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Glossary Term

ADUs Definition

Accessory dwelling units can create potential additional rental income, but buyers review zoning, cost, access, parking, rent rules, and execution risk.

By Don Favia · Updated September 17, 2026

Direct Answer

An accessory dwelling unit (ADU) is a self-contained home on the same lot as an existing or proposed primary residence, including a single-family or multifamily building. It can be attached or detached and has its own permanent facilities for living, sleeping, eating, cooking and sanitation. [1] Accessory dwelling units can create potential additional rental income, but buyers review zoning, cost, access, parking, rent rules, and execution risk.

Check the Property Before Counting the Income

The definition does not establish that another unit can be built on your lot. Use California's ADU definition as a starting point, then ask a qualified architect and the local planning or building department to review the proposed space. For sale preparation, see the ADU potential guide.

This is for general informational purposes only. Consult with your CPA, tax advisor, and/or attorney for guidance specific to your situation. Consult a qualified architect or structural engineer and the applicable building department for property-specific construction, safety and approval questions.

Sources

  1. [1] California Government Code section 66313(a), ADU definition