Downland Gridshell

The Downland Gridshell Building, commissioned by The Weald and Downland Open Air Museum, marked Britain’s first major timber gridshell project, and was completed in 2002. The prototype to this building, the Manheim Garden Exhibition Hall, built in 1975, was the result of the work of a remarkable engineer and pioneer, Frei Otto.

Christopher Zeuner, the then museum director, was a visionary client. His decision to build a timber gridshell, was controversial and required commitment and courage to see it through to completion. His decision to appoint the Green Oak Carpentry Company as a consultant post planning was unusual, but enabled the experience of the carpentry team to contribute to the design of the structure from an early stage, which brought about significant improvements to problem solving in the technical design phase.

Architect Steve Johnson from Cullinan Studios and Richard Harris from Buro Happold were outstanding designers, and engineers and possessed the necessary commitment and vision to skilfully guide the project through to completion.

Gridshells, are without doubt, the ultimate lightweight structures. The total weight of timber excluding the node clamps is 6-7 tons, which is remarkable for a 50 metre long and 15 metre wide structure. The term gridshell attempts to describe the structural system, in effect a grid of timber that has shell action.

The site’s gradient necessitated cutting into the chalk to build the 50x12m archive store as a partially earth-bermed structure. The Carpenters installed the whitewood glulam elements forming the archive store structure, the floor, boundary arches, roof and cladding as well as the gridshell itself. Fresh sawn oak laths (35 x 50mm) were finger jointed, and feather scarfed into 50-metre-long pieces and assembled onto the scaffold. The timber grid, utilised Peri formwork props to achieve the lowering. I designed an adjustable ‘node clamp’ that avoided the necessity of slotting the laths, making the structure stronger and less prone to breakages. Despite setbacks, including one of the wettest years on record and the passing of Christopher Zeuner, the structure was successfully completed and demonstrated remarkable teamwork.

The building received acclaim for its innovation, winning several awards, including a RIBA regional award, BCIA Small Project of the Year, the Wood Awards Gold and the shortlist for the Stirling Prize. The building stands as an example of what collaboration between client, architect, engineer, builder and carpenter can achieve when united around a common goal and a bold vision.