You're right to be concerned about this.  If you don't simply want to look for another place (and even if you do), I'd advise hiring a lawyer to handle the transaction for you.It may be possible to get some indication from the local building code official what the government's view on this would be.  If the seller is required to get a certificate of occupancy for the closing, it may be the seller's problem.  Otherwise, I'd want to be sure at the very least that the work was all up to the building code standards, because otherwise there would be compliance costs.