Heightened appeal

Telford Homes is getting technical with timber in the capital. TiC reports.

THE CREDIT crunch and the drive for sustainability is wreaking havoc on the construction industry’s bottom line. But it is also injecting innovation and convincing contractors and architects to build out of their comfort zones.

In October, developer Telford Homes will have completed what architect Waugh Thistleton claims to be the tallest residential tower built entirely in timber, although this fact is not strictly true.

The Stadthaus in Murray Grove, Hackney is a nine-storey box and is made from crosslaminated timber panels supplied by Austrian manufacturer KLH.

The ground floor and first floor slab are concrete so it’s effectively an eight-storey timber structure sat on a concrete box.

It took just nine weeks for the structure to go up inside an area of 17m x 17m, explains Telford’s construction director James Gaffney.

“We managed to do that with one visiting mobile crane, a team of four men and a lorry coming between two and three times a week from Austria,” he says.

Normally Telford, who is also the main contractor for Stadthaus, would not consider building anything above three storeys in timber, never mind nine.

But after having the scheme brought to them by architect, Waugh Thistleton nearly two years ago and travelling to Austria to inspect the cross-laminated timber panels’ performance, they were convinced it could be done.

NHBC and BRE approval

Stadthaus has been approved as a pilot scheme because the system is not a complete structure until you clad and waterproof it. The panels are protected by a dry lining system internally and an Eternit board rainscreen cladding on the outside.

It took Telford more than 12 months to receive approval from the NHBC as a pilot scheme with the backing of an extensive report from the BRE, which manufacturer KLH commissioned.

For a building of this type Telford would normally have gone for a concrete frame or low bearing masonry, but KLH’s system proved to be just the ticket.

The panels alone satisfy Hackney council’s 10% renewable energy criteria and although more expensive than a concrete frame, Gaffney explains that if it had used concrete, Telford would have needed to invest more money in micro-renewables to meet the target.

“We would have had to have gone down the biomass boiler route, he says, “so we would of had a concrete structure with a biomass boiler within a very small building.”

Timber absorbs carbon throughout its natural life and continues to store that carbon when cut. The fabric of the Murray Grove tower will store over 181 tonnes of carbon. By not using a concrete frame, a further 125 tonnes of carbon is saved from entering the atmosphere.

Journey to Austria

Gaffney explains Telford was initially pessimistic on its trip to Austria in January 2007 to inspect the system.

“We wanted to know about its structural stability, the extent of its movement and how we would fire protect it,” he says. “But every question we had KLH had an answer for.”

KLH provided full-scale mock-ups in a laboratory setting to demonstrate the system’s acoustic performance to avoid levels of noise transmission between apartments.

Gaffney explains that the cross-laminated panels also have a very slow charring rate. “It’s not like a matchstick timber frame where if unprotected it catches fire very quickly. It’s a very slow charring rate and we treat the timber -structure in the same way we would treat concrete, then we clad it in plasterboard dry lining to comply with building regulations.”

Gaffney says the panel system is more structurally sound than traditional timber frame. “It is a very user-friendly structural substrate. For instance, if you are fixing something onto it, the other following trades working on it find it very easy to fix cladding or dry lining to it.”

In terms of shrinkage and deflection, Gaffney explains that the panels combined shrinkage or structural deflection in the floors or walls is a minimum of 3mm a floor. “You could quite easily get that shrinkage or deflection in a concrete frame,” he adds.

Project architect Kirsten Haggart says the cross laminated panels can go higher than eight storeys. “With Stadthaus we’ve allowed for a maximum shrinkage due to moisture and also compression of 3mm. According to KLH’s engineers, Techniker, that was erring on the side of caution.”

Haggart says it and Telford have taken a lot of advice from KLH to meet Part E of the building regulations. “Because it’s so new we’ve had to be very rigorous about testing,” she says.

All of Techniker’s detailed design work was then vetted and approved by Telford’s structural engineer, Jenkins and Potter.

Market pressures

All of the 29 units at Stadthaus were sold before the project got out of the ground last November, ten of which were completed for Telford’s development partner, The Metropolitan Housing Trust. Gaffney explains that due to the housing downturn, if the units were to go on sale today it would have found it significantly more difficult.

“It is fair to say on developments we have on the periphery of London, sales are significantly slower and it’s going to be a very difficult year,” he says. Telford operates in North and East London and will have completed approximately 1,000 units in the last year. “The market in east London is slightly more vibrant than perhaps other more suburban areas,” he says. “Many of the developers announcing office closures and delaying new works are in the more suburban or rural areas.”

Telford’s policy of selling early and off plan, and its partnerships with housing associations, has ensured that it has a secure development pipeline within tough market conditions.

Surge in creativity

The benefit of trialing and testing new materials, such as KLH’s timber panel system, is saving on the build programme and physical construction costs, says Gaffney. Stadthaus cost just £3m.

Telford is currently readjusting its supply chain to include companies like KLH and micro-renewable energy suppliers, which previously it wouldn’t have gone near.

“The drive towards renewable energy targets is expanding the supply chain in different ways,” he says. “It is also making our existing supply chain, particularly in mechanical and electrical packages, look at different systems.”

Those fearing their bottom line in investing more money and time in alternative energy and materials need only to be reminded that, unless they react, their schemes won’t happen.

And far from sustainability stifling creativity, in the case of Stadthaus you only need to look at the post-war brick housing that surrounds the scheme to see that its design is reacting to modern needs.