If basis follows the same rules as everything else, it is cost minus depreciation allowed or allowable. Donee will have a lower basis to begin depreciation anew. As for filing the 3115, it depends. Was the property profitable or showing losses? Were the losses even useful or disallowed because of AGI? If the donors' tax bracket is low, how much will the additional $9k depreciation net them, if anything? You can let them decide if it will be worth your fee. (To those who like to do everything "by the books," the IRS isn't going to complain if landlords didn't take a deduction to which they were entitled.)