just after the end of World War II, the U.S. has built its homes, schools, and hospitals so thoroughly with AC in mind that most buildings have no built-in defense against the heat at all. The air conditioner made possible America’s cavernous McMansions, megamalls, and frigid glass office towers, engineered like ectotherms, liable to soak up a heat wave like a cold-blooded lizard sprawled out on a rock on a scorching summer’s day.
America’s AC Dependence and Its Hidden Vulnerability
The Rise of Air Conditioning and Its Consequences
American homes used to reflect the cities they were built in. Cool air flowed beneath the floorboards of New Orleans’ breezy raised shotgun houses. Boston’s winter winds met the saltbox house’s long, sloping roofs, and Pueblo tribes used thick blocks of mud to build adobe homes that withstood the desert’s daily fluctuations. But in 1947, an engineer named Henry Galson transformed how America builds with his invention of the window air conditioner, a low-cost AC unit snug enough to nestle into a residential window. With millions of service members returning from World War II, the nation needed more housing, and it needed it fast. Cheap air conditioning allowed builders more flexibility to mass-produce the suburban tract home as a solution to America’s post-war housing crisis — even in hot climates like the Sunbelt. Air conditioning made large swaths of the country newly habitable, fueling the spectacular growth of many now-flourishing metropolises across the American South and Southwest. In less than a century, the AC transformed blisteringly hot Phoenix from a small desert town, population 65,000, into the largest city in the country. The likelihood of an American dying on a scorching hot day fell by a staggering.
The Danger of Power Outages in a Heat Wave
But the roaring, life-saving success of the AC has also embedded a profound vulnerability: the moment the power goes out, as it’s prone to do in a heat wave — or that electricity bills get too onerous, which tends to happen when the AC is cranked — the nation’s cold-blooded buildings convert into furnaces. In most conventional American houses, if you lose power in the middle of an extreme heat wave or in a blizzard, you’ve got hours before you need to get out, said Alexander Gard-Murray, executive director of Passive House Massachusetts, a group that encourages the state to build naturally cooler buildings — or passive houses — from the start. Some techniques are state-of-the-art and technologically novel, others are ancient, and still many others are basic common sense: don’t build facing the sun, plant trees, add an awning, and replace heat-radiating asphalt driveways with gravel. Notably, none of these strategies involves shoving your AC unit out the window. But they can help your air conditioning work a lot less hard — which, by the way, could cut your electricity bills at a time when America’s electrical grid is desperately straining to keep everything online. Most importantly, it ensures that if something does go wrong, if the power goes out, you’re still going to be okay.
Researchers estimate that if Phoenix were to experience a two-week blackout during one of its regular heat waves — knocking out air conditioning citywide — it would quickly kill 12,800 people, or roughly 1 percent of the population, while a full half of the city would require emergency medical care. Arizonans will always need AC to stay safe from the heat, but they could be far more resilient to temporary lapses if their homes and neighborhoods were better designed to stay cool without it. If Phoenix planted enough trees to shade half of its streets — which would be enough to lower temperatures by at least a few degrees — 27 percent fewer residents would die in such a blackout, according to the study. If every building installed a cool roof — simply painting it with a white material to better reflect sunlight — then the death toll would plummet by 66 percent.
This is not just a thought experiment. Driven by extreme weather and an aging electrical grid, the number of power outages has doubled over the past two decades. After Hurricane Beryl knocked out power for millions in Texas in 2024, at least dozens — and possibly hundreds — of people died from heat-related causes, meaning the outage killed more people than the storm itself. It overcomes you really fast, said Patricia Solis, executive director of the Knowledge Exchange for Resilience at Arizona State University, which focuses on Maricopa County, where many die from heat-related causes each year, many inside their own homes, their air conditioning broken, turned off, or unplugged. One of them was Stephanie, a 72-year-old who died in Phoenix in 2018, a day after her electricity was cut off over a $51 unpaid bill. Another was Patricia Miletich, a 70-year-old with memory issues, whose busted AC was blowing hot 110+ degree air into her RV when she died in June 2024. Upwards of a significant number who succumb to heat inside their homes live in mobile houses, structures whose thin walls, poor insulation, and cramped concrete quarters make them especially expensive to cool with AC, and especially deadly without it.
Practical Solutions for a Cooler Home
Simple and Affordable Adaptations
It’s not as hard or expensive as you might think to build a cooler home, one that does at least some of the work needed to keep things more comfortable in extreme temperatures. Something as simple as facing an RV away from the sun, adding an awning or garden trellis, or installing vinyl skirting around the foundation to prevent hot air from coming up through the floor, could make a difference to be in if the power goes out, says Solis. And even in less catastrophic conditions, these age-old adaptations would make an AC unit cheaper to run. When she began her work, some mobile home park owners sought to outright forbid residents from adding cooling features like a small window garden for purely cosmetic reasons. Solis and her team later helped pass a law to allow such features.
The Passive House Standard
Even earning the gold standard of building cooler buildings — a Passive House certification from Phius — isn’t some space-age, super advanced crazy thing, said Gard-Murray. It’s not about doing extraordinary things; it’s about doing ordinary things extraordinarily well, like making sure your walls are airtight and thick enough to act as a buffer against outside temperatures. If most American buildings absorb heat like a plastic water bottle left out in the sun, a passive house is built like a thermos, keeping things relatively temperate regardless of the temperature outside. To illustrate that, a group of architects once built two mini-houses, one according to normal building codes and the other like a passive house, plopped them in a park in New York City, and filled both with 1,800 pounds of ice. One month later, the mini passive house had 40 percent of its ice left, while the other one had only 7 percent. You can imagine how much safer that makes you if your AC ever goes out, and makes it up to 90 percent less energy-intensive to run — enough to cut your utility bills in half — when it’s on. If we’re much more intentional about insulating the property, the heating and cooling systems have to do a lot less work, said AJ Patton, founder of the Chicago-based developer 548 Enterprises, which is currently building Chicago’s largest-ever Passive House-certified affordable housing complex. Too often we’ve used sustainable technologies as a luxury item, said Patton, but the biggest benefits to these homes are for lower-income households who could really use the savings on their bills or are more vulnerable to having their power cut off.
As of now, only about one percent of homes being built in the US are built according to passive standards. One might assume that building such a sensible, sustainable, and safer home must be prohibitively expensive, or else it would be much more common. But in reality, at least in Massachusetts — where passive designs are now the mandatory norm in many cities — a survey found that such buildings only cost as little as a small percentage more than conventional buildings. Equally important in a country with a notorious housing shortage, the municipalities in Massachusetts that have opted into more stringent requirements continue to build more housing than those that haven’t, and they approved more new housing permits after the change. There could be a lot of factors at play in those differences, but at the very least, it shows that requiring strict standards in this case might not crash housing production, Gard-Murray said.
The real reason why these building techniques don’t happen more often comes down to a lack of awareness, experts told Grist, along with the fact that the biggest financial benefits are for whoever pays the utility bill, not the developer who has to pay the upfront costs. It doesn’t help either that the Trump administration has rolled back policies that helped defray the extra costs of energy-efficient buildings. Some projects like Patton’s lost out on $300,000 in expected incentives in real time. The moronic government policies of the last 18 months are not helping us, said Mark Ginsberg, a founding partner of Curtis + Ginsberg Architects, which has completed about 25 multi-family passive projects in New York City, most of them affordable or supportive housing. There are too many people burying their heads in the sand and saying climate change isn’t real, he said. That’s easier when the AC hides the worst effects of extreme heat from us. But on the verge of a heat wave poised to put many at risk, it may be past time to give our AC a little boost, too.