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Published:  22 August, 2008

Kingspan reported 33% year-on-year growth in its offsite division last year

Offsite manufacturing is set to grow, and that's good news for timber. Keren Fallwell reports

The UK prefabricated frame and panel building systems market is expected to grow by more than £250m in the next four years, according to a new report, and timber will be a major part of that growth.

AMA Research says the sector, which by product is 50% timber frame, grew by up to 14% last year to an estimated £625m and, by 2012, it could be worth £883m.

And while the construction sector is contracting in response to the economic downturn, enthusiasm for modern methods of construction remains strong, especially as the Code for Sustainable Homes (CSH) is raising the energy efficiency bar.

Contractor Osborne, which uses open panel timber frame and developed its Innovare structural insulated panels (SIPs) system using panels supplied from Germany, has demonstrated its commitment by investing in its own SIPs manufacturing facility in Coventry. "The factory represents a significant investment in the future of offsite manufacture," said divisional director Colin Mitchell.

It is also fundamental to Osborne's understanding of how the CSH will work, he added. Open panel construction is the company's "bread and butter system", used for anything five storeys or higher, but for anything lower, or where higher code levels are required, SIPs are Osborne's "method of choice".

The company believes that, using Innovare SIPs, it can achieve level 3 of the CSH without including any systems for renewables. "Code 3 is not that difficult; the issue for us is getting beyond it to code 4, 5, and 6," said Mitchell. A development in South Nutfield in Surrey using the Innovare system comprises the first inhabited level 5 dwellings in the UK.

The company took prefabrication a step further when it built staff accommodation at QEQM hospital in Margate. Open panels were used, as the higher code levels were not required, but each bathroom was installed as a complete pod. "Pods are now pretty standard," said Mitchell, "and they're easy to do."

He believes in future there will be wider use of prefabrication of the building envelope. "There is scope in SIPs panels to prefit windows in the factory, particularly if we're talking about air seals etc being increasingly important in the way we deliver higher codes. I can also see internal and external finishes being applied," he said.

He added that timber is ideal for prefabrication: "It's a simple material to use and there's always something you can do with the byproducts when you're using timber. I'm very much a fan of timber frame and timber as a material," he said.

Streif/OSM already pre-installs windows and doors in its German manufactured closed panel system. The walls comprise modular closed panels made from timber frame construction clad externally with OSB and internally with fibreboard and insulated with mineral wool and vapour diffusers. "When bolted together on site this strong and versatile combination is earthquake and hurricane proof and provides excellent airtightness, sound and thermal insulation," said director Andrew Flux.

He, too, believes that the volume of prefabrication will rise in line with the CSH demands. And timber will have a key role, not only because of its strong environmental credentials, but also because it is well-suited to factory manufacturing.

For Eurban, which designs and installs cross-laminated timber panel structures, it can be the procurement, rather than the product, which defines an offsite manufactured project.
"It depends on what vehicle is used for procurement and who undertakes the design," said director Jonathan Fovargue. "If we're supplying components designed by someone else, they tend to be less sophisticated than the ones we design."

So for Fovargue, the success of prefabrication is down to adopting the right procurement process and the interface with the design team. "The market is accepting of MMC but people have to establish what value they're getting in terms of cost per square metre," he said. "That's why the method of procurement, the interface with the design team and at what stage you're brought into the project makes all the difference. The building is successful when on the shelf; it's whether it's developed into the building."

Driven by the CSH and the need to reduce costs, Stewart Milne Group, which currently produces and builds in open panels, is developing a closed panel system.

Prefabricated timber roofs provide many benefits, including reduced crane time as they can be erected in a day

The new system, expected to undergo small-scale trials in the next 9-12 months, will enable the company to achieve up to level 6 of the CSH. The system also offers the benefits of build speed and reducing costs. Stewart Milne's prototype Sigma house, built at the BRE's Innovation Park using the company's first concept of its closed panel system, comprised two four-storey units which were completed, "from grass to keys", in 10 weeks as opposed to 28-30 weeks using conventional methods.

The company has pod systems and complete offsite construction in its "long-range strategy", and through a combination of closed and complementary hybrid solutions will move towards a more modular solution.

With the housing market collapse, all offsite manufacturers will be under pressure to find new markets and to differentiate themselves with value-added solutions, said Stewart Dalgarno, director of product development. But whatever they are, timber is well-placed. "The product performs from an environmental and sustainability point of view, it's workable, and if you look at other markets across the globe – Germany, Austria and Scandinavian countries – they're all using it," he said.

Christine Hynes of ecoTECH believes her company's process is four years ahead of anything else on the market. "We don't make anything on site at all," she said. The closed panel system comes complete with Secured by Design windows, wiring, integrated plumbing and pods, resulting in few people required on site. "All that happens on site is commissioning.”

The pace of build means the house can be watertight in a day. At the BRE's Innovation Park, the company's three-storey house, comprising a self-contained disabled apartment on the ground floor and a two-storey house above, was completed, with furniture installed, in just 11 days.

EcoTECH's system can meet CSH level 4 and next year will launch an advanced integrated panel which will "meet a higher requirement than code 6", said Hynes.

But while she is confident about her own company's offsite credentials, she believes prefabrication in general could be more sophisticated. "Dumping a load of pieces of wood, which are pre-cut, on site does not mean offsite manufacturing. Offsite manufacturing should mean that the end product in components comes off the conveyor belt, is quality checked, put on the lorry, brought to site and clipped together," said Hynes.

Top work

Prefabricated timber roofs offer particular planning and cost benefits.

Able to be secured in just one working day, they enable the building to be watertight earlier and contribute to a faster build process, reduce the number of site deliveries and crane time, provide a safer working platform, cut waste and reduce the amount of materials stored on site. The insulated panelised systems also provide warm, useable living space in the roof.

In the UK, many of the major housebuilders use prefabricated timber roof solutions, whatever the structural fabric of the building.

For James Jones & Sons' JJ-IntelliRoof , Donaldson Timber Engineering's SIRS roofing system, Wolf Systems' smart roof and Roof Space Systems, who all offer prefabricated roof systems, topping out a building is all in a day's work.

James Jones development engineer Ross Brown estimates that such systems can cut the build time by at least two weeks. Using Donaldson's SIRS product recently, Opal Homes erected three roofs and six dormer windows in just one day.

James Jones and Roof Space Systems help the housebuilder further by providing installation teams.

Osborne used an open panel timber frame system for staff accommodation at the QEQM hospital in Margate. Each bathroom was installed as a complete pod