The centrepiece of a £57m sports centre in Milton Keynes is a 170 m long indoor ski slope with real snow. Concreting the 15° slope was just one problem this multipurpose building presented.
“The tallest building in Buckinghamshire,” proclaims one lurid poster. “The largest indoor ski slope in Europe,” boasts another. The posters, which brighten the walls of developer Capital & Regional’s site office, are referring to Xscape, a 51 000 m2, £57m sport and leisure complex currently under construction in Milton Keynes.

Xscape is the first of a new type of leisure venue set to be rolled out around the UK and Europe. Squeezed into the distinctive cylindrical building is a 170 m long indoor ski slope, soon to be blanketed in 1500 tonnes of real snow; a 16-screen cinema; 10 000 m2 of retail units, bars and restaurants; a 6000 m2 tenpin bowling alley; and a health and fitness centre, with swimming pool. The combined facilities are expected to attract up to 5 million people a year.

The scale of the building and the sheer number of different functions crammed into it have made it a challenge to construct, says Paul Walker, project manager of design-and-build contractor Sir Robert McAlpine. He has to ensure that the complex is ready for its May opening. For Walker, the biggest challenge has been the building’s shape, and especially its curved aluminium roof, which rises from ground-floor level at the back of the building to a peak of 45 m, where it crowns the glazed, semicircular wall forming the raked front facade. “It’s been an extremely difficult building to service from a construction point of view, with the roof reaching down to the top of the ground floor on three sides,” he says. In fact, with such limited access, the exercise has sometimes felt more akin to keyhole surgery, with most of the plant and materials being taken into the huge building through one entrance.

The ski slope runs almost the full length of the 240 m long building, descending 30 m from the eaves at the building’s gable end before levelling out at the skiers’ bar and café at the single-storey rear of the building. Tucked beneath the slope is the cinema complex on the first floor, while the shopping mall and bowling alley occupy almost the whole of the ground floor.

Fortunately for Walker, the project was let as a two-stage contract with 12 months between stages. This extra time gave him and his novated design team a chance to build a rapport with the client and to start scheduling the works. “The first stage was only pricing preliminaries and assessing how we were going to build,” says Walker. “Stage two commenced with the fixed-price, lump-sum part of the work.” The project started on site in October 1998. Once the steelwork had been erected, the roof had to be tackled. It was to be constructed from the gable end down.

Walker admits that this is not the usual way to install a roof, but because most construction work was scheduled for that end of the building, around the cinemas and bowling alley, it made sense to start there.

The task of installing the roof was handed to roofing subcontractor Project Services. The shape and size of the roof meant that standard installation methods were ruled out. The roof had to be installed by a gang of specialists tied to the ridge by rope. Before work could begin, the installation team had to spend one week on a basic rope-access techniques course. And even after training, each group of six installers had to be monitored by a supervisor paid to ensure their safety. It was not only the roofing subcontractor that had to be trained in rope access. In order to inspect the work, McAlpine also had to have trained personnel capable of traversing the broad expanse of aluminium – a task that Walker seems only too pleased to have delegated.

He was anxious to complete installation of the 27 000 m2 roof early in the programme, so that work could proceed below unaffected by the weather. The aluminium was delivered, unformed, to site as a coiled sheet. Each coil was then divided into 70 m long sections of roof.

At its widest point, the roof spans almost 200 m, so the panels could not be run out directly from the forming machine into position. Instead, the subcontractor had to pre-form cladding panels in 70 m lengths on the ground next to the building. A huge crane then lifted these pre-formed lengths 20 at a time before depositing them in the centre of the roof, where they could be manhandled into position. The wind had to be monitored continuously during this work to ensure that the workforce was not in danger. “Fortunately, we put the roof on in the summer, so very little time was lost,” says Walker.

The disadvantage of completing the roof early in the programme was that it cut off the core of the building from the outside. And once complete, the only way into the building for equipment and materials was from the ground floor or through the front facade at the gable end. “We were always aware of the problem of access,” says Walker. Because of height restrictions on the ground floor, most materials had to be delivered by crane through the gable end and manhandled to their final destination in the space. “We had to leave a designated route through the building from the gable elevation,” explains Walker, an experience akin to trying to push furniture through a letterbox.

The limited access had a huge effect on the way the works were programmed and built. For example, the walls to the cinema were erected while the roof was being installed, but when it came to installing the stadium seating for the expected 3500 viewers, the potential difficulty of manoeuvring prefabricated seating banks through the building precluded their use. Instead, concrete seating banks had to be cast insitu. And, as Walker explains, the cinema air-conditioning plant also had to be installed much earlier in the programme than usual, “just to ensure that we could get the air-handling units to the plantroom above the cinemas”.

Placing the cinema on the first floor also required some nifty structural engineering. More than 5000 tonnes of structural steel have been used on the project. On the ground floor, the columns, which sit on 1200 piles, are laid out in a regular 7.5 or 10 m grid. But this was not possible on the first floor, because of the layout of the cinema. Instead, huge transfer beams had to be installed to carry the irregularly distributed weight of the cinema and the loads from the ski slope and building above to the regularly arranged columns on the ground floor.

On site, in place of the crane, a massive wall climber lift now scales the raking front facade; its trussed gantry bridging the gap between the two shiny, metal-clad escape stairs either side of the main entrance. The final glazing panels are now being eased into place as the lift moves slowly downwards, closing off the access routes into the building as the centre nears its opening date and the team gets ready to start laying the snow on the ski slope.

The ski slope in Milton Keynes is unusual. It will be one of only two in the UK that uses real snow. To stop the snow melting, the slope has been constructed in an insulated box to keep the temperature at –6°C. “People have been building freezer stores for years and years,” says Walker, “but not on a 15° slope.”

The slope itself is constructed of reinforced concrete laid on a steel frame. The 15° angle meant that the concrete subcontractor was working at the limit for laying concrete before a top shutter would have to be used to hold the concrete in place. “It’s hard concreting up a slope,” Walker explains. The task fell to the civil engineering specialist on the project, John Doyle. The team had to use an electric winch attached at the top of the slope to pull up the concrete tamping device. The slope has long been finished and the insulation team is hurriedly clothing the concrete in 150 mm slabs of insulation ready for the start of the snow-freezing process.

Now, with less than two months to go before the first skiers take to the slope, Walker is bracing himself for an onslaught of fit-out contractors swamping the ground-floor shopping mall. “The stores always wait to the last minute before they begin fit-out,” explains Neil Garrard, marketing manager at developer Capital & Regional, “because they have to start paying rent as soon as they move in.”

For Walker, this is just another logistics problem he and his team will have to tackle. There are already 500 operatives working on the site, but if fit-out is to proceed smoothly, the army of shop-fitters will have to be organised to keep the one access route on the ground floor open. At the moment, Walker is sceptical that all will be ready in time for the opening. “It’s not like fitting out a normal shopping mall. It’s an unusual building to work in,” he says.

Walker is hopeful the same firms will be used for the construction of future Xscape complexes. Capital & Regional has announced that the next two schemes are in Castleford, West Midlands, and the Ruhr, Germany.

How the cold room was constructed on a hill

One of the toughest challenges has been to build the ski slope in a freezer. To stop the snow melting the temperature is maintained at –6°C. McVie Installations was the cold room specialist charged with building the 200 m long, 60 m wide and 13 m high insulated box to house the ski slope. Its workers had to construct insulated walls, an insulated ceiling and insulate the 15° slope while standing on it. According to director Jim McVie, the hardest part was fitting the ceiling. “We’d planned to use a cherry-picker to install the drop rods to support the ceiling, but the structure could not support its weight.” McVie had to use a rope access team, similar to the one used by the roofers. Four mobile access platforms were imported from the USA so that workers could install the insulated panels on the walls and ceiling. They worked fine for the walls, but the ceiling was 2 m beyond the reach of the platforms and they had to be adapted. The ceiling panels had to be installed so that each new panel would rest on the one below. Once all the panels were in place, the seals between them had to be fitted from above. The seals are critical to the success of the installation. Usually, cold rooms are constructed from flammable foam-cored panels, but because of the fire requirements, non-combustible rockwool insulated panels had to be used. To stop water vapour entering the insulation and freezing in the panels, which reduces their insulating efficiency, the panels have to be completely sealed.