CONSTRUCTION PREFABRICATION
choosing off-site manufacture. In addition, prefabricated concrete panels offer a better fi nish than those made on site, which is useful if the surfaces are to be left exposed to help with cooling. Yet Edwards warns that decisions about
People who design buildings don’t always think about how you’d get more prefabricated stuff in them by leaving walls down
prefabrication on future Hammerson projects ‘will come down to cost as well, and not enough is known about that as yet’. URS-Scott Wilson is hoping to use building information modelling (BIM) to close the gap between designers and contractors, which will aid off-site construction. ‘BIM allows people to get more detailed information at an earlier stage of the design, which will help with prefabrication,’ says Peter Sutcliffe, the group’s head of building services. ‘The major sub-contractors are all looking to maximise prefabrication, which makes a lot of sense,’ he adds. While prefabrication of risers is already commonplace, Sutcliffe says a new growth area is the prefabrication of building services in ceiling voids. URS-Scott Wilson
Case study Schools go for pre-cast solution
Prefabrication has been embraced by the Barnsley Building Schools for the Future programme, where four schools have been built using pre-cast walls, fl oors, ceilings and columns from Laing O’Rourke’s Design for Manufacture and Assembly (DfMA) range. Carlton school was completed
in 2010 using a prototype of DfMA, while Green Acre, Springwell and Shafton are using the latest version. Windows can be supplied prefi tted, and conduits for power cables are pre-cast into the slabs. The Barnsley schools were
designed by BDP using the DfMA range. James Warne, environmental engineering director at BDP, says the panels offer signifi cant energy savings, with integrated insulation providing a U-value at least 20% above the Part L 2010 requirements. The DfMA walls are load-
bearing, which reduces the need for a frame to be built separately before cladding. Warne argues that this offers dramatic savings on materials and suggests that 30% of materials delivered to traditional construction sites are thrown away. DfMA offers a choice of fi ve
window openings, and their environmental performance is already predetermined at a minimum 2% daylight, meeting
26 CIBSE Journal June 2011
BREEAM requirements. ‘Part of the attraction is that pre- determined result,’ says Warne. BDP assisted Laing O’Rourke in
developing DfMA, and the range was named Passive (energy- related) Product of the Year in the CIBSE Building Performance Awards 2011. Anna Winstanley, director of strategic design at Laing O’Rourke, says: ‘The
architects are able to produce bespoke designs while adopting a consistent approach to the structure and the M&E.’ DfMA has also been used
for student accommodation for Imperial College, London, in the construction of the University Hospital of North Staffordshire, and to create offi ces for the Ministry of Defence.
is also doing more prefabrication of plant rooms and entire buildings. For example, it recently provided prefabricated energy centres for four new Tesco stores that comprised CHP units, absorption chillers, pump sets, buffer vessels, water treatment and pressurisation equipment. The fi nal assembly was completed in the stores’ car parks. URS-Scott Wilson took this approach
because of the benefi ts of shortened build times for the programmes. Tesco can build a new store in 26 weeks, yet it can take 20 weeks just to source the engines for the plant room, Sutcliffe says. Therefore the client opted for prefabrication. URS-Scott Wilson is currently working
on designs for a student accommodation project where both the superstructure and the mechanical and electrical services will be prefabricated, although Sutcliffe is unable to divulge details of the venture. He adds: ‘We are fi nding this more and more – as people tighten the build programmes, prefabrication is the only way out.’
DfMA has been used for Shafton school in Barnsley
DfMA has yet to be sold to
commercial developers, although Winstanley is convinced that this is due to the recession and acceptance is just a matter of time: ‘We were looking at an offi ce project in the City of London, but it was stopped because of the recession. I’ve no doubt the industry recognises this as the way forward.’
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