General speaking, any unpermit additional in the property will have troubles for resell or refinance. Only few lenders can accept property without permit with higher rate. many clients will not choose the unpermit property to avoid trouble. It also depend on appraisers. If they put your property "subject to" on the report, you will have trouble. But if they just ignore the unpermit construction and doesn't put anything in the report, you will be fine. We just close one loan with same situation as you that previous owner build storage in the car garage, lender get it pass. I dont think you have 法律上 的风险 but just loan related issue.