Cooling like it's 400 AD 🌲
Climate Solutions // I S S U E # 6 0 // E X T R E M E H E A T
The Sun House
By Cadence Bambenek
In 2007, my mom broke ground on her home deep in the northern Wisconsin scrub oak forest. It sits on an eight-acre plot on a small hill overlooking the Totagatic River, a small tributary that feeds into the Namekagon River, and, eventually, the Mississippi.
She liked the idea of retiring to a home that was almost off the grid. “Live off the land a little more, so-to-say,” she says. With a bit of research, she ran across the concept of the “double-envelope home.”
As the name suggests, it is a home within a home.
Six-inch-thick logs of Southern yellow pine—valued for their good insulating properties—are stacked one on top of another like a giant Lincoln Log set. Then there is an inch-wide air gap, two inches of foam insulation, another airspace, and then a final set of six-inch Southern yellow pine logs.
Those thin layers of air are where the magic happens. It’s where the warmth circulates throughout the house.
To collect heat, she brought in specialized windows from Canada, the best on the market at the time, to tap a free source of abundant energy: the sun. In my family, the home became lovingly known as the Sun House.
To store heat on cloudy days, heat pumps were attractive—but exorbitantly expensive, and wouldn’t work well in the sandy terrain of northern Wisconsin. Instead, the sun streams through the wall of windows and heats up a poured cement floor in the basement, while a sunroom above captures still more sunlight. The solid pine walls soak up the warmth and slowly release heat through the night.
Her favorite thing? The circulating air within the walls brings the whole house to the same temperature. The basement is as warm as the loft. She now spends $600 a year on propane to supplement heat from the sun, keeping the house 50°F through frigid winters where temperatures can dip to -30°F. But a small wood stove can bring the entire house to a comfortable 70 degrees.
By leveraging the sun, “it takes advantage of technology people used hundreds of years ago,” my mom tells me. “I still think it’s more energy efficient than most homes built today.” Conversely, in the hot summer months, because of the angle of the sun, the roof takes the brunt of the sunlight, the inside stays cool.
A log cabin may not be for everyone. But the physics behind it are universal. As early as the 5th century A.D., Socrates was talking about how to build his own version of a Sun House in ancient Greece.
As we think about cooling the next generation of homes (and buildings), the lesson from my mom’s house remains the same: leverage timeless design principles with better technology. And many of the technologies and materials used in the Sun House are far more affordable than they were back then. In 2007, my mom couldn’t pay to install heat pumps and photovoltaic solar panels. Today, they’re probably cheaper than the wood. Built in 2021, the Sun House would likely be net-zero (using no fossil energy)—as the house kit’s manufacturer originally promised, but couldn’t quite deliver.
Tomorrow’s technology may make net-zero the new standard: 3D printed buildings, modular housing built in factories and assembled on-site, as well as mandatory net-zero construction codes in California, Japan, and elsewhere are already resetting expectations.
We’ve outlined the steps to envelop your own home below, and some of the things that can be done without getting out a toolbox.
How to envelop your home
Air conditioning is a climate Catch-22. It amplifies the problem it’s trying to solve.
So what’s to be done?
First, we can advocate for better design codes (along with urban greening, cool roofs, and walkable/bikable cities). One such roadmap, California's “Energy Efficiency Strategic Plan,” has mandated energy savings across the largest US state (and the world’s fifth-largest economy). Most newly-built homes in the state must now come with enough solar panels to satisfy their electricity needs.
Here at home, there are a few approaches you can take to cool your home and reduce your AC use, while helping cool your city.
Envelop your home
Passive cooling is the name of the game. Globally, air conditioners consume more energy than any other household appliance, roughly 10% of global electricity. One Arizona State University study found waste heat from AC raised night-time temperatures in cities by nearly 2°F.
An airtight envelope can prevent as much as 15% of cooling (and 40% of heating) from being lost in “leaky” homes. The tight barrier through the windows, roof, floor, foundation, and insulation can make sure hot air stays out and cool air stays in. While this is easiest to do during construction of a new home, there are changes you can make to an existing home to improve its seal.
Windows
Unsurprisingly, homes lose much of their energy through the areas that open to the outside: doors and windows. First, the easy thing: seal your home by caulking the cracks and openings around door and window frames, and use weatherstripping on the doors and windows themselves. Here’s a handy guide. Then the big stuff: double or even triple-paned windows (standard in “net-zero” homes). If that’s out of your budget, you can look into window insulation film instead. Window insulation kits will cost you about $20 and YouTube has you covered for installation tips.
Walls
Insulation is your best defense against energy loss in the home. Almost all older homes can use extra insulation to bring it up to today’s standards. According to one study, doing so would reduce CO2 emissions from heating and cooling by 80 million tons. And while it may be pricey to retrofit your home, you’ll save money on energy bills in the long run—an average of 15%, according to the EPA. Energy assessors can do a home energy audit to tell you what type of insulation you have and where, or if you’re feeling bold, you can try to do one yourself. The U.S. Department of Energy has a helpful primer on everywhere your home should be insulated and to what level depending on where in the country you live.
Roof
Roofs save—and produce—energy. First, roof insulation seals the home envelope. Next, painting your roof white or using a light-colored shingle can also help lower the temperature. Dark colors and dense materials like asphalt capture radiation from the sun and slowly release it over time. Light, reflective colors bounce the sun’s rays back so your home doesn’t absorb as much heat. Eco-friendly alternatives to traditional asphalt flat or shingled roofs include wood shingles, clay tiles, or reflective metal roofs.
Finally, the biggest impact may be installing solar panels on your roof. Solar panels are a major component of net-zero homes, enabling the house to produce its own energy.
Rental options
For those renting or not ready to shell out to update their home, there are still a few things to do to cool your home passively. Try a “night flush”: open the tops of windows to vent hot air out and let the cooler night air in. If you have a ceiling fan, turn it on and make sure it’s moving counterclockwise to blow cool air down. In the morning, close your windows and blinds to trap that cool air inside and block the heat from the sun.
Wait to use large appliances that produce heat, like the stove, washer and dryer, and dishwasher, until the evening hours. Or skip some of them all together and grill out or hang clothes to dry outside. Speaking of outside, think about adding plants to cool your home. Planting trees, especially on the sunny south and west-facing walls, can lower the temperature by as much as 6° F through shade and transpiration.
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Hothouse is a weekly climate action newsletter written and edited by Mike Coren and Cadence Bambenek. We rely on readers to support us, and everything we publish is free to read.
