Raising level of lawn - suitable gradient?

[Paul-man]

Our 75m.sq lawn is a mess following building work. There is some "topsoil" and lawn left in places but clay on the surface the area where a new soakaway has been dug in.

The garden slopes away from the house at an angle of about 1:18.

As we have a nice high DPC on the house we are thinking of laying brand new topsoil on top. This will also raise the garden to a suitable level to step down from our decking without the need for a step.

1) What would be a suitable gradient (Aware that we need some drainage, but 1:18 makes the kids' slide lean precariously!) I was thinking perhaps about 1:50?

2) If we laid, say 4" / 100mm of new topsoil (average) on top of the existing ground, would we need to blend in the new soil with the old, (have a tiller onsite) or could we just lay it on top?

We are also re-doing the borders, but would probably dig a greater depth of topsoil in here to make for easier planting.

Would any of you tackle this a completely different way?

Thanks as ever

 

[r896neo]

Your plan sounds fine. No real need for a slope at all but a small one would help assuming the area it falls towards can handle it. i.e under your decking?

You can dig over the borders and ideally add some rotted manure to those rather than just top soil. As for your filling use unscreened topsoil that has stone in it still and then finish the surface with an inch or so of screened or if turfing and inch of grit/sharp sand. Unscreened soil will be cheaper and importantly settle a lot less so it should stay a little flatter in the next year or two.

It wouldnt be essential to rotovate if adding 4'' but it will help with drainage as adding 4'' of loose stuff on top of a very compacted hard layer might be like a giant sponge for the water. By rotovating, even very roughly/ (or running the teeth of a digger through it if one is still around) you will break it up and blend the two better.