6" of top soil?
I'm wanting to lay a completely new lawn but being a rank amateur gardener but a grafter I've gone all guns blazing into completely stripping my back garden. I've removed maybe 3 tonne of pea gravel and maybe a further 2 tonne of rubble buried in the earth and an existing rockery. I have used some of the pea gravel as a thin layer of drainage and now need to raise my level 6" to meet the new required level of my future lawn. I've read 6" of top soil is required to lay new turf on. My question is do I need a sub soil between my drainage layer and top soil or can I go with a straight 6" of top soil directly on top of the drainage level?
Any advice would be greatly appreciated.