I have an end unit townhouse built in 1986. It's three stories including the garage level, and it's built on a slope. The garage level opens to the street in the back, but that level is below grade on the opposite side (front) of the house.
To accommodate the grade change, there is a vertical jog in the foundation wall on the side of the townhouse, so the foundation wall becomes a pony wall.
The problem is that the foundation wall jogs down too low too soon, and it is now below grade in one area, leading to a rotting sill plate and sheathing:
Note that the Great Stuff is my doing - a temporary fix to seal things up. There hasn't been meaningful water infiltration in this area, but it does appear that at some point mice got in there (they definitely haven't been there in at least a year).
The landscaping is in the control of the condo association. Although I could go to them and ask them to have the landscapers regrade, there's no guarantee in continuity in the landscaper, or any kind of institutional memory even if we retain the same one, so this problem could just reoccur the next time they add mulch.
So, since I need to replace the rotted sill plate anyway, I'd rather just try to come up with a solution that avoids the possibility of reocurrence by cutting away the rotted studs and sill and adding 6-12 inches of height in concrete along the ~2-3 feet of foundation pony wall. This would also require adjustments to the exterior siding, but that seems easy enough.
The questions are:
1) Does this make sense, or is there a better alternative?
2) Does the wall need to be supported while I do this, and if so, how? Can I just screw some 2x4s to the studs above where I'm going to cut them, and have those run down to the floor at an angle?
If it's relevant, this is a gable wall. Also, you can see the trusses running perpendicular to this wall that support the floor above - the light is attached to one, and the other is right above the wall on the right.
Appreciate any suggestions!