Depth of topsoil

[amatureleccy]

When laying new turf how much topsoil should it be layed on.

I ask because I am digging up my patio. Underneath is the usual sand, cement and rubble which is not good for laying turf on. How much topsoil is needed tells me how deep I have to dig (don't want to go deeper than I need to).

Thanks

 

[DAZB]

A depth of 3 to 5 inch will suffice.
I got this info from this site..... http://www.atstecks.com/topsoil.htm
It is aimed at the US but the quantities and depths won't change.