Making the point

It was not only the scheme's incredibly short construction programme that was making Scrine apprehensive. There were a host of other challenges to overcome. "There were a large number of complicated services to install, space inside the building was restricted, and there was a ban on out of hours working," explains Scrine. Outside the building things were no better: "There was no site storage, and we knew there'd be the usual problem of deliveries to a City site," he adds.

The ambitious project will see the reincarnation of Britannic House. The drab 1960's megalith that was petrochemical giant BP's old hq will be turned into a stunning speculative office block and given a new name: CityPoint. The building's rebirth will involve recladding the entire tower, extending the office floor plates, and adding a new seven-storey annexe, a top floor restaurant and a basement health club. The revamp will set developer Wates City of London Properties back over £160 million.

"With capital tied up in the scheme we had to pressurise its construction," says Rodney Clutton, joint managing director of Wates City. To ensure the developer received a prompt return on its capital, the refurbishment went ahead only after Wates City had pre-let the new annexe and first eight floors of the tower, along with floors 20 to 22 to a brace of US legal firms.

This made the services engineers' already difficult task of meeting the 90-week construction period more formidable. Scrine's biggest worry now was how to schedule the works to allow the tenants to occupy the building months before the services were complete.

Despite Scrine's reservations, AMEC Capital Projects Building Services¹ successfully tendered for the project and were appointed in late 1998, when it was still known by its more familiar moniker of Matthew Hall. The JCT 81 (with amendments) contract gave AMEC responsibility for the detailed services design of the shell and core installation and for a gamut of services including: mechanical, electrical, public health, fire engineering, fire alarms and security and, unusually, a £4 million building package.

Consulting engineer Foremans produced a concept design for the scheme, based on a four-pipe fan coil system serving the offices. Fortunately for the contractor, fit-out to the tenant's floors was outside the contract.

"We were appointed on 6 October 1998 and were given a completion date of 14 December 2000," says Scrine, "and somewhere between these two dates we had to achieve some 70 handovers to allow the tenants to move in." AMEC had just three months to review the design concepts, assess their buildability and to investigate how the services could be co-ordinated. "The conclusion was that if we wanted to meet the programme, our installation had to be right first time," says Scrine.

Rather than rush into design, AMEC decided to take a step back. "It was worthwhile because it allowed time to get our mindset clear," explains Scrine, "We had a three month design audit period to understand the job and to look at how the services would fit. But the biggest challenge was getting design certainty."

In the countdown period before the project took off, AMEC Capital Projects Building Services called on the skills of another part of the AMEC Group, the equally concisely named AMEC Central Engineering and Design, who in turn called in consultant Ove Arup to help finalise the design. Other specialists on-board at this early stage included the boiler, chillers, pumps and air handling unit manufacturers. "It was a very intensive period," recalled Scrine.

AMEC assigned a team of 22 cad draughtsmen to the project. They worked with the design team to produce three-dimensional detail drawings, while the ductwork contractor was linked to the network through AMEC's file server. "This had the advantage of giving us co-ordinated drawings at a very early stage," explained Scrine.

The scale of the installation is impressive. There are over 40 separate pumped systems and 70 separate air handling systems. "With such a difficult site we knew that we were going to have to use extensive off-site assembly and prefabrication for many of the services and equipment modules," explained Scrine, "Or, to put it another way, things had to be built-in and not bolted on."

"The extent of prefabrication on this project is unrivalled in terms of its complexity," says Scrine. Over 95% of the primary and secondary pipework has been prefabricated, and 60% of the plant has been delivered to site as prefabricated modules ready to drop into place. Everything from pumpsets to distribution boards were modularised.

“If we wanted to meet the programme, our installation had to be right first time” – Bob Scrine.

Aside from the programme advantages, prefabrication also reduced the size of the workforce and their facilities, on the congested site. It also brought the usual quality benefits factory manufacture brings to an installation. Most important of all, prefabrication allowed the modules to be stored off-site. Nevertheless, in the rooftop plantroom many of the ahus would have to be craned into position and wrapped in tarpaulin before the steelwork roof structure was in place.

"We had some big discussions and debates with co-ordinating contractor John Mowlem," says Jerry Gardiner, senior mechanical project manager. The three-month design review period finished in January 1999, and AMEC started installing the services in February 1999. By Easter, the boiler and chiller plant were safely in the depths of the basement plantroom.

Four separate plantrooms were created in the refurbished building, with floors 24-35 served from a rooftop plantroom. However, the weight of the plant including the cooling towers was too heavy for the existing structure so, 125 m up, the top two floors of the building had to be demolished and rebuilt to cope with the increased load. "It worried me stiff," admitted Oliver Simm, project director of co-ordinating contractor John Mowlem.

Structural constraints forced the engineers to use over 20 pipework and ductwork risers, and a series of electrical risers clustered around the building's central core. Aside from the rooftop plantroom serving the tower's top floors, there are three main plant areas. The basement serves the floors up to level 14 and, via a separate riser, up to level eight of the annexe. Level 14 plant supplies the offices up to level 23 while a smaller plantroom on level eight, in the west annexe, serves that side of the extension.

The majority of AMEC's work was in the basement, where the boilers, part of the air handling plant and most of the electrical installation is located. "With the three tower cranes fully occupied feeding materials to the cladding contractors racing up the outside of tower, we knew getting plant and materials into the basement was not going to be easy," explains Gardiner. "It was obvious that the only way we could keep things under our control was to put in our own crane."

Project manager John Shreeves and Partners had lumped all builder's work relating to the m&e into the services package. "This meant we had to cut holes and build all the walls connected with the services and paint them afterwards," explained Scrine, "but having the contractor under our control allowed us to decide what to build and when." With a builder's work package valued at over £4 million, AMEC employed its own contractor.

Commissioning

To meet handover dates for tenant's floors the services installation had to be prioritised. Working with the contractor from the project's outset was specialist Burgess Commissioning. Its role was to ensure the right first time principle, that AMEC was keen to embrace for the main service runs, was extended to the service connections on the tenanted floors.

The contractor had two deadlines to meet for the tenant areas: an A-date and a B-date. The A-date was the date installation had to be complete to that area for the fit-out contractors to connect to, while the B-date was when services had to be live ready for the tenants to move in.

At the first B-date of the end of August 2000, Scrine had to prove that the services systems would deliver. This involved the commissioning contractor testing off-site. For the air supply system the volume control dampers in the ductwork were pre-set by inserting a perforated plate in the ductwork to simulate the predicted pressure drop of the ductwork system.

On-site, a portable ductwork leakage test unit was connected to each branch duct via the damper access door, the dampers set and the branch velocity probe calibrated again using a perforated plate to simulate the resistance. The same principle of simulating the floor load to set valve positions was used for the water services.

With the project about 90% complete, the team is confident of meeting the December 2000 deadline. Bob Scrine admits that next time around there are some things AMEC would do differently: "There is room for improvement," he says. "Next time round we'd ensure the modular plant was pre-wired before coming to site.