RECONCILING COMPETING PHILOSOPHIES

We are on a trajectory towards engineered wood being a mainstream construction material, but as Martin Self, Co-founder and Design Director of Xylotek explains – how will this timber revolution play out?

Wood’s role in the transition to lowcarbon construction seems inevitable. But how that looks, architecturally and industrially, demands careful thinking about the nature of wood as a resource and as a material to transform into the stuff of buildings.

We need clarity of thinking now about the paths available: does engineered wood become standardised and industrialised like steel? Or do we exploit the diversity of tree species and material characteristics? Should we maximise volumes used to lock up carbon, or seek to minimise use of a precious resource? How do we reconcile timber production with ecological crises including the growing threat of diseases and climate change on forest ecosystems?

These are some of the questions that frame the competing philosophies of designing with wood. We need to reconcile these questions to create an ethical and practical way of using wood in construction. First, consider the nuances of designing with wood. Its complex behaviour and variability mean it is not a material simply to ‘apply’ to realise an architectural vision (in the way that, arguably, steel and concrete are).

Theoretically it is possible to limit wood to formalised standards of product and design codification, in the same way that we codify steel and concrete.

But as a natural material, wood has more complexity and variation. We can negate that variation through standardisation, but we risk degrading wood’s complexity to the lowest common denominator. The other way to deal with wood’s individual characteristics is to design with sympathy.

Osnaburg pavilions

The way to achieve sympathetic design is through considered creativity at the very start of the process. In Xylotek’s work we seek to be involved early in projects to act as a bridge between the architectural skillset and that of the analytical engineer. For example, on the Osnaburg pavilions project we worked closely with the architect (Nex) during the scheme design stage.

A methodology emerged that allowed us to create these complex forms with minimal wastage, and an efficient use of jigs. For example, the lath’s curving and twisting paths were form-found to trajectories that could be made from initially straight oak lamellas. A parametric digital tool – in which those key physical behaviours were embedded – was used with the architect to iteratively home in on the layered geometric basis of the pavilions and their play between repetition and randomness. Then through design, engineers Format joined the team to bring further optimisation and refinement to the structure.

In the microcosm of a small pavilion project, we tested a holistic approach where the design worked in sympathy with the material behaviour, the spatial intent and effect of the pavilions, and the pragmatics of fabrication and construction. On these pavilions the aim was to minimise the timber section sizes to achieve a filigree effect. But in other projects the motivation can become the opposite – to maximise the carbon locked up. This raises a critical question in design with timber: how much timber to use?

Buildings and carbon storage

On the one hand, engineers are trained to ‘optimise’, which in this context means minimising section sizes and finding the lightest-weight structures. This philosophy has the benefit of saving resources, and reducing carbon released into the atmosphere through the transport of timber (which can account for around 50% of its embodied carbon). By using less material, the environmental impact of production and transportation is reduced, which can help to minimise the overall carbon footprint of the building. Of course, trees don’t regenerate instantly, and the processes of extract and transport attract costs, so by minimising the use of wood, there are fewer concerns about deforestation and biodiversity loss.

On the other hand, some projects drive to maximise the carbon sequestered in a building. Mass timber buildings have the potential to store large amounts of carbon on a long-term basis. But it is only effective if the carbon remains locked up when the building reaches the end of its life. That’s why it’s essential to design buildings for the re-use of timber products, and we consider this very carefully in our projects.

Ultimately, the best approach will depend on the specific context and goals of the building project. In areas where deforestation is a concern, minimising material use may be the better choice. However, in areas with sustainable forestry practices, maximising timber use may be more appropriate. Additionally, other factors such as energy efficiency, cost, and aesthetics may also play a role in the decision-making process. www.xylotek.co.uk

All of this demonstrates that, as an industry, we need to be more rigorous and nuanced in our plans to transition to wood. We should be wary of taking the easy route and specifying from a narrow range of standard products. Instead, we should understand the underlying drivers of forestry, treelifecycle, and the overall environmental impact.

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