Accessory Dwelling Units

California law has significantly expanded opportunities for adding second and third dwelling units to properties where only one dwelling had previously been allowed.

The law now permits up to 500-square feet of a dwelling's existing space, such as an attached garage, to be converted to a junior accessory dwelling unit (JADU). Parking space lost as a consequence of a garage conversion need not be replaced.

Additionally, area larger than 500-square feet can be converted or added as either attached or detached space to create a conventional accessory dwelling unit (ADU). State law now invalidates home owners association restrictions that prohibit or unreasonably restrict the construction or use of an ADU or JADU on a lot zoned for single family residential use.

Below are some of the requirements pertaining to JADUs/ADUs prescribed by California law. Local jurisdictions may adopt less restrictive measures, but not more restrictive. Consequently, all that is described below is applicable throughout the State, with possibly greater leeway in some localities.

$ Funding Assistance $

A number of government reimbursement or tax credit opportunities are presently available for some ADU related costs.

California Housing Finance Agency: $25,000 Pre-Development Cost Grant Program
Bright in Your Own Backyard planning assistance by Hello Housing
US Dept of Energy $2000 tax credit (to builders) for energy efficient units
Federal Solar Tax Credit: 26% through December 31, 2022 (new detached ADU structures are required to have photovoltaic systems)

Size

Up to 500-square-feet — 500-sf is the State's maximum allowed size for a Junior ADU. A JADU is only allowed as an attached part of a new single family dwelling or as a conversion of existing space within a house.

Up to 749-square feet — 750-sf is the size at which development impact fees can be imposed on ADUs, which can be substantial in the Bay Area.

Up to 800-square-feet — 800-sf is the threshold at which a locality can begin to limit greater ADU size based on conditions, such as limiting space to 50-percent of the primary unit's area. In other words, 800-sf is the minimum ADU size that a local ordinance must allow if it can adhere to setback requirements. Note that 800-sf provides only 6.8-percent more area than the 749-sf space that requires no development fees.

Up to 850-square-feet — 850-sf is the minimum area that a local ordinance can establish as the maximum allowed size of an ADU that is either a studio or 1-bedroom. Note that 850-sf provides only 13-percent more area than the 749-sf space that requires no development fees.

Up to 1000-square-feet — 1000-sf is the minimum area that a local ordinance can establish as the maximum allowed size of a multi-bedroom ADU.

Up to 1200-square feet — 1200-sf is the maximum floor area allowed by State statute for a detached ADU, but only if the primary dwelling is at least 2400-sf.

Other than a requirement not to exceed 50-percent of the primary dwelling area, the State does not limit the maximum size of an attached ADU.

Owner Occupancy Requirement

In the case of a JADU, Government Code Section 65852.22 requires the property owner to occupy either the primary unit or the JADU, unless the parcel is recorded as a land trust.

In the case of an ADU, Government Code Section 65852.2, prohibits a local jurisdiction from requiring owner occupancy of an ADU permitted between 1/1/2020 and 12/31/2024.

Photovoltaic Requirement

Newly constructed detached ADUs are required to have a photovoltaic (PV) system (unless there is insufficient unshaded rooftop area for an array).

The PV system requirements do not apply to alterations or additions to existing homes, including detached additions where an existing detached building is converted from unconditioned to conditioned space.

Other Title 24 Energy Code Requirements

An ADU's compliance requirements are based on its classification as either an addition to an existing residence or as a new building as described in the 2019 Residential Compliance Manual - Chapter 9, Section 9.3.5

Fire Sprinkler Requirement

A residential fire sprinkler system is not required for ADUs unless they are required for the primary dwelling unit. If an ADU is to be constructed in conjunction with a new primary dwelling unit, both units will be required to have a sprinkler system.

Note that it might be desirable or necessary to install a fire sprinkler system in order to possibly extend the limits of new construction. California's Fire Code restricts the farthest point of new construction to be within a distance of 150-ft from fire equipment access. But some localities extend this limit if the new construction includes sprinklers—as Alameda County does (affording an additional 50-ft). This can be critical when the site for a desired ADU is located far from the road, such as in the case of a flag lot.

Sanitary Sewer Utility

Castro Valley Sanitary District: Permits and Fees
East Bay Municipal Utility District: Rates
Hayward Sanitary Department: Charges
Oro Loma Sanitary District:

Useful / Interesting ADU Webpages

Government Sites

California Department of Housing and Community Development

Alameda County ADUs

City of Danville ADUs (includes permit ready ADU plans)

City of Hayward ADUs

City of San Jose ADUs (preapproved ADU plans)

San Mateo County - Second Unit Resource Center

ADU California - a U.C. Berkeley scorecard of local ADU ordinances

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NGO Sites

APA|CA - Position statement on ADU Standards by American Planning Association - California Chapter

Californians for Home Ownership - an L.A. based housing advocacy group

Housing Trust - Silicon Valley - Santa Clara County housing trust

Accessory Dwellings - a volunteer ADU advocacy group based in Portland

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Commercial Sites

Google: ADU Images | Plans

AARP - The ABCs of ADUs

Dwell - online magazine of inspiring design

Houzz - online resource for ideas

Realtor Magazine - Your Questions About ADUs Answered

California's ADU allowance created a cottage industry, so to speak, that has seemingly popped up overnight. There are now numerous consultants and fabricators all with stylish websites vying for your attention and dollars. Below are links to some of these sites that you may find useful or interesting.

Inclusion of these here is not an endorsement by Alaco. They're simply provided to offer a comparison of competing alternatives.

Like the legislation that promotes ADUs, most of these companies are relatively new. As with any startup, particularly in an uncertain economy, their future viability is surely precarious. It should go without saying that you ought to be especially cautious when committing to a six figure purchase.

Also, before purchasing an online course, book or consultation, consider that all the information you probably need is already available on the Internet for free. We hope that we provide or otherwise link to much of it right here.

Abodu - a Bay Area ADU fabricator - intro article

Alternative Living Spaces - a shipping container ADU fabricator ~$100k

Bay Modular - an Oakland based ADU fabricator

Blu Homes - Vallejo based prefab dwelling maker

Building an ADU.com - an online ADU consultant offering courses and books

California Modulars - a San Jose based design / Stockton based prefab firm

Habitat - a Bay Area based ADU fabricator

Maxable - a California ADU consulting firm

Modative - a Los Angeles based design-build firm

Modern Empathy - a Bay Area based modular ADU design/build firm

prefabADU - a Fairfield based ADU fabricator

Google Sites

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