Processing houses into streets: the status quo in the building-recycling business is radical downcycling. The energy stored in supporting structures and walls is crushed to pieces, which will be used to build roads.
The only economically significant form of recycling buildings in Germany is the processing of building rubble into gravel materials.
The reuse of larger building components is problematic, especially with regard to logistics and transportation. It would be easy to reassemble redundant Plattenbau buildings elsewhere - were it not for the costs of non-destructive disassembly, transport, storage, and reassembly. A few pilot projects - such as in the Cottbus slab housing block district of Saxony-Madlow, where in 2001 the architectural firm Zimmermann+Partner had the parts of a disassembled high-rise apartment building reassembled into new town houses on an adjacent site - point to ways in which, at least locally, large components can be sensibly reused, both economically and in terms of energy. However, this presupposes a need for the “dismantled” areas, which is more likely the exception in shrinking cities. On a smaller scale, marketplaces for used building components offer networks and structures for the regional use of “secondary” building materials.
However, these exchanges only have a niche existence in the construction industry; they are primarily of interest to budget-conscious “do it yourself-builders” and aficionados of historical elements. In Germany, “professional” component must be certified through extensive testing in order to obtain building regulation approval. For used components this is possible to a very limited extent.
It follows that the status quo of recycling buildings is the use of the smallest fragments -rendering the process completely energy inefficient. According to statistics compiled by Initiative Kreislaufwirtschaft Bau (Society for the Recycling Economy in the Building Sector), between 1995 and 2009 an average of 210 million tons of mineral construction waste was incurred annually.
This represents approximately sixty percent of the total waste volume in Germany.
Of the construction waste, eighty million tons came from building demolition. Each year, nearly forty million tons of this is processed into recycled building materials.
The bulk of this recycled material is reused in Germany for road construction.
The demolished housing estates of East Germany thus serve as important “urban mining grounds” for the country’s new infrastructure as slab buildings are converted into highways. But this is only economically and energetically sensible if the dismantling site, the processing plant, and the road construction site are close together: economic viability end after about twenty-five kilometers. It is also likely that at least in the eastern part of the country, the supply of recycled materials from demolitions in the near future will far exceed their demand.
For several years, therefore, attempts have been made to use the recycled debris in higher-quality form, such as aggregate for recycling-concrete (“RC-concrete”). In Germany, this is still in the testing phase, in contrast to Switzerland, where RC-concrete is already in use. Initial studies on the energy efficiency of RC-concrete versus conventional concrete, however, show only a slight advantage, which is not even gained from the material, but from the shortest transport distance between the crushing facility and the concrete plant. In contrast to gravel pits, both are usually located relatively close to urban centers. This advantage accounts for only a few percentage points in the overall energy balance: the production process comprises eighty to ninety percent of the primary energy used for ready mixed concrete. Cement plants account for the world’s third largest source of annual CO2 emissions, just below power plants and vehicles.
The key to reducing the carbon footprint of our building thus does not lie in building component recycling, but by extending the life cycles of buildings, for example through the use of existing shells or parts of buildings rather than demolitions and new constructions . In order to achieve a general change in mindset, energy balances must consider a building’s entire life cycle. Here, too, Switzerland is a pioneer, where the energy efficiency rating takes into account the “gray energy” used for the manufacture of the building materials that are used and thus stored in the building themselves.
A building in which preexisting elements are used has a significantly better energy balance than a new building. Buildings are too valuable to merely reduce them to piles of rubble and road gravel.