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). 

I'm excited to see what will happen with the new ADU legislation (accessory dwelling unit) that they passed and how infill developers will be taking advantage of said legislation.

While my immediate priority is a day job in the real estate field, my wife and I are nearly done with the architecture plans to build a detached Accessory Dwelling Unit (ADU) on our property and add an immediate cash flow generating rental unit.

One thing to look into it to see if you can put an accessory structure.

Most the info came from the county accessory website that is already free.

When it comes to tax strategy for a property with an accessory dwelling unit (ADU), there are a few considerations to keep in mind.

We are considering pulling equity (HELOC) and adding an accessory dwelling unit in the back yard.

(The law, which went into effect Jan. 1, allows STRs only in your primary residence, but a carriage house is considered an accessory unit to your primary and is allowed.)

Moisture resistant drywall will be used in all wet locationsAll ceramic tile will be installed on 1/2" cement board or a concrete PaintNew Switches, Receptacles, GFCIs and cover plates to codeHardwired smoke detectorsCarbon Monoxide DetectorsBathroom: Install Ceramic tile on walls for tub and floorInstall new pre-hung 6 panel hollow core doorNew Toilet with ring and supplyNew Vanity with faucet, drain and supply linesInstall new light fixtureInstall bath exhaust fanNew medicine cabinetInstall New TubBathroom Accessories (Toilet paper holder, towel bars, etc.)Bedrooms / Living room:Install new pre-hung doorInstall all trim ( Door Casing, Base, Shoe)Install Flooring material (Carpet, Hardwood,Laminate )Install New Light fixtureInstall Closet door (Type to be decided)Kitchen:    Install Ceramic floorInstall New kitchen cabinetsInstall Counter top (Granite/Corian/Laminate)Install New Undermount sink and faucet Install Ceramic backsplash with accentInstall Light fixturesInstall garbage disposal (if applicable)Install Dishwasher (If applicable)Install all trimInstall pre-hung pantry door (If applicable)All material types will be selected by you and installed by us.