Question
I just recently expanded and leveled our front and back yard (slight grade away from the house). I had to use a lot of fill which was rocky earth. Now I need to cover the whole front and back yard with topsoil. The question i have is how deep does the topsoil have to be to be able to sustain grass? Someone told me about 2 inches, but I'm not too sure about that.

Answer
Hi Jennifer, To grow a really good turf, try to avoid layers.  Loose soil on top of clay holds too much water in rainy periods and dries quickly in the heat. Deep root growth is essential for good turf but roots tend to fan out and not penetrate a different soil type. The top soil you add should be 60% or so, the same soil as your fill.  The balance should be organic matter (bark, compost) and a little sand.  
I'd spread 2-4 inches of compost, bark and sand mix over your soil and then till it in to a depth of 8-10 inches. Then rake out any rock brought to the surface. This will give you a uniform consistency and allow for deep root growth.
Just adding two inches of soil to what you have will not support grass.  It needs to be at least 8" deep.  Jim