Our townhouse is an interior unit. The grading along the back of the house is level for the most part but drops sharply just beyond our AC compressor. Please take a look at the pic:
Picture of back of house
We're talking of replacing the wood "retaining wall" that the builder erected with a stone wall. The picture is at least a year old so today all of the rock and dirt to the right of the wood is slipping underneath the wood and we're concerned that the compressor will start to shift. Please also note that we have a narrow crack in the wall where the foundation corner is (where the siding starts behind the compressor). If we run a stone retaining wall perpendicular to the back of the house (to the right of the gutter pipe which is also there), do we have to be concerned about the retaining wall exerting force on the foundation wall? I don't want to see that crack get larger. Also, where the wall meets the foundation, should we put some type of mortar there to keep water from running in between the block and the foundation wall?

Thanks,
Buzz

The retaining wall should not be connceted, in any way, to the foudation wall.

Any retaining wall should have granular backfill that will allow drainage away from the home.

My plan isn't to tie it into the foundation at all, but there will be blocks that butt right up to the foundation wall. My concern was that water that runs down the house would make it's way between the retaining wall and the foundation and create erosion there...even if it's a small gap. Our HOA is not always good at cleaning gutters in a timely fashion, and our gutter terminates directly above this area.

Block or stone? Either way, neither should even butt up against the foundation wall. At the very least, the retaining wall should be separated by a premoulded joint filler. Such a low retaining wall need not be built on a footing, but can be built on a 4-inch, and preferably 6-inch, bed of crushed stone with its top at the lower grade. Ideally, the outer end of the wall should turn 90 degrees into the little slope and terminate there, maybe 2 feet back. This very modest retaining wall will not adversely affect the foundation, as long as the two remain completely independent.

Thanks Richard. Makes sense. What is premolded joint filler? Can you explain or post a link to illustrate?

Thanks!

It's an asphalt-impregnated fiber "board"...it's often used in joints in concrete sidewalks or concrete curbs. It's compressible to allow for expansion and contraction, and relative movement. You can probably get some at a masonry supply yard...I imagine it would be pretty cheap.

Perfect, thanks!