Remortgaging jointly wont make any difference, its the title deeds that count. Even then it all depends whether the ownership is a joint tenancy or tenancy in common. If a joint tenancy, survivorship applies and the property immediately belongs to the other joint tenant, the value falling outside of the estate and therefore IHT. If a tenancy in common it will however form part of the estate (albeit only the %age of the property owned by the tenant in common) and therefore be included in IHT calculations.