Third-party mortgage

BY MICHAEL SHANG · SIXTEEN YEARS IN COMMERCIAL BANKING · UPDATED 2026-11-06

// THE SHORT ANSWER

A third-party mortgage is a mortgage over property owned by someone other than the borrower, such as a director's home or a parent's house, given to secure the borrower's debt. The owner takes on a guarantor's risk without necessarily signing a guarantee: if the business fails, the property can be sold, and whether the owner can be pursued beyond its value depends on whether the document also contains a promise to pay. Lenders often treat it as they would a guarantee, with disclosure of the debt, independent legal advice and a clear limit, because courts have set such security aside where the owner did not understand it.

BASIS  Practitioner judgment from sixteen years in commercial banking, set out in How Bankers Think (Highbank Press, 2026). Every borrower on this site is a composite constructed for teaching, not a client. The market is mid-market commercial lending as practised in New Zealand and Australia; where a convention differs elsewhere, the page says so.