Building the round strawbale house: June 2012

Was the mantra that was repeated over and over by my labouring wife over several months of preparing the house site for the pouring of the slab. This is the last expensive thing we need to do before getting on with the relatively cheap mudbrick making. I really can't blame her it has been a bit of a slog but we can now see the end of this stage of the house build.

To ready the site for pouring the concrete slab it is simply a matter of digging the trenches, adding a layer of sand (road base?), boxing up, covering it in plastic and setting out the steel reinforcing. We have done these steps but of course we added an extra level of difficulty.

Firstly we put up the frame and roof before the slab, which is not normally the way it is done. The main reason we did it this way was to get the house build started quickly so that we would be able to extend our planning permit (ie. frame stage finished). It has had an advantage in that we don't have to worry so much about the weather when preparing for and when we eventually pour the concrete. But we have had to dig the trenches by hand (or pick, shovel and wheelbarrow), which added up to moving about 16m³ of dirt. This was done over a period of a month on the weekends. Because the outer edge is curved half the trenches ended up being curved. The total length of trench was about 160lm. The dirt we moved was dumped next to the house and will be used for the mudbricks and render later on.

The next step was covering the bits of land with about 8m³ of sand. This was done by wheelbarrow and shovel. We compressed the sand by hitting it with a bit of 4x2. The sand needs to be slightly wet to do this well, too dry and it won't hold it's shape, but too wet and it is too sticky.

The boxing up was also a bit different and I think a bit easier (and cheaper) than if we had a square slab. The entire outer edge of the slab is curved, so I decided to use 3ply because it is easy to bend instead of 6x2's that you would normally use. I used scraps of 4x2 and 3x2's upto about 500mm long to stake the 3ply. The bits of wood were staked to the ground with 250mm galvanized fencing nails (these will be re-used for fencing once the slab is done) and then the 3ply nailed to it. The slab is 150mm above the ground level so the 3ply was cut into 200mm strips. Because the 3ply is curved this adds strength to it and hopefully it will hold up on the day of the pour.

Laying the plastic we thought would be a bit of a nightmare seeing as how half the trenches are curved and at odd angles to each other and the added difficulty of working around posts. But it wasn't all that difficult and only took a day. We used about 400m² of plastic to cover an area of 200m², I guess it was in the up's and down's of the trench walls, the overlap of the plastic and a little extra in the trenches so when the concrete is poured it doesn't pull the edges in too much.

The last bit of the preparation really highlights one of the reasons most people don't make a round house. Trench mesh is straight and is really, really hard to curve. So we had about 80lm of straight trench which was easy to lay standard 3xL11TM in. The outer edge and inner trench which made up 80lm of curved trench needed to have 3xN12 bar, which is 12mm notched steel bar, which needed to be curved. This ended up being not too hard to do, but did add a lot of extra time over installing standard trench mesh. There also ended up being a lot of extra cutting of the slab mesh (SL82) because it has to follow the edge of the slab. We also had to navigate the 10 central posts and cut more than half the 18 6000mm x 2400mm sheets used to fit around the posts. But myself and the wife got the job done in about 4days with a bit of help from the kids.