Stonemasons, chisels, BIM and beyond

1. Visitors enjoy the new

London 2. Purcell’s work

Afew years ago, I was fortunate to be taken on a tour of the Palace of Westminster by Parliament’s principal architect, Adam Watrobski. Nothing unusual about that of course; MPs and Lords arrange such visits all the time. But this was different. I had been invited to see the parts of the Houses of Parliament few get to see: down in the cellars; up on the roofs; in and out of usually locked doors, back stairs, sidling through cramped offices and climbing through windows onto catwalks.

The aim was to demonstrate that Barry and Pugin’s magnificent seat of government and home of UK democracy was falling apart. And so it was – from its leaking cast-iron roofs via its spalling, friable stonework and its patched-up heating, ventilation and cooling systems to its pongy drains. And that is before you take into account the wear and tear on the interior finishes, the result of the human and mechanical friction of more than one and a half centuries of constant use.

Visits such as mine were part of a briefing exercise to get us all used to the enormous scope and cost of the works required – that this was an ‘in-the-bones’ job, way more than a cosmetic exercise. Today, we see that the most essential parts of this repair work are under way, with cast-iron roofs and other areas of the palace shrouded in scaffolding that becomes especially elaborate over Elizabeth Tower – better known as Big Ben after its famous bell that chimes the hours. This is where Purcell, long involved in the palace’s rolling repairs, is working closely with Strategic Estates, as architects, on a four-year programme to restore Elizabeth Tower, which is one of the most visible parts of the Parliamentary Estate.

This is a prestigious and emblematic job, not only in itself or from a craft point of view, but also as a symbol of London and of parliamentary democracy in a World Heritage Site. Elizabeth Tower will be complete before parallel building work starts on the palace’s extensive restoration and renewal project so a job that prosaically, if elaborately, involves restoring the tower’s stonework, roof, clock and clock faces – while also adding a lift and modern services – takes on a far greater importance than the very challenging elements of the brief suggest. This is nothing less than stewardship of a global landmark. Craft and technology interweave: on one hand there are stonemasons with chisels, on the other, a parallel virtual existence – the palace is the first parliamentary project with a full BIM model.

It is not unnatural that buildings in World Heritage Sites recur in this side of Purcell’s work. Also in London, the prime example would be Tower Bridge of 1894, no less a Gothic historicist confection than the earlier Palace of Westminster though the Barry involved in this case was Charles’ youngest son John Wolfe Barry, who was an engineer. The architect, the City of London’s Horace Jones (not in the same league as Pugin) died just after construction began and, all in all, it is a strange hybrid structure but still – we wouldn’t wish it wasn’t there, would we?

Purcell’s work here was intervention rather than restoration. JWBarry’s twin high-level walkways, 42m above the Thames, are pure engineering – almost unadorned horizontal steel trusses, which act in tension to support the horizontal drag on the towers of the suspension bridge sections at either end. Beneath, the bridge’s central bascules rise and fall. The walkways provided an alternative route across the river for pedestrians at a time when the bridge had to be raised often for tall and large ships, and later became part of the structure’s visitor exhibition. Now you can see down through them to the traffic passing far below or the bascules,

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Lloyd Burnell, Director, Aerospace Bristol

themselves, as they are raised. The design job here was to insert two structural glass floors, one in each of the walkways. It is a very simple, if mildly terrifying, adaptation of a Grade-I listed building that kept the tourist cash tills ringing.

There are landmarks and landmarks. Clevedon Pier? A lovely, delicate little cast-iron structure reaching out into the Severn Estuary. Perhaps a bit too delicate given that in 1970, while being weight tested for insurance purposes, two of its spans collapsed into the sea. Demolition loomed but a strong campaign locally and nationally saved it. Purcell’s part in this was to develop techniques whereby the pier was disassembled, taken away for conservation and repair, then reassembled on site and eventually fully reopened. Steamers once again call there.

Not everything in the world of conservation and restoration presents such visible results however. A large part of the work of conservation architects – who, in turn, represent a large segment of the profession overall – consists of surveying. If you don’t look hard and record everything, you’re not going to be able to maintain historic structures very well. The technology available here has evolved rapidly in recent times, from drone photography to digital surface mapping and 3D modelling.

Take Durham Cathedral. This aweinducing building is ecclesiastically correct in being aligned east–west – yet this means it is perversely set athwart its steep peninsula in the River Wear rather than lengthwise along it, as would have been structurally much simpler. Along with its companion castle, it almost overhangs the gorge on the west, supported by a stone plinth. This, in turn, becomes part of a historic and much-patched perimeter wall running right round the peninsula, which includes not only the castle and cathedral precincts but also several university colleges aside from the original one located in the castle itself. I spent three years living within those walls. If you walk around the outside of them as they crown the peninsula, you’ll know that this linear architecture is an indispensable part of the overall experience of the place. Grade-I listed, they have been much neglected. Purcell’s condition survey ranged from the micro – how loose is the mortar? Is that ivy causing damage? – to the macro: long views of what is (again) a World Heritage Site. The juxtaposition of new technology with old, traditional craft techniques takes various forms. There is no recent cut-off date: as explained in the next essay, it’s also all about the overarching concept of significance.

As a visitor to the Aerospace Bristol museum at Filton, it’s obviously the flying machines you’ve come for, and there’s a whole separate specialist restoration/ conservation industry involved with those. What most people won’t immediately pick up is the way the buildings themselves – hangars, ancient and modern – are adapted and revealed not simply as a backdrop to the exhibits, but in knowing contrast to them. The timber lattice Belfast truss, for instance, is to be found in hangars of First World War vintage, two of which survive, listed, on Filton Airfield. Filton later played a pivotal role in the development of Concorde, one of which is here in a purposebuilt, climate-controlled new hangar designed for maximum dramatic display. This was a project ranging from a conservation management plan to newbuild, and included liaison with a separate exhibition designer, Event Communications.

Dealing directly with a building of significance is one thing, but a lot of the effort in this intertwined story of conservation, adaptation and new-build

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GREG HARDING ANDY SPAIN

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5 3. Adaptive reuse of

4. Canterbury Cathedral’s

Window 5. Climbing the

6. Old pottery kilns at the

Excellence 7. The

concerns proximity to what we might call the ‘significant other’. So at CoRE (the Centre of Refurbishment Excellence) in Stoke-on-Trent, led by Purcell partner Jamie Coath and associate Andrew Dobson, one element of the work consisted of conserving and adapting the significant building – old pottery kilns, factory and pub – while another dealt with proximity: a new building, separate from but linked to the old, was to act as an entrance hub. The net result of all this is a hybrid complex of considerable technical sophistication.

Again, time slips here. At StCatherine’s College, Oxford, the commission for a new set of student-room pavilions and a graduate common-room building deals with two significant others: first the listed architecture of Arne Jacobsen’s original college from the early 1960s, second the additions made to the college over a quarter of a century from 1993 by architects Hodder + Partners. Stephen Hodder’s meticulous additions, drawing on the language, materials and landscape of Jacobsen, have themselves now become a considerable presence, a composition to which Purcell now responds in its phase of buildings that are ‘completing’ the college. Thus, architects pass the baton down the years.

Let’s finish with some other cathedrals – Canterbury, Liverpool Metropolitan and Clifton – and add to the mix the shell of Battersea Power Station by cathedral architect Giles Gilbert Scott, who designed Liverpool’s Anglican cathedral – a sister to the Metropolitan. Battersea, itself, could be considered something of an industrial Rievaulx Abbey or Fountains Abbey – neglected and open to the elements, but now on its way back to useful life. Imagine getting to grips with that behemoth, from the surveys and the identification of suitable repair materials to the total and historically correct replacement of its previously decayed concrete fluted chimneys, which I regard as an unsung triumph. Purcell has a tripartite role here within the team of other architects and engineers, serving as conservation architects, heritage advisers and heritage assessors, vetting proposals for the re-use of the building.

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As for the real cathedrals, the Great South Window at Canterbury, a medieval masterpiece of prodigious scale, was starting to give way. The causes of its troubles had to be dealt with before it was repaired piece by piece, and all by hand. Historic deformities had to be preserved, otherwise the glass would not have fitted back into place. Achieving this recovery required designing the setting-out tools.

Six centuries after the construction of Canterbury Cathedral, things were equally spectacular in Liverpool. The Piper/ Reyntiens cathedral lantern tower at Frederick Gibberd’s space-capsule creation may have been by the same artist/maker stained-glass team as found at Basil Spence’s earlier Coventry Cathedral but, in Liverpool, experimental construction techniques have plagued the building almost since it opened in 1967. The enormous tapering cylinder of the lantern tower was leaking. What was needed was a repair methodology but – unlike in Canterbury – there was no conservation precedent. This is a grant-aided work in progress. What is significant and to be preserved at all costs? What is replaceable, and – given that the recent past is often more obscure than the distant – how, actually, was it made? Bringing this project to a successful conclusion requires the gaining of a new knowledge for a new kind of conservation and repair – as discussed by Jon Wright and David Hills in the next essay.