The Build - Foundations
The foundations were built using old car tyres filled with hardcore (also known as sub-base – basically a type of crushed stone that packs down solidly) built up in stacks (piers).
Straw bale walls about a third the weight of a twin-skin blockwork wall and are also much better able to accommodate ground movement than brittle cement and concrete but the foundations would need to be strong enough to take the weight of a green roof. Car tyres are problematic to get rid of (protected from ultra-violet light they will last for 30,000 years!).
Using them as foundations helped me avoid the use of concrete and saved the tyres going to land-fill. The gravel came from a local quarry 5 miles away. I would have liked to completely avoid the use of concrete in the foundations but ended up using a precast concrete paving slab as the base for each pier. This gave me something to pack the stone against and also helped to spread the load of the pier over a wider surface area.
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