With prefabrication coming back into style, a radically revised production system could finally free precast concrete housing of its negative associations.
Pssst – wanna buy a heavy precast concrete housebuilding system, complete with 5000 m2 factory? Given the number of 1970s precast concrete system-built council houses that are now being pulled down, you could wait for the right punter for a very long time with this offer. In fact, the man whose brainchild it is – John Miles, the Arup main board director responsible for new technological ventures – has been waiting six years to sell his concrete housebuilding system.

But at last, a jubilant Miles is on the verge of clinching a sale to two enthusiastic buyers. Construction giant Taylor Woodrow and pioneering housing association Peabody Trust are both in final negotiations with Arup to form a joint-venture company called Project Meteor.

The company is about to build a live-in prototype of the housing system in Acton, west London.

If successful, it could lead to a fully operational production plant within 18 months.

Certainly, off-site prefabrication is all the rage, with deputy prime minister John Prescott exhorting the housebuilding industry to increase output and plug the widening gap between households and homes. But virtually every modular housing system nowadays is based on trendy lightweight steel or timber frames. So why revert to heavy precast concrete, a dinosaur of a construction technique that has been stigmatised by rain-sodden grey walls, catastrophically bad workmanship, poor thermal insulation, repetitive production-line layouts and council sink estates?

Miles is convinced that there are several compelling reasons: "It is a low-cost, robust material. It comes with minimal wastage, because there are no offcuts," he argues. "And it can be used for medium- and high-rise developments up to 40 storeys."

Miles cites additional attractions of the proposed Meteor system that are so novel they directly contradict the experiences of the 1970s. "With high-quality shuttering it can provide a smooth, self-finished surface. It has good sustainable characteristics of high thermal mass for low energy consumption, good acoustic attenuation and robustness and solidity. And each module can be customised to customers' requirements."

The key to Arup's born-again heavy concrete housing system is that it does not adapt existing modular systems, but has been designed from first principles and informed by the latest advances in manufacturing technology. The factory production lines planned by Arup show more than a passing resemblance to car manufacturing: hardly surprising when you discover that Miles is an evangelist of Sir John Egan's lean construction principles, and previously worked at Egan's old firm, Jaguar.

In Arup's plan for the new production line, concrete panels for floors, ceilings and walls can be cast to cure overnight. These are assembled into volumetric modules, which then progress through the factory along a continuous, semi-automated production line. The modules are progressively fitted out at set workstations, where the appropriate kit is on hand. But rather than mass-producing a standard product as happened in the 1970s, advanced IT-based manufacturing techniques enable each module to be customised by varying the size of panels and the location of window and door openings.

Arup claims that erecting and finishing off each house on site could take as little as two weeks, whereas conventional housebuilding methods take up to 16 weeks.

Each module measures up to 10 × 4 m in area. Open-sided modules can be joined to form large internal proportions of any length and up to 10 m wide, with flexibility for internal partitions. Pitched roofs made of two structural concrete panels create usable loft spaces, a distinct advantage over conventional, timber truss roofs.

Among the drawbacks of the system are the weight of the modules, typically 20 tonnes, which requires a heavier-duty crane than housebuilders generally use. Modifications to the concrete external envelope during the lifetime of the house could be even trickier, requiring a diamond disc cutter to slice through the steel mesh reinforcement and special connections of new and old materials.

While Miles proudly builds up Project Meteor as a high-quality "Mercedes product", he also recognises that low capital costs are critical if it is to break into the highly competitive housing market. The system is therefore aimed at two distinct housing sectors in which the other two consortium partners specialise.

One target market sector is leading-edge sustainable social housing, in which Peabody is recognised as a market leader. A typical experimental product could be a prefabricated version of Bedzed, Peabody's high-density green housing development in south London.

The other target market sector comprises typical low-cost standard house types built by traditional private-sector housebuilders, where cost estimates show Meteor as competitive (see below). On such sites, the products would come with the concrete structural panels concealed behind brick outer skins and tiled roofs, making them indistinguishable from conventional house types, though better insulated, less defect-prone and more durable. Such an upgraded traditional product is being investigated in association with Taylor Woodrow's housebuilding arm, Bryant Homes.

Project Meteor still has between 12 and 18 months of product development and testing to go before its industrialised housing system can be made available to Britain's housebuilders and housing associations. During that period, the consortium will have its work cut out to sell its born-again heavy concrete system to a highly sceptical housing industry.

How the figures stack up

Full construction cost estimates – excluding landscaping and infrastructure – show how Project Meteor could compete on some, but not all, standard house types. Costs do not include snagging, which would further favour high-quality off-site prefabrication. Conventional terraced house in south-east England
Conventional construction
Meteor modular construction
£24,700 Four-bedroom detached house with integral garage
Conventional construction
Meteor modular construction
£41,700 Mid-range, three-storey block of six apartments
Conventional construction
Meteor modular construction

Gearing up for take-off: Five stages of Project Meteor

An industrialised building system such as Project Meteor demands a protracted sequence of research and development. See below for the sequence

Stage 1 Theoretical studies

Since 1996, Arup’s advanced technology group has explored the concept of a high-quality volumetric precast concrete housing system along with an agile industrialised production line to manufacture it. Shown left is a CAD image by Arup of what this production line would look like.

Stage 2 Test adaptation to standard house type

In August, Bellway Homes built a one-off house using six concrete-panel modules as part of its conventional housing development in Northampton. Ribbed concrete panels were conventionally cast in Derby, assembled on site and finished internally by drylining. The modules were designed to fit into Bellway’s standard house type. The house (shown left) was sold on the open market for the same £148,000 price as neighbouring conventional houses.

Stage 3 Construction of test modules

In September, Taylor Woodrow constructed two volumetric house modules (left) using Project Meteor industrial processes at its plant in Leighton Buzzard. Flush, 75 mm-thick wall panels were cast with a smooth internal self-finish on a sophisticated industrialised tilt-tray measuring 10 × 4 m and assembled using stainless steel bolts.

Stage 4 Construction of two working prototype houses

Over the next 12 months, the consortium plans to construct two prototype house types, with volumetric modules all cast, assembled and fitted out by Taylor Woodrow in its Leighton Buzzard plant. One prototype, shown left, will be a block of four townhouses and maisonettes to be developed by Peabody Trust on a site in Acton, west London. An innovative, low-energy design with adaptable interiors by Arup Associates won a government-sponsored project design award this year. The other prototype will be a conventional apartment block to be developed by Bryant Homes.

Stage 5 Full industrialised production

Provided the two prototypes and marketing prove successful, full commercial production of concrete modules could begin in 2004. Production lines would be set up at Leighton Buzzard and eventually other factories across the country, each one producing up to 1000 houses a year as well as buildings like this apartment block (see previous page).