It was a mild spring evening in the Schiffbauergasse in Potsdam when Hans Joachim Schellnhuber gave his much awaited speech to the assembled convention of Germany’s Bundesstiftung Baukultur. Schnellnhuber sees wood as the building material of the future - the only way to filter carbon from the air in large quantities and to bind and store it in new buildings for periods up to 100-200 years. In this way, building materials function as carbon-reducers and cities as carbon stores. A simple and captivating line of argument, particularly convincing as an alternative to the energy-intensive and hugely CO2-generating steel and cement production for standard building construction. The applause for the award-winning climate researcher and globally renowned consultant was enormous and filled the hall to the rafters. 

Only Werner Sobek, a star among the world's engineers, shook his head several times, took the microphone, publicly disagreed with all the points of his esteemed predecessor and then announced his own lecture.

The audience's curiosity could hardly have been greater when he took the stage the following morning. Sobek demonstrated that only 30 % of a tree cut in the forest is used in the production of building materials. The rest, such as the root system, branches and leaves, bark and remains that fall off during sawing, are destroyed by bacteria or by burning.  In this way the carbon re-enters the atmosphere in form of CO2. "Leave the trees in the forest!" he exclaimed to the audience and "Stop building!".

What can we draw from these contradictory positions of two knowledgeable researchers? Does it mean that we have to stop new construction immediately? Stop all activities and come to terms with the status quo? In light of the existence of millions of old buildings with oil burners and uninsulated exterior walls, to me this seems to be no solution. Nor can the lack of housing in urban locations be mitigated by the refurbishment of the existing old buildings in stock. And what can be said by the predominantly young people in Africa or Asia, whose cities with millions of inhabitants are yet to be built in the next few decades?

The area of consideration

In their study "Taking Responsibility", Kunibert Lennerts and Norbert Fisch looked at the "path to climate neutrality in the building sector". The path already begins with defining the appropriate area of consideration for the real estate sector. The ‘polluter pays principle’ (Verursacherprinzip - 40% of German greenhouse gas emissions) and not the ‘source principle’ (Quellprinzip) of the federal government (16 %) should be attributed to the building sector. This includes not only 120M tons of on-site emissions from oil and gas boilers, but also 122M tons from electricity and district heating, as well as 54M tons of grey emissions for materials and construction processes per year.

At first this sounds logical, responsible and considerate of the bigger picture. But according to this calculation, the building sector would not be able to achieve these extended goals without the de-carbonization of the energy sector with the balance-sheet  of electricity and district-heating, as well as of the industrial sector with cement and steel production. In other words, if the energy sector does not deliver green power, very little goes in the real estate sector.

Power demand will continue to grow exponentially in the coming years, from 190 GW today to almost 500 GW by 2045! Therefore, the de-carbonization of power generation is the decisive factor for achieving all climate protection goals. And the energy industry is essentially responsible for this.

Without green power, little is possible

Such a reduction in greenhouse gas emissions can be achieved faster and more effectively through the massive expansion of renewable energies, which is in any case necessary, Lennerts and Fisch argue. Then there will be enough green power with which we can continue to build in steel and concrete without a guilty conscience. As a start that makes sense to me. The 16 blast furnaces and 53 cement factories in Germany should be able to be supplied with green power in the near future. But back to the building sector. What is it doing now for de-carbonization?

New construction burdens the balance sheet

As long as materials and building products such as concrete, steel, aluminium, glass, PV modules and technical equipment cause high CO2 emissions during their production due to the use of fossil fuels, new construction is responsible for over 20 % of national, building-related greenhouse gas emissions. That is around 62M tons per year. This almost completely devours the possible savings through operational optimizations, the expansion of renewable energies or the reduction of consumption.

With the use of fossil-derived building materials without a well-organized circular economy, new construction, even as timber construction, cannot contribute to a reduction of emissions in the building sector. Because even the most innovative timber construction releases emissions. The bitter truth.

Focusing on the existing stock

Halving CO2 emissions by 2030 can only be achieved by focusing on measures in the renovation of existing buildings that can be implemented in the short term. In this way, the negative balance of new buildings could be compensated for and the existing potential could be exploited. On the fast track to a climate-neutral heat supply for buildings, fossil fuel heating systems (5.4M oil and 13.9M gas) must be replaced by electricity-based heat generators. These can be powered on a building scale by photovoltaics on roofs for electricity production and electric heat pumps. At the neighborhood and district level, the aim is to expand and de-carbonize district and local heating networks. The ecologically sensible options for further improving building envelopes have been exhausted. In Germany, about 90 % of existing buildings are poorly insulated. Even more insulation leads only to small savings in heating, consumes resources and thus increases emissions. That’s one reason for the existence of millions of energy-inefficient buildings, including those with smooth façades from the 1950s to 1980s.

There is a lack of skilled workers
In recent years, not even 1 % of the existing building stock has been renovated for energy efficiency. Lennerts and Fisch demonstrate that a short-term doubling to 2 % is not feasible due to the shortage of human and material resources in Germany.
If one assigns a proportionate number of employees from the construction industry to the energy-related renovation measures, then about 350,000 employees are necessary for these activities. Therefore, doubling the 1 % renovation rate would require an additional investment volume of at least 62B Euros and another 350,000 employees. But where are they supposed to come from?

"Too bad, but we can't save the climate".
With that, the whole beautiful calculation collapses. At this point, the real estate industry is already saying that it cannot achieve halving the greenhouse gas emissions for the building sector by 2030 on its own. Unbelievable. After decades of discussion and debate, the real estate industry still comes to the negotiating table empty-handed: too bad, we would love to take responsibility, but given the current lack of staff and materials, we can't do more.

We can operate existing facilities more economically. That costs nothing.