Timber takes to the sky

Famed for its mention in the Domesday Book, Birmingham suburb Sheldon will soon be reaching for another high. TiC reports.

A SWANKY city-type apartment will rise in the sleepy West Midlands suburb of Sheldon later this year.

Eight storeys of timber frame containing flats equipped with bohemian balconies and highbrow wooden flooring, will give residents a taste of city living and breathe life into the dreary post-war housing that currently swamps its inhabitants.

But it nearly wasn’t to be. The £11m Horizon project hit a snag late last year with complications over the original design, which was to be in lightweight steel-frame.

A new design and manufacturing team was drafted in at the 11th hour with the promise of a cheaper and quicker design.

Speedy switch over

The project has been onsite for just under 20 weeks and with piling complete and the first lot of timber frame in place, the project has been dragged back from the brink of collapse to being ahead of the clock.

Timing has been made up in no short part to the switch in materials. Not only has timber frame fitted inside the budget, says project manager Robin Brown of contractor and client, White Fire Group, but also it has allowed construction to move at a quicker pace.

“We suffered some delays in the design changes going across from steel to timber but we’re hoping we can grab it back using timber,” he says.

Brown says the time can mostly be clawed back by the speed of erecting the timber frame, allowing the interior fitout to begin much earlier. “With a steel frame you need to put on external applications before you can get stuck in to the fitout. With timber you can start the fitout a lot earlier and be water tight without the windows.”

After the first four-storey block of timber frame is placed into position, it will take between three and six weeks for the first batch of engineered timber flooring to be put into place.

Timber component manufacturer Timber Developments (Trusses) appointed consultant and engineering firm, Rushmoor Engineering Services to provide structural calculations for the designs of the floors, roofs and walls.

Disproportionate collapse (DC) calculations determined that engineered timber was going to be used for the project says Rushmoor managing director, Clive Teague.

The floors and roof to the top eight storeys will be designed using engineered Finnjoist Ijoists and timber kerto ring beams from Finnforest.

The DC calculations determined that the long lengths and continuous design of engineered timber fitted the bill. “If it was any higher than eight storeys then timber wouldn’t have been used,” says Teague. “Engineered timber is excellent because it has very long lengths and you can put edge beams all the way along the rim of the lengths, so if a wall gets removed there is a beam above it to carry the load.”

Teague says the growth in engineered flooring is currently being driven by the residential sector. The company is onsite with Bellway Homes for a 130-unit residential development on a former hospital site in Farnham in Surrey. It has also installed engineered timber flooring most recently for Taylor Wimpey and Laing Homes.

Teague says while contractors have switched onto the merits of using engineered timber flooring, client acknowledgement is further behind. “Contractors have switched onto the benefits and in a lot of cases timber frame and engineered floors have become the norm. The dimensional stability of it is good and they don’t change shape with moisture content so you don’t get any lumps and bumps in the floor.”

Rushmoor was appointed to the project in December, Teague recalls. “We were brought in quite late to turn the building over from one system to another which caused some complications with the foundation loading, but that’s all been designed into the system now.”

Thermal mass

Teague says the debate about thermal mass is as much a red herring as anything else. He
says the new generation of floating floors with a timber chipboard deck on top of the I-joist is providing the thermal mass to improve the building’s energy efficiency. “The floating floors are pretty well proven,” says Teague. “It’s not as heavy as concrete and not as much mass but that’s good because it is more responsive to heating.”

The use of timber also ensures the building meets the demands of the environment. “There is a lot of carbon produced in making concrete and steel and little used in transporting and processing the timber,” says Teague. “If you talk about engineered timber as manufactured long lengths of I-beams then they are very economical. An Ibeam is much more economical than a solid joist. There is much less timber in it. It’s a lighter beam. It is a very efficient structure.”

Despite its merits, Brown says there were some challenges switching from steel to timber on the Horizon project. He says lightweight steel frame is still a fairly new modern technique. “It just seemed to be quite complicated in terms of design and just getting it there, when timber was a lot more simpler,” he says. “Although the engineering has been much more difficult.

“When you start going up to eight storeys in timber frame you’ve got to account for disproportionate collapse. And each of our apartments has got an external space so we’ve got a lot of balconies and it’s quite hard to hang balconies off a timber frame structure.”

Installation

Due to the late appointment of the timber frame manufacturer, the first batch of flooring to go in the first four storeys of the structure will go in loose, with individual I-beams cut in the factory and installed onsite individually, says Teague.

“We produced the designs for the first four storeys but by the time the drawings are done there won’t be enough time to make the beams and I-joists into cassettes which can be lifted in.”

The next two blocks will be made to fit, says Teague, with the I-joists, solid timber beams around the edge and the decking being made into one panel and then lifted in.

“They will go in much faster,” he explains. “Typically it will take two days to lift and secure the cassettes where as it will take two weeks to do it loose.”

Suburbanite living

When the project is completed, Brown says residents will have the taste of living in a city centre-style apartment slightly out in the suburbs at a slightly cheaper price.

“It’s going to be a stunning building,” he says. “It’s very contemporary, cutting edge and with lots of glass. And all of that off a timber structure.”