our roof

Our roof has been on for a little while now and this is how we went about installing it:

We decided to go for the “classic cream” colorbond colour, as it seems to perform pretty well in the hot Australian sun. This table shows a comparison of the thermal efficiency of the different colorbond colours, which means how well they absorb radiant heat (the fancy term for this is "adsorptance"). Not surprisingly, the darker the colour, the more heat it absorbs. While we really liked some of the darker colours, we weren't too keen on having a super-hot roof, so we took our pick between "classic cream" and "surfmist", which have the one of the lowest ratings. The only lighter colour there is is called "whitehaven" but it wasn't available through our supplier yet and we also thought the very bright white might be blinding potential future neighbours. The last thing we want is to be an eyesore to anyone!

Up on the scaffold, getting ready for some roofing!

We got our corrugated sheets delivered together with our custom-made flashings and the pile of roofing material looked surprisingly small! After we put the rafters on, we covered the ceiling with a layer of breathable house wrap, which we will be putting around the outside of all our wall frames as well. We thought it would be a good idea to ventilate our roof cavity, so the hot air will not simply be trapped underneath the corrugated iron. To do this, we raised the battens by a few centimetres with little blocks. Even though every single cm in our tiny home will be valuable real estate, we thought that it would be worth "loosing" 4cm in height to hopefully have less heat coming in during summer. We’ll see how well it works. 

Our ventilated roof cavity. From bottom to top, there are rafters
(not visible here), housewrap, blocks for extra spacing, rafters,
anticon and corrugated sheets (also not visible).

We were a little worried about the chance of condensation occurring underneath the corrugated iron in winter, which could lead to issues such as mold or rot down the track. We got a product commonly know as “anticon” (we got the Knauf brand Space Blanket), which seems to mitigate the chance of condensation under the roof. It sits above the roof battens and below the corrugated iron sheets and depending on what brand you choose, it consist of either fibreglass or mineral wool lined with a reflective foil on one side. 
The raised battens should create a big enough cavity below the anticon for its reflective layer to work to its full extend. Wherever the silver foil touches another material, it will just end up working as an unwanted conductor of heat and cold, instead of reflecting the radiant heat. So we took great care that the anticon didn’t sag too much during installation and hopefully it will stay in place over time.

Cutting the anticon to size

A builder friend advised us to make sure to get the first corrugated iron sheet as parallel to the long side of the house as we could (thanks Zev!) and we put a string line across the front of the house to make this job easier. Apparently things can get out of hand pretty quickly if the first sheet isn’t lined up correctly, as any errors made with the first sheet only get worse down the track.

Aligning a corrugated sheet with help of a stringline.

The first sheets are up - time for some rest!

It took us a little while to get our head around what flashings we needed for the roof. We were a little concerned that our low roof pitch could cause rain water to get into our build between the corrugated iron and the gutter, so we decided to install a gutter apron. This should direct rain water that runs off the roof and that might get blown towards the build, straight into the gutter. We’re still not too sure if that was necessary or not though.

For the other three sides, we picked some standard barge capping and used infill strip to stop water from driving rain also insects getting into our roof.

The little bay roof took a lot of fiddling around and even though it is tiny, it took a lot longer than doing the big roof! We think it was totally worth the time and headache though, as we are in love with our bay window already! 

We calculated that the "standard" treated pine fascia boards available would add up to around 70kg, which we decided would be too heavy. So we painted some of the very light weight western red cedar boards we bought for our cladding and to make them stand out by painting them teal. It just made things a little tricky, as they were bevelled, but we are pretty happy with how they turned out! Thanks to Ines and Tabea for your help :) 

The roof from below. The gaps between the rafters will be filled with insulation

Tabea doing some touch-up work on the fascia boards

Barge capping to cover the ends of the corrugated sheets

The little bay roof

A corner of our bay roof

tie-downs and connectors

Before we started working on the roof, we decided to increase the structural integrity of our frame. A lot of it has been learning-by-doing.

After installing some tie-down fittings (e.g. double-sided stud-ties) we found out about even better ones (e.g. hold-down brackets plus bolts). As it didn’t make much sense to remove the fittings that were already in place, we ended up with a bit of an overkill in some areas.

We used:

• Threaded rod to connect the bottom of the trailer frame to the top plate of our building. Ideally, the threaded rod should have been made of high tensile steel, as that is common in buildings in cyclone-prone areas. However, we couldn’t find the high-tensile rods anywhere in Perth and as we didn’t have time to ship them in, we thought we’d at least use the standard threaded rod. We thought it's still better than using none at all.

• Hold-down brackets, bolted through the bottom plate and trailer base and then screwed sideways into the studs.

• Double-sided stud-ties, to connect the top and bottom plates with the the studs.

Hold-down bracket on the left, two double-sided stud ties, as well as
threaded rod connecting top plate to the trailer frame.
Probably a bit of an overkill, but no point in trying to remove the stud ties now...

• Speed bracing (which comes in long rolls), to reinforce our little wall at the rear. Ideally, this should diagonally connect the top and bottom plates, but the two little windows on that wall were in the way, so we ended up with a bit of a free-style version. We made sure to wrap the bracing around a corner to connect the small wall with the larger walls, and also to wrap the bracing around the trailer base.

Speed bracing on the rear wall.
The bathroom and loft windows
got in the way a bit!

Speed brace wrapped around a corner and underneath
the frame of the trailer. Double-sided stud ties connect the bottom
plate to the studs.

• Bugle batten screws in a variety of lengths to connect the structurally important stud connections. We became a huge fan and ended up screw-joining many of our noggins with them.

• Uni-ties to tie down some of the rafters to the top plate, in particular the rafters at the short ends of our roof that might be experiencing strong wind loads.

A uni-tie wrapped around a rafter.

If we had to do it all again, we would use the nail gun just for pinning, simply to make assembly of the frames easier, and then use bugle batten screws to join all connections of the frames. As tie-downs, we would probably only use hold-down brackets (plus the necessary bolts and screws) and high-tensile cyclone rods. If our windows and wheel arches weren’t in the way, we would have used a couple more of those threaded rods going all the way from the top to the bottom. 
The double-sided stud-ties we used didn’t seem to have a very deep grip and also created thermal bridges bypassing the complete wall insulation.
Speed-bracing makes sense in some situations, but bracing requirements of each wall need to be looked at individually and bracing them with structural plywood sheets, either on the inside or outside, should do the job in most situations. 

We chose the connectors and tie-downs to the best of our knowledge (and from the limited range available in Perth...), after researching what is common practise in timber-frame buildings in Australia, New Zealand and the States. We're pretty happy with how it turned out but wouldn't go as far as saying that this was the best way possible. So let us know what you think, what other cool connectors you have seen or used and how you liked them!