Concrete footings and slab floors
Concrete footings and slab floors have been used more extensively with strawbale construction than any other types of foundation.
Concrete used in footings needs to be reinforced with steel trench mesh, and the slab needs to be reinforced with the usual reinforcing mesh. The strength of the reinforcing required will depend on the soil type and the engineers report, as well as the load generated by the building. In order to make the footings 250 mm above the ground (the most desirable height), it will be necessary to form up the footings and allow 100 mm above the slab floor for the internal wall. This may involve two pours.
We are more inclined to go with the formwork for the external footings and slab floor at 150 mm and a level floor internally. We keep the bales dry by bringing up the damp course 50 mm, turned up on the inside of the bale and turned down on the outside of the bale. This is a lot quicker but means that you need to be more aware of moisture during construction.
Advantages of concrete footing/slab floor:
• very solid, substantial, permanent foundation
• accepted by all Councils, providing they are built to the Building Code of Australia (BCA)
• can be engineered to suit most soil and load-bearing requirements in Australia
• very quick and cost effective to build.
• extreme use of high embodied energy in the manufacture of cement, concrete and steel, and therefore is not a sustainable building practice.
However until more sustainable footings can be approved by accreditation with the BCA, we cannot see any real alternatives at the moment.