Gothic builders accomplished incredible feats with little more than a plumb line, compasses and a chunk of chalk. Until now, you could only imagine what they’d have done with 21st century design and construction technology – but soon that will change. With the completion of the fan-vaulted laminated oak lantern, 106ft up the tower of St Edmundsbury cathedral, you’ll be able to see precisely what happens when age-old carpentry skills and church building technique meet the era of laser measuring and computer-aided design.
St Edmundsbury’s, in Bury St Edmunds, is the UK’s newest Gothic cathedral. Originally the parish church of St James, it was “ecclesiastically reassigned” in 1914 with the creation of the diocese of St Edmundsbury and Ipswich. After this, thanks, in the words of sub-dean Canon Michael Hampel, to the “small matter of two world wars”, nothing much happened for a half century. But from 1959 development work got seriously under way to reflect the building’s elevated status. Masterminding the undertaking was renowned Gothic revivalist architect Stephen Dykes Bower. He oversaw a rebuild of the chancel and construction of transepts and side chapels, and became so committed to the project that, on his death in 1994, he left £2m to the cathedral in his will.
The Dykes Bower vision for the building was all but completed with the construction of the £12m Gothic tower, which was 50% funded by the Millennium Commission and finished in 2005, but one element was missing. “He had plans for a fan-vaulted ceiling, but we had no money left,” said Hampel. “The tower was clearly incomplete, as you could see the steel girders, but we thought we’d have to live with it.” This changed, he added, when an anonymous benefactor stepped forward and more money was forthcoming from the Dykes Bower estate.
To turn the latter’s aspiration into a finished ceiling design, the cathedral hired Cambridge-based architects Freeland Rees Roberts. “I suppose we were chosen because of our broad church architecture experience,” said Henry Freeland, “and perhaps the fact that I’m architect to King’s College Cambridge chapel, where the fan-vaulted stone ceiling provided some of our inspiration”.
The rest of the project team were restoration contractors FA Valiant, decorative contractors Hare & Humphreys, Taylor Made Joinery Interiors (TMJI) and, co-ordinating everything, the cathedral’s ex-clerk of works Horry Parsons who came out of retirement specially.
“Having me overseeing three separate contracts is more cost-effective than having a main contractor and sub-contractors,” said Parsons. “It’s also more complex, but when people know precisely what they’re doing and are committed to the project, it works.”
The ceiling is being built up in sections, with the structural double-curved rib framework, comprising eight separate 3x2.5m 350kg sections, going up first and the central circle of the vault and four surrounding fans, an interlocking puzzle of round and rectangular 30mm-thick panels, then slotting into place within it.
To make sure the finished whole fitted precisely in the tower, TMJI, whose CV includes work on the restoration of Windsor Castle after the 1992 fire, insisted on a laser “point cloud” survey of the building. “This gave an incredibly accurate map, recording 29 million points within the ceiling space,” said Parsons.
This mass of data was then applied to Freeland’s design and the finished plans imported into TMJI’s 3D CAD system to create tool path drawings for its five-axis Reichenbacher CNC wood machining centre.
According to Freeland, there were initial concerns about sourcing the quantity of timber with the environmental credentials required. But eventually a supplier of FSC-certified Italian oak came good.
The medieval way would have been to use this material solid, but TMJI built it up into laminated engineered components. “These are stronger and much more stable and predictable,” said Freeland. “The less movement you get in a timber structure 45m above ground the better.”
To minimise the degree to which the timber expands and contracts further, environmental conditions in the tower were evaluated and ventilation designed into the structure and a gap left around the perimeter.
“The idea is to ensure temperature and humidity are as similar as possible above and below the ceiling,” said Freeland.
To reduce the risk of any movement that does occur affecting the structure of the tower, the ceiling is also designed so there’s no direct timber to stone contact. “It appears to sit on the stone pilasters, but the timber springs from two universal jointed stainless steel brackets in each corner,” said Freeland. “The tas de charge ribs are false, in that they hang from the timber above, with the vault springing from just above them.”
The final ceiling comprises a total of 2,544 parts, each finished by hand by the joiners, and weighs in at five tonnes. To avoid too much final adjustment of such a complex and hefty structure high up in the tower, the TMJI-team test-assembled it in the workshop.
One initial idea had been to lift it into place with a self-climbing hoist, but that was a challenge too far. “The scaffold Valiant built, with just the right sized traps for the components, was complex enough,” said Freeland.
In keeping with its medieval forebears, the finished ceiling will be highly ornate, gilded and painted in blue, green and red by Hare & Humphreys and finally embellished with the coats of arms of the Church of England’s 42 dioceses ready for the official unveiling next March. “Some of the decoration will be done before erection, but as we’re using oil gilding, which tarnishes if touched, a lot will have to be completed in situ,” said Parsons.
And, said Freeland, this hi-tech structure will also include another final original Gothic flourish. “Like medieval craftsmen, the TMJI joiners have left their personal marks on the timber and we may also include a plaque listing everyone involved, which will be visible from the walkway above the ceiling, so that generations to come will know who was responsible.”
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The ceiling was preassembled at TMJI to make sure it fitted together before being dismantled and lifted in sections into place in the tower |
