What is Passive House?
Updated: Mar 6
TLDR: Passive House is a building standard that emphasizes better wall construction, a tight building envelope, and great HVAC systems. Homes built to this standard are, quite simply, better homes. They are quieter, promote the health of their occupants, and cost less to heat and cool. They are built to the highest energy-saving standards in the U.S.
Passive house is a concept that started in the US and Canada back in the 70s, as a response to the OPEC nations choking global oil supply and forcing energy prices higher. The goal was to develop a set of building standards that led to structures that were much more energy efficient. As global oil restrictions eased in the 80s, enthusiasm for energy efficiency waned, and the project stagnated in North America. However, scientists in Germany and Sweden picked up the ball and ran with it, developing a full standard and constructing the first passive house in Darmstadt, Germany, in 1991. They also founded the Passive House Institute (PHI), which is headquartered in Darmstadt.
Interest in the US picked up again when architect Katrin Klingenberg, who had worked with the European founders of PHI, constructed a home to passive house standards in Urbana, Illinois in 2003. Since then, the movement has grown and the standards have spread. Not only have they spread, but they have been adapted because the United States is such a large country. As the Twittersphere pointed out in 2020, if you drive four hours in America you’re still in the same part of the country, whereas if you drive only two hours in Europe, the language may have changed twice and the name for bread rolls has morphed four times. Because America is so large geographically, the PHI standards have been adapted to different climate zones. Passive House Institute U.S. (PHIUS) was formed and the differing standards based on climate zones were adopted. Here is a map of the climate zones in the U.S.:
What this means is that for each zone in the U.S., different passive house standards will apply in order for a structure to attain the Passive House certification. To draw a simple comparison, you won’t need the window that insulates well against North Dakota cold if you live in temperate Northern California.
So where does the name come from? To put it simply, a passive house doesn’t have to have systems that work as hard in order to keep its indoor environment controlled and dry. A passive house can let its design and construction work with the local geography and climate for much of its heating and cooling. Passive houses achieve this by combining an air-tight building envelope with a lot of insulation and being designed to work with the sites they sit on. For example, in Tennessee we would build a passive home with large windows under a substantial overhang on the south side. The overhang will keep out the harshest summer sun while letting in plenty of light in the winter. A moderately high solar heat gain coefficient and low U-value will let in solar heat during the winter while the low U-value will slow down the flow of convection heat from one side of the window to the other. I take a deeper dive into window ratings in this article:
Staying comfortable in today’s weather extremes requires some work, and the large amount of insulation in a passive house alleviates much of the heating and cooling. However, we still have to consider fresh air, humidity, and air quality. The HVAC system in a passive-house building might be a lot smaller, but it runs continuously, supplying you with fresh, filtered air.
While a well-insulated building envelope decreases the energy required to heat and cool a home, an airtight building envelope not only contributes to that effort (by eliminating cold drafts, for example) but reduces moisture penetration both into the wall cavities and into the home itself. An airtight envelope also helps keep pollutants at bay, stuff like pollen, smoke, and dust. What this means is that you are in complete control of your indoor air environment.
First of all, you need fresh air coming in and stale air going out. Next, put in a heat exchanger so the masses of moving air equilibrate as they move past one another, thus taking work away from your heating or cooling system. After that, you could add a purification system to eliminate the dust and allergens, and you can also add humidification or dehumidification. In the end, you want an HVAC system that keeps you comfortable and healthy.
Lots of people still think you want drafty walls in your house. With traditional construction, that’s true. Normal wood walls in volume-built homes are built to let air in, to dry the moisture that also flows freely through them. In other words, the failure and the mitigation are both built in. With the passive house standard, we basically build better walls, which changes the focus of our HVAC system.
To sum things up, to build to the Passive House standard is to build a better building. The walls are better, the homes are better insulated, there are fewer mold—and other pollutant—issues, and the HVAC systems more completely care for the occupants. Also, Passive House is not new, it’s simply unusual for the mass-produced American market. In today’s housing climate of entire new neighborhoods thrown up as cheaply as possible, it’s important to know a more careful, longer lasting, and healthier alternative exists. Give us a call at (615) 898-9115 today so we can start work on a home you can be proud of.