Retrieve, rework, reinstall

Whether you build a con­ven­tional house or one that fulfils the cri­teria of the cir­cular economy, urban mining and cradle to cradle makes a big dif­fe­rence at many points from planning to com­pletion. To find out what this means in con­crete terms, however, you first have to build this type of house. This is exactly what the City­förster archi­tecture firm set out to do with the recy­cling house, designing an expe­ri­mental resi­dential building and over­seeing its con­s­truction until the keys were handed over.

The recy­cling house in Hanover’s Kronsberg dis­trict was com­pleted in summer 2019. “It is a pro­totype that tests the pos­si­bi­lities and potential of dif­ferent types of recy­cling in a real-life labo­ratory and demons­trates a cycle-ori­en­tated and resource-saving planning approach,” says Nils Nolting, architect at City­förster, who super­vised the project. “We used recycled and reclaimed mate­rials to an extent not seen in any other building in Germany up to the time of com­pletion.” The aim was to signi­fi­cantly reduce grey energy and save con­siderable resources in the building con­s­truction process. City­förster drew on various sources to achieve this. In terms of the carbon foot­print, including transport routes, the project also bene­fited from the fact that many of the com­ponents could be sourced directly in the region.

As far as pos­sible, City­förster initially used second-hand com­ponents. “Around 90 per cent of the façade cladding is made from used com­ponents, as are all the windows and exterior doors,” says Nolting. Recycled com­ponents and mate­rials were also used almost entirely for the interior fit-out and outdoor areas: for example, trade fair con­s­truction panels for interior walls, floors and doors or used con­crete paving slabs as screed repla­ce­ments on board pile cei­lings and as lawn stones, kerbs and walls.

Packing, storing and cleaning building mate­rials

Between retrieval and reinstal­lation, the com­ponents usually had to be reworked. A few examples: Pro­filed building glass, which is now used as façade cladding, was in the meantime packed, stored, cleaned and sorted  before instal­lation; window ele­ments were upgraded for energy effi­ciency with 3‑pane glazing before instal­lation. Various steel U‑profiles also had to be stored tem­po­r­arily after removal before they were cut to size. They now serve as fall pro­tection in the stairwell, as a sub­s­tructure for stair landings and as steel frames for floor-to-ceiling doors.

Where City­förster was unable to find used com­ponents, the team used recycled building mate­rials from the building mate­rials market: including various pro­ducts from glass recy­cling (foam glass gravel, gra­nulate and panels), various recycled chip­pings and façade insu­lation made from recycled cocoa bean jute sacks. “We also used indus­trially recycled mate­rials,” explains Nolting. “The foun­dation made from recycled con­crete was the first to be approved in Lower Saxony.” If material had to be sup­ple­mented else­where, the team used recy­clable building pro­ducts. “Like most building pro­ducts, we installed the shell made of glue-free solid wood ele­ments in a recy­clable way” says Nolting. “This means that when they are dis­mantled, they can be broken down into their com­ponent parts again without any loss of quality.” Cir­cular con­s­truction site orga­ni­sation also meant using almost all the lef­tover mate­rials from the con­s­truction process.

Working through the service phases in a non-linear way

“Designing and con­s­tructing against the backdrop of limited avai­la­bility of resources, raw mate­rials and building mate­rials places com­pletely dif­ferent demands on the design process than on ‘con­ven­tional planning’,” empha­sises Nolting. “For example, planning with used com­ponents and their dimen­sions and quan­tities deter­mined by the existing situation of the ‘raw material sources’ requires an agile, partly ‘reversed’ planning approach – a non-linear pro­cessing of the service phases, spe­cific detailed solu­tions and special legal framework con­di­tions.” Another challenge is the pro­cu­rement of sui­table used com­ponents: “ A pro­fes­sional used com­ponents market has so far barely been estab­lished.”

In this respect, the framework con­di­tions for the recycled house were favourable. The client of the house, the Hanover-based housing and con­s­truction company Gundlach, was able to supply a large pro­portion of the used com­ponents itself. Their own stock, demo­lition and remo­delling pro­jects pro­vided a really good material basis for the project – an important pre­re­quisite for the success of the project. “We had direct access to used building mate­rials with know­ledge of their avai­la­bility in terms of time and quantity,” explains Nolting. “We were also able to verify the material pro­perties of the com­ponents based on the available docu­men­tation on our own building stock.” The data on used com­ponents plays an important role, as it must be pos­sible to plan with the used com­ponents. “For this, it is helpful or even necessary that dimen­sions, con­s­truction dra­wings, U‑values, etc. are known or can be obtained,” empha­sises Nolting. “In addition, all com­ponents must be approved and their product pro­perties must be veri­fiable, for example by means of con­formity marks, delivery notes and data sheets.”

Planning the shell con­s­truction starting from the windows

Once the City­förster team had estab­lished the basic planning para­meters and iden­tified material sources, the detailed planning began with used com­ponents. “This required new design methods,” says Nolting. “We had to translate the ‘coin­ci­dence’ of the available building mate­rials with their spe­cified quan­tities and dimen­sions into dedi­cated planning –  similar to a jigsaw puzzle.” This resulted in unex­pected design and func­tional benefits during the con­s­truction process. As an example of a tem­poral, non-linear shift in planning ser­vices, Nolting cites the element planning of the solid timber shell con­s­truction in com­bi­nation with used com­ponents: “We had to plan the shell con­s­truction at an early stage based on the existing, unch­an­geable dimen­sions of the used window ele­ments and the façade cladding made from used mate­rials.” Once the approval planning had been fina­lised, the extended building shell (shell, façades, roof) was deter­mined. At this point, it was also clear which mate­rials were sui­table for which use – and above all: that they were available. Then con­s­truction began. “Many other design decisions – such as those relating to the interior fit-out and open space design – were made gra­dually during the con­s­truction phase,” says Nolting. “In some cases, we also had to react to the changing avai­la­bility of building mate­rials over time.” The building was the­r­efore further designed during the con­s­truction process.

Between scarcity and abun­dance

“The ‘quantity game’ also played a role here – in other words, too little and too much of the mate­rials used for the respective planned purpose,” explains Nolting. “We were able to com­pensate for insuf­fi­cient quan­tities of mate­rials by using other available mate­rials in ‘missing places’.” If larger than required quan­tities of certain mate­rials were available, the team was able to either create addi­tional, ori­gi­nally unplanned added value on the building itself – or find uses for lef­tover mate­rials in other con­s­truction pro­jects.

“In order to enable the reuse of com­ponents on a broader basis in the future, we need access to infor­mation about the pro­perties and – timely! – avai­la­bility,” sum­ma­rises Nolting. “Com­ponent infor­mation could also be dis­c­losed as part of a demo­lition notice. This would also make com­ponents available on a larger scale for cir­cular reuse.”

Smaller archi­tec­tural firms and deve­lopers will have to be patient until the necessary infra­structure has been deve­loped to build houses according to the cri­teria of the cir­cular economy, urban mining and cradle to cradle with similar effort applied in con­ven­tional pro­jects. Nevert­heless, there are already sources of used and recycled building mate­rials in many regions. Early research at com­ponent exch­anges and online mar­ket­places is wort­hwhile in order to plan and con­s­truct at least parts of a building sus­tainably.

House & energy

A living space of around 156 square metres extends over two full storeys and a stag­gered storey. Attention was also paid to energy effi­ciency in terms of ope­ration. Despite the extensive use of recycled com­ponents, the house achieves an energy standard of at least KfW Effi­ciency House 55. In addition to the insu­lation, the building ser­vices con­tribute to this: An air-to-water heat pump with solar thermal support heats the building, accom­panied by a con­trolled domestic ven­ti­lation system with heat recovery.

Text: Lars Klaaßen, March 2024

Photos: © Olaf Mahl­stedt, Sascha Priesemann/ Fa. Gundlach, Hans Schaper/ Fa. Gundlach, City­förster Archi­tekten

About the author:
Lars Klaaßen, jour­nalist, has been working as a free­lance author and editor — among others for  taz, Süd­deutsche Zeitung, Deut­sches Archi­tek­ten­blatt and sci­en­tific insti­tu­tions — since 1989. He spe­cia­lises in the fields of archi­tecture and urban deve­lo­pment, con­s­truction and housing as well as energy tran­sition and climate change. www.medienbuero-mitte.de

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