Right now I am on a learning curve and in discussions with container home builders for the structural part of the build, structural engineers for foundations, and crane drivers for feasibility of delivering containers to the part of the block I want the house on. But that is all side issue stuff for now, the real meat in the sandwich is the bushfire assessment. The site is at the very top of a steep forested gully, which makes it a ring in for Bushfire Attack Level Flame Zone (BAL FZ) – the nastiest classification you can have. Well done me. I guess that comes with a lovely block in the middle of the bush with a bit of a view.
So the important conversations are with Bushfire Assessment consultants. There is a lot to consider to comply with AS 3959 – it’s pretty scary that I can already write that Australian Standard down without having to look up the number, along with AS 1530.8.2 (and if you’re after general FZ information it starts on page 74 of AS 3959).
One of the most challenging issues so far is the corten steel walls that come with shipping containers. This is strong stuff, built for being at sea for 25 years or so and taking a battering. Container builders say it’s fire proof, which is logical being steel and all, but for BAL FZ that’s not enough; materials either have to be non-combustible and 90mm thick, or have a Flame Resistance Level (FRL) of 30/30/30, or comply with AS 1530.8.2 – which involves someone spending a huge amount of money for CSIRO laboratory testing of the material when exposed to incredibly high temperatures and flames. No-one has tested corten steel. Blue Scope steel says that no steel is ever fire tested and it’s all about having steel as part of a wall system, but they only have a tested “system” for roofs, not walls.
Blue Mountains City Council have been very helpful so far, and I have a copy of an approved DA for another container home in the area that has not been built yet. That one is clad in a fibre cement system, in fact it has three layers outside of the corten steel – special 16mm fire resistant plasterboard, membrane then 6mm fibre cement sheets.
Understandably Council says that someone needs to put their money where their mouth is and prove that corten meets some sort of building standard. Steels are not all alike, and many a shed has buckled under a bushfire – integrity after a fire as well as flame resistance is part of the rating system. So I am trying to find any information that will support using steel panels, corten alone or even with weathered steel cladding over it, as the outer part of an external wall in BAL FZ.