Analysing the ecological life cycle of buildings

What is the best way to minimise the ecological footprint of a building? How can resources be conserved – not only in heating, but also during construction? What materials should be used in order to protect the environment? And which ones can ultimately be recycled?

Looking for answers to these questions when planning wagnisART, a 138-unit sustainable residential development on the site of a former military barracks, the Munich-based cooperative developer Wagnis eG contacted the Institute of Energy Efficient and Sustainable Design and Building at TUM.

That was three years ago. Prof. Werner Lang, the head of the institute, and his researchers presented the planners with the answers to their questions. The project in Fritz-Winter-Strasse in the north of Munich is the city's first cooperative residential complex for which the energy needs and CO2 emissions have been calculated and optimised across the entire life cycle.

"The project was a unique opportunity for us to work with the cooperative developer and the future residents to study the ecological impact of a larger housing project," said Lang. To assess the primary energy needs and greenhouse gas emissions over the entire life cycle, the researchers looked at a wide range of factors: the building materials, the heating energy and electric power consumed during the use of the building, the necessary maintenance processes – and the future demolition.

They also took into account the "soft" factors that cannot be measured: for example, the ideas on sustainable construction and utilisation contributed by the future residents in the planning phase – or the measures taken in the interests of a good socio-economic balance among the residents. These factors will be utilised in future projects as well.

An investigation on this scale for a larger residential development is unprecedented, says Patricia Schneider, an architect who headed the project at TUM. "Past planning approaches have generally been limited to the optimisation of energy use during occupancy." The "gray energy" needed for construction and demolition has been left out of the equation, she says. The same applies to the "soft factors" of social sustainability.

To find out how much energy the buildings would need across all life cycle phases, Schneider used a publicly accessible database to compute a 50-year life cycle assessment broken down into four phases: production, use, renewal and disposal.

Some results took her by surprise: "For example, we were stunned to discover that the biggest "gray energy" factor was the reinforced concrete skeleton needed for the buildings. It accounts for more than half of the greenhouse gas potential and primary energy use," says Schneider.

The researcher was also amazed at the sheer scale of the gray energy in the buildings: "If you take into account all phases of the life cycle, it turns out that the material in the building represents the same quantity of greenhouse gas emissions as 46 years of operations.

Moreover, the energy consumed in construction and demolition would be enough for the residents to heat their units for 14 years. This shows that the construction of a building has an enormous impact on the overall energy life cycle balance. And that the selection of suitable materials and careful planning can help to keep the environmental impact to a minimum."

It makes a big difference, for example, if residents can live without underground parking. "Due to the cement manufacturing and the steel in the reinforced concrete structures needed underground, the greenhouse gas potential is enormous," says Schneider.

In the wagnisART project, the planners were able to reduce the number of parking spaces by about half thanks to a new mobility concept. This reduced both the cost and the environmental impact.

The TUM researchers' results will be available to all architects and planners in the future. Other projects slated to receive similar planning support right from the development stage are now on the drawing board.

The cooperative developer Wagnis eG, the external sponsor of the research project, received funding from the Supreme Building Authority in the Bavarian Ministry for Internal Affairs, Construction and Transport.

"We need more housing. It's all the better when projects are socially progressive, suitable for all generations, and ecologically sustainable," said Joachim Herrmann, the Bavarian Minister of Interior Affairs and Construction:

"I not only advocated funding for the wagnisART project. We were also very happy to support the accompanying research project of the Technical University of Munich." The project partners received further expert support from the Supreme Building Authority's department for experimental housing construction and construction technology.