Is increasing the amount paid to the bank—from 300,000 dinars to 350,000 dinars—in exchange for building a house through an Istisna' (manufacturing) contract, considered permissible or usury?

Istisna' is when a person requests an institution or an individual to manufacture something for them with specific specifications and materials provided by the manufacturer, in exchange for financial compensation. The Islamic Fiqh Academy has permitted it under two conditions: clear specification of the item to be manufactured (its type, quantity, and characteristics), and the determination of a deadline. It is permissible to defer the entire price or pay it in installments, and a penalty clause may be included. There is no objection to the bank's profit in this transaction because it is a sale, not a loan, and profit in sales is permissible. It is also permissible for the bank to agree with a contractor to execute the project in what is known as parallel istisna'.