We recently had 30" of water in a 1000 year flood. House is gutted so now's the time to fix a recurring problem I had. The previous owners made an add-on to the house where the concrete is only 2" above grade rather than the 6" for the rest of the house. Regular, heavy rain has slowly been rotting the lowest part of the wall. I can't prevent another 30", but is there something I can do to waterproof against the routine 3"? It's a straight 23' run with an outside corner and another 12' run. Both walls tie into the existing house and closed in a corner that was previously patio. I know the best solution would be to bring the slab up to the 6", but that is cost prohibitive at the moment.
If you can not work on the inside and raise it then work on the outside. What I would do is use a roll on sealant and add drainage along the exterior walls and draw it away. Consider getting about 10 ft away them use perforated pipes to leech the water lines into the ground and at its ending, possibly look into a 3 ft hole filled with rocks.