On March 2020 I bought a new construction single family home with a accessory unit for 725k I have been house hacking living on the in-law unit.

For all you potential (and current) house-hackers out there - Freddie Mac announced recently that they are expanding their lending guidelines for conventional mortgages to allow rental income from Accessory Dwelling Units (ADUs) for both purchase mortgages and no-cash-out refinances for single family residences."

I live in a 3 unit building and I have discovered it is possible to add two ADUs (Accessory Dwelling Units) to my property in California.

Just be aware that generally houses with accessory apartments (sometimes called Mother Daughters) usually require a permit, and require the owner to live in the property. 

Accessory Dwelling Units. 

I've been doing research after seeing so many accessory apartments listed as multifamilies in long island.

One strategy may be to buy a single family home with an accessory unit or guest house. 

Former accessory, rezoned to owner occupied multi just before listing.

Connecticut recently passed legislation that allows “Accessory Dwelling Units” sometimes referred to as Auxiliary Apartments.  

We too thought we could just change it to a legal 2 family or accessory apt.