"By using existing technology combined in new ways, we have come up with simple and logical solutions that make it possible to transform an ordinary office building into a building that produces more energy than it consumes," says Kjetil Trædal Thorsen, director and partner in the architectural firm Snøhetta.

Snøhetta is one of the partners in Powerhouse, along with the construction company Skanska, the environmental organization ZERO, the aluminium company Hydro and the property management firm Entra Eiendom. The goal is to develop and construct buildings that produce more energy than they consume, during their lifetime.

"As far as we know, no one has previously renovated an existing office building to this energy standard. This is unique, yet at the same time it is something anyone can do," says Thorsen.

Huge potential

About 80 percent of the buildings in use today could still be in use 40 years from now. So to reduce the immense energy consumed by buildings, it is imperative to do something with the existing ones.

The total annual energy consumption of office buildings in Norway is 5-6 TWh. If all office buildings were renovated so that they produced more energy than they used, it would free up enough energy to power about 300,000 homes.

"The potential for reducing energy consumption in existing buildings is enormous. By combining very low energy use in the building with local energy production from solar cells for example, office buildings can be producers instead of consumers of energy," says Bjørn Holm, director of projects and development at Entra Eiendom.

"Green" solutions for old buildings

At Kjørbo in Sandvika near Oslo, it is expected that the two buildings will use solar cells to produce over 200,000 kWh annually. This power can be supplied to the technical installations in the buildings and also at times to the power grid.

The key to reaching this goal lies in the integration of energy-efficient technical solutions and a comprehensive architecture. The total energy requirement for the buildings' heating, cooling, ventilation and lighting is likely to be around 100,000 kWh, excluding user equipment. The energy used in the production of materials used in the buildings also needs to be taken into account, so that the overall result will be a small energy surplus.

"Through the collaboration of Powerhouse, we have created green solutions that can be implemented in existing buildings. The experience gleaned from this project can be used in other projects, and in the long term the additional costs of building in this way can be reduced to a minimum," says Anders Danielsson, CEO of Skanska Norway.

The renovation project in Kjørbo will see the buildings getting a façade of charred wood, while the indoor environment will be improved to a fully modern standard.

Aluminium profiles

Philipp Müller from Hydro Building Systems is one of the building experts who have worked most with the solutions and material selection.

"Even when you take into account their complete life cycle, including all the energy used to produce building materials, the buildings will still be energy positive. This is probably one of the world's most energy-efficient renovation projects," he says.

"At Kjørbo we will reuse existing structures and building elements. We also want to ensure that all new materials are recycled after use, without losing any of their qualities. This is one of the reasons we are using aluminium, including for all the window profiles," says Müller.

Entra Eiendom has now submitted a framework application to Bærum municipality for the renovation. Meanwhile Entra is in dialogue on a leasing agreement with the consulting company Asplan Viak, which has also participated in the development of technical solutions for the project. The renovation project is planned to start in the first quarter of 2013 and to complete about a year later.