“We’re very happy with 90 per cent”

Christiane Weihe

Take a derelict housing estate, use it to build a new one and, in the process, throw nothing away – can it be done? That’s what the City of Heidelberg is currently attempting to do. In Patrick Henry Village – a former housing estate for US Army families on the edge of town – every brick, toilet bowl, water tap and light switch is logged so that as much as possible can be built into the new design or passed on for reuse elsewhere. We talked to Heidelberg’s First Mayor Jürgen Odszuck about this pilot project. He is well-acquainted with the building trade: before studying architecture, he worked on building sites and, among other things, later served as Deputy Director of the Building Inspectorate in Erlangen.

Mr Odszuck, from your experience in the building sector, when did the option of reusing building materials start to play a role?

It was the established practice for centuries, but it was forgotten about in recent decades: everything had to be as quick, easy and cheap as possible. But with the multiple challenges that we face, such as the climate crisis and resource scarcity, it’s clear that this can’t continue. And the building sector can make a major contribution: after all, it produces around 40 per cent of CO₂ emissions worldwide.

Heidelberg is currently pursuing a very proactive approach to urban mining in the building sector. How did that come about?

The city is developing the Bahnstadt district on the site of a former railway freight yard, where it is consistently applying sustainability criteria with a climate-neutral heat supply. Combined with the passive house standard for all buildings, this will reduce CO₂ emissions by 85 per cent compared to the national average. However, we also see that it will take quite some time to offset the emissions from construction. We do need to address the issue of what we use to build new houses.

You have now launched a pilot project. What does it involve?

Our aim is to reuse most of the material from the demolished buildings in the new construction project. We started by setting up a digital cadastre. We now know with a fair degree of accuracy what kind of raw materials are contained in each building. In fact, we have very accurate data for a 15-hectare site. Material estimates were verified by drilling in ceilings and walls, which was also necessary due to the possible presence of harmful substances. We are now finding answers to the question of what we can reuse in the newbuilds and what we can find other uses for. We are also preparing invitations to tender for the new construction project.

Are there any plans to introduce a cadastre for the city as a whole in future?

We have considered it, because the cadastre was easier to set up than we thought. Even with basic data – the year of construction, type of use and class of building – it is possible to produce estimates of the material that a structure contains, generally with a margin of error of less than 10 per cent. In my view, however, it is only worthwhile setting up a cadastre for sites where relevant changes are pending in the next 10 years.

How much material will you be able to recycle in Patrick Henry Village?

In total, we’re talking about some 466,000 tonnes of material, including around 235,000 tonnes of concrete alone. If 90 per cent is recycled or reused, we’ll be very happy. In some cases, it’s simply not worth it – if the plaster is contaminated with asbestos, for example. It would cost too much money and energy to remove it.

And what are acceptable costs overall, compared to a newbuild using primary raw materials?

We’ll be happy whether we’re in the red or in the black. The point is that this is a far more environmentally compatible and climate-friendly way of building, and we are also trying out new methods and processes. And we shouldn’t forget the macroeconomic costs associated with environmental and climate impacts.

Are new frameworks needed to facilitate this kind of pilot project?

Certainly. For example, reuse often fails when it comes to proving the quality of the building materials obtained from recycling. But for many of the materials reclaimed from buildings that are decades old, certificates no longer exist. And the people who are keen to use these materials are justifiably concerned about problems with guarantees. New approaches are needed here in order to mitigate the risks for the persons concerned.

Thank you for talking to eco@work.

The interviewer was Christiane Weihe.

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Talking to eco@work: Jürgen Odszuck, First Mayor of the City of Heidelberg