Can you imagine a “harmless” building? That’s the impetus behind a Passive House, a new or retrofitted building with the singular goal of minimizing energy consumption. One such project, a home in Oregon, is so air tight that it was heated last winter with $12 and the help of the family’s Xbox.
With about 50,000 Passive House units worldwide — and about 100 in the United States — the movement is doubling every year. I spoke last week with Sam Hagerman, a construction company owner and president of Passive House Alliance United States. Below are excerpts from our interview.
What is a Passive House?
Passive House translates more closely from the German to mean harmless building. It’s not directly related to houses. We build commercial buildings to the Passive House standard too.
It’s a performance-based energy standard. Building code in the United States is mainly prescriptive. It tells you what materials to use and how to assemble them. A performance-based standard like Passive House gives you benchmarks to hit in terms of energy consumption. Passive House has a specific maximum energy you can spend per square foot on heating and cooling (4.75 kBtu per square foot per year). It also has a total per-square-foot limit on energy consumed at the site by the structure (38.1 kBtus per square foot per year).
The third measure is an air-tightness standard (air exchange rate less than 0.6 air changes per hour 50 pascals). That’s speaks directly to the fact that Passive House concentrates on minimizing the heat load in the house. If you don’t spend much energy heating the house, you spend radically less energy overall. It follows that the best way to reduce the heat load in a Passive House is to make sure you have an airtight envelope. If you managed for air, you’ve managed for water intrusion and energy leakage. Air is the easiest thing to lose. A very tight house, like an Energy Star 3 house, gets six air changes per hour. We’re 10 times more airtight than that.
You mentioned that Passive House is translated from German. Did this movement come from Germany?
The super-insulated home concept started in the United States and southern Canada. In the ’70s there was a movement to build houses to emphasize air tightness, along with super-insulated walls. They started to study the heat requirements and tried to figure out how to eliminate a traditional heating system. In 1980, a book called The Super-Insulated House talked about an air exchange rate being less than one air change per hour. At that point, a lot of this research done through the university system was being funded by the Department of Energy. When Reagan was elected, the DOE’s budget was slashed and redirected. All the funding for this type of energy conservation went by the wayside. A lot of the American scientists went to Europe. The Europeans had been studying, in Sweden and Germany, along the same lines. Into the early 1990s, they made these concepts more formalized with computer modeling and specific standards. That was all done under the auspices of Wolfgang Feist in Germany. He came up with the name. One of his protégés moved to the United States and promoted Passive House in 2003.
How many Passive Houses are there? How fast is the number growing?
There are about 50,000 units in existence. I’ve seen 300-unit apartment buildings in Austria that are Passive House. The past two Winter Olympics have had Passive House buildings, whether they’re dormitories or apartments or administrative buildings.
Probably only 10,000 of the buildings are certified by any of the certification agencies. The certification agency in the United States is PHIUS. There are around 100 structures built or being built in the United States. Just a few years ago, we only had one. We’re seeing now that sense of doubling every year. The idea of Passive House has reached critical mass in the design community and the energy efficient community. It’s a cohesive system that allows you to understand how to measure a building and implement it using sound building science principles.
Could a Passive House certification be combined with LEED certification?
I think people would do both. I have a project now doing LEED Platinum and Passive House. Passive House has a laser focus on energy consumption, specifically heat load. It doesn’t address other aspects LEED addresses, like site use, water, toxicity of materials. It is only about energy. But it’s more effective on addressing energy than LEED. The sustainable building marketplace is huge. Passive House folks tend to be focused first and foremost on energy.
How much more expensive is it to build a Passive House? Do developers feel they can build these and still make money?
I think developers do. It’s difficult to justify it unless you take the cost out over 10 years. We need 10 to 15 — or even 20 years in some cases — to show it will save energy. That’s primarily because energy is cheap right now. Natural gas is cheaper than it has been in decades.
We’re addressing these issues in terms of what the real costs are and balancing them against energy savings and, most importantly, home performance. The structures are durable because they’re so well-built. They’re unprecedented in comfort. There are no drafts. They’re super quiet. Because Passive Houses have a constant influx of heat exchange to fresh air, the indoor air quality is superior.
There are plenty of reasons to justify a 5 to 10 percent increase over conventional construction. Our goal is to make this as affordable as possible. If it’s a great idea, but comes at a huge cost premium, its adoption will be completely minimized.
Is it possible to retrofit an older house to meet the Passive House standard?
It’s possible to retrofit, but it’s widely considered to be more difficult. If the house has a basement or you can’t access the foundation, you have to make an allowance for the heat loss to the ground. The difficulty of retrofitting a house to the Passive House standard is this concept of insulating the building to the ground. It’s sometimes not possible.
Other than that, if you’re taking the siding and roofing off the structure and you’re replacing the doors and windows, you have a really good shot at doing a Passive House retrofit.
What are some specific Passive House buildings in the U.S. you can talk about?
The first Passive House in Oregon is a house that looks quite conventional. Its heating bill last year cost $12 [of electricity to run the ductless mini split]. The joke is that these are houses you could heat with a hair dryer. That house in Salem, the heating system never came on. An Xbox was heating that house. It was able to generate enough heat on the coolest days to heat that house. [Free heat gains from occupants and passive solar satisfied two-thirds of the heat demand.]
If you’re not the one paying the heating bills at a Passive House, would you notice a difference from a conventional building?
We’re working on a Passive House project now that’s a commercial retrofit of an office space. It is 1,500 square feet. The fire marshal has the space rated for 75 people. An airtight building rated for 75 people needs to have real planning around making sure the air quality stays good. We used a heat recovery ventilation system that has carbon dioxide sensors. When the carbon dioxide levels go up, it will ramp up the equipment to bring in more fresh air.
These spaces are extremely comfortable. It’s a space that doesn’t have any drafts, so you’re not cold at your desk. You’re not hot when it gets hot outside. You’re protected from outside noise. The indoor air quality keeps everybody awake and alert.
What’s next for the Passive House movement?
We’re reaching the point where there are enough Passive Houses around that more than a few people can experience them. As we get more units built, more people will find out how great they are by being inside them. That will give the idea legs.
We’re at the point where we have proof of concept. Those of us who are practitioners have known this all along, but it’s taken this long to get enough structures so the proof of concept is on the ground. That you can measure for air tightness and calculate the heat load for a building, the whole built community is developing this knowledge across a broad base. These are the kinds of things we need to understand and practice to build Passive Houses.
Photo, top: Sam Hagerman
Photo, bottom: A Passive House in Bethesda, Maryland / By Peabody Architects