The cost of affordable housing prompts many people to consider renting out a suite in their basement to help with mortgage payments. In some cases these are legal suites and in many cases they are not. If the tenant is a family member that is not a problem but if it is a complete stranger you may be violating local by-laws. If it is a legal suite then the lending institutions will take that into account when calculating the cost of your monthly income and how much of a mortgage they will give you.
For a good article on this subject see