John Kelly wrote:
Anyway - I'm doing a lawn. The level of the ground needs to be raised so
I'm going to need to buy topsoil. The problem I have is the condition of
the existing ground. It was recently a building site and is basically
hardcore stones and rubble with a fair amount of sand and poor quality
soil. What depth of good quality topsoil should I use for planting
grass? I don't need a bowling green type lawn but I don't want one which
is patchy either.

What you have should provide some drainage, although I would remove the
larger lumps of concrete etc. first as they will cause brown spots even
2 foot down - think about crop marks and arechaeologists. If you work
some (lots of) humus into what you have and rotovate it in then it will
improve water retention in dry spells. It will also make what you have
far more useful. It is important that the base is as evenly mixed as
possible, you can't just throw a blanket of goodness over badness and
expect the badness not to come through. Think sheets and matresses.
Then I reckon a minimum of 4 inches of resonable quality loam,
depending on the type of mix you will be sowing.

You need to interpret the site: low lying and boggy will need improved
drainage, while arid will need the water retention improving with
(potentially huge) amounts of rotted vegetation. Think riding school
waste.