Big blue

While Her Majesty has recently opened grander projects like the £134m Tate Modern, and sleeker buildings, like the £43m National Botanic Gardens in Carmarthenshire, she will not have seen one of more imagination and greater technical skill.

From the outside, the building doesn't look like a technical challenge. In fact, its vast expanse of gun-metal grey cladding makes it look like a high-tech shed that you might see while driving along the M4 in the Thames Valley. But inside, the building gives you a feeling of Close Encounters of the Third Kind.

Bathed in an eerie blue light, courtesy of the 32m-high west wall, which is entirely clad in dark blue glass, the interior is a mix of steel walkways and stairs, all suspended from the ceiling. This provides a huge column-free space at the bottom of the building, which leads up to the main attraction – a 450-seat Imax cinema that looks like it has crashed through the ceiling and is suspended, perilously, above head height.

Responsible for putting this complex design together is 31-year-old Louisa Finlay, project manager for the main contractor, Kier Build, and an incorporated member of the CIOB. Finlay joined the project three years ago after learning that Kier had won the tender for the £22m design-and-build contract (the rest of the £45m is being spent on fit-out and exhibitions). "I was working at Tempsford Hall [Kier's Hertfordshire headquarters] and asked to join the project because it was so glamorous," she says. Her wish was granted and she joined the project as design manager working under Nigel Lelew. When Lelew left Kier last year to join rival Balfour Beatty, Finlay was picked to replace him.

The biggest challenge for Finlay was managing the construction of the complex structure needed to suspend the giant Imax cinema and the three floors of exhibition space that fill the 11000m2 building.

Project structural engineer Arup, along with the architect, MacCormac Jamieson Prichard, devised a clever and unusual way of supporting the Imax cinema and the three tray-like exhibition floors without using a grid of columns.

In simple terms, the structural design of the cubic building is a portal frame. The columns, spaced at intervals of 8.5m, are 32m high and provide over 30m of column-free space. That's where the design stops being simple. The exhibition trays and the Imax are supported by gerberettes. First used on the Pompidou Centre in Paris, gerberettes are steel plates built into the concrete columns.

The gerberettes look like giant Nike swooshes skewered by the 1100mm x 750mm concrete columns. Weighing 10-15 tonnes, each gerberette supports the exhibition trays at one end, while the other end is connected to a 273mm-diameter steel hollow tube that is tied to the foundations. Because the gerberettes cantilever out from the column, the trays and the trusses supporting them are 5.5m shorter than if they had to span from column to column. "This meant we could use thinner floors and bigger head room," says Arup engineer Kate Benton.

Up close, the gerberettes are two plates of steel with thicknesses ranging from 60-100mm, says Benton. The plates are connected by a giant steel pin that sits on a cradle built into the concrete column. Concrete is poured between the plates covering the cradle and pin.

Sequencing this complex process, surveying the results and managing the communication between concrete contractor Swift Structures and steel contractor William Hare was Finlay's responsibility. "It was a tough job, but they got there in the end," she says.

If that wasn't enough, Finlay also had to manage the construction of the 32m-high west façade, which is also hung from the roof truss. The problem, says Finlay, is that the blue glazing units are very heavy. Each glazing unit that fits into the standard transom and mullion curtainwalling system is made from two pieces of blue Schott glass with an interspacing louvre.

Finlay and Benton calculated that the weight of the wall would deform the frame. So, to stop the frame moving as the glass units were loaded, the frame was pre-deformed. This was done by tying the top of the frame to three bolts in the basement below and jacking down the frame until it was deformed to the same amount as it would be under the weight of the curtainwall. Then, as the glass was added, the cables were loosened. Finlay explains that this was a very tricky job requiring the full-time skills of the best site engineer to make sure that the frame did not move too much. Perforated anodised aluminium cladding was installed on the outside of the blue wall to prevent overheating from sunlight.

The design team tinkered with the idea of using resin-filled glazing to save weight. "The deep blue is hard to achieve. We looked at using two pieces of clear glass sandwiching a blue gel and travelled over Europe to look at solutions. But in the end there were worries that the gel might disintegrate under UV light. There were also concerns that the colour wouldn't be consistent because the gel was made using a batch process," says Finlay.

While these structural elements challenged Finlay's design skills, her management expertise was put to the test by the innocuous-looking north and south walls. Each side wall is covered with fabric and backlit with blue light "so that visitors will not be able to make out where the wall really is," says Finlay. Between these walls and the columns, work was congested with trades jockeying for position, explains Finlay. Drylining contractors had to get high up to the roof, while the tensioned fabric contractors, lighting subcontractors and the contractors working on the cables for the suspended walkways all had to work in a space just a couple of metres wide.

"It was impossibly tight for all the trades up the walls either side of the canopy," Finlay says, referring to the curving canopy that marks the underside of the Imax theatre.

Like many London construction sites, the Wellcome site has been hit by skills shortages. Finlay complains that there was a terrible shortage of drylining installers. "We had lots of specialist work, especially for the Imax and high-level work, so subcontractors were more interested in tendering for less risky jobs. In the end, we used two drylining contractors, Whiteways and Astins," she says.

Young, talented and female Industry leaders are forever bemoaning the lack of bright, young managers in construction. They say that low wages, long hours and poor site conditions are a big turn off for talented graduates and schooleavers. But in Louisa Finlay, Kier has unearthed a young star.

Finlay is Kier Build's project manager for the £45m Wellcome wing extension to the Science Museum in London. For most contractors, a prestigious lottery project means a wise old head. Kier has dared to be different. Finlay is just 31 years old.

But it is not just her youthfulness that is encouraging. Finlay is a woman. In an industry with just over 1000 female construction managers, the fact that such a young one is managing a high profile project is amazing.

Finlay doesn't make an issue of her gender or her age. "I'm no feminist, I just get on with it," she says modestly. "But," she adds ruefully, "of the five girls in my year only two are still in construction." Finlay explains that when she was studying for her building degree at Bristol Polytechnic (now the University of the West of England) there were five women and 25 men at the end. Now only Finlay and a friend who works for BAA are left in construction from the girls on the course.

Asked why she persevered with construction, Finlay replies: "It's long hours and its dirty work, but at the end of the day you can walk outside and say I built that." While most of her colleagues don't arrive on site until 8am, Finlay is at her desk by 7am even with a long drive from her house in Hertfordshire. And the working day rarely ends before 7pm, she adds.

Like all good project managers, Finlay has a great rapport with her peers and the footsoldiers on site. From sparks to carpetfitters, she takes care to enquire gently how things are going and cheerily gees them up. She knows construction is about getting people to work with you, not for you.