A Joint Borrower Sole Proprietor (JBSP) mortgage allows you to add another person (or people) to your mortgage - without sharing ownership of the property. By taking another applicant’s earnings into account, a JBSP mortgage can help you meet your lender’s affordability criteria. It can even help you borrow more. Your supporter will be jointly responsible for paying the mortgage, but they won’t legally own the property at all or appear on the deeds. How does a JBSP mortgage work?