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Grow your own

16 Jun 21 A building made entirely from Scottish trees is helping prove that UK homes shouldn’t need to rely on imported timber. Lisa Russell reports on the benefits of using home-grown products

Scotland has vast forests and Scottish builders make extensive use of structural timber in housing. On the face of it, that sounds the perfect match: chop down a tree and use the timber locally to help create a nice new home while reaping environmental benefits.

This article was first published in the May 2021 issue of The Construction Index magazine. Sign up online.

Analysis has suggested that around 85% of all new homes in Scotland are built using timber – almost three times more than in England and Wales. Unfortunately, the structural timber currently used in Scottish house-building is imported. 

There are perfectly valid reasons why this is the case, not least the fact that standard Scottish timber is of a lower grade than that of the key exporters. But a demonstration project is seeking to prove that the country’s own trees can safely be given a major role in new homes. The project has created a whole house – and an entirely new structural timber product – to make the case.

Use of softwood grown in the UK has historically been confined to low-value applications, such as fencing and pallets, or for burning as biomass. Recent UK government statistics show that, in 2018, the UK was the world’s second-largest net importer of forest products including timber, behind only China.

The hope is that the new demonstration project could lead to a major boost both for Scotland’s economy and the industry’s environmental impact.

The project run by a consortium of partners: Construction Scotland Innovation Centre (CSIC); Edinburgh Napier University Centre for Offsite Construction & Innovative Structures; Scottish Forestry; Confederation of Forest Industries; and sustainable homes consultant SNRG, an offshoot of energy company Centrica. 

The consortium has recently completed the first phase of a project that has received funding from Innovate UK’s Sustainable Innovation Fund. The aim is to prove both the technical and business cases for using Scottish timber to create the structural elements of buildings. This is an essential step towards encouraging investment in local facilities that could produce the laminated timber products used in house-building.

The reason for there being only limited use of local timber at present boils down to material differences between Scotland’s trees and those grown in some other places such as Canada and parts of Scandinavia. 

High-end imported products use grade C24 timber. Scotland can produce C24 timber but not without generating a lot of wastage, so it hasn’t been worthwhile. Historically, as a standard, what Scotland produces is C16, says Sam Hart, innovation manager at CSIC. “It’s still a structural timber - it’s just not quite as strong.”

Edinburgh Napier University (ENU) had already been involved in producing a new strength grading, C16+. What the current work has been aiming to do is prove that C16+ is suitable for what is actually built in the UK. “We’re not trying to build 18-storey skyscrapers, like they are in Norway,” observes Hart. “We’re just building medium-height housing.” 

The earlier work by ENU had indicated that home-grown wood should be perfectly suitable for structural use and the next step was to set up a pilot project in a live environment. Securing funding from Innovate UK provided the stimulus to make faster progress. “This type of work would happen anyway,” says Hart. “But it would happen over a much longer period and would be slower to develop. The quicker we can make this happen, the greater the benefits.”

The initiative has seen the manufacture of the first housing unit built with Scottish-sourced laminated timber for its floors, walls and roof. 

CSIC’s 35,000 sq ft Innovation Factory in Hamilton has the UK’s only vacuum press, making it the only place in the country capable of creating these mass timber products at scale. 

SNRG is the developer on the project, while Ecosystems is subcontracted by SNRG to deliver the units. Ecosystems is taking material from BSW Timber, manufacturing the panels at CSIC’s facility and constructing the demonstration units.  It was also natural for Scottish Forestry to be a project partner in a venture of this nature, where the raw materials can take decades to grow to size.

The Innovation Factory carries out ongoing work aimed at increasing the use of timber in construction and has machinery, equipment and operations that are focused on the sector. At the same time, the Scottish Construction Leadership Forum’s post-Covid recovery plan has been exploring how to develop more resilient, sustainable and localised supply chains, which fits in very well with making more use of the country’s trees. 

The hope is that the demonstrator project could ultimately lead to the mainstream use of home-grown timber in Scotland and the rest of UK construction. Scaling-up production would also require investment in manufacturing and so could see the development of the country’s first manufacturing plant for engineered timber.

The project has produced a pair of modules to form the downstairs and upstairs of a complete two-storey home. The modules were completed at the end of 2020 – allowing a Christmas tree to join the furniture in the living area – and will shortly be fitted out fully and stacked together to create a whole house that will be used in as realistic a manner as possible while being monitored. 

The house will then be moved to Glasgow and showcased at the COP26 United Nations conference on climate change, set to take place in November this year. The team is keen to make industry both in the UK and elsewhere aware of how new uses can be found for timber that has traditionally only been consigned to low-value applications. “And we’ll also be able to show them all of the data that we’ve collected from the previous months as a showcase of the performance and the benefits of building in this way,” says Hart.

The two rectangular boxes use glue-laminated timber (GLT or glulam) for the structural floor, cross-laminated timber (CLT) for the walls and nail-laminated timber (NLT) for the roof. The units for the project have been produced using Sitka spruce, which is very prevalent in Scottish forests. The building will also have weather-screen cladding made from home-grown timber. 

The project has done much more than simply make Scottish versions of existing products. It has also produced a new component that holds up the floor from above, allowing the living and kitchen accommodation across the whole ground floor to be completely open-plan. This was an added bonus in the first phase of the project, says Hart.

Ecosystems and ENU collaborated to apply their new engineered timber product, the ‘Glue Laminated Timber Portal’ (GLTP), which is a CLT/glulam hybrid. In this instance the GLTP served to carry the first-floor shower room/landing slab using slender, 100mm beams. Ordinarily, these would have needed to be twice the depth, but the GLTP formed a ‘cradle’ arrangement where the 100mm beam was partially cradled from the 300mm glulam forming the top beam via a couple of intermediate posts that created the door opening. 

Subsequently the GLTP has been further evolved as part of a configurable kit of parts that can be assembled and disassembled to respond to a variety of span and loading criteria. This further evolution is currently being prototyped by Ecosystems at the Innovation Factory.

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For the current building, one module will be lifted on top of the other and, as part of the second phase of work, they will be fitted out internally and externally. The design features technology to monitor performance. Physical testing is also taking place.

The upcoming use of the building will be as close as possible to how an actual home would be occupied. Hart explains that data will be fed back into a ‘digital twin’ model, allowing the performance to be assessed. 

Increasing the use of home-grown timber in commercial construction and house-building would help reduce reliance on imports. Greater use of this local natural and renewable resource is seen as having the potential to deliver a range of environmental, cost and economic benefits for Scotland and the wider UK. 

Using more home-grown timber is also expected to lower costs significantly for the construction industry – initial figures suggest a potential reduction of as much as 10% compared to imported CLT. Broadly speaking, one tonne of CO2 is saved for every cubic metre of timber used compared to traditional building materials, claims Hart.

Things fell into place for the current project with an approach by Matt Stevenson, who is head of offsite manufacturing at SNRG.  “They wanted to champion the sustainability of using home-grown timber,” says Hart. “When this Innovate UK challenge came up, we agreed that it would be a suitable source of funding and so we applied.”  

The resulting grant was really intended just for a feasibility study to prove that it could be done, but “we really overperformed”, recalls Hart. “We proved it could be done and then actually built it.” 

The original brief was simply to manufacture cross-laminated timber but one of the project partners, BSW Timber, offered to supply the materials. 

“That meant we could move the money from paying for timber into labour and factory resources,” says Hart. “And through being able to do that, we also managed to produce the manufactured nail-laminated roof and glue-laminated floor.” The new glue-laminated portal has been designed by Ecosystems Technologies with engineers from ENU. 

Despite the name, the nail laminated timber is an all-wood product, as it has been manufactured using timber nails – though the beech for the nails is the one timber component that had to be imported. 

Hart adds that the biggest surprise was the quality of the raw materials sent by the sawmill. It was of course important that the sawmill produced materials in a way that could be replicated, rather than deliberately picking the very best non-standard pieces. But the results turned out to be of a very good quality both structurally and aesthetically, says Hart. 

“The aesthetic side of it is important because all of the walls that we are building using the cross-laminated timber will be exposed,” he says.” We want to get the benefits of the feel and the look of timber.” 

He says that the timber didn’t need nearly as much defect-cutting as had been expected, adding that the expertise and ability of the people at the sawmill drove the quality. That reduced the wastage and in turn increased the productivity. 

Hart recalls the completion of the first 13m-long panel. The surface that will be visible is produced face-down in the press; everyone was over the moon when it emerged. “It was an absolutely brilliant surprise,” he says. 

CSIC is largely funded by the academically-based Scottish Funding Council. “But we are very much industry-led and industry-driven,” says Hart. “This is something that would need to be taken forward by industry partners.” 

As part of its work to improve the commercialisation of timber, CSIC has a steering group of about 30 stakeholders, including forestry, sawmills, specifiers, designers, engineers, contractors and house-builders, “who are guiding and leading us on that research to ensure that we’re aiming and focusing on the areas that they need”, says Hart.

Taking the structural timber initiative forward in the longer term would involve setting up one or more big factories to produce the components. The hope is that the current project could help demonstrate the viability of this. 

Production of a business case for industry needs to draw on data about how well the products work, the scale of demand and the availability of enough natural resources to supply that demand. Hart is confident that the evidence is there to make a case strong enough to persuade the industry to invest.

The result should be to move timber further up the value chain from the basic applications such as fencing, pallets and biomass. It costs a sawmill or a forester more to supply this better timber: drying it down to a lower moisture content means higher costs in the kiln and probably more of an effect on the environment because of the heat treatment. But it is worth doing if the result is more carbon being sequestered and if that timber is worth more, says Hart. 

And the Scottish government is already committed to getting more Scottish timber into construction. 

Location is an issue that will need to be addressed if, or when, a major manufacturing facility does become a reality. Academics have shown the biggest benefit accrues from locating it near the supply of the timber – but transporting big panels isn’t easy. CSIC’s vacuum press at the Innovation Factory will produce panels that measure approximately 13m by 3m – not something that could readily be moved down winding rural lanes. 

This article was first published in the May 2021 issue of The Construction Index magazine. Sign up online.

Phase two will move into a testing regime to assess thermal performance, airtightness, acoustics and fire resistance. As this issue of the magazine went to press, the team was waiting to hear whether this second phase has also secured an Innovate UK grant. The work will need to happen anyway - “but if we do get it then it will be absolutely all systems go”, says Hart. 

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