Footing preparation

Other methods

Dig the footings to the required depth.

Build form work for the concrete pour 150 mm above ground level around the outside of the footings. You will need to come up a minimum of 100 mm off the ground level (same depth as slab floor).

Prepare the slab foundations as a normal slab, with moisture barriers, plumbing outlets, electrical and telephone conduits and of course the reinforcing mesh as specified.

You may like to consider using a chicken-wire nailer for rendering when using cement renders; earthen or lime renders do not require netting. Build this in place to attach the bottom of the netting to the footing. This is an important detail, because if the plaster seals well to the footing there will be no place for the entry of insects into the bale wall from the outside. One way of doing this is to use a 50 mm x 25 mm hardwood nailer that runs around the top edges of the footing.

We ste all thread started bars into the concrete details on another page called the Hybrid Method (under construction).

We prefer to use a bottom-plate system for many reasons. We use two 4 x 2s (100 mm x 50 mm) on their edge with noggins every 450 mm. The photos on this page will give you a good idea how to use a bottom-plate ladder system.

The main benefits of our new hybrid system is that you have a very strong method of tying the bales down and at the same time giving an accurate pre-compression.

With teh low cost high tensile fencing wire and gripples we take the high- tensile wire through the bottom plate and up through the top- plate assembly. We use the gripples to tension the high-tensile wire, and we put this wire through every 450 mm.

The concrete slab is usually engineered for the soil type below your building. If you are pouring a concrete slab at the same time, install a 200mu plastic vapour barrier that completely covers the base of the slab and footing trench. Then put the reo into place. Take care not to put holes in the plastic membrane. If you do, make sure to tape them up.

Hardware required for strawbales at the time of the concrete pour will depend on the method of strawbale construction; the hybrid method uses starter bars of all thread every 1.8 metres in pairs on the outside of the bales and inside the bottom plate.  That is right up against the bales.

If you are building a load-bearing strawbale house, then the high-tensile-wire-and-gripple system is more than adequate. The top plate assembly should mirror the bottom plate assembly, with the exception that we make the top plate ladder assembly 100 mm narrower than the bottom plate. This allows the high-tensile wire to act as a triangle in the pre-compression. This gives more strength to the wall.

Door frames should also be made ready at this time and placed in position. They should be marked on the form work and anchor bolts should be put in place before the pour. Alternately, you could use dyna bolts after the pour. After the pour you will need to provide a white ant barrier in combination with a specific damp course that is at least 550 mm wide. These two barriers are fixed to the top of the footing. The bales can now be raised!