The brief for the Design for Manufacture competition sets a target cost of £60,000 for a minimum 74.4m 2 dwelling, equating to a construction cost of £806 per m 2. Most market-sale housebuilders building outside labour-rate hotspots expect to provide basic homes within £800 per m 2, in part through bulk purchasing power, but mostly through buying each build package on competitive tender from labour-only subcontractors. Yet affordable housebuilding, despite its name, tends to be about 25 per cent more expensive.
Following its own review of housing supply by Bank of England monetary policy committee economist Kate Barker, the Treasury wants productivity gains. It is under pressure to stem house-price inflation by increasing housebuilding by at least 56,000 homes a year - chiefly by doubling the supply of affordable units.
The Treasury could just give social housing grants to the housebuilders and ask them to build more. But several studies since the mid-1990s have highlighted how the private sector's advantage will become unsustainable. The UK is falling behind northern Europe by depending on skilled trades at the expense of any mechanised processes or components that reduce site working. For example, in The Netherlands, joiners hang frames and doors swiftly with a machine not unlike a nail gun. In the latest productivity study comparing EU nations, Skills and the Construction Process, the University of Westminster's Linda Clarke and Christine Wall found that speed of construction was about four times greater on Dutch sites than on British ones, and that the average labour input of structural trades in the Netherlands is half that of Britain or Germany.
Clarke & Wall's study also identified that site supervision on UK sites constructing affordable housing is double that of similar sites in the Netherlands and Germany.
It is the overhead associated with managing skilled trades and worries about the lack of experienced site management that continue to concern the housebuilders too.
To a far greater degree than is recognised, housebuilders have been investing tens of millions of pounds in Modern Methods of Construction (MMC).
Barratt Developments - nearly wiped out in the mid-1980s by a scare about site practice after using timber frame to cut the cost of starter homes - has set up a joint venture with steel-frame constructor Terrapin.
Advance is an edited version of Terrapin's modular system, used to supply homes to the MOD and NHS. Redrow Homes' Framing Solutions with partner Corus has been developing a third-generation steel-frame system based on the 1990s pioneer Sure Build. And Westbury has spent £25 million on its Space4 factory in Castle Bromwich to produce insulated loadbearing walls and floors for its standard house types. Its regional housebuilding companies, free to choose whether to build with Space4 or to undercut their costs through tendering trades, have mostly moved over to Space4.
The key difference between these three volume-builder approaches to MMC and those already employed by Peabody Trust at Murray Grove or Raines Court apartment blocks in Hackney and Stoke Newington, is in the view on how much construction should be offsite. Raines Court, for example, had fullyfitted kitchens and bathrooms supplied within sealed units with facing finishes, fenestration and recessed balconies already intact. Access decks, balconies and staircases were also craned into place and bolted to the apartment modules.
By comparison, the most technically comprehensive of the three volume-builder solutions above is Advance, which puts a two-and-half-storey house together in less than two days. This comes complete with bathroom and kitchen pods, finished interior walls, push-fit preinstalled plumbing and electrics, and even a plaster ceiling rose. But it then programmes six weeks to face with brick and tile the roof. Housebuilders see little advantage in accelerating the programme from the commonplace 16-20 weeks to less than the 10-12 weeks it typically takes a buyer to complete on a purchase. Neither do they court trouble with the mortgage lenders by ignoring the construction detail most comforting to build insurance: a cavity wall. Losing sales while would-be purchasers struggle with their lenders' surveyors questioning construction, is not good business. That is exactly what happened to the trail-blazing Urban Splash when it offered the first market-sale scheme to be built volumetrically (AJ 7.4.05, page 10).
Intriguingly, mortgage lending to homebuyers is policed more anxiously than the commercial lending negotiated by housing associations. This is particularly the case with affordable-housing providers focusing on temporary accommodation for key workers, such as Keep London Working. There, rental streams are expected to pay off development costs and furnish profit well within the design life, with the prospect to redevelop later. This market has freely nurtured MMC suppliers such as Spaceover, the company behind Baron's Place in Waterloo, designed by Proctor and Matthews. It is important to stress that Spaceover, although thoroughly MMC, is not a manufacturer but a construction manager, buying space on production lines to put together its own specification.
Avoiding the investment in plant reduces financial risk and clearly helps on price as the Spaceover units, allowing 25m 2 per person, are being achieved substantially within the £60,000 threshold - even after land is added to procurement cost. Spaceover's focus on design life, speed of construction and simplified refurbishment for future tenants, dominates. With the market sale buyer, anxieties about whether asset appreciation will protect the lender offering the interestonly loan seem more important.
These lending issues, dictating a structural solution based around cavity-wall construction, have encouraged the masonry industry to focus on modernising its processes. Ibstock has been developing interlocking rain screens, and brick makers are investigating the productivity potential of thin-joint masonry as a facing material, laid quickly on site with a pump rather than trowel. With Bowker Sadler's scheme for Lovell, next to the City of Manchester Stadium, bricks are even being supplied as preformed panels from a Hanson factory in Kirton, Derbyshire. But they are, nevertheless, being used to dress a panelised structural system, Kingspan Tek-Haus.
Hanson even bought a stake in steel buildings erector TIS, in expectation of supplying volumetric masonry-clad houses. But this failed excursion underlined the chief weakness of the off-site industry. Building units in a factory shed is not manufacturing, it is simple creating better working conditions. Only real manufacturing lines generate volume, and, to date, that has only applied to components.
This is the weakness in the UK's MMC focus so far.
Consider Yorkon, whose affordable housing schemes have had the most profile, acclaim and dissemination to date.
Since 1999, when Peabody first signed it up, Yorkon has gone on to supply less than 500 homes across four projects, in a five-year period when the industry has built more than 900,000 new homes.
This is where the Design for Manufacture competition comes in. It promises a prize of 1,000 homes, and this has the potential to make the winner the MMC's new pacemaker. Those 1,000 homes would also constitute the single biggest order of MMC to date, by a factor of about eight or more, which might finally buy some economies of scale.
But don't bet on a Japanese house planttype winner, because the investment to get a single plant up and running would be akin to UK construction plc in any year.
Expect a winner that will be on site for about 10 weeks, assembling the house with a reduced number of specialist subcontractors - foundation, structure, and facing materials. The challenge to the architect is to rationalise their use and create value from their combination.
David Birkbeck is the chief executive of Design for Homes, a board member of the Housing Forum and runs the Prefabulous Homes seminar series