The residential sector in the U.S. is responsible for about 15% of the nation’s total energy use, according to the Energy Information Administration.1 Heating and cooling are among a home’s biggest energy hogs—and reducing these needs can go a long way toward lowering a house’s environmental impact. Enter the concept of the passive house: structures specifically designed to reduce total energy usage by tightly controlling how much heat enters and leaves a home.
Passive houses are gaining popularity all over the world. The International Passive House Association says that they’ve certified new Passive Houses (along with houses retrofitted to be passive and low-energy buildings) that represent 3.3 million square feet of living space.2
What is a passive house?
The broad concept of a passive house, also called a passive home or building, is a structure designed to be as energy-efficient as possible. They’re called “passive” because they rely on things like insulation and ventilation to keep a home at an ideal temperature, as opposed to only using “active” systems like conventional air conditioning and furnaces. Though most homes that are passive are purpose-built that way, it is possible to retrofit existing homes with passive-house principles to up their efficiency.
Architects in North America started thinking about how to reduce a home’s energy needs in the 1970s in response to mounting oil prices, and by the 1980s “passive houses” became a movement. But, as interest in energy conservation in the United States waned, Germany took the helm. The Passive House Institute was founded there in 1996 and has since been considered the most rigorous arbiter of energy efficiency qualifications in the space.
The Passive House Institute rates buildings based on their energy efficiency, evaluating many different individual components, while also assessing how comfortable the inside environment is in relation to those energy savings. Passive homes can have HVAC systems, but they’re typically highly efficient ones like heat pumps. These structures can also rely on renewable energy from sources like a rooftop solar array. To become a certified Passive House, a few criteria must be met. These include:
- A comfortable internal temperature year-round, with a minimum of 68 degrees Fahrenheit in the winter and no more than 10% of all hours in a given year above 77 degrees Fahrenheit.
- A minimum efficiency for both heating and cooling, which is measured by how many watts it takes to heat one square meter of living area. A certified Passive House should only use 10 watts per square meter of living area. A standard building with a centralized hot water heating system, for comparison, uses about 100 watts per square meter.
- Evaluators also verify that the house meets the standards for “airtightness,” which is measured with a metric called an “air change”—that is, how many times the air in a room recirculates out in an hour. Passive Houses should top out at 0.6 air changes per hour at 50 Pascals of pressure.
Outside of the standards set forth by the Passive House Institute, the term “passive house” doesn’t have a very strict definition, says Christian Kaltreider, a building science research engineer at Pacific Northwest National Laboratory. It more or less refers to “the concept of a house that’s designed to passively heat and passively cool itself as much as it can.” To do this, passive houses include elements such as excellent insulation, airtight construction, efficient ventilation systems, and high performance windows. If a house has very good insulation and airflow, it can greatly reduce the amount of heating required in the winter or air conditioning in the summer.
How are passive houses designed for energy efficiency?
When designing a house and what to put in it, there are a number of strategies that can improve energy efficiency. Typically, passive homes are purpose-built to meet those standards, but that doesn’t mean that an existing building can’t adopt many of the principles of a passive home. In many cases, even in an older house, sprucing it up with a few fixes can inch even the most inefficient abode closer to passive territory.
Robust insulation
Having excellent insulation can improve the energy efficiency of any home. Proper insulation in the walls, roof, and floors will minimize heat from leaking out in winter and prevent it from creeping in during the summer. The correct level of insolation varies by region. Homes in milder climates can get away less, but those in hotter or colder areas will have higher insulation demands to meet that standard. For a house in a cool-temperate climate, the Passive House Institute says that insulation should lose only 0.15 watts per degree of temperature difference per square meter of exterior surface.
Airtight construction
If the construction in a house is not airtight, heat will escape in the winter and enter in the summer, driving up energy costs. Passive houses avoid air leaks common in places where small gaps might exist, such as around electrical outlets, switch plates, door and window frames, baseboards, attic hatches, wall or window mounted air conditioners, the entry points for pipes and wires, and where your dryer vents pass through walls.
If you’re working on converting your home to a passive (or passive-like) one, you’ll have to start by identifying any leaks. The best way to find these spots is to hire a contractor who specializes in insulation to check out your home. Checking airtightness can also be rolled into a broader Home Energy Audit, though those also fold in assessments of appliances, HVAC, and other major home systems.
High-performance windows
Like with walls and roofs, windows in passive houses are highly insulated. Instead of single-pane windows, they have more efficient double or triple-paned windows. The gap of trapped and sealed air in between panes acts as an insulator and prevents heat transfer both in and out of the house.
Some passive constructions also feature special “low emissivity coatings” for windows that will minimize the amount of ultraviolet and infrared light that passes through glass without compromising natural light.
Cool roofs and walls
Passive homes also often also take into account how the exterior color of a home can impact the interior temperature. Darker colors tend to absorb more heat from the sun than lighter one, which tend to reflect more heat away. Similarly roofs painted lighter colors tend to be cooler and minimize that heat gain—and adhere to the principles of passive homes. Roof overhangs that create shadows on the walls of a house are also a great way to minimize heat.
Minimized internal heat sources
Inefficient home appliances and light bulbs use a lot of energy. Efficient appliances use a greater proportion of their energy to do their job than inefficient ones. The best way to think about this is to imagine an old incandescent light bulb: While it does produce light, it also gets very hot when it’s turned on—that’s energy escaping as heat. Not only can this balloon your energy bill on its own, but it also increases the need for cooling to expel that excess heat.
Good ventilation
Passive homes also rely greatly on good ventilation, and there are principles here that can apply to any home, says Kaltreider. One big idea is called “comfort ventilation,” or the concept of creating airflow that directly aims to cool the people in a house rather than the whole house itself. You can achieve this with ceiling fans, window fans, or anything else that can create airflow. This method maintains comfort without using huge amounts of energy to cool down spaces that aren’t being used. Comfort ventilation can make individuals feel 4 to 5 degrees Fahrenheit cooler than what the actual air temperature is, says Kaltreider.
A second big strategy is called “exhaust ventilation,” which is the concept of removing hotter air from inside the house and replacing it with air that is cooler. Most houses already do some form of this in bathrooms: Once you take a bath or shower you can run a fan that moves that warm, humid air out while bringing in outside air that is cooler. There are whole house fans you can get that operate on basically the same principle, creating large amounts of airflow to constantly cycle out warm air.
Night flush
“Within exhaust ventilation is a more specialized and targeted and effective strategy that we call ‘night flush,’” says Kaltreider. When the summers are hot, the air outside is usually still much cooler—with night flush the idea is to store coolness inside a house during those cool nights while flushing out the warm air. By the end of the night, the air and the surfaces inside the home will be cooler. And as the day warms up, you close the house off from the outside, sealing that coolness in.
To properly use night flush, you need materials around the house that are good at absorbing heat. Concrete, marble, granite, dry wall, and metal, for example, will take heat in from the air, leaving the surroundings cooler. You can further strategize so that airflow in a house runs across these surfaces—the air will cool as it hits these materials, feeling even more refreshing when it gets to you.
Can any home become a passive house?
Even if your house wasn’t explicitly designed and built to be a passive house, some of these passive house strategies—like airtightness and good insulation—can still be used to retrofit your house. Passive houses also do not need to be single family homes. Buildings like Second + Delaware Apartments in Kansas City, Missouri, and the Park Avenue Green apartment building in New York City are some of the largest examples of passive houses.
- Monthly Energy Review, U.S. Energy Information Administration, Jul. 2024 ↩︎
- Passive House Certifications Worldwide (Cumulative), Passive House Institute ↩︎