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SDC has recently completed an ambitious project to re-roof The Plaza building at Center Parcs Longleat Forest, Wiltshire.
The Plaza was constructed in a dome shape in 1993, using a glulam primary arch structure to support a series of glazed panels. Inspections in 2010 revealed that large areas of glazing had either cracked or moved within their retaining seals, while the glulam beams beneath were also beginning to show signs of wear. This led Center Parcs to conclude that the existing system, although suitable at the time of the original installation, required intensive refurbishment and that replacing the roof with a new covering was more viable than commissioning extensive repairs. Instead of glass, the new roof structure would comprise an insulated structural deck covered with a single ply membrane and ETFE triple layer cushions.
Operational Holiday Village
The 100m diameter building, which houses the Subtropical Swimming Paradise, restaurants, and retail units, forms the focal point of the Village. As such, the original brief was to undertake the refurbishment work at night in an effort to minimise disruption to guests. Contractors were also advised during the tender period that the repairs to the glulam beams were to be carried out by operatives on mobile elevated work platforms and specialist rope teams because erecting access scaffolding in the internal pool areas was not permitted.
However, recognising that the need to complete the work at night using abseiling techniques would increase costs and be harder to manage from a safety point of view, SDC devised an alternative solution. Based on the principles of a suspension bridge, the main contractor proposed fixing cables to the primary beams, from which a solid working platform would be hung with the aid of vertical suspenders. While the deck would still need to be erected after hours by a team of steeplejacks, the benefit of this strategy is that the refurbishment work could be conducted during the day since guests would be shielded from the work above by a solid, weatherproof, platform.
With the delivery strategy resting upon the success of the bespoke temporary works solution, a sample panel was constructed at SDC’s service yard in Chawston to validate the proposals. The 22m deck, designed to span between one of the roof’s sixteen segments, was installed by a team of steeplejacks in an attempt to replicate the conditions on site. Reflecting on this after the event, the Site Manager Gary Sullivan recalled ‘when the mock up was built, we made the guys install it as if they were on site so we wouldn’t let them touch the ground. We made them put the whole deck up from an external scaffold and they had to go in and do it all from ropes. So even though they were only a couple of metres off the ground, real lessons were being learnt.’ After the mock-up had been completed, a double-glazed unit was dropped onto the structure to confirm that the platform could withstand the imposed load in the event that a section of the existing glazed roof collapsed during removal.
Set in 400 acres of natural woodland, a standout feature of Center Parcs Longleat Forest is the peaceful setting. Nevertheless, this presented a further challenge – how would materials be lifted onto the roof? Given that the use of large cranes would not be possible due to the close proximity of the surrounding trees, SDC decided to erect a scaffold tower to the west of the building. The tower, hidden from the view of guests by camouflage netting and a row of trees, contained a stairwell for operatives and a hoist for the vertical distribution of materials. Connected to the scaffold tower was a bridge that took personnel over the top of the aforementioned trees and onto the roof. From here, materials were distributed using a series of hoists, pulleys, roller beds and trollies.
Another issue in need of resolution concerned the threat of snowfall. Once the temporary deck was in position and the existing glazing had been removed, the platform became exposed to the elements. Despite being completely waterproof and possessing a superior U-value to the former roof, each section of the stepped platform only had a safe working load of 0.5 tonnes. Thus, if the site received more than 30cm of snow, the deck would be deemed unsafe and the building would need to be closed. According to the Project Director Adam Knaggs, this problem was overcome by ‘installing trace heaters in the winter months that were connected to a dedicated generator. The generator had a weather sensor in it that – if it started to snow – kicked in and heated up the deck so snow didn’t settle.’
Even after the project commenced in 2013, the complexity of the project combined with the requirement to learn new systems meant that the first of the sixteen segments took 35 weeks to complete. Part of the reason for this, Sullivan explains, is that ‘the temporary works platform took about five weeks to install in the first few segments.’ Yet, as the scheme reached its conclusion in December 2015, the last section was finished in a mere 11 weeks. Knaggs suggests this because ‘every sector we got a little bit better, a little bit quicker and found ways to overcome problems. We got more and more refined as we went through.’
- 2 and a half years to complete.
- The building is made up of 450 timber frames that would stretch 2.5 miles if laid end-to-end.
- Internal area of 6,816m2, making it the largest building within all the Center Parcs Villages in the UK.
- 1,706 panes of glass were removed and recycled.
- 10,000m2 of camouflage netting was used to hide the external scaffold.
- Refurbishment work was limited to three segments at a time.