Legal Question in Real Estate Law in California

You will need to disclose that you know the addition was or at least may have been done without permits. There is no limitations on un-permitted work. So you can either try to get it retroactively permitted (if it is up to code that will mostly consist of just paying some fees) or you can sell it the way it is with notice to the buyers that it lacks permits and they can deal with it as they see fit after they buy it. In many areas the second option is very common as long as there is no problem with the work that was done. Properties may be sold many times without clearing the permit issue; it just gets ignored. You would have to ask a local real estate broker whether that would work in your area.