I hear people have experienced a lot of problems with damp in earth floors, which naturally would make a mainstream building practitioner sneer told you so, so I’m certainly not going to claim, ah, but ours works. Ask me again in five years time. We’re experimenting, and it is taking a risk trying out this sort of thing in Scotland, though I imagine the difficulties would be greater in the west than the east. One way or the other, I certainly wouldn’t want anyone to think of the method we’re following as a recipe.
Particular limitations we face are a) the fact that our buildings are on three levels, ie on a hillside, and b) that we’re on solid undisturbed clay, which is great in one way but in another makes it feel rather silly digging this solid stuff out only to replace it by some other material. So we’ve let the depths of our sub-layers be governed principally by the position of the draining-ditch that runs off all excess water down towards the pond at the foot of the property. This means that in order for the bottom of the lowest layer of the floor to be a couple of inches above the base of the foundation trench (a self-draining trench which falls slightly towards the draining-ditch), while at the same time allowing for adequate headroom at the lowest point of the ceiling, we essentially have about the depth of two car tyres, plus about four inches, for the sub-layers.
The reasons we’re measuring in car-tyre units are, firstly, that we’ve used car tyres for the foundations (not all of them, we started by using a drystone wall foundation, but felt we were using too many of our good stones). These tyres contain rammed clay/stones in the rims with a self-draining core of stones. Secondly, as we had an easy supply of used tyres, it seemed a good idea to incorporate tyres in the lowest, draining, layer of the sub-floor, which otherwise consists of large (I can’t remember the exact size, must be about 2 ins) gravel. The gravel stones tend to be round rather than sharp, so roll around a lot. Hence the tyres, to stop too much roll. This does leave a squodgy top surface to the layer, ie the very tough reinforced rubber, even after ramming the gravel well into the rims, so we’ll be keeping an eye on whether that is going to pose problems later. It was this springiness which made us change from our original plans for the second sub-layer and not pack the insulation into a second layer of tyres but simply have it lying free over the whole floor surface. This insulation layer, which is still the equivalent of a tyre’s depth, consists of straw bound together with wet clay and very well tramped down. The two layers thus amount to less depth than is recommended in the recipe we found in Permaculture Magazine, but we are hoping that the tyres will make up for some of that depth loss by providing a certain degree of damp-proofing, while the top layer will not be all clay/cob anyway: a lot of it will be taken up with large oak or elm slabs which we acquired, as well as some old pourous bricks (as these came from an old ’30s picture-house, we like to think they were some cheap offer, of the non-refusable variety, made through some kind of Mob connection – and hence of Italian manufacture, so: an Italian-style kitchen floor, to make the ladies swoon….)