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Structural timber prototype uses 100% waste from demolition

Words:
Stephen Cousins

Building-scale installation validates use of reclaimed timber for structural glulam and cross-laminated timber frame construction

Dr Colin Rose presents from the pilot building at the launch event at Here East
Dr Colin Rose presents from the pilot building at the launch event at Here East Credit: Digby Oldridge/ UCL

A team of researchers at UCL has developed what is understood to be the first building-scale prototype of a glulam and cross-laminated timber (CLT) structure made from 100% waste timber from demolition.

The 3.5m-high by 2.5m wide by 2m deep modular structure was designed by UCL’s Circular Economy lab, in collaboration with Portakabin and other partners, and manufactured at the UCL Here East campus in London.

It comprises a glued-laminated frame with CLT wall and floor panels, demonstrating a higher value use of secondary timber, which in the UK is typically chipped, downcycled or incinerated.

According to Colin Rose, lead researcher on the project and co-founder of start-up UK CLT, the project aims to show how reuse as part of the circular economy can be achieved through a scalable process.

  • Cross-laminated secondary timber (CLST) and glued-laminated secondary timber (glulamST) pilot building exhibited at the UCL Festival of Engineering
    Cross-laminated secondary timber (CLST) and glued-laminated secondary timber (glulamST) pilot building exhibited at the UCL Festival of Engineering Credit: Gersende Giorgio/ UCL
  • Cross-laminated secondary timber (CLST) and glued-laminated secondary timber (glulamST) pilot building launch
    Cross-laminated secondary timber (CLST) and glued-laminated secondary timber (glulamST) pilot building launch Credit: Digby Oldridge/ UCL
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'The UK produces four and a half million tonnes of timber waste a year, of which 2 million tonnes comes from construction and demolition,’ said Rose, 'Even if you ignore everything that's not from construction and timber waste produced during the construction of new buildings, you're still talking about a lot of material. We just need to change attitudes so that people think of it not as waste, but as something that can be reused, and establish more of a market and the infrastructure to handle it.’

Engineered timber is already considered a low-carbon alternative to structural materials such as concrete, steel and masonry, but finding new structural uses for waste timber could increase the built environment's capacity as a long-term store for sequestered carbon.

According to official figures, around 56% of waste timber in the UK is incinerated for energy generation, 32% is downcycled to non-structural particle-based products, 9% is incinerated without energy recovery or disposed to landfill, and 3% is exported.

Credit: UCL

Furthermore, opportunities for regular domestic CLT production are limited, unlike European producers with access to plentiful primary forests, the UK has just 13% forest cover, making secondary timber a more viable and cheap local resource.

All timber in the prototype was sourced from locations in London, including two demolition sites and a site run by Community Wood Recycling. “Overall, we're trying to source the materials directly from demolition sites, because it's cheaper, and you're saving timber that would otherwise be going in the skip,' says Rose.

All the materials are fully traceable and Product Passports, stored on the Madaster platform, maintain a digital record of key information. The structure incorporates reusable connections designed to enable future disassembly, upgrade and reuse, and when no further reuse is possible, the timber can be recycled into panel products such as chipboard or MDF.

Cross-laminated secondary timber (CLST) and glued-laminated secondary timber (glulamST) manufacturing process steps
Cross-laminated secondary timber (CLST) and glued-laminated secondary timber (glulamST) manufacturing process steps Credit: Gersende Giorgio

One challenge of reusing secondary timber for structure is the potential degradation of its mechanical properties. UCL researchers recently carried out structural performance tests, including non-destructive full-scale bending tests, demonstrating secondary timber’s feasibility as a feedstock for CLT production. This aligns with research by Simple Works engineers and Edinburgh Napier University testing glulam, said Rose: 'All the results have been encouraging and shown predictable performance.’

Looking ahead, Rose says he’s keen to work on a large-scale demonstrator project, with the ultimate goal being to make it simple for architects and engineers to specify reused timber from a centralised reliable location, including the necessary certification.

The UCL prototype was exhibited at two events in July, during the Festival of Engineering, at UCL Here East and at the University’s Bloomsbury Campus on Bedford Way in London.

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