Legal 2 family vs accessory apartment

[Joseph Escamilla]

Hey everyone I am currently in the process of looking for my first deal. Ideally, I would love for it to be a house-hack that allows me to live for much cheaper especially because I am in an expensive market (Long Island)

In my search for duplexes i see that some are listed as “legal 2 families” while others are listed as “accessory apartments”. I was wondering if anyone would be willing to shed some light on the difference between the two?

My main concerns are:

-if it’s an accessory apartment am I technically not allowed to rent out the other unit when I decide to move out? From what I’ve researched it looks like I have to keep it as my primary residence in order to rent out both units.

-i know it probably differs between markets but does anybody know the process/cost of converting an accessory apartment to a legal 2 family? And would it even be worth it?

Any help/information would really help me narrow my focus. Thanks everyone!