You would have to get permission from your lender if you want to rent your property out while it currently has a residential mortgage on it. Most lenders are agreeable to this but not all, and it will depend how long you’ve had the mortgage as well. It’s normally referred to as getting their ‘Consent to Let’, and as always, it can be more straight forward with some lenders than others – also they may increase your interest rate slightly to reflect the increased risk of the property being rented out but your lender will confirm if this is the case or not and for how long their consent is valid for.