Currently the dpc is about 1" above the outside concrete surrounding my 1908 'villa'. I've dug out to get me the 6" height required, what I'd like to do is spread pea shingle over the clay subsoil, but then I thought, if I do that, during the hot summer, the clay beneath can dry out, shrink n I'm likely to get subsidence. So now I'm thinking I'd better spread concrete all across, that way the ground can't dry out beneath the concrete and I won't have any problems.....................or am I totally wrong and just a big fartypants?