RSHP's uncharacteristically conservative British Museum extension

The first of three tricky tasks facing Rogers Stirk Harbour was this: how to insert a £135m factory into Georgian-rich Bloomsbury, between Bedford Square on one side and the British Museum’s Edward VII wing on the other?  Because a factory is essentially what the World Conservation and Exhibitions Centre at the British Museum is – complete with offices, distribution warehouse and movements of large trucks.  It’s at the top, laboratory-grade, end of the industrial scale. Yes, it contains the big new exhibition gallery where the recent Vikings exhibition was staged, but that is just a fraction of the whole.  Not for them the grand public promenade of Foster’s millennial Great Court project.

Their second task was to make convincing architecture out of what is not only industrial, but back-of-house, space.  The WCEC, as it is known for short, is the opposite of a gateway building. It’s an extension that – truck movements aside – is entered from the main museum buildings lying alongside and behind it. Graham Stirk, the partner in charge here, admits this was a challenge. A visible entrance and the sequence of spaces behind it makes a building more legible. Without that, you are really just designing boxes, in this case a rear and side extension that happens to be highly visible while also being very secure and private.  So – one would like to think in memory of Inigo Jones and his plain barn-church in Covent Garden – Stirk and the Rogers team set out to design the handsomest boxes in England.  The building, then, is expressed as four linked green-roofed pavilions rather than as a slab-structure. ​

And the third task?  To make pleasant subterranean spaces. This is an iceberg building. Planning constraints forced the maximum height of the building down to the cornice level of the Edward VII wing, while the minimum height – where it approaches the backs of the Bedford Square houses – becomes the ground. In consequence the whole building is sunk deep into the ground, as the section shows, while a fifth pavilion is wholly sunken, its glass roof set among gardens. The mighty hole they dug to drop the whole sequence of pavilions into was as impressive as the hole they dug to build the Pompidou Centre.

Beyond the massing of the building and the need to mostly obscure its visible operations, was the tricky business of  material contextualism.  A nod to the museum’s Portland stone was in order. Now Rogers does not do punched-window masonry over a classic prefabricated steel structure, as this is. So the design evolved with two skin materials – long planks of obscured glass screening the curtain walling, interspersed with tall sections of fossil-rich Portland stone deliberately sliced delicatessen-thin.  The main museum is smooth Portland, of course, but RSH went for the livelier texture of the roachbed variety. The visual solidity of the mother museum is rejected in another way, too: the new building, though rectilinear,  eschews conventional corners, adopting instead the device of overshooting plates. This further emphasises the thinness of the stone sections of cladding. 

Patterning on the kiln-fired glass cladding planks (an obscured section with a clear edge running round each one) is a bit of an architectural in-joke: it’s of the skyline of Portland where the stone – cut in identical-depth pieces – comes from.  Despite all this classiness in design and making, and the way this system allows the workers to see out while outsiders mostly can’t see in, this cladding can’t avoid looking just a bit like those 1970s draughty frosted window louvres. Oddly it’s on the western elevation, directly overlooking the back of the Bedford Square houses, that the glazing becomes completely clear, though with brises-soleils. The whole new complex is free-standing but very close to the old buildings: one consequence of that is some fine architectural chasms, glimpsed from the glazed links, between old and new. 

So from outside this is as self-effacing and conservative a Rogers building as you could imagine, and a little disappointing for that.  Inside however, they let rip with the industrial aesthetic. The look is very lab-like, workbenches festooned with suction pipes to remove unwanted dust and fragments. At the top is a top-lit studio where light materials such as paper and textiles are worked on. There are offices and communal areas aplenty. At the bottom is the heavy stuff – the get-in for the large stone object workshop can accommodate an Easter Island statue. The wholly sunken pavilion has a toplit atrium and glass pavement lenses in its walkways, so daylight levels are good. Stirk talks of the need for adaptable spaces that can absorb future pieces of as-yet-uninvented equipment. So it’s long-life, loose-fit, in the famous phrase of Alex Gordon. Stirk had high-ceilinged New York warehouses in mind and there’s something of that generosity of space here. He also fully subscribes to the Louis Kahn “served and servant spaces” philosophy . Vierendeel steel trusses define a ceiling zone where all the overhead equipment is visibly housed. And one complete floor  above the exhibition gallery – which is 70m long by 16m wide by 6 high - is an impressive, generously arranged,  plant room.

Rogers’ Meccano-like constructional clarity is present and correct throughout – you can see how everything bolts together, in square-section dark grey-painted steelwork, and it’s neatly and satisfyingly done. Vivid Rogers colours are only apparent in the lift cores. This is very far removed from the cramped and dingy basement rooms where many of the staff previously worked.  Notoriously the largest object they could previously X-ray was a mummified cat. Now they have hospital-grade facilities.  

However, it’s really all about the trucks. The world’s great museums are forever exchanging objects with each other, and many will now send materials to be conserved here. Cavernous vaults to contain some 200,000 delicate organic objects from the collection are ready to receive their cargo, once every object has passed through a freezer to kill any bugs.  The BM previously had no lorry get-in, and large objects had to be manhandled up the front steps.  A conventional ramp to a basement would have wiped out way too much square footage, apart from looking vile. The solution is a bit of urban trickery: a full-size articulated truck lift masquerading as a section of granite pavement rises from the ground to swallow the vehicles.  A convoy of three can be stored inside the building if need be. 

The WCEC finally gives the British Museum the scientific and conservation facilities that it deserves, and consolidates its international reputation. We the public will mostly never see these spaces, apart from our journey through the openings made in the back of the Great Court,  anterooms and then the glazed link to the new gallery. Stirk has plans to set up a circuit- route from other galleries to the new space so it is no longer a cul-de-sac.  But it’s the workers who win out in this building that celebrates  the secret life of this cultural factory. You may not see them, but you’re glad they’re there.