The wheels have not fallen off, not by a long shot, but they did get a bit wobbly this week. Before you read on, this is a technical post about wall structure and cladding, so if you have something better to do with your weekend like a good book, a movie, or maybe watching grass grow then carry on with that. If you are interested in the nitty gritty then read on, but be warned, you might need to sit down with a gin and tonic at the end of this lot like I did.
I have put a moody mountains picture up the top of this blog post because it calms me, and reminds me why I am doing this. The project is progressing but I’d really like to get my DA in SOON.
Optimist that I am, I have been carrying on thinking that I have at least two options for my wall structure to meet BAL Flame Zone compliance. This week they both became a lot less certain, and probably more expensive. Darn you Flame Zone, darn you.
Option 1 bites the dust; well that’s a bit melodramatic, Option 1 bent down and tasted the dust and stood back up again, thinking about whether or not it would like to spend more time with the dust. After getting the NASH standard wall structure info (see previous post) I sent that to the company I am hoping will do my container build, and they said no worries we can build anything you want if you provide the specs, and something like that should only add about $2K to the cost of your build. Yes, $2K! So I thought right, we’re on.
The company has been amazingly helpful so far with such an out of the box build and a hundred emails and calls from me, and they are pretty busy developing a lot of cool new off-grid container homes. I’m fairly sure in this case they didn’t actually take a look at the NASH wall extract I sent before replying to my email in such an encouraging way, because when I then sent them the full house design and asked for a quote using that NASH wall structure, the first wheel went wobbly.
They recommended that I stay with the polyurethane spray foam insulation that they use as standard, because not only is it really effective, it also reduces the risk of condensation happening. Condensation can be an issue with the corrugated container steel if the corrugation gaps aren’t all filled by insulation. Normal flat batts are not so good. There might also be an issue with the type of internal framing they would have to add in to support the NASH wall structure in a container.
I can see their point but from what I have found so far, polyurethane foam is organic and therefore considered potentially combustible, so will not meet BAL FZ requirements. I am yet to see a BAL FZ approved wall system that doesn’t use mineral or glasswool insulation.
The condensation is also a risk but I reckon (being the builder architect that I am, NOT) that risk would be greatly reduced because of the thermal barrier in the NASH wall. Condensation happens due to the difference between the inside air temperature and the outside temperature – like if you sit in a vehicle with the heater on in winter and the windows up, and it fogs up the glass and drips moisture (not so much in these modern days with the aircon on though as that removes condensation).
So if, from the inside of the house to the outside, you had just plasterboard then normal flat insulation batts then corrugated steel then the risk of condensation, and therefore corrosion of the steel, is high in extreme temperatures. Like the temperatures you get in winter in the upper Blue Mountains; warm heated house inside, minus 2 outside. However, the NASH wall system has from the inside to the outside; plasterboard, insulation, plasterboard, 20mm air gap (air is a good insulator), then the steel. So I am guessing/hoping the condensation risk would be far less as the temperature difference by the time you get to the steel would be minimal.
Maybe you could also drill tiny, less than 2mm holes in the bottom of the steel wall to allow more air mixing – but small enough not to allow ember attack because as we know from BAL FZ, embers grow up to be bigger than 2mm.
So this wall system is not written off yet, it’s just a matter of whether the container builders can adapt it to a container wall system, and how much it will cost. The walls would also end up being about 130mm thick, which is a bit of extra space to lose in an already tight space.
Option 2, INEX cladding. The magic silver bullet that, in my starry eyed optimistic state, looked like it was a standalone BAL FZ cladding solution. A silver-bullet-proof werewolf caught this bullet in it’s teeth and spat it back out. Being a tough little bullet it’s only partly damaged by the wolf’s teeth so maybe I can still use it, but it lost a lot of its sparkle.
Reading the INEX specs for use in bushfire zones it says “No fireproof plasterboard required” and that it gives FRL 60/60/60, double that required for BAL FZ. I really wanted that to mean that all you needed was the INEX cladding to meet BAL FZ requirements, without any other wall layers.
My bad. As with everything in BAL FZ, the INEX weatherboard was tested as a system, and that system included R 2.5 rockwool or glasswool insulation underneath it. So adding the INEX cladding onto a steel wall with polyurethane foam insulation under that will not match the approved BAL FZ specs.
An option here is looking at how much it will cost to add the insulation to the outside of the steel under the INEX, instead of having the poylurethane foam on the inside. And looking at the relative cost of this compared to other solutions. If it’s affordable, that would make for thinner walls inside the container and a bit more space.
So, I am back to getting some more quotes and information on feasibility from the experts, and we’ll see what the best and most affordable option is. A tent with a heater is looking pretty good at this stage. I miss my block of land, the view I don’t get to sit and look at yet, and the cool fresh mountain air.
Patience, persistence…and a bit more persistence…and some stubbornness for spice ; the essential recipe for building a container home in a Flame Zone. Mix thoroughly and roast slowly over the flames.