It is the exterior walls of the basement. The house is being built now. Footer has been poured and the foundation wall has been poured. With the steps in both the footer and the foundations between the garage and the basement I was concerned the it should be waterproofed and that it should have been included in the bid price of my new home. I am not wanting you to share sides in that concern but only in your opinion of what should be classified as an exterior wall and an interior wall. Thanks again for your help.