It is well understood that the NCC is not well suited to addressing the design compliance of mass timber structures. This can then require a Performance Solution as part of the design process. To many, this feels irrational — surely, if you’re relying on the Eurocode (and the Europeans have been doing this mass timber stuff for a long time), a detailed report justifying their verification methods seems like an unnecessary quirk of Australia’s compliance framework.

But that view misses the bigger picture.

Reframe the Context

Approaching Performance Solutions for mass timber with a grudging, “we’ll just do this to get it past the RBS,” not only misunderstands the intent of the pathway (see Part 1), but overlooks a key opportunity in the design process.

The NCC wasn’t written for CNC-milled, digitally coordinated, precision pressed CLT/GLT elements - nor the screws, dowels and brackets that all these elements are connected by. The timber design code, AS 1720, was developed to consider a vast range of potential scenarios. The result is a highly effective code - but only for the purposes it considered. The prescriptive nature of it reflects not just the lack of timber research available at the time of its development but also the huge variability that the Australian construction industry poses as a delivery process for timber based construction - and one skewed to the residential context.

This gap between code and capability is not a flaw in the system — it's a space that a design support by the Performance Solution performance pathway is primed to fill. The Performance Solution then acts as a framework that allows the deployment of mass timber's potential tailored to the Australian market, leveraging the research of many markets and enveloped in a rigorous risk management approach.

In this reframing one can see that Performance Solutions can be a thing to embrace.

Mass Timber is Sensitive and Discrete

"Sensitive and discrete" are usually terms used for that new flame you are dating when your friends ask why they have not been able to meet them yet. But in mass timber design these terms are central to how to design rational and cost-effective structures.

Sensitive: Timber is a very dynamic static material and timber connections are even more so. The interaction between timber's orthotropic characteristics (mechanical and physical properties are unique and independent in three mutually perpendicular directions) and steel's high compressive strength and isotropic properties (steel though can also be complex in its behaviour creates a dynamic that is highly sensitive to small deviations in many factors. Without going into the details of this, simply put a small change can result in big variations in structural performance. So timber is sensitive.

Discrete: Mass timber is rather unique as a building material in that it has bounded envelopes for costs and design. CLT is built up from layers and when you step up from a 5 to 7 layer panel the cost increase is not linear, it is a big jump. This is similar across many areas such as block gluing glulam or finding that connections dictate a timber element size when there is just not enough timber fibre to stick enough bolts, dowels or screws into.

Embrace Performance Solutions

This design context means that a Performance Solution can be much more than a necessity for compliance and provide a way to seek out the inherent strengths of timber design that are missed in the non-nuanced local codes.

Due to the discrete nature of mass timber if the designer can rationally justify a small improvement in performance this can often lead to large cost savings or significantly reduced installation complexity. And where stepping outside of codified requirements could have led to an asymmetric risk context, Performance Solutions require the interrogation of the engineer's assumptions that allow this to be done confidently and with a transparency that allows non-specialists to be positioned to evaluate and hopefully approve an innovative design that is fundamental to project feasibility.