A head for heights

Crashing through the roof, the stone came to rest above the North Quire aisle, damaging the 14^th century vaulted ceiling beneath. Although the ceiling caught the pinnacle, it was badly damaged and needed bracing to prevent its collapse.

The day after the storm the cathedral called in Malvern Scaffolding to secure the area with fencing to prevent any of the public wandering into the danger zone. A local firm, Malvern Scaffolding has a long-standing relationship with the cathedral, having carried out a number of access contracts on the building in the past.

It was critical to support the damaged vaulted ceiling so, working with structural engineer Andrew Waring Associates to produce an approved method statement, Malvern Scaffolding designed a mobile shoring scaffold that could be erected in a safe area and then wheeled into place.

This avoided the need to work in the danger area and the pre-assembled scaffold took less than 10 minutes to wheel into position beneath the ceiling.

With the ceiling supported, the stones embedded above it could be removed. Malvern Scaffolding then started erecting a birdcage scaffold from which to carry out the internal repairs.

The impact of the falling pinnacle had released a huge cloud of dust and so to prevent any more dust spreading into the cathedral during the repair works it was crucial to seal the area around the birdcage scaffold.

This was achieved by building scaffold frames within the high-level arches and then sheeting the whole area. Wherever there was a join in the screen, the sheeting was overlapped by one metre and taped. Foam padding was used to seal all the areas around the stone arches and fully encapsulate that area of the side aisle.

A further issue was the risk of damage to the Quire organ, a magnificent pipe organ by Kenneth Tickell, one of the 20^th century’s foremost organ builders. Fortunately, the organ was not damaged by the falling masonry, but almost half of its 3,500 pipes were badly contaminated by the cloud of dust.

Phase one of the clean-up therefore involved removing 1,500 organ pipes for cleaning and refurbishment. To do this, Malvern Scaffolding erected a free-standing birdcage that included a Haki stair access and 500kg-capacity Niko hoist and track to lower the pipes in their timber ‘coffins’.

With the pipes cleaned and ready to be re-installed, Malvern Scaffolding had to ensure that the risk of further dust contamination was minimised.

“We used the same scaffold materials and procedures that we use for the hygienic scaffolds when working in food and drink processing factories: all clean kit, no paint on tubes or fittings and composite scaffold boards meaning no wooden products on site,” says Malvern Scaffolding managing director Steve Fellows.

All this was done while minimising any disruption to the cathedral and its visitors.

While completing the internal scaffold, Malvern began erecting a temporary roof covering over the damaged areas to keep out the rain and allow repairs to be carried out under cover. The temporary roof was supported by a scaffold tied into the main clerestory wall, which allowed the aisle roof directly below to be kept clear of scaffolding.

Over the next two years Malvern Scaffolding erected a series of scaffolds to provide access for repairs to various parts of the internal and external structures.

Once these repairs had been completed the final piece of the jigsaw was to re-build the pinnacle with new stonework, requiring access to the full height of the cathedral tower. Standing at 55m, this is the tallest scaffold ever built by Malvern Scaffolding. And from the environmental and logistical point of view, it is also one of the most challenging.

The company worked closely with the client to work around religious services and other critical events so that life in the cathedral could carry on as normal. A more difficult requirement was to erect this major scaffold without disturbing the peregrine falcons that nest on the tower.

In collaboration with Worcester City Council ecologist Chris Dobbs, Malvern Scaffolding installed a nesting box away from the main tower to encourage the falcons to raise their brood on one of the roof pinnacles rather than the main tower. This proved acceptable to the birds, which adopted the nest box and laid four eggs. But simply relocating their nesting site was not enough; peregrine falcons are easily spooked and further measures were required to avoid the risk of them abandoning the cathedral altogether.

“In order to establish how the birds might react to the scaffolding, we did some initial noise testing,” explains Fellows. “While the birds were being viewed on the ‘nest-cam’, we built a small test structure located where the main scaffold would subsequently be erected.

“Despite this going well, and the falcons not responding adversely to the noise, the ecologists still felt that the risk of the falcons abandoning the nest was too great. So it was decided to postpone the start date by six weeks, by which time the chicks would hopefully have hatched and fledged. This was not good news for us as we knew it would put pressure on the programme,” he says.

Malvern Scaffolding used this hiatus to do some research and put together a plan of work designed to minimise the impact of the erection team on the peregrines.  Fellows discovered that the birds dislike bright colours, so he had his operatives dressed all in black with black (rather than day-glo yellow) hi-vis vests. “Additionally, all operatives were issued with walkie-talkies to avoid the need for any shouting,” he adds.

Worcester City Council’s biodiversity & landscape adviser Chris Dobbs says: “The team took a real interest in the birds and the result was a highly successful year with four strong fledglings – one of the best results of observed nests in the UK that year. These were difficult circumstances for the job and very well resolved.”

Anchoring the scaffold to this ancient monument was another challenge for the Malvern team. The 14^th century cathedral tower is built from sandstone blocks with numerous areas of ornate carving and delicate stonework; consequently there is a limited number of places in which to tie the scaffold into the structure.

“We found that self-tapping M12 bolts worked best in the sandstone.  These can be removed and the holes can be easily repaired by the stonemasons,” says Fellows.

From the ground up to 22m, the birdcage scaffold had very few tie points and so relied on the size of the structure to give it stability. At the top, the birdcage was tied into the beams within the roof space, providing additional support.

“The high-level scaffold at the northeast corner of the tower presented further challenges regarding wind loading, given the limited availability of suitable tie positions,” says Optima Scaffold Design director Russell Marlow. The design therefore made maximum use of non-invasive methods, such as bracing the sides of the scaffold against the cathedral buttresses to limit lateral movement.

Where anchor ties were required, Fellows consulted master stonemason Darren Steele to ensure the stone was strong enough to take the loadings. In some areas it emerged that ties could not be installed as per the design so, after consultation with Optima, new tie patterns were established for those areas. “This was all happening as we were building so it needed some fancy footwork from all concerned,” comments Fellows.

Finally, on the upper-most section of the tower, Malvern wrapped tie tubes fully around the top turret to secure the top lifts.

With the tower fully-scaffolded, the next challenge was to lift the new stones for the replacement pinnacle up and into place. The largest of these carved stones weighed more than 700kg and this had to be raised to a height of 44m and then manoeuvred into place.

Malvern Scaffolding used three one-tonne chain hoists – the biggest it could find – two of which had the capacity to lift up to 30m height. The company attached the hoists to a one-tonne capacity Niko scaffolding runway system so that the stones could be lifted and traversed through the sequence of movements to get them from the ground to the top of the tower.

The first stage was to lift the stones 22m to the top of the birdcage. They were then traversed across the bridge-beam section, which was uprated to support a 750kg live load. The third stage was to lift the stones from the main birdcage and swing them into the complex area of beam-work that was required to support the tower scaffold.

Finally, the stones were lifted to the full 44m height and manoeuvred into place. “The way we constructed the scaffold meant the stone could be lifted and tracked then lowered almost to an inch of its final resting place,” says Fellows.

On 27^th November 2023, exactly two years after the storm, the new pinnacle was blessed in a topping-out ceremony that marked the completion of the restoration work.

SITE TEAM

Client: Worcester Cathedral

Stonemasons: Neil Berry, Darren Steele

Building restoration: Ellis & Co

Architect: Acanthus Clews

Scaffold design: Optima Scaffold Design

Scaffolding contractor: Malvern Scaffolding

Structural engineer: Andrew Waring Associates

Biodiversity & landscape adviser: Chris Dobbs (Worcester City Council)

PLANNING THE PROJECT

Malvern Scaffolding started work on the project having provided a provisional quote based on a ‘discussion concept drawing’ of the tower scaffold.

And despite there being considerable additional works internally to support the main roofs and various alterations as the build continued, it managed to stick to that budget price.

“By reducing the number of materials being used we were erecting at a faster rate,” says Malvern Scaffolding managing director Steve Fellows. “The programme had a 12 week build but we managed to reduce this by two weeks. This included all the additional support work so we were not only on budget but also beat the programme.”

Malvern used Haki-tec 750 beams, tube-lock scaffold and Klawz ‘double on double’ scaffold fittings bought specially for this project. The Klawz system helps scaffolders reduce the amount of tube required and speeds up scaffold erection. On this project, it reduced the weight of scaffold materials by about six tonnes.

“Throughout the project there were numerous instances where unforeseen issues were thrown at us, whether to do with ecology, structure or access,” says Fellows.

One such section was the Quire and northwest transept roofs where 17 tonnes of beam-work and framing would be erected. “The location and magnitude of the scaffold directly above the aisle, nave, and transept led to much investigative work in order to set out significant beam-work and establish suitable support methods to carry the 17-tonne scaffold framework,” says Russel Marlow, director with Optima Scaffold Design.

Optima decided that internal support scaffolds would have to be built inside the roof voids on the existing medieval trusses with further supports on to the main wall plates. “None of this had been accessible to us previously and it all had to be surveyed and designed on the fly whilst the scaffold was being erected,” says Fellows.

These support scaffolds created further complications since the roof had to be opened up and then made weatherproof on a daily basis as the work continued. “Once the internal support and the external scaffold was connected then we needed to ensure that no water ingress came into the cathedral. Each standard that protrudes through the roof had its own specially made lead cover to help with the weatherproofing.”

The internal supports were also designed to prevent the whole scaffold slipping down the roof. Optima carried out a series of highly complex calculations to work out not only the imposed loads directly on to the roof but also how the loads would be transferred on a sloping roof through to the internal scaffolds.

The scaffold in numbers

Total height: 55m

22m Haki stair access

22m-high birdcage built with ‘Klawz’ fittings to increase speed. Tube-lock scaffolding used throughout to accelerate erection and reduce manual handling and risk of damage to the building.

3 x one-tonne & 1 x 250kg lifting points using Niko track
3 x one-tonne chain hoists lifting to a height of 30m
750mm Hakitec beams to bridge between 22m-high birdcage and nave roof. Some sections uprated to carry imposed loads of the 750kg carved stones.

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