Grow your own

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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