The carport was enclosed but no additional concrete was poured. The sill was screwed directly into the concrete. As a result of being so close to to ground, water has come in under it about 2-3 inches. I was wondering what would be the most cost efficient method to remedy this problem? Could we put water proofing membrane around the sill and bottom of the framing studs then pour concrete or cinder block on the exterior, making the foundation higher (as it should have been prior to construction) even though it's only the perimeter that is higher? Please help.
I would consiter putting in a temporary wall a foot back. Remove the existing wall Or at least the rotted wood cut it off at the bottom and pour a new stem wall that is taller. With the best method being to dig a new footing and put some perf pipe in a sock at the edge of the footing for drainage (Basicly a French drain). With a new stem wall the water won't be able to rot out the sill plate, with drainage the wall should not weep.
I had this same issue when I built a workshop on-grade on an existing slab. The solution I used was to take a piece of 1" x 4" L-flashing, lay down a thick bead of asphalt emulsion sealant on the concrete pad at the exterior, and tuck the tall leg under the siding of the structure, and the short leg was set into the 'bed' of asphalt emulsion sealant. I then put more sealant over the edge of the metal and troweled it smooth.