Creating the exterior
With the frame complete, it was finally time to layer up! That’s right, it was time to get this house snug as a bug, in a rug. The plan was to achieve this status with several external layers that would brace, insulate and clad the steel structure, and transform the frame into a home.
Delightfully, this proved to be a most exciting and productive time, and it was relatively quick work to check off each step, but of course, that meant I completely neglected this blog. Now, as I write out each step, I find my memory hazy of the nitty-gritty details….
I appreciate that we developed improved practices as we progressed, and we definitely came up against a few issues that we had to problem solve, but right now… well, I can’t quite put my finger on them. That said, if anyone happens to read this and wishes to know more details about ANY stage, or has ANY questions, I’d be more than happy to dig a little deeper through that memory of mine. I will strive to do better with the interior!
ONIONS HAVE LAYERS
You know what else has layers? A well insulated home.
Hardwood Bracing (or Plybrace) is cross laminated hardwood used as structural bracing for homes. Though the steel frame is strong in itself, (seriously, we have climbed all over it, attaching the roof and cladding and it is solid,) this layer provides bracing against wind pressure. We chose to line the exterior of the steel frame with sheets of Gunnersen Plybrace, fixed down with 10-16 x 16mm Wafer Head Tek screws every 150mm. To measure, cut and fix the sheets to the house took about four days. As the cladding had to be attached along every vertical, the process of attachment was by the most time consuming aspect- though really it was rather easy work and was actually quite enjoyable.
Our process was pretty simple:
Insulation is essential to create a comfortable home; it keeps the warmth in during winter, and the cool inside throughout summer. It creates a barrier against heat transfer. However, internal insulation can only be installed between the frame construction, so any stud and track that touches both the interior and exterior surface of a building is without protection. If the frame is built from steel, (which is highly conductive), a home will be highly susceptible to Thermal Bridging. This means that heat will easily travel through the steel into the home, undoing the work of the insulation. To prevent this we needed to create some form of thermal break to reduce this effect.
Foilboard is an Australian produced, dual laminated foil reflective panel of EPS (fire retardant). It was our thought that we could install this on the outward face of the frame to help reduce thermal bridging. Further the reflective foil may create a radiant barrier which, if installed correctly, will deflect radiant heat away from the interior. For such a system to succeed you need to ensure a suitable air gap, so that will be our next layer. For now, however we have successfully installed a 40mm layer on the roof and a 10mm layer along the two short walls. Regrettably due to the width restrictions of a tiny home, we were unable to squeeze in both the foilboard and the required air gap along the long walls. (More on that below.)
We found that it was easy to puncture the skin of the reflective foil, so this is something to be aware of. As the seams between the panels are sealed with a reflective tape, we used this to treat any damage. It was straight forward to install, and despite initial concerns, found we were able to place our weight on the panels without issue, though avoid stabbing it with your knees and fingers. We started at the far end of the roof and installed each sheet at a time, marking up skylights and hand cutting the openings back on the ground with a few runs of a large utility knife. The living area skylight proved to be a perfect man hole for access onto the roof.
As mentioned above, we had to skip the Foilboard along the length of the home; yet we still wanted to ensure the Plybrace had some protection. Consequently, we decided to install House Wrap along the two walls. Ametalin Silverwrap- a reflective, Class 2 (Medium) Vapor Barrier and Water Barrier, was the product we ended up applying. To be honest, it wasn’t an easy decision- I don’t believe it would be deemed the best product on the market, but it was affordable and at .10mm thick, fitted comfortably within our width restriction. At the very least, it should prevent water from damaging the Plybrace underneath. It is foil coated on one side, blue (anti-glare) on the other, and since cavity battens were installed across the entire house to create an air gap, it may deflect some radiant heat.
For the installation of the house wrap, we started from the bottom and worked up. The rows overlap and are sealed together with foil tape. We attached it around the corners and up onto the roof, to ensure a good seal. We cut the window and door openings with a knife and taped the flaps around the steel openings.
Windows and Doors
Excitingly, and not to mention, finally, the next step was to flash and install the windows and doors. As the length of this page is already stretching the friendship, I plan to cover this under an upcoming post. For now, be assured that all went relatively smoothly, if rather slowly.
(Plus Cavity Battens)
With the completion of the door and window installation, it was FINALLY time to get stuck into the final layer- Corrugated Iron. To clad in CGI was an early, and easy, decision. First, it would create an air cavity, so if any moisture snuck under the cladding, it could travel down the vertical corrugation. It is also highly durable and therefore will not require any maintenance. It also strikes a very Australian aesthetic, which rather appealed to me. Initially, I was fairly taken with the idea to break up the silver of the iron by cladding the ends in Colorbond CGI (Red dust/Terrain), however due to a lengthy delay in availability, I ended up with four walls of Galvanised CGI.
Installation was straightforward and quick work, tacking each sheet on with a screw or two and then coming back to complete each wall. We did suffer a couple of screw collisions, (with the steel frame beneath), so there are a few funky angled heads, not to mention, the occasionally miscount- skipping either too many or too few corrugations. We attached the sheets along every second crest, running a chalk line from end to end and then marking every second. (It seems an extra effort, but it was the times we didn’t bother and became too cocky, that these mistakes were made.)
As we wanted to create a bigger air gap to assist in the function of the radiant barrier, we installed strips of fluted plastic to act as cavity battens. These were cut from three sheets of Polycarbonate Roofing. We needed something that would allow moisture to pass through and so took a gamble that strips of this roofing material would do the job. I can’t imagine that much could go wrong with the pieces, but we shall see. There are a few items on the market of similar design- Cavibat being among them, but these don’t appear to be sold here in Australia. The CGI is attached with Hex Head Screws (with seals), and these run through the cavity battens, into the Plybrace, and lastly into the steel frame. We tacked them on with spray adhesive, to keep them in place as we attached the CGI sheeting.
We used the Makita Cold Cut Saw, to cut the iron to size. This worked moderately well, despite destroying the original blade; however, after some research, I realised that there were special blades available for cutting CGI. Admittedly, I didn’t notice an immense difference in the quality of the cuts, but it did the job without chipping the teeth, as happened with the previous, so clearly an improvement! I did notice that the cuts were better, and less noisy when cutting along the crest, so we ended up flipping the sheets when the cut would land in the valley.
With the walls and roof clad in CGI, it was time to wrap things up with the installation of the fascia and corner edging. Stratco has a custom flashing design-builder on their website, and this made it easy work to order what was required. The two skylights additionally demanded custom flashing, so we ordered that likewise.
It’s pretty pricey stuff, in the sense that it adds up quickly, and this was a key reason why we folded our own flashing and pans for the windows & door using a roll of aluminium. I certainly underestimated the cost of the flashing, and to my shock, it almost equalled the cost of the CGI. As it was all cut and folded to size, it was speedy to install, though I failed to order any Terrain coloured screws for the fascia. For now, we used galvanised heads, but if I come across some coloured hex screws, I may replace them.
Once all the flashing was complete, it was time to pop in the skylights, a nerve-wracking moment. I had been concerned how we would get them onto the roof as they weigh around 25-30kg each, nevertheless it turned out to be pretty straightforward. With a person on a ladder each, we carried each box up onto the roof. So, maybe a tad risky but it worked. The skylights were then dropped in, over the flashing, both a perfectly snug fit, and then zapped into place with a handful of screws.