Interview with Passive House Pioneer

March 03, 2011
March/April 2011
A version of this article appears in the March/April 2011 issue of Home Energy Magazine.
Click here to read more articles about Passive House Approach
(Passivhaus Institut)

Mary James, author of two books on Passive Houses, conducts an exclusive interview with Wolfgang Feist, scientific director of the Passivhaus Institut (PHI) in Darmstadt, Germany, and now also professor of building physics at Innsbruck University.

How many Passive House (PH) retrofits have been certified by PHI?

Some ten buildings have been certified as retrofits, but much more have been done but not certified, mostly in Germany and Austria.

Has the slightly more relaxed PH standard for retrofits, the EnerPHit standard, changed this situation?

It just started in May, so there hasn’t been much time. But there was a quite good reaction on the ground. Doing refurbishments is much more difficult than new construction. Most haven’t been able to meet the new-construction standard, but they will be able to meet the EnerPHit standard.

At the PHI conference in Germany in 2009, there was a presentation of a theoretical study of phased retrofits, in which building components are sequentially improved with an eye to eventually meeting the PH standard. Have there been any case studies of phased retrofits?

No, because it could take 15 to 20 years to do the whole thing, including changing windows, retrofitting the roof, and adding external insulation. For most of these projects there is no ongoing monitoring and so no data. The results, the final performance, we just get from buildings that do the whole process. But most refurbishments in Europe are done step-by-step in the phased way, because that’s how people can afford it. They just start with things they have to do anyhow, and that might be windows, or it might be a new roof, or new cladding. Most people will wait until these replacements are necessary anyway. Otherwise you have the whole cost, and it is much too expensive. The problem is that an evaluation of this approach will take a very long time.

I agree that is how a retrofit generally gets done. But this approach requires a long-term plan, and the problem with that in the United States is that people tend to move so much.

Yes, a long-term plan needs to be somehow fixed to the building. Frequent moving makes it more difficult in the United States. But when people move into a new building, they tend to make changes, so that is another opportunity to add high-quality components.

How has the PHI been communicating this message that, when making a change to a home, you should do it with the long-term efficiency of the building in mind?

We communicate it all the time. It’s most important to educate architects and all of the craftspeople that work on-site. We started a new educational effort last year, the PH designer course. This special course on PH construction is a European Union-funded educational program that started in October last year. Already 900 people have taken this PH training. In the United States you have a similar education available [offered by PHIUS]. The knowledge and background needs to be available to all people who are involved in refurbishments. What’s really good is that in Germany there are incentives for doing refurbishments. If you exchange a window and get a very good-quality window, you can get a low-interest loan from a government-owned bank that is 1–2% below market interest rates. The loans are linked to requirements for the components used, such as the quality of the windows or a certain amount of insulation. It has to be better than what meets the ordinance or building energy standard. We have spent some billions of euros in the last year for those incentives for better retrofits.

Those incentives have been available for a while, haven’t they?

Yes, those incentives have been available for four years, but we are always lifting the bar. When they started, there were no monitoring requirements or quality assurance. But we soon realized that it was very important. Now to get a loan you have to meet quality assurance measures. For example, there has to be a calculation of the values, a quality check on-site for thermal bridging, and a pressurization test. I tried to have that type of requirement linked to the money from the beginning, but I wasn’t successful, since the financial sector first organized it and didn’t fully understand. Later there was some monitoring in some of the first buildings where this money was used, and it was realized that a quality assurance check was needed. Now the requirements are maybe too radical, because I want to see most of the money going to substantial improvements of the buildings and not quite so much to engineers giving advice. But it is much better to have some quality assurance than none.

Have low-interest loans then been the most successful strategy for promoting retrofits?

Yes, in my opinion low-cost loans are the most successful strategy. Now we are also asking for tax reductions in Germany, since loans don’t affect how high your taxes are. At the moment, since we have very low interest rates, it might be better to take a loan even if you have the money and spend your money on something else.

How does the climate type affect a PH retrofit? Can it make a retrofit more cost-effective?

This research has to be done in the different regions worldwide. We have done research in some different climates to see what measures should be taken. But refurbishment research will have to be done on a regional basis, because there is not only the question of climate issues but also the question of what the local building traditions are. What does a typical existing building look like? The typology of local buildings needs to be ascertained. For a government that wants to promote refurbishments, this might be one of the best investments.

What are the typical buildings you find, and what are the best refurbishment recommendations?

We have done it in Germany, and now there is [research] being done in Belgium. If you are doing a room retrofit anyway, you can always find measures to improve the overall performance of the building. For example, if you are adding a new roof anyhow, adding more insulation at the same time won’t greatly increase the cost. And it is always a good recommendation in a retrofit to improve the airtightness of the building. If you are planning to improve it, it doesn’t cost much more to do it very well. I don’t agree that it is much more expensive to do it to a very high performance standard. On the contrary, you have to uncover the exterior components anyhow, and that is the bulk of the work that needs to be done. Similarly, adding airtight sheathing can be done in a very well-improved way from the beginning. Doing it just not so well will have some cost, but doing it better than it is normally done won’t make much of a cost difference.

Why did you move to Innsbruck?

I’m still the scientific head of the PHI, but now I am also teaching building physics at Innsbruck University. It’s very important to make this knowledge available for engineers and architects, as part of their education. In Innsbruck we have a newly established part of the PHI. It’s a good development to foster the PH concept.

Are there any cooperative partnerships with universities in development in the United States?

No, but at Parsons The New School for Design in New York, they are already teaching this approach. It’s good to see that Parsons is very involved in this type of education, as it’s a very traditional architecture school, concentrating on the arts.

Building physics is not a common part of an architectural education in the United States.

Building physics isn’t taught much at universities in Europe, either. That’s a problem. We have missed some of this study in the past 30 years, because energy was so cheap. Nobody cared about it.


Mary James is the editor and publisher at Low Carbon Productions and former publisher of Home Energy. She is the author of Recreating the American Home: The Passive House Approach and coauthored Homes for a Changing Climate: Passive Houses in the U.S. with Katrin Klingenberg and Mike Kernagis.

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For more on the Passive House approach and to purchase the author’s books, go to:

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