| My sister just bought a house on a small city lot. The neighbor has a low fieldstone wall across his lot (3-4 stones high, with each stone about 4" deep). She was thinking it would look good to extend his type of wall across her lot on either side of the step/walk up. This would allow her to put in some soil amendments without everything washing over the sidewalk.
His lot is level. He placed the first course of the wall on the sidewalk rather than dig a trench in the yard. The problem we're facing, though, is that the sidewalk in front of my sister's lot slopes up to the left, maybe 6"-8" over the 35" (small city lot, remember). So if we put the first course on the sidewalk the whole thing would be slightly tilted.
What I'm trying to wrap my mind around is, if we want to keep the wall level across the slope we'll obviously have to dig a trench for the first course. How do we determine how deep to dig the trench if it slopes from side to side? Should we figure that the shallowest end has to be at least 3" deep on the 4" stone and dig level for that? That would mean that on the deeper end it might be up to two stones below the level of the sidewalk, which seems extreme. Or would we make the trench in "steps" to keep no more than one stone deep?
And is it outright odd to have the wall on one side of the walk slightly higher than the other side or should they be equal heights?
I'm hoping someone can clue us in. She loves this house and it is perfect for her. I'd love to help get the yard to the point where she can garden. Thanks. | 
