A trip through time

Brownfield sites present a multitude of problems: poor ground conditions, expensive clean-up operations and government agencies breathing down your neck to make sure you've got it right. But not many of them include the discovery of a Roman mosaic.

This was just one of the difficulties facing contractor HBG on the redevelopment of the old tramshed site in Bath. The 1.75-acre site was home to a disused 1904 tramshed and ancillary buildings, which HBG converted into flats with car parking, offices and a restaurant.

Building on a brownfield site in a world heritage city such as Bath was always going to throw up challenges, though an archaeological find of national importance was not what the client, Future Heritage and Frogmore Estates, expected when it carried out the ground survey.

"We found a Roman mosaic three feet square, 57 Roman coins, pottery, glass and rings," says Alan Martin, project director for Future Heritage. "We had to work very closely with Bath Archaeological Trust. It even dug the service trench for the utilities." Animal bones were also discovered, but the site was declared free of any infectious diseases.

The tramshed roof had to be removed because it contained asbestos, but the foundations were in surprisingly good condition. "They went down to 8.4m and were still watertight," says Martin.

But some new piles had to be put in and although the tramshed isn't a listed building, it is right next to the Corn Market, which is. This not only dictated the method of piling, but meant that the Corn Market had to be constantly monitored for vibrations. A vibration alarm was set up on site which set off lights and a siren if the vibration was too high, and fed directly into the engineer's office.

We had to replace every window - and no two were the same

Although the tramshed wasn't listed, it might as well have been given the stringent planning conditions, says Martin.

"We had a better chance of getting planning consent if we agreed to keep the existing buildings, which we did, but the planners put a lot of constraints on us. For example, we couldn't build higher than the existing building and we had to retain the steel windows on the river frontage. Because the windows had deteriorated, they had to be replaced with new steel. Every one had to be custom-built because the brick had slipped and no two windows are the same. That's what makes the development unique, but also difficult for the contractor."

The amount of alteration that has been incorporated into the programme means the project may overshoot the 67 weeks originally planned. HBG aims to hand over by the end of June at the latest. The final account should also fall within the £8m budget.

Seven months of enabling works were carried out before HBG got on site in March 2001. There had been some surprises before then, and others cropped up along the way.

"Each area has created new problems, which we couldn't have foreseen until we got on site," says Craig Allen, HBG's project manager. "For example, in April this year we discovered four fuel tanks in the ground which we had no idea were there, despite the extensive ground survey."

With a single 6m-wide road the only way in and out of the 1.75-acre site, material deliveries became critical

The reason why the tramshed site is such a desirable location is that 400ft of it looks onto the River Avon. However, this only created more problems for HBG, says Allen.

"We had to pull down a section of the river bank to take the surface water drainage. We have to rebuild it before we leave, and have talked to the Environment Agency extensively, firstly to get permission to pull down the bank and secondly to make sure we rebuild it so it doesn't collapse in future. With the river so close by we also have to be very careful not to let any pollutants escape into it."

HBG also had to divert a main sewer that serves around 50 homes.

Allen rates retaining the facade and the restricted site access as the two biggest challenges on the project. "We had to construct a building within a building. The only part of the original tramshed we retained was the brickwork facade. We built a steel frame within it to create the new building, which was difficult in itself because the building is such an odd shape. Even though we had calculated it precisely, when the time came to bolt the two together, we were still crossing our fingers. But it worked perfectly. The phasing between building the steel frame and the facade renewal was critical, but it worked very well."

Despite building on a 1.75-acre site, access was through a single 6m-wide route, so logistics became critical. "We put up a schedule on site so each manager could book delivery spots and also appointed a logistics manager to keep the site moving all day," says Allen. "Material deliveries were critical, especially when we had a tower crane on site. We had to keep the crane working for as long as we could. We had daily site meetings to make sure everyone was aware of the priorities for that day. We also discussed with Waitrose supermarket down the road when they were having their deliveries to make sure we could avoid a clash if possible."

Future Heritage is a Bath-based developer and was keen that nothing would be done to harm its reputation in the city in redeveloping the tramshed.