New Visitor Centre at Conisbrough Castle, South Yorkshire, grade I

Conisbrough Castle is an amazing medieval castle, easily the country's best example of a Norman keep. The cylindrical keep, a staggering 30m tall, dates from 1159-1200 and was built by Hamelin Plantagenet, half brother to Henry II. Unusually the site was abandoned before the Civil War, and therefore, already indefensible, avoided being slighted at the end of that conflict.

The project

Capstone has been the consulting Structural and Civil Engineers for English Heritage for the conversion of the Custodian Lodge into an interactive interpretation centre for visitors. Recently opened, this new centre houses the reception, exhibition space, shop, staff accommodation, and education facility, all within the refurbished original building and new extension which more than doubles the original footprint. The changes have brought significantly increased numbers of vistiors.

The engineering challenges

A key requirement was programme: speed of construction to ensure the 'downtime' for the site was minimised. Hence we developed a structural form for the extension, its roofs, its floors and elevations with that need in mind. Prefabrication and offsite construction was proposed for secondary roofs and suspended floors. A further challenge was the topography. Changing levels across the site dictated the need for an earth retaining structure to the rear, which we designed as a 'gravity structure' in masonry, and a change from ground bearing slabs to the rear to suspended structural slabs to the front.

The solutions

We designed and detailed a series of exposed feature timber trusses over the new extension. Despite the large open space of the education room, Capstone was able to design out the need for a steelwork frame (often imposed by engineering firms who rely a little too much on their steel frame design software!), and instead kept to traditional cavity wall construction with the introduction of bedjoint reinforcement where needed.

Client - English Heritage
Funder - Heritage Lottery Fund
Value - £530,000