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Curving away from covention

Cowley Structural Timberwork's imaginative approach has resulted in lightweight frameworks that echo the structural properties of insects A series of imaginative softwood timber structures - vaults, domes, 'pods' and shellgrid roofs - has emerged from the relatively modest workshops of Cowley Structural Timberwork, in the village of Waddington, Lincolnshire.

Gordon Cowley, founder and managing director of the firm, has always been interested in the creative aspect of timber engineering, rather than in massproduction; as he explains: 'We have always been design-led - I am fascinated by design.'

He has spent a lifetime in timber, even growing up in a timberframed house.

He started off working with a relatively innovative timber company - one of the first to offer trussed rafters to architects in the mid '60s - on all aspects of the business: shopfloor supervision, design and marketing, advising on British Standards. In 1978, when that firm was taken over, Cowley bought his desks for £135 and set up on his own. He was soon modifying standard trussed rafters into new configurations - 'We didn't care for the 'toast-rack' approach' - at that time a ground-breaking concept. 'And we wanted to be a catalyst for architects who wished to explore the potential of wood. In some cases the sale came first and the 'how to do it' came second, ' he says.

The 'how to do it' has built up over 20 years and now encompasses a drawing office with sophisticated CAD technology and workshops with the latest machine tools. For very large timber structures, Cowley assembles components in a former crane factory in Lincoln, a vast space wellequipped with gantry cranes.

That was where he made a huge dome, 14m in diameter and 8m high, recently completed for the British Library of Political and Economic Science building in London. The dome, which has an inset glazed panel, is set over a new circular ramp and forms part of the refurbishment of an early 20th-century warehouse by Foster and Partners for the London School of Economics. The stressed-skin construction consists of an upper and lower skin of 16mm (two 8mm thicknesses) OSB (oriented strand board) with ribs of laminated veneer lumber (LVL). For ease of delivery, the dome was fabricated in 'orange peel' sections and waterproofed with a GRP covering.

Stressed-skin structures - also known as monocoques - can be formed into curves and are also capable of long spans. One of the longest spans ever achieved by a stressed-skin structure is the 21m roof of Darlaston swimming pool (see pages 4-5) by Hodder Associates which was formed of stressed skin panels fabricated of LVL ribs and cladding.

The enclosure of large spaces by structures which maximise the structural efficiency of timber is a concept which fascinates Cowley. 'I like the idea of distributing forces through a large number of lightly loaded components rather than a few heavily loaded ones, ' he says. 'I like structures based on lightweight frameworks - think of the structure of an insect rather than that of a mammal.'

This thinking has produced a number of innovative roofs. The concept and fixing techniques of the double-curved timber gridshells (described in detail on pages 6-7) by Gensler were developed further to create a much larger-scale structure. This was the roof of an all-weather practice pitch for Norwich City Football Club. The structure was designed with Norwichbased architect Lambert Scott Innes and structural engineer John Westmuckett of Parkman, who acts as structural consultant for Cowley Timberwork. It is a geodesic structure which is similar in principle to the gridshell, and uses the same jointing methods, but is designed to be covered with PVC fabric stretched between the nodes.

A vaulted gridshell structure, two storeys high, has recently been installed in a woodland site to house the workshop/office of a firm of timber craftsmen. It was designed by Feilden Clegg Bradley and structural engineer Atelier One. The gridshell is formed of locally coppiced chestnut thinnings, finger-jointed and pre-drilled in their green state into long lengths, which were then curved and bolted at their intersections. The structure is braced with Douglas fir purlins.

A geodesic dome for a Sikh temple is currently being assembled in the workshops at Waddington. It is formed of a series of 140 x 140mm pine glulam elements, which are connected at their ends by a series of specially designed ring-like stainless steel nodes.

Softwood timber is an excellent material for the fabrication of small, highly crafted elements. Probably Cowley's best-known work in this respect consists of the ellipsoid enclosures - popularly known as 'pods' - for Peckham library, by Alsop Associates, winner of British architecture's top award last year, the Stirling Prize.

The pod on the ground floor is a two-storey-high tulip-shaped enclosure containing an interview area with a storage space above, reached by a timber staircase.

The pod was formed from a series of paired softwood timber ribs, curved to create the shape, and lined on the inside with fibreboard and on the outside with a double layer of OSB. An external skin of 1.5mm-ply tiles was stapled to the OSB.

Upstairs, in the Early Learning Centre, there is a different variety of pod, consisting of two 2.4m-diameter enclosures mounted on diminutive legs and lined on the inside with bench seats. 'The brief for this pod, ' explains Cowley 'was 'make me a tennis ball'.' Each pod is a geodesic dome formed of double-curved hexagons.

A series of curved T20 softwood timber members was screwed and glued together to form 180 triangles in two different sizes; the triangles were then fixed together to form double-curved hexagons and clad with ply so that the grain radiates from the centre of the hexagon. The pods were fabricated in relatively small sections to enable them to be transported through standard doors.

Cowley has recently worked with Zaha Hadid to push the creation of complex shapes one stage further. An exhibition of her work in the Kunstmuseum at Wolfsburg, Germany, is made up of pod-like structures - a combination of truncated cones, cylinders and flats - some two storeys high, which house audio-visual displays. The structures were formed from double skins of curved and flat panels of 6mm ply. The cavities between the flat panels were filled with expanded polystyrene. The curved panels were bent to shape around softwood formers and the cavities were filled with expanding foam (of the type used in boatbuilding to give buoyancy). The surfaces were then sanded and painted.

Creative work of this quality is inevitably time-consuming and not best suited to competitive tendering procedures. Architects who know and trust Cowley's work tend to become involved in partnering agreements, which is what he prefers. Ideally a concept should involve the collaboration of architect and timber manufacturer from the outset. As Cowley explains: 'You do not get a view of how the building is conceived by looking through bills of quantities and standard methods of measurement. Give us your philosophy of the building. That way I can give you added value.'

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