Planning · Glossary
Accessory Dwelling Unit
Updated 2026-07-18
Accessory Dwelling Unit is an independent residential unit located on the same legal parcel as a proposed or existing primary dwelling. California law limits many local barriers to ADUs, but site constraints, utilities, fire safety, and objective standards still apply.
What it means
An ADU may be attached, detached, or created within existing space and includes permanent living, sleeping, cooking, and sanitation facilities.
Why it matters for land decisions
ADU potential can add housing value, but it should not be assumed from lot size alone.
- Confirm a lawful primary dwelling.
- Check water and wastewater capacity.
People also ask
Does every California parcel qualify for an ADU?
No. State protections are broad, but eligibility depends on residential use and applicable health, safety, site, and statutory rules.
Can an ADU use a septic system?
Potentially, if the onsite wastewater system and site can support the added flow and the enforcing agency approves it.
Official sources
Related terms
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