Return of the Forests: Scotland’s timberbuild r&d

Alongside Scotland’s building culture turning to the most readily available natural material in its own backyard, timber r&d developments in the industry north of the border are also broadening. Here we look at the work of the Centre for Timber Engineering (CTE) at Edinburgh’s John Napier University – the UK’s first timber engineering centre – as well as an intriguing experiment in experimental roundwood construction.

The various strands of timber-building activity across Scotland hasn’t, of course, come from nowhere. The incremental growth is off the back of at least twenty years of gradual development, grassroots activism, and take-up by business and the academy. The latter two really only kicked in over the last decade, although recently, and particularly since devolution, their involvement has been accelerating. Taking the longer view, the longevity and staying power of both Gaia Architects Network and Reforesting Scotland magazine are witness to how the early participants have flourished, amidst considerably changed circumstances. Indeed a quick glance through early Reforesting Scotland’s is a reminder of how architects are but one part of the larger interconnected web of communities which make their livelihoods from these Northern forests1. Look through the old Reforesting Scotland’s and a remarkable tapestry of players are given their day, from smallholders and crofters, foresters and folklorists, ecologists and biodiversity conservationists, carpenters and wood craftspeople, the many paths which are fed from a forest economy. In not altogether dissimilar fashion timber was taken up by the Gaia Architectural Network, focused around Howard Liddell, one of the original first generation eco-architects and, after a link-up with a group of Southern Norway based admirers, is very much still going strong There are others of course to this honourable list, left out in such a simplified narrative. In updating the story, however the technocrats, politicians and career academics need to be introduced into the mix.

The advent of devolution has moved things along, and a slew of directives and legislation has meant that the building Industry has been incrementally taking on board sustainable concerns in a way that didn’t happen a few years ago. A decade ago timber not only didn’t resonate, but was positively disliked by both the mainstream building community and the Scottish population at large. If the vast majority of buildings being timber frame in construction, what didn’t happen were buildings being clad in timber; behind the render and the breezeblocks, or older stone, the timber remained invisible. This, even though, in medieval times timber cladding is acknowledged as common, and further back cruck-framed buildings and long houses were found in the Highlands.  But Scottish timber traditions disappeared, unlike in Norway where communities steeped in a culture of timber building along with intelligent detailing and coating remained.

Timbers return and the degree of confidence associated with the material being economically, as well as ecologically, sustainable, received a significant boost with the arrival of the Centre of Timber Engineering (henceforth CTE), launched in the autumn of 2003. Alongside CTE, the increasing numbers of buildings, across building types – some of which were reported on in the last two pieces – have all helped broaden the profile of timber in construction north of the border. Yet, as has already been seen, despite changes in the air and increasingly on the ground, there remain real uncertainties as to how strong, and how prolonged this timber recovery will be.

The specifics of Scotland’s 17% current wood cover can be divided across the particularly heavily wooded regions. In the South West counties of Dumfries and Galloway and Argyll, wood cover rises to around a quarter of land, and in some parts to nearly a third. In the more northerly Highland regions, because so many of mountainous areas are not forestable the amount swings between 9% low and 17% high. A part of Moray, in the far North, also reaches 25%. Of this, and the vast majority – 98% – is rurally located.

The country produces nearly 2.2m3 million tonnes of softwood annually, dominated by between 70 and 80% – Sitka spruce, with Scots pine comprising the majority of the remaining wood. Most of this wood, unfortunately, is of the kind of quality that heads straight for chipping and pulping. The majority of construction quality timber continues to be imported from the Baltic. While there are undeniably indigenous Sitka stands, which are considered good quality – which are growing and can be used by the processing industry to be kiln dried and planed all round – invariably imported Sitka from the Baltic continues to have the competitive edge. It is less knotty, longer and generally of higher grade. It is around these issues, how the various species of home-grown woods, the Sitka and Scots pine, though also European larch, and small amounts of oak, can be grown to good enough quality to compete with imported wood, that the core starting point for those considering sustainability issues is to be found. Repeatedly, from specifying home-grown timber, researching quality improvements in timber, through to attempts to increase the home-grown share in the market, and arguments about the materials merits or otherwise the heart of the story turns on whether Scotland can genuinely provide significantly increased amounts of timber for the country’s building industry. While Scottish forests are grown to FSC specifications, so that the main procurements have a chain of custody, this isn’t such big news in the environmentally savvy Nordic region. Transportation costs and fuel miles are an obvious, if debated, issue. And in terms of reforesting Scotland, while replantation, according to Forestry Commission figures, is increasing, this remains small in scale. So in 2004/5 4193 sq hectares were reforested, up from 3489 hs in 2002/3. The Forestry Commissions Scottish press officer, Derek Nelson, says that the current planting programme is at about 8000 hectares a year, and any new or replantations require a balanced mix of species, dependent on soil type, and landscape, for purposes of biodiversity. Indeed, for the last decade grant aid eligibility has been based around the requirement for mixed growth2. As to use of indigenous timber, there are, apparently, no exact figures of the amount of home-grown wood returning into construction in Scotland compared to imports. But as David Sulman, Director Executive of UK Forest Products Association says, the assumed 80%/20% ratio of imported timber to home-grown that applies to the UK as a whole, should hold fast in the Scottish instance as well3.

Looking at the mainstream uses of the timber there are incremental changes, which could yet be harbingers of more fundamental changes on the horizon. Nearly two thirds of all new homes in rural Scotland (63% in fact) are timber frame, and this takes up much of the mainstream industrial softwood sector, the machined Industrial scale timber taking an increasing share of the housing market. Timber frame is anticipated to rise to 75% by 2010. As far as this sector is concerned, the majority of this is stipulated in C16 or C18, the Euro convention, an example of the quality issue headache in Scotland, which produces its softwood as C24 products. This is a primary reason for most of the timber destined for framing being imported rather than being sourced from indigenous products. The way ahead, according to the mainstream, though forward looking parts of the industry are ways of re-engineering the timber, enabling a real rethink about how more home grown resources can be used. Both the industry and the research are focused on this as the way forward.

The largest of the Scottish companies are BSW Timber – with three Scottish sawmills (plus two in Wales, and also a recently purchased Latvian mill to provide higher grade and longer length timber) – and the Forres based James Jones and Sons Ltd. Both are producing around £300 000m cubed sawn wood from their Scottish mills. BSW have just launched their new product Accoya, which uses an acetylation process to produce a robust and stable engineered wood for external uses such as decking and joinery. The products sustainability claims, including strength, decay resistance and durability comes with a 50 year guarantee and has been supported by testing at CTE. James Jones’s success story has been the development and marketing of a homegrown I-beam joist product, manufacturing in their factory near Fores. There was something rather deflating, however, in hearing that while the central small section of the I-beam joist is made from indigenous wood, the end pieces are not. Even so, in all the timber industry has been investing £15 million year on year on the quality of timber products, for instance, the ability to specify sustainable higher insulation, deeper walls and joists.

Another company, the house-builder and developer, Aberdeen based Stuart Milne, machine produce timber frames from home grown timber, using OSB. One result has built a 7 storey timberframe in N England. Part of the mainstream Industry, Stuart Milne’s mass-market approach may yet translate into reducing the materials loop: they are already demonstrating zero energy prototypes at BRE this summer. The Forestry Commissions Derek Nelson feels there is a growing demand for flats, which may push larger timber-frame construction even, if the primary structures are the one or two storey timber frame semi or detached housing. The ability to do this, and informing those in the business depends, Nelson points out, on the quality of the client-architect team. With an annual build of 25, 000 house units compared to England’s 160, 000, architects are beginning to introduce and integrate timber as a structural material. Housing Associations, particularly, have been keen to maximise homegrown timber, although the need to ensure the architects awareness of C16 materials has been important. One practice, Glasgow based John Gilbert Architects, have been involved in a TRADA Timberframe collaboration producing C16 quality 3and 4 storey medium rise, as well as other Housing Association projects in different towns across Scotland. And Andy Bruce at HurdRolland have been developing stable ecological middle storey developments, in social housing in Glasgow and Perth, under the rubric Albion Housing.

What needs further maturity is research and development to help Scottish timbers search for its missing competitive edge. This is certainly a central theme at CTE, the wood engineering centre based at Napier University‘s Merchistoun campus, within the dept of the Built Environment. Indeed CTE has the distinction of being the first and still, so far, only timber engineering department up and running in Britain. Opened in autumn 2003, in part as a response to the need for increased timber engineer training in the industry, its Scottish based location can be interpreted as reflecting an increased regional interest in using home grown timber, and the need to grow a more effective research base. After a somewhat rocky managerial start, CTE has developed into concentrating on four core areas: taught courses; research; professional development (CPD); and knowledge transfer, with a single undergraduate in either civil or timber engineering and two post-graduate course, timber engineering, and timber industry management.  CTE views itself as having strong industry links and partially because the Building Performance Centre is sited within the same department, it has built up a good track record of private sector on a consultative basis.

Peter Wilson, CTE’s press relations man, though also an architecture writer and publisher, is adamant that the centre is in a strong position in specific areas. A primary research project has been a four year, £1.3 million EU funded research analysing maturing sitka spruce; looking at internal strengths and load bearing properties. A second research project is on developing an online teaching presence of timber engineering. This again is EU funded, and is shortly to go live providing national on-line access, for remote teaching. The Centre is also working with the Forestry Commission developing a spectrum of factual information to promote and persuade the Scottish Planning Profession of the benefits of timber, a group who have traditionally been resistant to timber build with a noted focus on its weaknesses, rather than strengths. Given CTE is the only national centre for timber engineering, Knowledge Transfer is central to its remit, and CTE are working with various companies to both identify and further develop projects. This has often involved post-graduates who bring specialist knowledge to companies they work with, such as optimising milling equipment. The development and diffusion of such specialist knowledge feeds into strategic research for the industry generally, and applied research for companies. Research that has been undertaken includes robust detailing on behalf of the ODPM; looking at multi-storey timber frame; and the dynamics of progressive decay and collapse. The centre also has a focus on acoustic insulation and isolation, and in further collaborative work with the Forestry Commission CTE has been looking at larch cladding, and at the FC’s Forest Research Rosslyn, ways of increasing the sitka yields.

If Wilson talks an enthusiastic talk about the current fashion for timber, he cautions that although Scottish architects are indeed wanting to build in timber, absence of good information, particularly regarding the quality of material is hindering the profession, numbering 4000 in the country, from taking it up effectively. To help with this Wilson’s CTE funded Arcamedia imprint is publishing a second edition of a handbook on cladding, which sold out its 15, 000 print run. He is also in the throws of launching a less technical, visual record of recent timberbuild projects, titled New Timber Architecture in Scotland, highlighting over 120 projects; crossing the spectrum from domestic through corporate/offices to fire stations. What he found, he states, is the regional variation, in both materials and climate, which fits with research into durability. Where cladding may work in the south with vertically inclined rain, on the west coast hard driving rain can be almost horizontal, requiring different cladding durabilities. Dr Ivor Davies’ ongoing research is looking at rates of decay in wood involving a number of contrasting exposed test sites across the Highlands, which will eventually feed into recommendations for external cladding design and detailing. Another central research area is on different tree species quality, focused on the trees themselves, and identifying why parts of trees/stands produce the best materials, which are knot and shake free, and therefore the highest quality wood. This blurs into discussion of engineered wood, and the belief held by some that the most effective solution is in re-engineering home grown wood to strengthen its properties. Although Wilson states that glulam and other engineered wood products are only a small part of the market, CTE are, unsurprisingly, involved in engineered timber research. The most advanced of this work is probably post-tensioned timber. Here shortish sitka elements are bolted and drilled together with rods running through the elements to make large scale beam structures. These are being used as components to bridges, of which forty have been completed. There are also various composite materials projects, and research into applying alternatives to glues for modified woods, similar to the Finnish Thermowood products.

If CTE is the current major hub of Scottish timber research, there are various other research projects happening across Scotland’s academic sector. One of the more interesting (to my mind) is the Edinburgh based research underway at the city’s other main technical university, Herriot Watt. Malcolm Chrisp, an engineer in the university’s Dept of Civil and Offshore Engineering has been collaborating with Charles Gulland, and his company, All Round Buildings, on lightweight structures made from wastewood for a number of years as part of his research focus on developing rural community technologies. The work, which dates back to the mid nineties, builds on a number of small, kit roundwood structures, built as flexible and temporary holiday homes for Gulland’s other business operation, Wigwam holidays. After receiving millennium related funding in 1996, two long houses for Palacerigg Country Park, to teach woodland skills. Following these a larger residential centre was completed in Straiton, near Ayr, for the charity, Kids in Need and Distress (KIND.) While many kit-based houses have been built in the Scottish countryside both Chrisp and Gulland believe these kit plans, which import both design and materials, ignore connections to both local architectural history, and local material or skills. Since the Scottish Executive published guidelines in 2000 recommending that local communities benefit from woods and forests, which were also important to sustainable rural development, both academic and entrepreneur view their work as chiming with the emerging direction of both Scottish building policy and practice.

Both the long house and KIND residential centre highlight the advantages of local timber being used by local communities for sustainable ends. They are simple, accessible designs, which are well suited to local skills, and prospectively self-build. In forestry terms Chrisp points out that during the fifty year growth cycle of an average Scottish forest, thinning takes place every twenty years, with the smaller trees are removed to ensure the optimum growth of the larger trees. The thinned wood traditionally went to pulp and paperboard, and for fire-wood. Prior to Chrisp and Gulland’s work the use of thinning as building material had been all but ignored in Scotland. Gulland’s background as a student at the Hooke Park forestry school – the pioneering Dorset woodland centre set up by John Makepeace in the nineteen eighties – explains the interest, as it was at Hooke Park that research and use in thinnings as structural material was first begun. After some attempts to build using lightweight thinnings in the South, Gulland moved to Scotland and set up All Round Buildings to pursue his adaptation of the Hooke Park approach to the Scottish context. Based in the southern county of Ayrshire, Gulland used locally sourced roundwood for his design of a simple whale-bone structural frame. This applied a bent pole geometry as the template for the buildings. After a couple of initial experiments Gulland linked in with Chrisp to research and build the two free standing ‘long houses’. The long houses whale-bone frame design consists of a series of round greenwood poles (bent into shape in a jig before construction) which makes a simple triangular form. The two rafters join at the apex, and the ground beam runs across the floor to be braced to the lower corners of each of the rafter poles. The horizontal floor beam sits on foundation poles, allowing the buildings to be sited on various ground contexts. The curvatures provide the sense of larger internal space, with average interior internal height being 3.6m, with width of 5.2m. The length is flexible, although for the long houses, six frames have been used. Poles have also been cross-braced between joining each rafter at floor-level to the subsequent next rafter at the apex4.

The long house build work ran alongside extensive testing within Chrisp’s Herriot-Watt engineering department for design verification purposes. The testing demonstrated that such structural applications of low-grade poles withstood the various legal load-bearing test required for the building type. The research also shows that giga-joules of energy per cubic metre was low compared to sawn and dried roundwood and machine timber: 0.5 to 1.7 and 2.3 respectively, and very low compared to laminated timber (5.4) or masonry (7). The R&D from the long house buildings was followed by the most ambitious application so far, the KIND community centre. Here three parallel modules are joined to a further two perpendicular modules, in effect, akin to the shape of a capital E. Given the building joined up five multiple modules the rafters at each of the module sections are integrated to support purlins at each of the roof ends, covering 350 cubic m’s. For foundations, the KIND building applies a rammed earth technique, widely used in fencing and building in Scotland. One metre deep holes hold the foundation poles in the soil, providing a strong, locally sourced and economic solution. In all the KIND development cost £570sq m, with potential for considerable cost reductions as and when further development happens.

Gulland and Chrisp envisage these buildings being appropriate to use as small offices, community, craft and rural public buildings and also as rural residential dwellings. Although they have not advanced as far as they would doubtless like, and even if there are increasing warmth and coolth question marks about lightweight structures in the warmer summers Scotland is experiencing, the very low energy requirements, and the localist approach could well make them attractive to architects, rural communities and individuals in those communities. Chrisp notes that in the next decade Scottish thinnings are expected to double to 14.5 cubic metres a year, so the potential wins from at least exploring such lightweight roundwood structures seem pretty obvious.

If this greenwood approach is too lo-tech for much of the industrial sector, looking at the overall spread of activity across the country a convergence of interest around timber and sustainability can still be identified, albeit through a myriad of interpretive lenses. The many different variables; from differing levels off confidence about timber quality, through fuel and product miles, and the increasingly urgent voices regarding changing climate suggest a growing recognition that Scotland’s forests may hold a key to twentieth century problems. That said, even if the sense the European wood sector is merging into one macro market, and Scotland’s woods aren’t at the top of the table, the momentum connected to some gear change in timber based architecture has happened. This being the case, the next years ought to be an exciting time for architecture and timber build right across the country.

This was the last in the three-part series on the return of timber to the Scottish building and architectural scene. The piece appeared in Green Building vol 17, no 1, winter 2008

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