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What if the way to get more timber into buildings was by putting less timber in?

Are we missing out on reducing the amount of embodied carbon in more buildings through the use of sustainable timber, by forcing “purist” structural solutions on our projects?

Timber is an incredible structural material with benefits that include: reduced embodied carbon, stunning aesthetics and is the one truly renewable structural material. However, my years of working in mass timber construction have consistently highlighted challenges or roadblocks posed by designers, clients or builders. Timber is often compared to conventional materials around the key technical disciplines of structure, fire and acoustics. It’s true to say that on a strict comparison basis that timber will often lose out on these.

So what if we were to use timber in conjunction with other materials? We could still get the sustainability benefits of timber but also use it where it works best and combine it with other materials to supplement its performance?

We can do this in one of two ways: at a material/product level, or at a holistic building level.

Hybrid products are not uncommon. Reinforced concrete is the best example of this. Concrete works in compression, steel in tension, and the combination of the two have allowed the construction of the vast majority of our cities. In the timber space we see very little, though you could argue that most mass timber buildings are put together with copious quantities of steel brackets and screws, they aren’t integral in the same way. Timber and concrete have been used together and there is some very interesting research into steel and timber hybrids but they don’t seem to see a lot of use on projects in Australia.

At Composite Systems we have developed a timber-concrete composite floor system, called Strongfloor, which is being utilised on its first projects and this has highlighted to me the benefits of combining materials into something greater than the sum of its parts. Long-spanning floors with no back-propping, high levels of acoustics and fire performance mean it is a suitable substitute for concrete in a great number of commercial buildings. And these don’t need to be the pure timber buildings – they could just as easily be built from a concrete or steel frame, just utilising the floor for its reduced embodied carbon or aesthetic benefits.

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 Strongfloor – Timber-concrete composite floor system

This brings me to hybrid buildings. These are becoming more common, particularly as we push ever taller in timber. The limitations of timber in terms of structural and fire performance have meant that a large number of building we celebrate as “timber” are in fact hybrid, with large amounts of concrete or steel supplementing the timber. Would we be better to be more honest and describe them as hybrid? Would clients, certifiers or fire brigades be more comfortable understanding them like that?

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Atlassian HQ in Sydney – A hybrid tower involving steel, concrete and lots of timber

Hybrid buildings also doesn’t have to mean tall buildings. When I talk about hybrid buildings, I would also include a combination of mass timber and lightweight timber framing as hybrids. There is a huge untapped potential, particularly in mid-rise residential buildings and hotels for a combination of lightweight framed walls and mass timber or composite floors. The cost of a pre-clad lightweight timber-framed wall could be less than 20% of the cost of a CLT wall, but a CLT floor might a fast and cost-effective mid-floor. We have already seen the combination of these to be very cost-effective and fast to install.

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 Parkland Estate, Rouse Hill – CLT and lightweight timber hybrid

The biggest challenge with mixing materials is the coordination across the interfaces. The more materials and products we bring into a building the more challenging they are to deal with, from constructability and tolerances to fire-performance and compliance. Assembling an experienced design team and considering early supplier and contractor involvement (ESI + ECI = ESCI?) can go a long way towards navigating these challenges and mitigating the risks.

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The ESCI process – you heard it here first!

So why should we be considering hybrids? Put simply cost and sustainability. The wider palette of structural materials we can choose from on a project, the more cost effective the solution is likely to be. By using materials where they do what they do best we can find more cost-effective solutions, using lower amounts of material and seeking minimise the environmental impact of our choices.

I should probably point out that I’m not saying that we shouldn’t be building pure timber buildings. Those trailblazers who have built some tremendous examples of timber buildings across the world should be applauded for bringing timber buildings into the conversation. However, the reality is that they still represent a tiny fraction of the commercial floorplates built every year. My aspiration is that timber can become a normalised part of the conversation when it comes to commercial building, rather than a niche material. If we can look at each individual structural component individually then we can make an informed decision based on the technical requirements for it. The question shouldn’t be “why should it be timber?” but “why shouldn’t it?”

Would I rather build one building with 5000m3 of timber in it, or encourage 500 buildings to use 500m3 in each of them? I know what would do the planet more favours and hybrids (products, buildings or both) might just be the answer. Keep an eye on us at Composite for our latest hybrid projects and products – there is some really cool stuff coming up!

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