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Gridshell at Flimwell
From Building for a Future Autumn 2001

David Saunders, project manager of the Flimwell Woodland Enterprise Centre, looks out of the glass-less window frame of his near-to-completion building and into the thick foliage of mixed growth immediately beyond. As he looks, Saunders can see chestnut everywhere. “Although I haven’t done the sums, it looks like 5 hectares of chestnut would provide enough wood to grow a new building every year.” We are upstairs in the building which is part of an experiment in turning an historically important, though generally ignored coppiced wood, into a potential core building material for the whole of the South East region. Seven years since the project was conceived, the Feilden Clegg building went up last year, with an adapted modular gridshell roof, cladding, walls and flooring, using chestnut. As with its larger, more expansive cousin; the Weald and Downland Gridshell building, (see my article in Building for a Future, summer 2000) it is an attempt to embed contemporary use in the midst of a traditional rural context. Unlike the Downland gridshell however, the energy which has generated this project has come from forestry, and rural industry, rather than building and architecture.

Indeed, the overall decimation and heavy decline in the rural economy since World War II, is reflected in the fortunes of chestnut as a material. A principal wood for the South East (Hampshire, Surrey, Sussex, and Kent) in the seventeenth century, it was used in abundance as a building material as far afield as London, though the historic connection is to the traditional hop growing regions of Kent, and the Eastern borders of East Sussex, where it once provided hop supports. As these industries have withered, with cheap softwoods replacing the hardwood chestnut, it became clear to those working in the region that if anything of the economy were to survive, new uses for the wood were going to need to be found. Especially as chestnut is such a predominant wood in the clayey Weald of the South East, with 19,000 hectares of trees growing.

The region also includes the heaviest amount of ancient woodland, and the highest proportion of deciduous forest cover, in relation to conifer. HIstorically, forestry in a variety of guises, has been one primary mainstay of the region’s rural economy. Today however, significant amounts of this woodland are neglected and further hectarage is not being used. If you ask why, the argument is rehearsed ad infinitum, it is just not economic or competitive to use locally-sourced wood against the low costs of imported soft and hardwoods. To many in the building industry, it seems a watertight case, but this ambitious project at Flimwell is setting itself the challenge of upsetting this assumption.

The problem clearly isn’t want of the resource; with an annual excess of timber of half a million tonnes a year. Each year, the core tree capital grows another 100,000 tonnes of potential timber. If this amount is used in a year then the harvested amount doesn’t actually affect the central reserve of core woodlands. Overall, the main surviving use of chestnut has been for fencing and outdoor materials but this takes up the best of the coppiced tree, leaving lower-grade material. This cannot be used for these primary functions because of the irregularities caused by knots, and uneven surfaces. Up until recently it has gone to be pulped as wastewood. But at the Woodland Centre, a whole new variety of uses are potentially being realised.

Amongst regional foresters and timber engineers there was the intuition that if a project could be put together which demonstrated that chestnut was a strong enough material to pass various materials tests it could once again be re-introduced to the building and construction market as a home-grown, and therefore far more sustainable, wood to utilise. The engineers were aware of the developments in timber and glue technologies, and felt that If these were applied to chestnut it could come up with interesting results. Furthermore, if thus demonstrated, and there was an innovative building - a living example of how it could be used packed with examples of designs, furnitures, and other uses the wood could be put to - this could only help the future of the industry. It was an attempt, therefore, to kick-start a part of the rural economy which though on its knees, was not yet completely dead.

There had already been a number of experiments using coppiced chestnut by those interested in potential timber applications of the wood. Some of the buildings of the local farm, where one of the woodland partners worked, had been replaced using chestnut. Subsequently, the roof of a local sawmill was rebuilt using the wood, after a successful test - hanging weights from beams - demonstrated that the timber would be strong enough to support the roofing. It was also known that there was a strong sustainable argument for this resurrection of the wood as a commercial material.

Those involved felt sure chestnut would measure up, but the wood needed to be comprehensively and formally tested. With a strand of EU money, called Life funding, and wood donated by a local sawmill, the Building Research Establishment (BRE) were brought in to the research picture. Firstly, English oak, (in 1995/6) and then the chestnut, (in 1997) were examined for their structural properties, and stress strengths.

The research had been enabled by the creation of a part-private, part-public company, Woodland Enterprises Ltd, comprised of East Sussex County Council, the Timber Growers Association and a local south-east company, Penrose Wood Industries. This was set up to develop ways to first steer, and then exploit the research alongside other concurrent initiatives to breathe life back into woodland industries. These include the setting up of a web site [www.woodnet.org.uk] and a very successful annual regional ‘wood fair’.
BRE’s research demonstrated that chestnut was indeed both safe and strong. What emerged from testing strength, stress, and durability capacities to sections of both chestnut and oak, was that much less hardwood was needed compared to softwood, to support or carry specific weightloads. If a building uses smaller sections, it will use less wood, and that wood immediately gains a competitive edge. This was good news for chestnut, as was the fact that the results have made their way into the review of British Standards for Temperate Hardwoods (BRE Digest 445) which will lead to the revision of BS 5268: Part 2. From this resource, chestnut could be considered for use by architects and the building industry. It also meant that research had shown that the best of the low-grade timber could be used for building. With deformations removed, the best of the remaining timber could be cut into small 350-500mm sections, and using finger jointing technology and Callano polyurethane glues, reconstructed into long slats - up to 30 feet - from which the modular roofing sections could be created. Structural engineers, armed with the materials research would now be able to model large-scale structures, such as modular gridshells, using the chestnut.

Now, the idea of a complete building - constructed from chestnut - was able to be envisaged. Woodland Enterprises began to look at this as a serious option. The concept of an actual physical woodland visitor centre had been in the ether for a while, but with the structural and materials research in, a feasibility study was commissioned. Once completed, this again showed the potential for developing a market for locally produced hardwoods, and chestnut specifically, and in 1996 a bid went in to the Rural Challenge, and was one of only six to successfully receive a grant of one million pounds. It succeeded because of its mixture of focus on regeneration, wood related employment, facilities for the local community - including the woodland community - and not least because of the research innovation regarding local hardwoods. From there, a competition was arranged, which produced a variety of imaginative entrants. The winners, Feilden Clegg, (these days, Feilden Clegg Bradley), were chosen because of how they envisaged trees from the locale being integrated into the building plan. Although this included chestnut, the plan didn’t envisage using the wood as a core building material. The Woodland Enterprise group, already envisaging the adapted use for the chestnut, went back to Feilden Clegg to ask for a rethink on how to apply the chestnut as the primary material for the proposed building. At the same time, the building went through a rethink, with the original woodland visitor centre concept being dropped. What replaced it, was a working woodland centre, which would provide training, work and be accessible to the woodland industries community. Feilden Clegg were able to develop a new building with a modular roof, rather than a purely gridshell roof as the original brief required.

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