I have looked into the same issue as it relates to Accessory Dwelling Units in Portland, OR.  

Once in a while I see a SFH with an accessory basement apartment, but I understand that I'm not supposed to rent both units if I'm no longer an occupant.

What you can do in a single family zone is to add a companion unit /granny flat or ADU, and the State has now made it a lot easier to build an Accessory Dwelling Unit.

San Mateo to be exact.I'm trying to find out more information about San Mateo County and what homeowners can do to potentially add an ADU or accessory dwelling unit.

If you plan to live in the home during the rental and rent a room or space to guests, you can apply for a Accessory Home Share permit. 

Buying a home with an accessory unit that is not metered for anything.

@Joseph WalzActually, this should be what I focus on- https://minneapolis2040.com/media/1427/pdf_minneapolis2040_12_7_2018.pdfMinneapolis final 2040 comp plan- page 165Allow Accessory Dwelling Units (ADUs) on both owner occupied and non-owner occupied property, develop a set of ADU templates that meet City codes to ease ADU construction and allow the use of tiny homes and other alternative housing as ADUs .

Before I make offers I always go to the tax accessory's web site to verify what they have as square footage and market value even though its just a reference number for me. 

He ended up being very specialized and had a huge inventory of accessories, not guns. 

I don’t see it as being an issue with your mortgage company as it’s an accessory building.