You hear about Passive Houses popping up everywhere from San Diego to Vienna, but what exactly is a Passive House? And how are they constructed? Curbed spoke to passive house professionals Ken Levenson of NY Passive House and San Francisco-based architect Bronwyn Barry to understand the green building trend that lowers carbon emissions and energy bills.
What exactly East a passive house?
“Passive House is the radical notion that you can reliably and consistently design a building that works for humans,” Barry explained. “It’s a standard of comfort and a methodology.”
Essentially, a Passive House is designed to be extremely energy efficient, so it doesn’t require a lot of energy to heat or cool. To be designated as a passive house, a building must embody a set of specific best practices that insulate it from outdoor temperatures while maintaining a stable indoor temperature and high air quality.
These best practices were developed over decades of research conducted by the Passive House Institute (PHI) in Darmstadt, Germany. Today they are used by thousands of architects, developers and contractors worldwide. When you call a house a “passive house”, you are saying that it was built to rigorous PHI standards for insulation and energy consumption.
How does a passive house work?
“It’s kind of like building a thermos,” Ken Levenson said, “but it’s a thermos with really good ventilation.” When you want a space to naturally maintain its temperature, whether it’s as small as a thermos or as large as a house, you’re going to follow many of the same rules. Passive houses should be airtight, have continuous insulation, triple-glazed windows and an excellent air quality control system.
The house design must also eliminate a phenomenon called thermal bridging which occurs when the temperature of one material is transferred to another through physical touch, such as a cold room in winter because the steel beam supporting the floor touches the frozen brick of the facade.
By thermally sealing the interior of a space, the internal temperatures of a home are more stable by default. Implementing passive house techniques is enough to make a house 90% more energy efficient than an average house.
Why would anyone want a Passive House?
Because Passive Houses are so energy efficient, heating and cooling them costs much less than other houses. And because the indoor air temperature is so constant, passive houses are more comfortable than a home where indoor temperatures fluctuate between sweltering and freezing.
“Once you live in Passive House and hang around Passive Houses, it’s amazing to realize how uncomfortable we are in conventional buildings,” Barry said, admitting that one of her clients, a couple, had told her that they had stopped going out-of-town trips because staying elsewhere felt miserable compared to their renovated Passive House.
The air quality in a Passive House will also be exceptional, eliminating any stale smells or fumes. The air in a passive house is continuously circulated and filtered. Passive houses are also more resilient to power outages or other emergencies. Even without electricity, the home will remain at a comfortable temperature for much longer than the average building, making it a popular choice for hospitals and senior residences.
But some of the benefits of living in a passive house are less quantitative. “On a cold winter’s day, you can sit right by the window without heating and without wearing two sweaters because the temperature of the window will be very close to the temperature of the room,” Levenson said. “Comfort is the number one advantage, especially in New York.”
How do you build a passive house?
“It’s built like any other building,” Levenson told us. “Ninety-nine percent of a passive house is made with the same materials, methodologies, workers, and schedules as a non-passive house.”
Most Passive House work takes place at the design stage, as each element must work together to produce the benefits of the methodology. It makes no sense to have a fresh air exchanger if the windows in the house are leaking. It is therefore usually to reinforce the insulation and thermal insulation in the design. In fact, the execution of a passive house construction is quite simple.
Also, a passive house doesn’t have to look like a hippie Earthship. The key principles of passivity can be adapted to suit very different building styles, from extremely modern homes to rustic cabins and historic apartment buildings.
How much does it cost to build a passive house?
Generally, the larger the house, the less its passive elements will impact the overall budget. A massive project like Cornell University’s Roosevelt Island Tech Campus dormitory will cost 2-3% more to meet Passive House standards. Levenson says building a more normal-sized Passive House will typically add between 5-10% to the construction budget. But it continues to become more and more affordable as the search for new materials and efficiencies evolves.
I want to build a passive house, what is the first?
“Find a passive house consultant or certified designer before you start designing,” says Levenson. “The worst thing you can do is wait for the house to be designed and then try to add the passive elements on top of it.” For help finding someone in your area, check out the North American Passive House Network or PassiveHouse.com.