Picking through a crate of reclaimed floor tiles, Micheal Ghyoot pulls out a model with a blue, gray and white art nouveau motif.

"These are easy to like, because they have this floral pattern," said Ghyoot, a researcher specializing in architectural reuse, holding up the square cement tile once common in many homes built in Belgium in the early 20th century. "And, in the '30s and '40s, they started producing more modern patterns, and these are super interesting as well."

The crate is just one of dozens containing tiles of varying styles, sizes and colors, all waiting to be cleaned and sorted for resale at Rotor DC, a Brussels-based cooperative specialized in salvaged building materials.

In a nearby warehouse, tall, solid wood doors complete with original handles are lined up along the wall, next to several large, gold-tinted windows rescued from a mid-20th century office building. On the grass outside, a photographer is arranging bathroom sinks on the wet grass, to photograph for the online store.

Since opening its store in a former office building in late 2016, Rotor DC has been promoting the concept of urban mining in Brussels. Material scouters seek out buildings slated for demolition, and experts carefully rescue anything that can be reused elsewhere, from Murano glass light fixtures to solid oak flooring and handmade decorative brickwork.

It's not the only such organization in Belgium, and similar stores exist across Europe, North America and elsewhere. But the Rotor design practice also provides guidance for projects looking to use reclaimed components, and publishes research on sustainability, circularity and the material economy.

Construction sector has a huge environmental footprint

The reuse of construction materials isn't a new concept. Medieval builders, for example, used bits of ancient Roman structures to save time and money, and some of those buildings are still standing today — especially in Rome. But industrialization and modern manufacturing methods, especially in the 20th century, shifted the focus away from reuse.

"The whole construction system — procurement, liability, regulation, scheduling, insurance, standards — was built around new materials," said Areti Markopoulou, academic director at the Institute for Advanced Architecture of Catalonia. "Direct component reuse in original form — windows, doors, beams, facade elements, sanitary fixtures, flooring — is still less widespread than lower-grade recycling or downcycling."

Reuse of building components may seem straightforward, but Markopoulou said it comes with an array of challenges: careful deconstruction, storage, certification and matching supply with new projects.

"We know how to crush buildings very efficiently, but we are still learning how to disassemble them intelligently," she said.

As a result, most of that waste ends up being repurposed as backfill on new projects, or ground cover — if it's reused at all. Today, construction and demolition waste make up more than a third of all the European Union's trash.

That focus on new materials comes with a major environmental cost: In the EU alone, the building sector consumes around 50% of all extracted material, and the associated greenhouse gas emissions are estimated to be between 5% and 12% of total national emissions.

"Reuse matters not only because it diverts waste, but because it can avoid the emissions associated with producing new materials altogether," said Markopoulou.

A 2019 report by UK-based charity The Ellen MacArthur Foundation pointed out that reusing materials made of steel, aluminium, concrete and plastic would reduce demand for new products. This shift to circular economy strategies could help the global building sector decrease emissions up to 40% by 2050.

Reuse gaining ground, but still niche

Ghyoot said that convincing contractors and architects to use secondhand building materials isn't easy. Any change takes time and can add to building costs, and a consistent supply of identical products isn't guaranteed when using salvaged components. Material sourced from older buildings can also be degraded, contain toxic elements or be difficult to disassemble.

"You have to rethink how you design, how you organize the workflow, how you work with builders," said Ghyoot, who is also a project manager at Rotor. "We do our best to facilitate that. But it remains a bit of a niche practice overall in the construction industry."

In the early days, Rotor DC did all the work salvaging building materials and preparing them for reuse. But that changed when they set up a system to buy back reclaimed building elements — from private individuals and, especially, general contractors and demolition teams.

"What we found out is that it was not a matter of skill from their side — they usually know how to do that properly," said Ghyoot. "But if you bring a bit of money into the mix, then they are ready to [put in] the effort because there is something in it for them."

AI, digital tools can support material recovery

Markopoulou and her team are also looking into how digital tools and artificial intelligence could be used to boost the recovery of valuable reusable components like solid timber, stone, steel and brick from demolition projects.

"Cities are enormous material reservoirs," she explained. "The idea is to use Google Street View, aerial images, scans, cadastral data and permits to estimate what materials and components are likely present in buildings, when they may become available and in what quantities."

The research has already been tested in cities like Barcelona, New Delhi, Helsinki and Singapore.

"We cannot yet predict every reusable window or beam, but we can already estimate urban material stocks well enough to plan for reuse at city scale," she said. "AI can't tell you everything inside a building, but it can radically improve how we predict urban material stocks before demolition or renovation even starts."

Markopoulou said these incentives and digital tools will need to be backed up by policy changes, highlighting how mandatory energy certificates shift the focus to more sustainable construction methods. Material and building passports, for example, which list detailed information on everything that makes up a structure, can help plan for eventual reuse and transform how we think of buildings.

"It's a change of mentality, because buildings were always thought to be permanent," said Markopoulou. "We need to design while taking into consideration where our materials will go after the lifespan of the building is over."

Edited by: Tamsin Walker