Is landscape fabric that stuff that blocks weeds from coming up but also blocks roots from going down? If so, 6" is probably a minimum. I've dug down a foot or more and still found strong grass roots. That was with KBG and/or Fescue.

Why are you putting down the landscape fabric? With 6 inches of soil, it's not likely that any seeds will germinate and grow through the 6 inches of new soil, is it?

I think he is doing that to prevent the new soil from immediately dropping lower into the gravel and sand, which I think is a good idea to keep the septic system working for awhile, but eventually I imagine that it will all drop down there, and the septic may fail. Having a septic system myself, I don't see any alternative.

Paul--Maybe I missed something, but I didn't see anything about a septic system.

No you didn't, it was me.

No septic system. I want to take the crushed stone from the top and fill it in with dirt. So underneat the dirt will be landscape fabric and hten about 2' of crushed rock. I was wondering if 6" was sufficient to grow grass on.

Six inches of soil is plenty, BUT...please explain why you want to use landscape fabric. Nobody uses landscape fabric under turf, so I'm wondering why you think you should.

I'm putting it on top of the french drain to prevent it from clogging fast. You are supposed to apparently from what I've read online. IN other words i have a 12" trench of rocks and landscape fabric on top, soil on that, then grass.

This prevents the soil from going into the french drain and clogging it up.

I understand what you are trying to accomplish, the optimal way of doing this would have been to use the fabric sleeve that go around the entire pipe because it will be difficult to ensure that the fabric stays in place anyway.

If you have an opening through which to clear blockages(i.e. run a snake through ) your best option may be to make sure that the river rock in the trench is compact and in place and place top soil over top of it lightly and spead you seed. The grass will cover the trench soon enough without a lot of work and time that might not get you very much benefit anyway.

I think the pipe is in fact wrapped in filter fabric.

anyways, it's already done. The dirt is down over the drain so :)

If the pipe is wrapped in fabric then there isn't or in this case wasn't a need to put the landscape fabric over top.

i too want to grow grass, above ground on my Terrace, which is composite (plastic) boards with a 1/4" gap between that floats about 6" above a flat membrane roof which is all new construction. i was thinking that i would lay down a root barrier fabric, then a moisture mat and build it up with dirt to 7" to then grow my grass.

is this a sound plan?