Summary
• BSW Timber’s intelligent panel timber build system, Pi, was launched at Ecobuild.
• The system is British-made and uses British-grown timber.
• Its low-tech manufacture means it is suitable for semi-skilled workers in satellite factories.
• Each floor is erected at foundation level.

This year’s Ecobuild was packed to the gills with innovative new building systems, but there was one in particular that caught the minister of state for housing and planning’s eye.

Margaret Beckett was one of the first visitors to BSW Timber’s stand to see Pi, the company’s new patented intelligent panel timber build system and she was apparently so taken with the concept that she continued talking about it long after leaving the stand.

She wasn’t the only one. Just a few hours into the launch the Pi team had several follow-up meetings with architects. And, out in the real world, away from the exhibition hall, BSW’s group marketing manager Bryan Crennell was so convinced by Pi’s credentials that he was using the system for his own self-build project in Sunderland.

Sole producer

Pi, which has been five years in development, was the brainchild of Icotech, and an exclusive deal with BSW Timber, Britain’s largest sawmiller, followed three years later. BSW is now the sole producer of the system in the UK and Ireland, manufacturing it at its mills throughout the UK, but currently focusing on its output through its timber engineering wing, BSW Timber Systems in Ramsgate.

But what captivated the housing minister wasn’t just the fact that it’s a British-made, British invention (and using British timber, to boot), but that its inherent simplicity makes its manufacture by semi-skilled workers in satellite factories in regeneration areas a real possibility.

The main elements of the Pi system comprise a laminated ply ring beam, insulated to prevent cold bridging, and insulated panels, including unique “slider” panels, which link the main panels, moving left or right to take up any tolerance. Because they sit slightly proud of the main panels they house the service voids within the wall and also provide the option to add extra insulation.

Panel construction

The panels comprise customer-specified insulant sandwiched between BSW’s C16 strength graded Easi-Edge studs and a sheet of OSB nailed on the inner side. The OSB is overhung slightly at the bottom, where it will wrap around the sole plate, and a larger overhang at the top wraps around the ring beam. These overlaps provide the system with extra “natural” airtightness, said Pi’s Graham Nield.

“The jig we’re producing these panels on at the moment is very low-tech because we’re exploring the idea of putting low-cost manufacturing into satellite sites,” he said. “There are guide rails for placement of the studs, the insulant is pre-cut and the nailing points for the OSB are marked on the jig, so it’s ideally suited for semi-skilled workers.

“Two operatives can manufacture a panel in just over a minute,” he added. Once the panels are made, they can either go to site for assembly, or they can be assembled in the factory for modular construction on site. If the latter route, then all the services, windows, doors, plasterboard, external cladding and so on, can be fitted before delivery to site.

Construction on site

When it comes to construction on site, everything hinges on the sole plate. “Foundations are typically out by 20 or 30mm here and there, but as long as it is level within plus or minus 5mm tolerance, we fit the sole plate exactly to its dimensions,” said Mr Nield. “That then becomes the dimension for the ring beam and our CAD software draws the panel building exactly to those dims and gives us the panel layout for our elevations.”

“There are no bespoke panels or ring beams as such,” added Norman Gore, BSW Timber Systems technical director. “They are all off-the-shelf lengths, so they can be trimmed on site if necessary – and the slider panels slide to accommodate any gaps.”

From this point, the house is built from the top down, so the next stage on site is the roof. The ring beam and roof trusses are constructed at foundation level, using the sole plate as the template. This structure is then crane lifted out of the way and a first floor storey comprising ring beam and wall panels is constructed in its place, again, at foundation level. Markers on the ring beam indicate the location of windows or doors and panels are simply slid to that point of aperture.

Adding value to the ring beam this way is particularly useful in a situation where skills sets might be an issue, said Mr Nield. And, building each floor at foundation level creates fewer health and safety headaches.

In its turn, the first floor is swung out of the way and the roof structure is fixed onto it. Meanwhile, back at the foundations, the erection team fits corner panels and one or two intermediary panels on each elevation before the first floor and roof are picked up as one unit and placed on top.

“We can then fill this ground level with building materials, getting them under cover for the following trades before closing it up,” said Mr Nield. “The panels just have to be slipped into the ring beam and we can close the ground floor in 20-30 minutes.” And about 20 minutes is all he reckons is needed per floor.

Medium-rise

The system lends itself to medium-rise construction and the Pi team is confident they can go as high as Building Regulations currently allow for timber frame. The ring beam system is inherently strong, providing full perimeter support and, if coupled with connectors at the corners, the issue of disproportional collapse is resolved. Each panel provides racking strength.

“It’s a very dimensionally stable system because we’ve taken out a lot of the horizontal layers that you would have in conventional timber frame,” said Norman Gore.

“Shrinkage in conventional timber frame is about 8mm per floor and we’re achieving about 2mm. This gives us parity with masonry and, as a result, we’ve solved one of the biggest problems there is with timber frame – the differential movement between timber and masonry.”

Thermal efficiency

The Pi system has already been used in a couple of developments in Oxfordshire and, as well as proving cost-effective and speedy to build, the houses are performing well in terms of thermal efficiency.

“We’re at a U-value of about 0.19 at present, but potentially we can go from Building Regulation-compliant to a U-value of 0.1, depending on the detailing,” said Mr Nield.

“For example, the floor is already designed as part of the lifting process, but if we’re getting into lower U-values and mechanical heat recovery ventilation systems, then we can look at designing floors to incorporate mechanical and electrical requirements.”

“We’ve found extremes of requirements in the people we’ve spoken to so far,” said Phil Wright, BSW Timber Systems managing director. “And, because it is so flexible, the system will evolve and there will be a time when we broaden what we offer as a package.”

The simplicity and flexibility of the Pi system have already caught the attention of local authorities, housing associations and self-builders – not to mention Mrs Beckett.