Single Family Addition to Create Seperate Unit?

[Tim Kaminski]

Hello,

I have small single family home with detached garage.

Interested in possibly adding addition by turning garage into extra

bedrooms and connecting to main house with "shared laundry room". This

way I could rent out a front house and back house.
Is this too strange to do? Is this illegal?
Curious on thoughts. I looked into ADU but lot size is 500 sqft too small to do. This would be workaround.