Do you have an “almost-launched” young adult living with you? Need space for an aging, but still independent, parent? If so, you have new reasons to consider adding a second unit to your home or lot.

If you have some extra space, even an extra bedroom, creating a separate, legal living space can be a cost-effective way to use your home to provide flexibility for evolving families, or even rental income.

In response to the pressing need for more affordable housing in the rental market, the California legislature recently passed legislation to make it easier for homeowners to create second units (colloquially known as “granny” or “mother-in-law” units and as “accessory dwelling units” by the law) by removing some of the regulations and costs associated with conventional second units.

Two Kinds of Second Units

California law allows for two types of second units: conventional accessory dwelling units and junior accessory dwelling units, and places some restrictions on what local ordinances can require.

Here some of the key state laws that apply to the different types of second units:

All Second Units

  • Must adhere to local

    lot-density

    ordinances

  • Lot must be zoned for single- or multi-family use
  • Lot must contain an existing single-family dwelling
  • Must be for residential use
  • Must not be intended for sale separate from the primary residence
  • Can be rented
  • Must include permanent sleeping, cooking and eating facilities
  • Permits that meet local ordinances must be approved within 120 days of submission
  • Do not require neighbor notification

Conventional Second Unit

  • Can be an existing structure (such as a bedroom or garage) or an addition
  • Can be attached to or detached from the primary residence
  • Cannot expand existing living area

    floorspace

    by more than 50% or 1,200 square feet of floor space

  • If the unit is a new detached structure, it may require additional off-street parking in some limited circumstances (e.g., if the unit isn’t within ½ mile of public transit)
  • May require a sprinkler system if the primary residence requires it
  • Detached units may require separate utility hookups and connection fees “proportionate to the burden” of water needs.

Junior Second Unit

  • Can only be created from an existing space within a home
  • Can’t exceed 500 square feet
  • Limited to one per lot
  • The homeowner must live in the building–either in the main living space or in the junior

    unit,

    unless the owner is a government agency or housing organization

  • No additional off-street parking space is required
  • No separate utility hookup required and no hookup fees can be charged
  • Requires a separate entryway

Check Your Local Ordinances

State law allows cities to have looser regulations, but they may not impose more stringent ones. Because they vary, it’s essential to check local requirements when you’re considering creating a new second unit.

Because the most recent changes to the state law occurred in January 2017, as of this writing some local jurisdictions are still working on bringing their ordinances into compliance, so what’s currently on the books may not yet agree with the requirements listed above.

(To date in Marin, only Novato, San Anselmo and Tiburon have brought their second-unit ordinances up to date to comply with state law, while San Rafael is expected to vote on a new proposed ordinance shortly. Other municipalities are working on theirs.)

Your architect can help you navigate the uncertainties of local ordinances during the planning stages of your project. They’ll work with your local building department to ensure your second unit meets all state and local building codes.