Problem Description
The problem fire engineers face when designers want an external wall within range of a fire source feature with A LOT of glass lies in satisfying this part of the NCC 2019 Amendment 1.
Unfortunately, with curtain walls, the glass occupies more than one third of the total wall area and as such, the traditional protection mechanisms afforded under NCC clause C3.4 are not applicable. Specifically:
On top of that, the NCC also requires external walls within proximity of a fire source feature (adjacent boundaries/buildings) possess a Fire Resistance Level (FRL). Clearly (pun intended), only the most expensive and aesthetically unpleasing glass will be able to satisfy the FRL criteria so what is the solution?
How to Treat Curtain Walls
The saving grace is buried in Specification C1.1 and is often something not easily found by some reading the NCC:
This hinges on the requirement that the curtain wall is non-loadbearing and is not a panel wall. As an additional benefit, no matter how many sprinklers you have on an external wall, the amount of water required to operate the system is capped under Australian Standard 2118.1-2017 at no more than 18 sprinkler heads simultaneously flowing.
The only thing left to deal with is the unsightly drenching sprinklers at random intervals on the wall and unfortunately, as at the time of this blog post, there is no elegant solution and there will have to be protruding sprinkler heads on the lovely glass façade.
What if You Don't Want Drenchers?
This is where fire safety engineering can be leveraged to justify the Performance Solution (omission of drenchers) on your curtain wall. Although highly-dependent on project circumstances, the following approaches may be valid:
Assessment of received and transmitted heat (also known as a CV1/CV2 analysis)
If the client owns both property titles then a conditional approval could be attained based on an imaginary easement
Conclusion
This is just a short and sweet informative piece to identify part of the code which a lot of industry professionals seem to overlook. We're constantly learning new interpretations and hidden clauses in the NCC and will be sharing them as time goes on.
In the meantime, please contact us for your fire engineering queries.