Along my concrete block walls, I have 1/2" furring strips every 16", then
sheetrocks are attached to the furring strips. The furring strips make it
possible for 1/2" electrical conduits and copper pipes to run across or up
and down the walls.

In some cases I have 3/4" pipes or electrical conduits, so I go with 3/4"
furring strips.

In some cases in a shower area, I have shower valves that sticks out further
and it needs 1.5" of space. Now, I can attach 2x2 or 2x4 turned on it's
face to the concrete wall and furr it out this way. Or may be at 1.5" I
might as well build a real wall butt up against the concrete wall, with it's
own top and bottom plates.

At what depth do you think it crosses the threshold form using furring
strips to a real wall?

Thanks in advance,

MC