What is the ruling on taking out a loan from a conventional housing bank to build a house, given the high interest rates and the unavailability of Islamic banks?

An interest-based loan (riba) is forbidden except in cases of recognized Sharia necessity, such as having no means to secure housing other than through it. If it is possible to rent without excessive hardship, then it is not permissible to take out a usurious loan. However, if the rent consumes an individual's income to the extent that nothing is left for their own sufficiency and that of their dependents, then this constitutes a necessity that permits the forbidden.