Gold! Well, magnesium actually…

For those of you who have laboured through the last few torturous posts on wall structure and cladding options, it’s time to breathe easy, I have some good news.  A new solution has popped up. Popped up in the way that things pop up when you spend months dredging the internet for options, I guess it was more wrangled out of the cyberspace abyss.

I came across this option earlier but that was in the days when I thought spray foam insulation was the only option for containers, so I was ignoring a lot of the multi-layer external cladding options.

Builders out there are probably familiar with it, it’s magnesium oxide board – very green, almost carbon neutral, fire proof, rot resistant and termite proof. Now that is the personal profile I have been looking for in a cladding option, I could fall for this one. Oh and one more vital personality trait, because I am such a classy gal, it’s cheap!

Less than half the price of INEX weatherboard in fact, and it looks to be less fussy with the wall system you need behind it to meet BAL FZ compliance. Plus it’s manufactured in big sheets and would be much quicker to fit than individual weatherboards, so less costly in terms of labour. I discovered INEX does do a renderboard which would also be quicker to apply, but you have to then render it which would probably chew up any savings. This magic MgO board only needs a coat of paint. It complies with BAL FZ through the FRL option, of having flame resistance level of 30/30/30 or more – typically this stuff is at least 60/60/60 or more.

There are a bunch of different magnesium oxide (MgO) boards and structural insulated panels available, some with dubious qualities as they are all made in China. There appear to be two here that are certified to BCA standards and have sufficient details on bushfire qualities – MgOBoard and Modak. Modak also do a very cleverly designed gutter that removes the accumulation of leaf litter and so reduces bushfire risk.

Modak's clever leafless gutter design, which is also anti-bushfire.
Modak’s clever leafless gutter design, which is also anti-bushfire.

From the specs it looks like the board just needs to be fitted to an external wall with some decent insulation under it, no special plasterboard as part of the wall system. If there is no need for plasterboard then I might even be able to have some container steel showing on the inside of the house,  which would be great to expose the bones of the house.

Exposed container steel inside home.
A container home showing some exposed container steel for character (from https://www.pinterest.com/pin/558305685030848306/)

I did hear back from the container home builders and they are not real keen on the NASH wall system – they do builds at low cost by making them all the same, so a whole new system would not be easy or cheap for them. They suggested I get the wall system fitted once the containers are on site, but there are more layers and labour involved in that than just adding battens, insulation and cladding to the outside. And now that I know that insulation on the outside is actually a good thing, not a bad thing, together with the fact thinner walls in the inside will give me more space, the exterior cladding option is looking like the best for me.

For anyone out there creating more space with more containers, and who has the time and skills to add interior walls, NASH steel clad walls for BAL FZ could still be a good option – as of this month the standards have been adopted into the National Construction Code.

I am meeting with my bushfire assessor this week, to look at running with the MgO board and getting the final documents together for my DA. Whoop whoop!

There is still the small issue of the roof, but once the rooftop deck is on (which could be MgO or INEX) there is only a small amount of actual roof left (one container at 28 square meters) so it should not be a big deal to whack on something BAL FZ compliant. MgO do some roofing products as well. Or maybe I could have a split level rooftop deck and no roof…

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A waiting game

I have been busy resuscitating Options 1 and 2 from my last post, and they are showing new signs of life. It’s amazing what desperation will do, and a good dose of CPR. If you have no idea what I am on about, read my previous post and if wall structure and condensation don’t thrill you then it’s best to move right along and wait for a more interesting post.

The months are ticking by, but I have been busy waiting on some more information from a few people before I get my final DA plans together. If you have never been “busy waiting” then you should try it, it happens a lot in Africa where you get stuck in queues for hours and can’t leave them in case you lose your spot. It looks like you’re not doing anything but you can’t leave or do anything else because you are in fact busy waiting. This feels just the same, I can’t move forward yet because I am waiting.

My bushfire consultant chased down the RFS over several weeks, as we were hoping to get them to look over the plans and provide some advice and maybe pre-approval. However, once he finally managed to speak to the RFS they weren’t really clear on the new NASH wall standards or other options for this type of build, and needed more details. I just confirmed with Council that the DA will go to the RFS anyway because it is BAL Flame Zone and will therefore incorporate an “alternative solution”. That involves not just the build structure but also the asset protection zone, position and set-back, dedicated fire fighting water tank and pump etc.

So it turns out there is not much point being busy waiting for any more RFS meetings in the hope of saving time and DA delays, when no time has been saved so far and the DA will contain all the full details they need to make a decision. Might as well have delays in the DA process now rather than wait some more to have them later.

I received a couple of quotes for INEX cladding, which as per my previous post now includes the bonus surprise of requiring rockwool insulation directly under it to pass BAL FZ compliance. The cladding and insulation has to be fitted to the outside of the container on-site, so it is not cheap but depending on the builder and labour costs it might still turn out to be the best option for the walls. I wonder if there is a DIY course on installing BAL FZ cladding. I am busy waiting to hear from the container builders, to see how much I can save if they omit the spray foam polyurethane insulation on the inside, which will never pass BAL FZ compliance anyway. They might also be able to pre-drill the holes for the battens to hold the cladding, as drilling corten steel would add to cladding labour costs.

There is some good news on condensation front. I spoke to a very helpful local architect, Ross Young, who sent me a wealth of information and explained the finer details of condensation. It’s all about water vapour and dew points, and my main query was whether having insulation on the outside of the build (under the INEX cladding) would be a problem for condensation. See the previous post for more details, but basically the container builders normally use spray foam on the inside to fill the corrugations in the container steel and reduce condensation risk.

Water vapour everywhere
Water vapour everywhere…

As it turns out, it is actually better to have the insulation on the outside since the steel essentially forms a vapour impermeable membrane, and it’s better to have one of those on the warmer side of the wall, away from the cooler dew point. So ditching the spray foam on the inside and adding rockwool or similar on the outside is more costly but otherwise a good option – it will also make for thinner interior walls and save on interior space.

The roof is another issue; all of the approved BAL FZ roof systems are for normal shaped, gable type roofs with interior framing, eaves etc. The shipping containers are pretty tall (they are high cube containers) so I am still pondering the possibility of using the NASH wall system under the flat roof, working inwards from the steel. While this could work cost effectively for the Flame Zone issue, having insulation on the outside for walls and on the inside for the ceiling could be problematic for condensation. The other option is to continue the external wall structure using INEX and insulation over the roof. INEX comes in flooring /decking too, so should work for the rooftop deck.

Where do all the pesky condensation-seeking water vapours come from? Breathing, cooking, showering and generally just living. I am also looking into heat recovery ventilation systems, to just bash this condensation issue on the head. They are not looking very cheap so far, although there are some wall units available that are not as pricey as the fully ducted types which all benefit from having a proper traditional roof to install them in. I don’t want to add a proper gabled roof as it would get in the way of me sitting on top of the house for the view with a G&T, at least without needing a safety harness and a table with shorter legs on one side. And aside from the little luxuries adding a roof would also be a waste of materials and money.

The container home builder that I have been chatting to is away in China for a few more days, so I am hoping for some answers soon after he gets back.

I shall continue to be busy waiting. The feature photo here is a lovely Blue Mountains rock over a valley that is whited out with mist – unfortunately whenever I see any sort of water vapour now my thoughts turn to condensation…