Waalaykum Assalaam

Conventional mortgages use riba (usury/interest), which is prohibited in Islam. It is one of the major sins. According to the majority of the scholars, the only time one can get involved in riba-transaction is when there is a dire need meaning that one is in life and death situation whereby eating swine will be permissible.

If you are not able to find interest-free loans from family and friends, you will have to reside in a house on rent. If the rent is too high, you have no alternative but to look for a property where the rent is relatively cheaper. The only way purchasing a house on a conventional mortgage would become permitted is that you have no accommodation in any way, shape or form, and you fear that you will have to live on the streets without a roof over your head. However, this is far-fetched, especially in the West, as there are many ways of getting temporary or permanent accommodation.

One can resort to shariah-compliant mortgage if one is desperate to have one. However, it should be borne in mind that even this is not 100% shariah-based, but still is a viable alternative insha Allaah.

wassalaamu alaykum