Engineered timber talks

Tesco is using a timber cassette roof deck for the first time in its new 85,000ft² store in Barnstaple and once the project is complete, it planned to review future use of the product. However, the review is now cancelled: the supermarket giant intends to continue using the roof cassettes where possible.

The company’s chief architect, Martin Young, told the 130-strong audience at last week’s Wood Talks seminar at the Building Centre that Tesco opted for timber cassettes because it wanted to improve the aesthetics and energy performance of the store – its second zero carbon outlet.

Since it started building timber-framed stores – the first at Wick in Scotland in 2006 – it has received good feedback from customers but many had asked why the roof was metal.

Supplied by Austrian manufacturer Glöckel, the roof cassettes comprise 19mm spruce ply on the interior face with a weatherproof membrane, mineral insulation and outer membrane. The interior finish is usually OSB but Glöckel introduced the ply at Tesco’s request.

Mr Young said Tesco planned to build a further five zero carbon stores next year as part of its target of being a zero carbon business by 2050, and that’s without purchasing offsets.

Nick Milestone, director of B&K Structures which sponsored the seminar and which has been involved in many timber frame supermarkets, including Tesco’s new store, illustrated how well engineered timber has become accepted as the company completes 38 projects this year.

Initially a steelwork company, B&K introduced timber in 2006 and it’s not looked back.

“We’ve evolved from being a structural steel company to the UK’s biggest hybrid steel and timber manufacturer,” he said.

The company has developed 3D modelling software for steel to design in timber, trained its own erectors, achieved FSC and PEFC chain of custody certification, and in 2008 was awarded the National Business Award for Innovation.

Starting out in glulam, B&K has broadened its engineered timber range to include cross-laminated timber and roof cassettes. While steel is incorporated into the structures, Mr Milestone demonstrated how using timber could tip the balance in making the project carbon negative.

“For one ton of steel used, 1.8 tons of CO₂ is created; for every 1m³ of wood used, 0.9 tonnes of CO₂ is embedded,” he said. “Steel still has its place but used responsibly we can keep our structures carbon neutral.”