Low-cost Modern Prefab to be Demolished
In 2000, CASPAR (City-centre Apartments for Single People at Affordable Rents) was a hot property. Built without subsidy by the Rowntree Foundation in Leeds, this competition entry was to be "an attractive building that would encourage economically-active single people to make the city centre their home... Use of advanced, pre-fabrication techniques has enabled the five-storey block to be built quickly to a high specification that includes triple glazing and more space than is usual in one-bedroom flats...Each unit in the CASPAR development was factory-built by Volumetric, a supplier specialising in pre-fabrication, and transported to the site half-assembled and half in a flat pack. Kajima UK, the contractors, were able to install the apartments by crane. As a result, the first apartment went on show just 66 days after the site was purchased and the building contract signed." (2000 website here)
photo by Russell J Smith
Unfortunately there were a few problems, apparently including putting the stronger, heavier ground floor units on the top and vice versa, described in the Guardian as "fatal mismatches". ARUP, the UK's leading engineering consultants, had a look and "said "Yipes — get out of there before the next storm." What they've actually said is that there is a 2% chance that the whole building will collapse in high winds. JRF have even admitted that, if the cost of repairing the fault is excessive, they will consider demolishing the whole structure." (Housebuilder's Update)
Not a happy day in the low-cost modern prefab world, and less a problem of design and manufacture than it is for on-site screw-ups.-"The Kajima system was "wonderful" but required precision in assembly and care of the pre-built units" -it was a mix of flatpack and 3D volumes, description below. However as Lord Best, of the Joseph Rowntree Housing Trust, said: "Caspar's form of construction was very much at the cutting edge of new techniques and the results have been very disappointing indeed." ::Guardian, ::Leeds Today
Pioneering design and construction
JRF's achievement owes much to its procurement route, picking architects Levitt Bernstein and contractor Kajima UK through a competition for a design that pioneers hotel construction methods in UK homebuilding. The result: time from site possession to project completion slashed from an anticipated 78 weeks to just 36. In fact, once the foundations and ground beams were in place, it took 13 working days within a period of just 18 calendar days to erect the three-, four- and five-tiered structure.
Here it is necessary to clarify terms used to describe construction making this possible: "volumetric" describes building assembly from square, rectangular or assymetrical blocks with internal and external traditional building finishes and fenestration, electrics, plumbing, tiling and joinery pre-prepared in a factory; semi-volumetric describes when half the building is built as "volumetric" units, and the other half delivered flatpacked as six panels for site workers to fix together. Leeds is semivolumetric and, to confuse matters, the supplier is Volumetric Ltd, part of Potton Group of Bedfordshire. The location of its plant at the other end of the M1 was one reason for flatpack delivery - to avoid transporting cubic metre after cubic metre of air 250 miles — but the 55 m2 apartments supplied as a single completed pod would have been too wide for a normal 3.6 m-wide load and so more costly.
At Caspar the factory assembled pod contains the kitchen and bathroom because of the preference for factory-controlled finishes for works typically otherwise troubled by programming of various trades such as plumbing, tiling and electrics, and by quality management or maintenance. All M&E; in the completed pod was fitted before delivery to site, except the ring main for the whole apartment and the pod was delivered wholly complete except for the kitchen's white goods, supplied separately later. The flat-packed half of each apartment contained the main bedroom and living area. The project team is generally of the view that the decision to go semi-volumetric proved a false economy, as the challenge of tight, steeply sloping site, large overhanging roof and semi-circular plan combined to exert unmanageable pressure on the assembly of flat packs to keep up with the pace of pod delivery.
All pods were craned into place floor by floor, and are self supporting to five storeys, having the capacity to take the superimposed load of aluminium monopitched roof and galvanised steel courtyard balcony and access gallery systems. The integrity of the system, proven in hotel building, uses elements familiar to UK timber-frame housing - 89 x 38 mm vertical timber studs with a sheathing of bitumen impregnated fibreboard enclosing rigid panel insulation. The performance specification for the structure is to a nominal 60 years, as for most new houses. ::Design for Homes