We are thinking of purchasing a period cottage (exact date unknown but somewhere 19th century) which has single skin exterior walls. Obviously it will be very difficult, if not impossible, to find a lender who will touch it - so the query is, is there a way of upgrading a single skin wall so that mortgage companies won't have a problem with it? I'm thinking of a scenario where they hold back a tranche of the mortgage until the upgrading works have been completed and inspected. Is there anyone who can shed light on this?