Architect Feilden Clegg Bradley recently completed the £6m Formby pool in Lancashire. Part-funded by the Land Trust, the building had to reflect its woody surroundings, so sustainably sourced timber was used for large parts of the structure, including its roof and supporting columns.
To preserve the natural feel, large glass panels with inconspicuous joints had to be incorporated. But for Andy Couling, partner at the architect, timber’s tendency to shrink and expand in a humid atmosphere presented problems for fixing the glass – the movement could cause the panels to shatter.
On completion of a preliminary design, Doncaster-based curtain-walling specialist Norking Aluminium was brought on board. Its designer Keith Roden thrashed out the details for working manufacturing drawings.
Describe the problem you faced
Couling We wanted the linear elevation to have a sort of marching timber appearance. But timber expands and contracts a lot more than steel, partly because it’s affected by moisture as well as heat. We’d estimated that there would be as much as 70mm of lateral movement along its length, or about 12-20mm at each column, where we needed to attach the glass panels. To avoid cracking, connection design was important.
We also wanted an essentially transparent facade, so we needed discreet joints. But they had to give structural support against wind loads, too.
Roden We had to design glass-supporting brackets based on the guidelines provided by a specialist that the architect had appointed. So we had to come up with something to make it work around their lines. But timber moves a lot more than you’d expect, so we were concerned about the tolerances we would need to build in.
How did you get together?
Couling We started by getting a specialist cladding architect – Montrésor Partnership – to help us with preliminary drawings for tender. Once we had these, we approached Norking, which makes aluminium fittings. The team at Norking were up for it but cautious about the risk. They’d have to guarantee the system and they knew they’d be in the firing line. We had to reassure them because they would be taking on an element of responsibility.
Roden The glass we fit is usually put into window openings, where you don’t have to take into account movement. But on this scheme, we had to be able to absorb all movement. Although we’ve done some jobs where movement is considered, this was different from most. But we decided we had to take it on anyway.
How did the relationship develop?
Couling We knew what we wanted to achieve but needed Norking’s continued assistance. They helped us preserve the original concept and became intimately involved. Much of the work resulted from round-table design meetings.
Roden A lot of the communication was done via computer and over the phone. But we met the architects on site maybe half a dozen times and also got together with other subcontractors to thrash out details.
Talk us through the solution
Couling We found we could limit the amount of movement if we split the roof into three sections. We considered T-shaped brackets for the column connections, but realised that the end grain into which they’d be fixed had poor traction. We considered other solutions and Norking suggested a strap. But we weren’t keen on that.
Finally, we agreed with them that aesthetically and structurally a T-shaped fin plate and U-shaped bracket would be best. The U, which attached to the mullion with a bolt, was wider than the plate so it enabled lateral movement. Whitbybird, the structural engineer, checked that it could take horizontal loads and passed on its calculations to Norking to ensure that it could accommodate things.
Roden Feilden Clegg Bradley and Montrésor developed their initial proposals. Schüco Aluminium provided the mullions. I then did the manufacturing drawings for the U-shaped brackets and T-shaped fins, which were made locally. Although they were based on Montrésor’s design, we had to ensure the tolerances. Also, over the pool hall there’s a section that twists, so we had to adapt our roof brackets in this area.
Are you happy with the end result?
Couling I’m very pleased with it. It’s a neat solution. The fins and jaws aren’t necessarily exactly in the middle of every column but you have to look very closely to spot this. And in a way this demonstrates that these tolerances were needed.
Roden I haven’t actually seen the finished project. I hope it looks as nice as people wanted, though ...
Specifier 18 May 2007
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