What Are They?

Accessory Dwelling Unit (ADU), Secondary Dwelling Unit (SDU), in-law unit, garden apartment, granny flat, rental unit, guest cottage, casita – whatever they are called in your area, this building type is coming into it’s own in California and around the country.

So what are they? In general, they are second dwellings on properties that are zoned for only a single dwelling. They are not the primary dwelling, but are smaller and are considered an “accessory use”, meaning they are not the primary use.

In some cities they must be free standing. In other cities, they can be in the same building as the main dwelling, or attached to the main dwelling.

To confuse things further, in San Francisco the City allows owners of apartment buildings with 4 apartments to add one more unit, and owners of apartment buildings with 5 or more units to add an unlimited number of units if these units are entirely within the envelope of the existing building.

Why Are They Popular Now?

In California the cost of housing in the major metropolitan areas is so high, that there is a crisis of sorts in housing. The State has passed legislation which forcefully encourages jurisdictions to permit these kinds of accessory dwellings as a way of adding housing units to the market.

The potential for home owners to be able to add a second dwelling to their property is very big.

  • You can rent the unit out for additional income.
  • You can move into the unit yourself and rent out the main house for even more additional income.
  • You can use them for “live-in” care givers for when you are older.
  • You can move your elder parents into them so they can be near you as they age.
  • You can use them as guest houses for visiting friends and family.
  • And in some locations, you can rent them out on a short term basis, as with AirBnB.

Having a second unit, and the potential for rental income, usually means that adding and ADU increases the value of your home.

These are just some of the reasons that ADUs are popular right now.