if it is a load baring wall you got a mess if you wont to do that you have to go 4 feet at a time you have to remove the wall bord if you have a large area to do if it is just around your water heater it is not that bad just take a chicill and clean out the bad wood and force the new wood underneath of the 1x4 then call your sellman and give him hell for telling you that there was no one buys in the walls the service guy