Lawn over old patio

First of all, I know there are many posts similar to mine and I've read through a lot but I just need a bit of advice still. I can delete this post after if needed, so as not to clog up the board with similar posts. So...

I am extending our current lawn by removing a patio and then either using seed or turf. I have lifted the slabs and there is a roughly 3 inch layer of sand and slate then a layer of membrane. Below that is compacted soil. Will I have to remove that sand and slate or can lay some top on top of it (while ensuring level with current grass) or should I mix top soil into the sand and slate? OR... and this is what I think is the right answer, should I remove all sand, slate and membrane and then put down 10-15cm (or however much to get it level) of top soil and then the seed or turf (level allowing for turf if going for that).

Is there a calculator somewhere to work out how much top soil I need? The area is roughly 400cm x 460cm.

Thank you in advance, I know this is probably asked a lot on this forum!

Best wishes, Lizzie x

 

I would do as you suspected and remove all the slate etc.
If you give the sizes x depth to a topsoil supplier they will quote you for cost.
The lawn will take a while to blend in with the old one.
If you are buying turf then the supplier may well be able to provide the topsoil too..

 

Thank you so much, I just needed that confirmation really. Much appreciated JR x

 

More topsoil depth the better, as we now seem to have hot 30c dry weather the more subsoil and topsoil will help it to not dry out so quickly and go brown

 

Brilliant thank you!