The building's heating requirements are more than 90% less than a comparable new building, thanks to the large south-facing glazed area combined with outstanding thermal insulation and the timber and concrete storage mass integrated into the building. A great deal of attention was paid to the building materials used, to ensure that they con-tained as little "grey energy" as possible; in other words only local timber cut and processed in the region was used in the construction.
Source and information: http://www.solaragency.org/Solarpreis2000 (de)