Look under "accessory units" on this link https://selling-guide.fanniema...  

Hi there - I bought a SFH in Oceanside (1700 sq feet on a ~7000 sq ft lot) recently and am planning to build an attached JADU (garage conversion + possible extension) & then later an attached or detached, larger ADU (accessory dwelling unit / granny flat / casita) in the backyard.

Maybe you sell your 1/2 of the duplex and buy a 15 unit apartment complex in the seediest part of seattle so that you can hit that coveted 2% ROI ;)

@Carlos CarbajalAccording to that link, “Existing law defines the term “accessory dwelling unit” for these purposes to mean an attached or a detached residential dwelling unit which provides complete independent living facilities for one or more persons.”But what if it’s missing a kitchen.

@Alan Mills if it is a “historical” building, then sometimes the replacement cost can be high if the materials originally used were considered coveted for the time.

I deal mainly in C-Class where I covet a good tenant who follows the rules and pays on time. 

You can make great returns on a house hack, maybe even pairing your residence with a cool STR if you find a single family with accessory in the Catskills or Hudson Valley.

@Alex Chau what you are considering building is called an accessory dwelling unit (ADU) or often times called an in-law unit or granny flat. 

Make sure that you are comparing your property to properties in a similarly coveted neighborhood. 

My goal was to have something for guests to play music on, while also giving me a hub to automate our smart accessories like doorbell, lock, and exterior cameras.