Hi I want to lay new patio slabs over my existing and have read some of the posts relating to this. The existing patio is exactly 150mm below my damp course and so it would seem this would preclude me from laying on top of this. If I were to create a gap betwen the walls of the house and the new slabs and fill with pea shingle would this be ok? If so what size gap should I use. I estimate the new patio would be approx 75 mm below the damp course. Any other suggestions??