KNOWLEDGE BASE
ADU Knowledge Base
Authoritative guides to the laws, technical standards, and processes that govern ADU design and construction — applied across 337 city guides on this site.
Pick the topic that fits your project stage. Each guide covers what the rule means, who it applies to, and what it means for your permit.
LEGAL & REGULATORY
Laws That Govern ADUs
LEGAL
California ADU Law: AB 670 & Ministerial Approval Rights
State laws requiring California cities to approve ADU applications ministerially within 60 days, prohibiting owner-occupancy mandates, and voiding HOA bans on ADUs.
Cal. Gov. Code § 65852.2 LEGAL
Coastal Development Permit (CDP) for ADUs
A discretionary permit required for most development within California's Coastal Zone, adding 2–6 months to ADU project timelines and imposing conditions to protect coastal resources.
Cal. Pub. Resources Code § 30600 LEGAL
HOA ADU Rights in California: What Your HOA Can and Cannot Do
Under California Civil Code § 4751 (AB 670), HOA rules that effectively prohibit or unreasonably restrict ADU construction are void by law — even if they appear in your CC&Rs.
Cal. Civ. Code § 4751 LEGAL
JADU: Junior Accessory Dwelling Unit
A dwelling unit of up to 500 sq ft created entirely within an existing primary residence, with a separate entrance and efficiency kitchen, subject to California owner-occupancy requirements.
Cal. Gov. Code § 65852.22 TECHNICAL STANDARDS
Codes & Engineering Requirements
TECHNICAL
Seismic Design Category (SDC) for ADU Structures
A classification (A through F) that determines the structural system requirements, detailing, and engineering intensity for an ADU based on its location's earthquake hazard level.
TECHNICAL
Title 24 Energy Compliance for ADUs
California's mandatory energy efficiency code (Part 6 of the Building Standards Code) governing insulation, windows, mechanical systems, and solar PV for all new ADUs.
PROCESSES & COMPARISONS
How ADU Projects Work
PROCESS
ADU vs. Garage Conversion vs. Home Addition: Choosing the Right Path
A side-by-side comparison of the three main ways to add living space or a rental unit — detached ADU, garage-to-ADU conversion, and attached home addition — covering cost, permitting, and income potential.
PROCESS
The ADU Permit Process: From Application to Certificate of Occupancy
A step-by-step overview of how ADU building permits are applied for, reviewed, and approved in California—from pre-application through final inspection.
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