Take off time

In the post-Egan era, contractors are supposed to be aiming for 10% reductions in time and cost. But when your client is Sir John Egan himself, there’s no supposed about it.

That was the challenge faced by Alistair Taylor, associate director of BAA’s commercial property arm, BAA Lynton. His target was to build a £6.8m, 6485 m2 office building at Stansted Airport in 30 weeks – and his secret weapon was cladding.

Taylor’s benchmark was the 38 weeks it took to build First Point, a slightly bigger office building at Gatwick, which was completed in July 1998. Taylor saw the potential for enormous improvement if only he could solve one of the nagging problems at other sites, which was how to speed up the cladding process. He was frustrated by the fact that cladding could not begin until the precast frame was completed.

The team decided to risk a pioneering framing system that allows cladding to start when the frame is still half-finished. Frame contractor O’Rourke was brought in to create a post-tensioned hybrid framing system. This was the first time BAA had used the system, which involves precast concrete columns and insitu concrete floor slabs.

For the floor slabs, the concrete arrives on site and is poured into the floor slab frame. The slabs are strong enough to brace the columns – and support the cladding – even when they cover only half the breadth of the building. The result at Stansted was that cladding contractor Van Dam was installing the first cladding sheets by week eight of the project – a significant improvement on First Point where cladding could not start until week 11.

“It is difficult to be exact,” says Taylor, “but starting the cladding early probably saved us £25 000 a week. Over three weeks, that’s £75 000.” Doubling up on trades did not mean that the process had to be twice as complicated.

Chris Gregory, associate director at architect Geoffrey Reid, describes the cladding as an ordinary off-the-shelf system from Schüco. He also realised that further cost savings could be made by changing the usual method of matching the vertical mullions to the internal space-planning grid. Matching the mullions to the grid makes it easier for occupiers to divide an office into smaller rooms, and tends to mean that mullions are spaced 1.5 or 1.2 m apart.

Approaching space planning from a new angle, the project team at Stansted realised that any office rooms required by BAA were unlikely to be narrower than 3 m. This meant that fewer mullions were needed, making construction speedier and more economical.

As well as the early start, another element played a key role in the fast and efficient cladding process, summed up by Gregory: “We tried to keep the building as simple as possible. Why be fussy?” The theme of simplicity was extended by using the same cladding system inside and out. “All the design and delivery could be done with the external cladding which provided for the entire building,” says Taylor. This meant there was the same lead-in and method of fixing, and no chance of muddling the systems. By contrast, First Point had three systems – two for the exterior and one for the interior.

Another major time-saver was reducing the number of temporary structures. The use of scaffolding and ladders was dramatically reduced by installing the emergency exit stairway, called a stair-in-a-box, at an early stage in the project. This then acted as access to the floors and roof. Assembling the emergency exit off site with the handrail already attached also saved time.

Does all this standardisation mean that airports across Britain will be littered with identical office buildings? Taylor says no, because the components can be used on different-sized buildings. The method of production is the key.

“The intention is to get the product component-based,” explains Taylor. “We can then use the same components and techniques, so that whether you build a two-storey rectangular building or a four-storey square building, the interface will still be standard.” Components such as cladding can be standardised in terms of type and method of installation, but the size and colour can change in line with requirements.

Taylor plans to introduce more off-site assembly for future projects. The stair-in-a-box, for example, will be brought to site with the cladding surrounding it already intact.

The big question is, did the team finish the building in 30 weeks? Sadly no. It took 31.

But Taylor and his team managed to exceed the 10% time saving recommended by Egan, and the project was a significant improvement on First Point.

BAA Lynton has not yet chosen the site for its next office project, but it is likely to be at Gatwick. It will carry all the project innovation with it, as well as the design team.

Taylor’s target for this next job is 25 weeks.