The client, contractor and supply chain entered an open and co-operative alliance to deliver the completed project within 18 weeks. 'If the building hadn't been ready we would have had patients in tents,' says Deans.
Because of the project's lightning-fast schedule, design and construction overlapped. Modifications were frequently last minute. Client and contractor adopted a flexible approach to the job, modifying their expectations, methods and materials to accommodate one another and keep the job on budget.
Condensing the project into 18 weeks meant there was significant overlap between trades. 'Normally you'd want to clear one stage before bringing on another. Ideally you wouldn't want so many trades on site,' says Whitehouse. Plumbing, wiring and installation of floors and walls commenced while the building's steel frame was still being assembled.
Whitehouse says that, to achieve fast, flexible, target-oriented construction, 'leadership was critical'. Because much decision making was on-the-spot and informal, mutual trust between the project leaders had to be implicit.
Minimum noise and dust disturbance was mandatory during construction: the hospital was fully operational all day, every day. Terrapin set out to meet the 18 week schedule using a system composed of modular, prefabricated elements. No wet processes were carried out on site.
The building is based on a 3.6m structural grid, opening out to 7.2m in places. Its steel frame consists of cold rolled, punched and sheared C-section elements, doubling as a hollow ducts for services. Columns and beams are bolted. External walls are steel panel cladding over insulation, fixed 150mm outside columns; the single-pitched roof consists of steel panels on purlins. Rainwater collects to a box-section gutter and down-pipes on the building's exterior. Internal walls are plaster board and flooring is board over metal deck.
Terrapin manufactured the system at its factory in Milton Keynes: Whitehouse claims the computer-controlled production system is accurate to within 1mm. Parts of the building were assembled off site and lifted into position. No materials were brought to site before they were needed, reducing on- site clutter and minimising potential for accidental damage. Stairs were installed as complete units. Plant was lifted onto the roof, fixed and connected at the end of the construction programme.
More than a century of ad-hoc building work on the cramped, enclosed 1,200m2 site allocated for the new building, had left the ground full of foundations, pipes and cabling.
Conventionally the ground floor would be a concrete slab but re-routing live services and building through existing structures would have increased cost and time. Terrapin minimised contact with the ground by suspending all floors from the steel frame.
But even so, Terrapin had to bridge over the obstacles and potentially lost 14 days within the first week. Site preparation took two weeks and erection of the steel frame commenced in week three of the construction programme. Lost time was won back by accelerating steel erection.
Cladding began in week four, while the frame was still being assembled. Services, which were on the critical path, were integrated as erection progressed. 'Construction took place as pyramid, with floors and services added inside while the steel frame was going up on the outside,' recalls Whitehouse. 'Stairs were swung into place as the frame was going up.'
Lead-in time was a critical issue for supply of the building's outsize lift and doors, required to accommodate wheelchairs and hospital trolleys.
Terrapin's lift supplier began sourcing a lift for the project before a contract was signed to meet the tight deadline. Following mechanical problems caused by overheating during the first weeks of operation the supplier put a mechanic on 24- hour standby to troubleshoot. Deans concedes the client team under-estimated lift use when it drew up the brief.
Doors were non-standard dimensions and had to be specially fabricated. They were installed in the last week of construction.