How to check if I could add an additional unit in Boston?

[Taylor Thompson]

Hi everyone, I'm looking at buying a SFR in Boston that zoned for multiple units,. Do people have suggestions on how to confirm if it's possible to add additional units (either by converting a large SFR or by adding a backyard unit), and what can be done without needing a variance? Any specifics (i.e. recommendations of contractors, lawyers, or city officials to speak with) would be really useful. Thanks!