Specification focus: Precast concrete: University of Birmingham accommodation

A t the start of the next academic year, students located in Mason Hall at the University of Birmingham will be housed in new accommodation. The existing blocks in The Vale, Edgbaston have been demolished and a new scheme to cater for more than 800 students is nearing completion.

Mason features six blocks, from four to six storeys in height, laid out in three crescents alongside a lake. Inside the blocks are 876 study-bedrooms, all with en-suite shower and toilet, generally segregated into flats of six bedrooms alongside a shared kitchen area. There are also a number of self-contained studio apartments on the top levels of the crescents.

The two-stage tender process to build the £36m development was won by Norwest Holst, which, along with Aedas Architects, DTA Consulting and Couch Perry Wilkes, demonstrated through life-cycle costing that a precast scheme would offer the best value for money. Having worked with Bell & Webster on a number of other projects, Norwest Holst turned to the precast manufacturer again, awarding it the contract for its 'fast-build rooms' panel system.

"The development was originally specified to be constructed using steel frame with blockwork," explains Michael Roadnight, contracts manager for Norwest Holst. "But we suggested this was changed to a precast construction. We have worked on a number of projects with Bell & Webster and found that it was quicker overall. As it is a university project, the timeframe was very important and we wanted to give ourselves the best possible chance to get the rooms up early. We also struggled to get to budget and using this method of construction helped."

During seven months on site, Bell & Webster erected 2,847 individual precast components. Its panels were used for the party walls between each bedroom and for the external 'window' walls. Internal doors are added later. Floor slabs span between the internal party walls and all load goes through these walls, rather than the external panels. All the panels are cast in Bell & Webster's factory, then transported to site and lifted directly from the lorry into position.

Despite being non load-bearing, the window walls are heavily reinforced compared with the party walls as they have been designed to accommodate the considerable window space. Each of the bedrooms has two windows one at a height for looking out while sitting at a desk, the other at a traditional standing height. This gives the building a staggered 'two up, two down' pattern.

Ground-floor slab

Erection starts with Norwest Holst's groundworks subcontractor laying the ground-floor slab and the steel subcontractor erecting the steel gable ends for each of the six blocks, which are designed to provide lateral restraint. All the blocks are more than three storeys high, so they require starter bars cast into the slab along what will be the centre line of each party wall. These slot into oval-shaped holes cast through the full height of the panels.

"Norwest Holst did all the groundwork and we build off an in situ concrete slab," says Bell & Webster's Roy Spurgeon. "We supply and erect all the concrete, leaving the contractor to do the finishing and roofing. We also installed all the bathroom pods, even though they're not manufactured by ourselves, as we're on site when they need to be erected."

Bell & Webster laid a sand/cement bed on the slab to provide a seal before the first party wall was laid into place. The panels are then propped until the windows and walls have been joined on. A series of overlapping loops connect the panels to the party walls, which are then married up and permanently connected by reinforcement bar. The joint between the two walls is then grouted to make the final seal.

Enhancing the speed of the construction is the smooth finish of the walls, removing the need for plasterboard or plaster skim. "The frames are now finished," continues Roadnight. "And the rooms have an exposed finish, so there's no plasterboard to erect." As the frame incorporates the internal walls there is also no need for internal dry-lined and external metal-framed walls.

As for meeting Building Regulations, the system provides the major contribution to the acoustic rating for the external envelope the choice of cladding dictates the final rating. It also complies with Part E for internal party walls and floors without surface treatment being necessary, except for floor coverings. "Quite often, a different construction material will have been specified," says Spurgeon. "But once we start talking about speed of construction, coupled with acoustic and fire performance, people tend to change their minds."