Adding a 3rd-4th unit to a 2 unit house

[Gerard Gonzalez]

I recently purchased a 2 unit multi family property near Westerly RI. Each unit has 2 bed 1 bath. They both also have very large basements. I have been thinking about converting the basements to one bed one bath and renting them as well turning this 2 unit into a 4. Was wondering if anyone has done anything like this before in the area or any area. If so can you please share your story. Would like to know if anyone had any potential pitfalls from this type of addition. Really interested in any code or zoning issues in particular.