This situation is often called the second mortgage of the house. But not all houses can be mortgaged twice, and certain conditions need to be met. For example, the mortgaged house must be a house with high market value, a commercial house, and a second mortgage of individual housing must be an existing house. In addition, the amount of mortgage loan is usually calculated as follows: loan amount = house value * mortgage interest rate-original loan principal balance. Generally speaking, a house with a loan can apply for a loan if it is a bank loan.