Within the city limits (I think both suburban and urban tiers) you can now have, by right, up to 3 units (2 in the form of a duplex and 1 in the form of a detached accessory dwelling unit).Of course, the problem is that construction costs are so high, ADUs are difficult, but if you have a garage that could be converted easily, that could be a good way to go!

What I beleive you want to research regarding the detached carriage house is a dwelling called an "Accessory Dwelling Unit" (ADU). 

You may also be able to find a home that has an accessory dwelling unit as well, if you are going to be living there.

Right now appraisers are having a problem with the accessory dwelling units.

Is this going to be converted to a rental as an accessory unit or into a two dwelling flat (the zone will determine which one you can do)?

@Vincent LudegnaAn ADU is an acronym for an “accessory dwelling unit”.

Therefore a two or three bedroom property cannot rent more than one bedroom at a time.The rental portion of the residence must be designated as an accessory use space.Must include the registration number in all advertisements.

Hi @Sam Leon I've looked at quite a few properties with Mother in laws/accessory suite/Accessory dwelling unit whatever you want to call it.

I am trying to add an accessory dwelling unit in San Francisco to a pre-rent control building and the city is requiring me to opt out of my Costa Hawkins rights in order to receive permission to build that extra unit.  

Using some of our own funds as well as the FHA 203(k), we renovated the house including an addition and converted the garage into an Accessory Dwelling Unit.