Summary
• B&K Structures showcased its cassette solutions at Timber Expo.
• The cassettes are made by B&K’s supply chain manufacturers.
• Competition will come from cross-laminated timber.

Among the many new product promotions at last year’s Timber Expo were B&K Structures’ (BKS) New Wood cassettes – floor, wall and roof systems that can provide structural and non-structural build solutions with factory-applied internal and external finishes where required.

The main driver for developing the New Wood cassettes was the retail sector’s desire to achieve the quickest possible build programme.

“The first project we used the roof cassettes on was a new Tesco store in Barnstaple, Devon and where the hybrid frame and the roof was erected in six weeks,” said business development manager Alan Wildsmith. “Two weeks later the wall cassettes were all in and the building was just waiting for the glazing, whereas, in the very recent past a store of that size would have been an eight-week programme before the roofing commenced.

“By using the roof cassettes we were able to eliminate roof purlins, previously a slow section of our works. It also meant we were laying between 550-700m² of roof cassettes per day.”

Two options

The roof cassettes are offered in two options – single-ply membrane or standing seam, both of which make the jointing of the cassettes very easy, without compromising on weather-tightness. Internal finishes can be either a traditional liner sheet or, where the timber aesthetic is required, a spruce board.

The BKS wall cassette, again developed initially for the retail sector, comprises a larch-clad panel to self-span between project grids (other coverings are available). As with the roof solution, the wall cassettes are fully factory finished with insulation, and internal and external coverings to the client’s specification where possible.

Similarly the floor cassettes are constructed according to individual project needs – they may incorporate acoustic insulation, for example – and dimensions are dependent on clear span requirements and transport restrictions.

The cassettes are designed by BKS and made by one of its supply chain manufacturers, the choice of which depends on the specifics of the project and cassette make-up.

“The baseline roof cassette is a sheet of OSB with a vapour control or breather membrane, a C24 softwood support joist, insulation (dependent on U-value requirement) and a further sheet of OSB,” said Mr Wildsmith.

“But variations include, for example, un-insulated cassettes for internal walls, which could have an acoustic layer installed, but not a thermal requirement; and cassettes for external walls, with the external/internal finish on them. And for cassettes that are required to span greater clear distances the C24 softwood joist could be replaced with a glulam beam.”

Joist choice

Solid timber joists are favoured, but metal web or I-joists have occasionally been used within the wall cassettes, and it isn’t always necessary to upgrade to glulam in order to achieve long spans.

“We’ve made 12×2.4m cassettes for the retail sector but didn’t have to step up to glulam because we’ve centrally supported with secondary members at 6m.”

The insulation is as per client specification – anything from recycled denim, or newspaper through to glass fibre quilt. On a floor cassette BKS would supply this open, allowing the acoustic finishes to be applied on top and the services to be installed within it, before the ceiling finish is applied on site by the contractor.

While cassette-based solutions are continuing to make their mark in construction, they, in turn, will face competition from cross-laminated timber (CLT) in certain markets, particularly commercial office buildings, hotels and student accommodation, said Mr Wildsmith.

“Two years ago we wouldn’t have imagined anyone looking at CLT for student accommodation but now it’s being seriously looked at by a number of builders in that sector,” he said.