Building on the past | ETH Zurich

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 Zur­ich, 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 ma­terial, 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 reno­vation 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.”