The original 2x4 that rested on the floor was removed in one piece with approx. 7" of the vertical studs attached to it. (This was under a closed set of 6 stairs that was removed first.) One side of the studs rested against a concrete block wall. The removal was done to allow access to the cold joint for the application of a waterproofing material whose surface is varied and uneven. Now I'd like to install a new 2x4, hopefully with closely matching 7" studs attached to it to be sistered in, since all the original studs were partly rotted from flooding. I can't drill down into the concrete floor because it would disturb the waterproofing, but need something to serve as "shims." I'm concerned about using construction adhesive of some kind since I think I need more time to do the fitting even if I check everything first. I'm an amateur at this sort of thing.

My son owns a house that had a one-car attached garage that was converted to a room by a former owner. Since the walls are finished, the only evidence that the room was a garage is the concrete floor, which has some slope, which is typical for garage floors. We discussed the idea of putting a false wood floor over the concrete. To maintain a high ceiling, keeping this sub-floor as low as possible in desired. The joists will be about 9'4" long. We know 2x4's are not normally used as floor joists, but I am thinking they will fine as long as a support is place in center of each joist. By doing so, the effective span for the 2x4 joists would be about 4 1/2 ft. Does this sound feasible? If two supports were equally spaced under the 2x4's, then the effective span would only be about 3'. I'm wondering whether one support would be sufficient. The joists will be spaced 16" apart, center to center. We would probably put 23/32" OSB panels down for the sub-floor.