As of 2019, the UK Government has committed to a “presumption in favour” of off-site construction for procurement of all new buildings by all key government departments. This multi-pronged research programme set out to show how timber can meet one specific public procurement need—more school buildings—quickly and with a minimum of disruption, as an illustration of the wider benefits and promise of precision-engineered timber.
The essential requirements of classroom space are established by government, making it feasible to develop a portfolio of designs that can be implemented in different locations and manufacture school-oriented construction components at scale. Since 1 tonne of timber contains sequestered carbon equivalent to 1.8 tonnes of atmospheric CO2, the in-built carbon capture inherent in timber-based construction also promises a significant contribution to net zero emissions targets—provided the construction processes are carefully designed.
With the overall goal of transforming timber construction through digital design and manufacturing, the project’s objectives included:
- developing timber building procurement models that leverage the vertical nature of the timber industry and CDBB’s expertise in novel contract development.
- defining digital workflows compatible with engineered timber, robotic cutting, and offsite manufacture but onsite assembly and available to a wide range of architects, engineers and contractors
- designing school building components that fit into those workflows and are engaging to architects
- showing the policy and pragmatic advantages of modular, large-scale timber, through evidence-based papers and research-based designs.
Process
The core research reflected twin needs for an evidence base and technological advances.
Evidence-based theory
The team gathered information on engineered-timber buildings at 11 UK schools, generating a data-driven appraisal complemented by interviews with engineers (Smith and Wallwork) and timber specialists (Eurban). This tranche of work allowed researchers to explore the hypothesis that appropriate use of off-site processes could enable the onsite construction phase to be completed during the school holidays. This was shown to be feasible for extension projects and is a significant advantage of off-site manufacturing.
The researchers also surveyed prefabrication timber construction projects internationally, including case studies in Australia and the USA. These investigations confirmed the potential cost benefits linked to off-site manufacturing, highlighted the thermal performance of precision-engineered buildings (close-fitting and draught-free), and solidified evidence of secondary benefits for the health of those using timber-constructed buildings (including improved emotional and psychological wellbeing). The findings from such desk-based research substantiated and richly-illustrated the case for constructing buildings—from schools and the wider public realm to homes—using CLT (cross-laminated timber).
Technological advancement
Not content with demonstrating the existing advantages of precision-engineered timber construction, the researchers wanted to go further and improve the state of the art with particular attention to reducing carbon emissions. They developed radical solutions to two traditional timber-engineering problems: joint strength, and flexibility.
Welding for strength
In engineering terms, joints are the weak points in timber constructions. Traditional solutions (nails, glue, brackets) struggle to support multi-storey timber construction and are also not ideal given the target of reducing carbon emissions. Metal hardware poses a problem at the end of a building’s life-cycle, needing to be removed and recycled—an energy-intensive process. Glue products may release harmful by-products during production, application and destruction, with negative impact on health and carbon emissions.
Partnering with The Welding Institute, CDBB researchers found a radical solution: rubbing timber pieces together at appropriate speed, natural polymers present in the wood form a powerful bond, stronger than conventional glues and native wood. The process is quick (2-3 seconds) and requires no additional ingredients. Operating the process at scale requires automation, prompting the researchers to work with the Robotics Facility in the Civil Engineering department to finesse the procedures.
“Proven to be compatible with a wide variety of different wood species and products . . . this process could be a game changer for the mass timber industry, reducing production time and costs. . . . [With] benefits for recyclability and the circular economy, we believe it could revolutionise the way that high volume timber products are manufactured.”
The Welding Institute (June 2022)
Watch a webinar on the wood welding technology (September 2020, YouTube)
Folding for flexibility
Designing a pipeline that combines 3D-modelling (and digital prototyping) with robotic-cutting, the second breakthrough was creating wood that can fold. Specifically, researchers challenged themselves to design structures that could be transported as flat sheets of wood (mitigating transport costs) and manipulated on site to create resilient and reusable forms.
The work was inspired by two traditional techniques: kerfing and origami. Kerfing is the process that creates the curvature necessary for musical instruments such as violins and cellos. Thin sheets of wood are finely scored, allowing the necessary manipulation. Origami is the traditional Japanese art of folding paper.
3D-modelling enabled researchers to design structures and then reverse-engineer the necessary cuts so that the wooden sheets would fold into shape. This reduced the need for physical prototypes—reducing the cost of raw materials. It also meant the designs could be translated into instructions for machine cutting, enabling successful designs to be reproduced at scale. A demonstrator at the London Design Biennale (2021) created in partnership with PLP Architects was inspired by the COVID-19 pandemic, and the increased desirability of creating adaptable spaces—within homes as well as in schools.
UnFolding Pavilion
Complex and beautiful, the machine-cut timber structures demonstrate the versatility of what can be modelled with a single sheet of engineered timber. The designs employ no fixings, but rely entirely on the origami-like potential created by precision-cut patterns. The main application envisaged by researchers and partners at PLP Architecture is as flexible room dividers, allowing simple, cost-effective and social reconfiguration of space—valuable for schools and for domestic settings. CDBB researchers prototyped wall panels that demonstrate the capability of flexible interior partitions to transform spaces easily, based on user-needs. The panels form part of the Design Museum’s Future Observatory, (London, 2021–2024).
Outcomes and outputs
Evidence from existing engineered-timber structures is gathered in reports including “Emerging trends in the application of engineered timber in UK school buildings” (Koronaki et al, WCTE 2023) and “Prefabricated engineered timber schools in the United Kingdom: challenges and opportunities” (Koronaki et al, 2021).
The commitment to shape policy was addressed practically with working papers submitted in response to a call from the UK Government’s Environmental Audit Committee (Ramage et al on Sustainability of the Built Environment) and to inform the Royal Institute of British Architects’ work on nature-based solutions (Debnath et al, Climate repair through the built environment). These briefings expanded on implications from the schools’ research, advising on how net zero targets may be met alongside the needs of the UK housing market as well as public sector construction projects. Researchers also contributed to a briefing for the Chilean government, offering context-specific guidance on timber construction for zero carbon emissions (Reyes et al, 2021).
Industry partners PLP Architects co-produced a video explaining the evolution of the timber-folding technology (as part of the Biennale exhibition), and BBC Radio 4 broadcast Wood for Good, an episode of the “39 Ways to Save the Planet” podcast based on CDBB work with cross-laminated timber.
Further outputs can be found via the CDBB Knowledge Base Navigator and on the Centre for Natural Material Innovation website.
So what?
Automation and off-site manufacturing embedded in the processing of engineered timber building systems can help to ensure the delivery of a high volume of primary and secondary school buildings is timely and efficient and meets sustainability standards.
CDBB research has consolidated understanding of the benefits associated with precision-engineered timber construction, translating that understanding into recommendations for industry and government. The published evidence base shows how prefabrication (necessarily offsite) has been used successfully for the construction of schools and other public infrastructure worldwide, resulting in faster and more cost-effective construction of such building types. Importantly, timber-based construction is also shown to have positive health outcomes for those involved in construction (a safer process), and for end users.
Technological advances made as part of the research have further enhanced the benefits, increasing the UK’s capacity to meet net zero goals (with the corollary of lessening the impact of human-induced climate change). Further investment is necessary to benefit from at-scale applications of the research findings. The results should be revolutionary.
Industry impact of this research
For maximum benefit, the research has delivered recommendations with regard to training, investment in production facilities, and the calculation of the carbon footprint of cross-laminated timber (CLT).
Training: The expertise required of designers working with engineered timber is more closely linked to the procurement process than in mainstream methods of construction. More engineers need to be trained in this domain, and the legal framework for procurement needs to recognise the symbiosis of design, production and construction.
Production facilities: There is considerable scope for investment and development of production facilities, and the potential to attract international investors, given suitable government support at a policy-level. If the final processing is localised, the most carbon-intensive journey--of a finished product to its installation site, typically by lorry—is reduced. Such regional distribution has economic benefits for the regions concerned, providing skilled employment opportunities and enhancing prospects for communities.
Carbon calculations: When measuring the environmental performance of CLT, assessors should account for its role sequestering carbon in addition to the carbon used in the production process—using CLT to construct facilities for the 120,000 UK students short of a suitable classroom would capture around 0.17 megatonnes of CO2 for the lifetime of the buildings, with potential for the timber to be reused again subsequently. This is in addition to other environmental benefits such as potential benefits for humidity and air quality. Comparable gains apply to all areas of timber construction, including homes. The ready reusability of materials from timber buildings should also be factored into calculations of whole-life carbon emissions, since reducing carbon footprint requires attention to what happens when a building no longer meets users’ needs. Researchers have recommended the UK government create a mechanism to credit timber buildings’ long-term storage of carbon dioxide by trading captured carbon.
The construction process of engineered timber structures requires the early involvement of all stakeholders, and researchers have petitioned for change to public procurement models to recognise this need. Researchers have also highlighted the inadvertent impact of post-Grenfell amendments to building regulations which fail to distinguish between flammable cladding and the use of structural timber in multi-storey buildings (see submission to RIBA).
“It is vital for UK construction to take part in research – there is no doubt that new thinking is required to meet our carbon reduction targets at the same time as modernising our industry. Michael’s team and his project are addressing this challenge and the insight our business is gaining through collaboration is invaluable.”
Simon Smith, Director, Smith and Wallwork
Wider benefits
At the outset, the UK’s capacity to manufacture engineered timber and plant-based material was judged to be very low. Building schools using prefabricated engineered timber construction methods brings opportunity for the procurement of these structures to stimulate the growth of tertiary engineered timber processing businesses. This is a very significant opportunity to establish a detailed manufacturing strategy for the production of CLT and plant-based insulation materials for both the UK and the overseas markets post-Brexit.
The research also indicates potential to improve labour conditions and diversify the workforce: Factory-based processes ensure consistent properties in every cycle and millimetre-level tolerances, reducing errors and risks associated with construction. Building UK capacity for such processing has the additional benefit of justifying investment in training and maintaining highly-skilled workers. Workers’ jobs are safer, and the pool of workers seeking such employment likely more diverse. Such benefits will be magnified if distributed regionally (as recommended), since investment should then support a ‘levelling up’ of prosperity across the UK as well as further reducing carbon emissions.
In common with all off-site manufacturing, prefabricating timber components for schools means on site assembly can happen fast, with less disruption—both to school users and school neighbours. The assembly process can even be accommodated within school holidays to minimise disruptions to the school programme.
The process of constructing buildings using timber has also been demonstrated to have lower associated greenhouse gas emissions than would be produced using conventional construction materials, such as steel and concrete. Additional health benefits associated with exposed timber spaces range from increased social interaction and improved emotional state to reduced heart rate and lower perceived levels of stress. With such promise, timber-based constructions are well-suited to accommodate young learners in the UK and elsewhere.
At the end of a structure’s life, timber elements may be reused, recycled, or burned as biomass fuel. When combined with sustainable management of forests (replanting, active management), constructing buildings using prefabricated engineered timber could facilitate the transfer of significant volumes of atmospheric carbon into the built environment for long-term storage in a cost-effective manner. This approach also secures a source of building materials that can be grown and harvested sustainably.
Innovation
Innovative timber-engineering techniques (welding and folding) have been highlighted above. Overall, the project adopted a multi-scalar approach to the use of engineered timber as a construction material. The benefits analysis reflects the whole life cycle of engineered timber products, ranging from forest management and carbon sequestration to supply chains and policies. Combining this with novel design methodologies and the principles of design for disassembly and modern methods of construction, this holistic approach produces emissions reductions that can meet UK sustainability targets for the construction industry.
Collaborators
- Department for Education
- Cambridge City Council
- Smith and Wallwork
- Waugh Thistleton Architects
- Cundall
- Kier
- ECOSystems
- PLP Architects
- Fawcett School
- The Welding Institute
Find out more
Learn about the origins and research need and meet the researchers on the Research profile.
Listen to the team on BBC Sounds - 39 Ways to Save the Planet - (broadcast 5 Jan 2021) - complete with sounds of cutting cross-laminated timber.
‘How do you produce more heat?’ asks Dr Shah. ‘Rub your palms faster (frequency), push your palms against each other with more force (pressure), rub your palms for longer (time) and move your palms over a longer distance (amplitude). Similarly, in wood welding, to generate more friction and heat, these are the 4 principal manufacturing parameters we can control.’
Learn more about wood welding as a rapid timber joining technique.
Future developments will be reported on the Centre for Natural Material Innovation website: https://www.cnmi.org.uk/
