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Passivhaus building design concept brought to midcoast

by: Paul Kando

A thousand building scientists, researchers and practitioners from forty-three countries gathered at Innsbruck University in Innsbruck, Austria over the weekend of May 27 for the 15th International Passivhaus Conference. Ours was an intensive exchange of ideas and techniques on how the Passivhaus design approach can be adapted to buildings in various climates and how local building traditions and techniques can be integrated with it.

In such a limited space it is not possible to do justice to the over one hundred presentations and nearly as many special product exhibits and site visits we were treated to over the past three days. So let me instead briefly describe what the Passivhaus design concept is and how it's adoption can benefit us here in Maine.

Passivhaus ("passive house") is a building design standard developed gradually over time, beginning in the 1970s, by two scientists: Dr. Bo Adamsson, a Swede, and Dr. Wolfgang Feist, a German. Feist currently heads both the Passivhaus Institute in Darmstadt, Germany and the Department of Building Science he founded at Innsbruck University.

The passivhaus concept is based on building physics and heat transfer calculations facilitated by a computer-based design tool called the Passivhaus Design Package (PHPP). The goal is to create a building that delivers maximum comfort and energy efficiency without relying on the active participation of the occupants -- a building that will function efficiently regardless of the habits of its inhabitants, hence the "passive" label.

Viewed from the outside, Passivhaus buildings are no different from other buildings. The term describes a minimum performance standard a building has to meet, rather than a specific method of construction. The standard applies not only to houses but to any building, regardless of size or the climate in which it is located.

The heart of the standard is simplicity itself: The building must not use more than 15 kilowatt-hours (kWh) of energy for heating or cooling per square meter of floor space per year; It must not use more than 120 kWh/sq. meter per year of total energy for all purposes; and it must not have more than 0.6 air changes per hour at a measured indoor-outdoor pressure difference of 50 Pascals. These are calculable values. In practice many Passivhaus structures outperform these requirements.

The devil is in the details. Passivhaus buildings rely on exceptionally high levels of thermal insulation, well insulated, thermal-bridge-free window frames with triple low-e glazing, thermal bridge-free construction throughout, an air-tight building envelope, and comfort ventilation with highly efficient heat recovery. The result is a house or building that uses no more than 10 percent of the heating energy required by an ordinary building of comparable size.

The average Maine house currently burns 850 gallons of oil per year, so it's Passivhaus equivalent will burn only 85 gallons -- translating to a heating bill (at a cost of $3.70 per gallon of heating oil) of $315 instead of $3,145.

Over 32,000 such structures have been built worldwide, so there is no valid "can't be done here" argument against the Passivhaus standard.

But isn't there a prohibitive extra cost involved? Passivhaus construction in the United States currently costs about 10-15 percent more than conventional building, principally because some of the components (notably the windows) are difficult and expensive to come by.

On the other hand, a Passivhaus home in Maine will not require a conventional heating system. Given this saving and the over 90 percent reduction in heating costs, the extra up-front cost is quickly amortized from savings on energy bills. The result is that the occupants of a similar conventional house will end up paying $50,000 to 60-000 more over the term of a mortgage.

What about our existing houses? Can they be cost-effectively upgraded to Passivhaus performance? This question has been the subject of our research at the Damariscotta-based Midcoast Green Collaborative. It began when my colleague Topher Belknap and I decided to offer energy audits to area homeowners and found that all the available computer software fell short of our expectations.

So Topher wrote a brand new energy audit software which incorporates features of the PHPP. This enables us, unlike other home energy auditors, to evaluate each house we audit in terms of passivhaus design principles and provide energy-upgrade recommendations consistent with passivhaus design.

Having conducted over 200 home energy audits, we have built a large database about area houses, including records of specific recommendations given in each of our energy audit reports. These records are, of course, confidential and implementing those recommendations is up to the owners of those homes. However, assuming that the recommendations are implemented, our research shows that the energy consumption of typical houses we have audited - many of them 19th century structures - can be reduced by 50 to 80 percent without major renovation. This is often accomplished through simple home repair well within the competence of the average homeowner, performed at the home owner's leisure.

The typical old Maine farm house may never fully meet the performance requirements of a new passive house at a reasonable cost, but it can come close enough for us to have reported on it for the benefit of the worldwide building science colleagues here in this stunningly beautiful city, cradled by the still snow-capped Tyrolean Alps.