Hangar management

When the Imperial War Museum decided it needed more space to show off its extensive collection of aircraft, rather than start afresh and build a new venue, it “recycled” an existing shed at its Duxford base.

The new building, dubbed Airspace, is a development of what was Hangar 1 with HOK, Mott McDonald and Laing O’Rourke widening and extending it to cover 12,200m2. Inside, aircraft - including a Concorde and a Vulcan bomber - are either parked into position or hung from the roof structure, an option made possible by re-using the robust steel trusses of the original scheme.

The process involved stripping off the original roof and cladding to leave nothing more than a steel skeleton and concrete slab. Guy Comely, vice president and senior architect with HOK, says that the now-defunct Public Services Authority, the designer of the original structure, was notorious for doing big projects too quickly. “Hangar 1 was over-engineered. But the additional girth of the trusses has allowed the client to suspend the planes from them,” says Comely.

The first exercise was envelope removal, a “straightforward” undertaking according to Hugh Fishenden, HOK’s internal project manager. In simple terms, Airspace can be thought of as a big metal tent, the new design blurring the distinction between roof and wall. The subcontract awarded to DGT Steel and Cladding weighed in at £1.9m.

However, it was not without its complications. Meant to last 30 weeks it was closer to 45 and the specified system was dropped by the contractor because of cost. “You couldn’t even call it value engineering,” says a disappointed Comely. In the end, an aluminium standing seam system by Rigidal was used but its aesthetic appeal was less impressive than the designers had hoped for. Neither main nor specialist contractor were available for comment.

The new roof build-up comprises an underside of decking with a layer of acoustic, then thermal insulation, topped off with the standing seam system that has been given a lustre finish to dull down its natural shininess.

If the architect had its way, long strips of ETFE would have been installed in the roof to flood the interior with light, but the curators vetoed the idea because of potential UV damage to exhibits. “The client required museum conditions – this was always going to be more than a simple aircraft hangar,” says Comely diplomatically, clearly aware of the irony in designing to prevent UV damage to planes used to flying at high altitude.

The faceted, angular roof profile of Hangar 1 has been smoothed and flattened to create the sleeker lines that now define Airspace. Bowstring girders and trusses from Corus, added at either side of the original structure, work to blend wall and roof. Elsewhere, engineer Mott McDonald has overseen the site-welding of T-sections to the existing trusses, further enhancing the aerodynamism of the profile.

A new demonstration area has been created, adding depth to the floor plan. New trusses, pre-formed to match the sleeker roof profile, and lightweight tapered I-beams, again by Corus, define the space.

The engineer was also involved in the exhibition hanging. It provided intermediate supports between the original trusses to correspond with an aircraft’s strongest suspension points. And it installed couplings, which allow rotation in plan without exerting additional force according to engineer Dave Bailey who says the heaviest single suspension load was 6,250kg. “And the original scheme wasn’t over-engineered,” he adds, a lone voice defending the PSA’s reputation. “Suspending planes was always meant to be an option.”