Carsten Hein is the lead designer in the timber team at Arup, based in Berlin. He’s fulsome in his appreciation of the qualities of timber and seamless in the solutions he offers for its challenges. These are rarely a major problem, he suggests. Mould in Passive House? Not a problem in Europe. Acoustic and fire issues? Yes, but there are ways to manage these, too. The conversation got technical, but fascinating. Here’s a taste.
- On Tuesday, 9 December, The Big Timber Debate Round Two will canvass some of the issues around the use of timber in Australia and the importing of timber. More details and tickets here.
During a near hour long interview with Carsten Hein, it was clear that timber was more than a material to this engineer – more like a passion, you’d have to think.
Hein is the lead designer in the timber team at Arup, based in Berlin, and though timber had challenges, he made it clear they are far from insurmountable.
When we spoke in late October, he and his team were applying their creative mettle to a new timber project they were working on – a “small” seven-storey tower.
“Currently, we are discussing the slab structure,” he said.
CLT (cross laminated timber) slab is structurally okay, he said. “But you have an issue with fire, acoustic and dynamics.”
Acoustics? Timber has no weight, he responded, it has no acoustical insulation.
“No matter [if you’re designing for] offices or dancers, you have to look at heel drop or people-induced impact sound transmission from floor to floor. And timber, with none of its own weight or hardly any, doesn’t provide any insulation.”
One solution is to apply a concrete screed. “So, you have two different independent systems with a spring in between, so you can tune it to two different frequencies.”
Another idea is to get rid of the insulation layer and connect the concrete to the CLT board, “make it a sandwich, a structural sandwich that reduces the amount of timber, reduces the amount of concrete, because we have the whole depths acting structurally.”
If the client wants a longer span, concrete beams will impact the weight limitation. “Then we start replacing concrete with timber.”
The discussion might veer toward three elements that might be used, including CLT, with timber beams and the composite concrete on top.
“So, three elements that still have the structural depths we would like to see using the timber interlayer as a spacer between the beam and concrete topping, but having the composite action between concrete, timber and timber; we still have the full height.”
CLT, he jokes, stands in Germany for “consumes a lot of timber”.
Water is another challenge with timber
If the timber is exposed to rain during construction, it can be a problem, Hein says, but there is a “very detailed description of how to deal with joints between the elements.”
It starts with two millimetres. “That’s a joint you don’t have to worry about. If it’s more than two millimetres and below five millimetres, you start dealing with it to make sure it’s not an issue for fire. At the same time, whatever sealing you apply also deals with humidity. That’s a side effect.”
Passive House
Hein also has quite a bit to say on Passive House and efficiently dismantles criticism that’s emerging around the system in Australia, with some architects actively opposing it.
Mould is cited as a growing concern in Europe, for instance.
So, “Is there a problem with mould in Germany?” we ask.
“No”, Hein answers. “Not at all”.
Germany has standardised guidelines for the use of timber to prevent this occurring, he says, and the regulations are derived from EU standards.
Rules have recently changed to encourage people to simply open a window.
“You don’t have to use mechanical ventilation if opening the window is sufficient.”
There are also ways to “force” natural ventilation, he says, such as electric systems that automatically open windows for five minutes or so.
“That does the trick for ventilation in terms of mould, it’s quite advantageous.”
Research
Among his schedule, Hein manages to work on research, such as a current program with the University of Berlin looking into the “system variation, or system optimisation of acoustics and dynamics governing the utilisation of the timber elements.”
He’s looking into “optimising the dynamic and at the same time acoustic behaviour of timber to figure out if you can kind of raise the utilisation of timber, make it more effective.”
There’s a lot more to listen to.
Watch here
The Fifth Estate caught up with Carsten Hein during a fleeting visit to Berlin in October, after attending the Year in Infrastructure Conference in Amsterdam, as a guest of Bentley Systems. We travelled to Berlin at our own expense.