Wharf speed

This high-density scheme has been designed to exploit its location to the full. Most of the residential units are concentrated along the Thames frontage. The spine is formed by five towers of up to 21 storeys, from which a series of terraced blocks cascade down. In a blatant reference to the building's riverside location, a prow-shaped roof tops each terrace, and gull-wing roofs will crown each of the towers. The rear of the development, fronting the busy Wandsworth Road, consists of three blocks housing the office space, a hotel and the accommodation for key workers.

"There ain't many people building a scheme of this complexity," boasts Steven Embrey, managing director of St George, south London.

High land and build costs mean design and construction times are important to the scheme's success. "Being a developer, our most expensive item is cash," says Pressley, "so the quicker a building is completed, the quicker people can move in." But the need for cash is not the only pressure: 90% of the apartments have been sold "off-plan". According to Pressley, "There's nothing that angers purchasers more than their flat not being finished on time." So, to ensure the apartments are completed in double-quick time, the housebuilder has borrowed construction techniques more usually associated with large-scale office developments, such as precast cladding and balcony sections and large areas of curtain walling.

The £200m development is being built in phases over six years, working down from Vauxhall Bridge in the north toward the site entrance at the southern end of the plot. Work started on site in November 1998, and phase one was the first of the residential towers, with its cascading wing of accommodation along with the first of the link blocks that stitch the towers together. It was completed in 18 months, releasing 180 apartments. "We used this cash to fund the next stage of the development," explains Pressley.

He has used this construction phasing to his advantage. By implementing a process of continuous improvement for both the design and construction teams and by using each previous phase as a benchmark for the next, he is able to monitor the effectiveness of any improvements. It took only 18 months to complete the first two blocks, and the next two could be built even faster. "The first phase was fairly traditional construction," says Pressley, "then we implemented a process of innovation."

The first big innovation was to change the method of construction of the building's insitu concrete frame. Working with a team from BRE, St George and its concrete contractor Stephensons adapted the method of table-form construction used to make the shuttering for the reinforced concrete floors. The large steel-framed tables of the first phase were replaced with smaller, lighter aluminium models to reduce the number of men and crane time needed to transport them from one position to the next.

At the same time, St George also moved responsibility for design detailing of the frame from the structural engineer to the trade contractor's package of works. The engineer's design was novated to the contractor, giving St George a single point of responsibility for the frame design. This had several advantages:

it allowed Stephensons to concentrate on standardisation and repetition of details and to focus on buildability issues, and it moved this element of the design to a later stage in the process so that the developer could tender the package earlier. Between the first two phases, savings of 16% were reported in programme time for the concrete frame, while the number of man-days was reduced by 39%.

Construction of the second phase is now well advanced. Work on the concrete frame and cladding installation has finished on the second tower, and fit-out of the apartments is drawing to a close. The second infill block is also nearing completion with the concrete structure virtually complete and fit-out under way; the first tenants are expected to begin moving in after Christmas. A deep excavation next to this block is signals that work has begun on the next phase: a team is starting to install the steel bars that will reinforce the pile caps in preparation for works on the next residential tower (see "How the site was prepared").

One unusual aspect of this project is that despite the the continuing fit-out of the upper floors of the second tower, many residents have taken possession of apartments on the lower floors. James Gaffney, senior construction manager for St George, is unfazed by this. "It is far from the usual residential development," he admits, but insists that activity take place during normal site hours. "We just have to make it a priority to separate work from the residents."

As well as speeding construction, the use of precast cladding elements helps Gaffney's team by keeping the facades free of scaffolding. Like the concrete frame, the cladding installation has evolved as the project has progressed. On the scheme's initial phase, the reconstituted stone cladding panels were installed without the windows in place. On the later phases, the panels were installed with the windows prefitted. A similar process of evolution has occurred with the precast concrete balconies: originally these had waterproofing added on site but they now arrive with the waterproofing, paving and a drainage gully already installed.

Another significant modification has been to method of construction of the gull-wing roofs. Tony Carey, managing director of St George, insisted on building the roofs using concrete. Casting these in situ involved an enormous amount of shuttering and careful control of the concrete pour. On the later phases, this will be changed to precast sections bonded together in position.

While the small number of trades involved in the building's envelope makes it relatively easy to programme, Pressley describes co-ordinating the fit-out as a nightmare. With the flats pitched at the top end of the market, quality is a big issue and St George has focused a lot of attention on minimising defects. "These buildings have masses of tiny rooms, like bathrooms and kitchens, where we have to drive vast quantities of trades through in a controlled way," he explains. Detailed planning is used to control the process. Each plot has 62 items on the fit-out schedule, each with a start and finish date, along with dates for quality checks. "It's not perfect, but it's better than it's ever been," says Pressley.

Phasing construction has also allowed the developer to adapt the design to respond to market conditions and the requests of residents. "We are always looking for ways to add value to the scheme as work on each new block commences," says Pressley. Currently there are 29 planning applications lodged for the scheme, including one to replace an eight-storey office block planned for the south-west corner of the site with a 40-storey residential tower.

The 40-storey tower will be constructed in the scheme's later stages. If the planning application is successful, and if Pressley's drive for continuous improvement and faster construction continues, by the time work starts on this tower St George's construction techniques will be in racing tune.