I haven’t found the pot of gold at the end of the rainbow yet, but I have at least found the start of the rainbow. External steel clad walls can exist in a Flame Zone. You may well ask, how can steel cladding and pretty rainbows be related? If you are not sure then you need to read my previous post first.
I heard back from NASH today (National Association of Steel-Framed Housing Inc) and they have new NASH Bushfire Standards coming out at the end of this month. There is a solution for using metal clad walls in BAL Flame Zone in it!
Little dance of joy.
Little. NSW Rural Fire Service don’t accept the NASH Standards for Flame Zone as a standalone, but might as part of a total solution – which according to NASH seems to mean that if you have water tanks dedicated for fire fighting, have AS 3959 rated windows and satisfy other aspects of the AS 3939 conditions, then the wall solution should be OK.
One key issue with steel in a BAL FZ is that steel is a conductor (although not as much as some other metals) so it would conduct some of the the radiant heat expected in the Flame Zone. There is potentially a LOT of radiant heat in a Flame Zone. The NASH solution therefore has a “thermal shield” in it, which going by the diagram looks like steel battens that create a small air gap between the steel and then an extra internal layer of plasterboard, creating a plasterboard sandwich on the inside of the steel (with insulation in the middle). A pic taken from the new NASH standards is below:
To me this looks a lot better than having to put plasterboard, membrane then fibre cement over the outside of the steel, and would have a smaller carbon footprint than all those extra layers. I am yet to cost it out.
I also don’t know how tricky or expensive this is to apply to a container build yet, as it has implications for insulation (normally spray foam) and also structure (achieving the gap between steel and floor frame for example). The full NASH document might include some other solutions, who knows. It’s a good start!
Thank you NASH. I had no idea you even existed until this week, but you are my favourite acronym now.