Building on the past
Demolition is not the only option: two ETH professors aim to give buildings and building materials a second life.
The principle of repairing rather than discarding, thereby conserving scarce resources and cutting carbon emissions, has now taken hold in many parts of society. Yet on construction sites in Zurich and cities around the world, the reality looks a little different. Here, older, smaller buildings are often demolished and replaced by new and larger ones. There are various reasons for this: a shortage of housing, a desire for greater urban densification and the need for better thermal insulation to protect the climate. As a result, cityscapes are changing rapidly. Meanwhile, all the concrete, bricks and steel produced at great energy cost decades ago either end up in landfills or – in the case of steel beams – are melted down and replaced with new steel, likewise produced with a great deal of energy. The construction industry remains one of the largest contributors to global warming.
Yet it doesn’t have to be this way. Catherine De Wolf, Professor of Circular Engineering for Architecture at ETH Zurich, calls for the creation of a circular economy in the construction industry. “We need to reduce demolition and adopt different building practices,” she says. This applies equally to buildings of an older vintage. If possible, they too should be left standing and then renovated and extended if necessary. Where this is impracticable, the building materials should at least be reused in other buildings to give them a second life. Four years ago, De Wolf was instrumental in ensuring that the glass canopy surrounding the outside escalators at the Centre Pompidou – the celebrated Paris museum of modern art and culture currently undergoing renovation – was reused rather than scrapped. The glass elements were given a new lease of life as partition walls in an office building.
Sustainable by design
Orte stiften Identit?t
Auch Maria Conen, Architektin und Professorin an der ETH Zürich, ist es wichtig, Bestehendes zu nutzen. In ihrem Architekturbüro Conen Sigl Architekt:innen besch?ftigt sie sich bereits seit Langem mit dem architektonischen Erbe. In ihren Bauprojekten versucht sie jeweils, bestehende Geb?ude durch Umbau und Erweiterungen bestm?glich weiterzuverwenden. Anf?nglich stand bei ihr nicht einmal der Klimaschutz im Vordergrund. Es geht ihr auch um kulturelle und soziale Aspekte. ?H?user und Orte haben eine Geschichte, und wir sollten nicht untersch?tzen, wie stark diese zur Identit?t der Bewohnenden einer Stadt beitr?gt?, sagt sie. ?Wenn man H?user abreisst, reisst man auch ihre Geschichten weg.?
Künftig sollen auch sogenannte Materialp?sse die Arbeit erleichtern. Damit ist ein digitales Dokument gemeint, das Auskunft über die gesamte Geschichte eines Baumaterials gibt, damit dieses sp?ter einfacher wiederverwendet werden kann. Eine von De Wolfs Doktorierenden arbeitet daran zu kl?ren, wie solche Materialp?sse standardisiert und harmonisiert werden k?nnen. Hinzu kommen die gesetzlichen Bestimmungen, die Sanierungen erschweren. Wenn jemand einen Altbau ver?ndern m?chte, muss er sich an die aktuell gültigen Gesetze und Normen halten, beispielsweise was die Isolation angeht. Doch die Normen sind zu stark auf Neubauten ausgerichtet und berücksichtigen Umbauten sowie den Kontext eines Geb?udes zu wenig, kritisieren sowohl Conen als auch De Wolf.
Neighbourhood identity
Maria Conen, architect and professor at ETH Zurich, also believes in repurposing what we already have. Her projects at architects Conen Sigl Architekt:innen have long focused on conserving the legacy of earlier construction. Her goal is always to make the best possible use of existing buildings through renovation and extension. Initially, climate protection was not even the priority; for her, cultural and social considerations are equally important. “Houses and neighbourhoods have a history,” she emphasises. “We shouldn’t forget how much this shapes the identity of the people living there. When you demolish their houses, you also erase their history.”
Instead, Conen argues, neighbourhoods should be redeveloped so that they remain recognisable to their residents. While there is nothing wrong with change per se, she says, a city like Zur?ich, which is currently undergoing rapid transformation, can quickly leave its own inhabitants behind. “In the past, we tore down far too much, far too quickly,” Conen explains. “If you only protect the most prominent historic buildings, those in between are unjustly written off as being less important.” That said, she is fully aware that not every building can be protected. If buildings are to last, they require regular upkeep. And if this maintenance has been neglected for too long, the building fabric is often beyond repair.
Nor is it always possible to reuse building materials. Yet the opportunities here, as De Wolf explains, are far from being fully exploited: “For example, a lot of wood is just burned, even though it’s very easy to reuse. And concrete gets crushed, although it could be cut into slabs for reuse as walls or floors.” Steel beams, on the other hand, are indeed sometimes recycled. “When steel is molten, you can reshape it into any form, but the processing takes a lot of energy,” De Wolf explains. “If you want to reuse the beams as they are, it requires far more creative input from architects and engineers.” And because their work is expensive and energy comparatively cheap, the idea of reusing building materials struggles to gain traction.
Reducing inputs
Removing building elements for reuse, as in the case of the Centre Pompidou, is similarly labour-intensive and expensive. “The cheapest option is often to tear something down, put up a new building and dump the rubble in landfills,” Conen admits, highlighting the unfortunate economic reality. “We therefore need to ensure that the cost and effort of circular construction are no higher than today’s linear approach,” De Wolf explains. One option, she suggests, is automating the process of reclaiming building materials.
Even after all that, finding people willing to reuse those materials can be almost as challenging. De Wolf spent countless hours trying to find a new home for the glass escalator canopy from the Centre Pompidou – a task that proved to be far harder than expected. Her solution is to work with the construction industry to develop online marketplaces for suppliers and potential users: “Our aim is to create an end-to-end digital ecosystem.” Beyond these economic and logistical issues, there are also technical and legal considerations. For example, are the reused steel beams structurally sound? Has the wood been treated with hazardous chemicals? And who will guarantee that they are safe? In future, says De Wolf, specialised civil engineers will be needed to answer these questions. At present, there are only a few experts in this field, and most of them are busy assessing the structural integrity of historic buildings.
The use of modular construction methods can make it easier to repair buildings and reuse their materials, but equally important is how the individual elements are joined together. While adhesive joints are difficult to separate, “interlocking or screwed elements can be easily taken apart,” De Wolf explains.
In future, additional documentation should ease this process. A digital record will provide information on the entire history of a building ma?terial, making it easier to reuse later on. One of De Wolf’s doctoral students is currently working on how best to standardise and harmonise this documentation. Another barrier to renovation is overzealous regulation. If someone wants to modify an old building, they must comply with current legislation on, for example, thermal insulation. Both Conen and De Wolf criticise that standards here are too narrowly focused on the new build sector and do not take sufficient account of the realities of reno?vation and a building’s specific context.
“Not all buildings and spaces have to be used in the same way,” says De Wolf. “It should be possible, for example, to take a poorly insulated building, heat it less, and use it, say, as a museum space.” And Conen points out that today’s buildings are designed to be as airtight as possible and thereby minimise energy losses. “But a chalet in the mountains is never airtight!” she adds. “Chalets were built according to a completely different concept – using locally sourced, natural materials and ensuring natural ventilation.”
Successful examples
Given the many hurdles plus the extra cost and effort involved in renovating an existing building or reusing construction materials, it takes a healthy dose of idealism to see such projects through. “The client really has to want it,” says Conen. “But I’m always delighted when someone seriously con?siders renovation over new build.”
Successful examples of renovation, conversion and the reuse of building materials are still often down to individual initiatives. One such case is a project currently underway at Conen’s architectural office. In the Swiss city of Winterthur, a municipal bus depot over a century old is being integrated into a new residential development. The depot and basement will be retained, along with the steel beams that provide structural integrity, thereby conserving all the grey energy in the building materials. New residential blocks on and next to the former depot will be built largely using timber construction methods and reinforced in some cases with concrete and reused steel beams. Even the roofing and glass skylights from neighbouring buildings will find a second life within the project.
What each of these projects demonstrates is that construction can be reimagined to conserve resources by incorporating and redeveloping existing architecture. De Wolf and Conen are working to gain wider acceptance for this approach and to overcome the technical and logistical challenges it still faces. De Wolf is full of hope for the new generation of undergraduates she teaches and her doctoral students: “They make me feel very optimistic about the future of construction.”?
CAS ETH in Repair and maintenance
The new Certificate of Advanced Studies at ETH Zurich focuses on scalable strategies for repair and mainten?ance of buildings and their components, and on the cost effectiveness of concepts for the preservation and value enhancement of real estate. It is aimed at professionals working in architecture, engineering and construction, industrial design, property management and risk management. Course graduates will have the skills required to orchestrate a process of sustainable change in the construction industry.
About
Catherine De Wolf Catherine De Wolf is Professor of Circular Engineering for Architecture and deputy head of the Institute of Construction and Infrastructure Management at ETH Zurich.
Maria Conen is Professor of Architecture & Housing, member of board of directors of ETH Wohnforum - ETH CASE and deputy head of the Institute of Urban and Landscape Studies in the Department of Architecture at ETH Zurich.