Quick Answer: California ADU building code 2025 requires: minimum 150 sq ft, maximum 1,200 sq ft (detached); 4-foot rear and side setbacks; maximum 16-foot height (detached); separate bathroom and kitchen; fire sprinklers if required by local code; and Title 24 energy compliance. Cities cannot impose stricter standards than state law allows.
California ADU Building Code Requirements 2025
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California’s ADU laws have been significantly streamlined since 2020. State law now preempts many local restrictions, making it easier than ever to build an ADU in San Jose and throughout the Bay Area. Here’s what the current code requires.
ADU Size Requirements (2025)
- Minimum size: 150 sq ft (efficiency unit)
- Maximum size — detached ADU: 1,200 sq ft (or 50% of primary dwelling, whichever is larger, up to 1,200)
- Maximum size — attached ADU: 50% of primary dwelling square footage
- JADU maximum: 500 sq ft (must be within the primary dwelling)
- Note: Cities cannot impose smaller maximums than state law (AB 2221)
Setback Requirements
- Standard new construction ADU: 4-foot rear setback, 4-foot side setback (state minimum — cities cannot require more)
- Converted existing structure (garage, shed): Uses existing setbacks — no new setback compliance required
- Front setback: Same as primary dwelling; ADUs generally cannot be built in front yards
- Separation from primary dwelling: Detached ADU must be on the same lot, no minimum separation required by state law
Height Limits
- Standard detached ADU: 16 feet maximum height
- Detached ADU within 1/2 mile of transit: Up to 18 feet allowed in some jurisdictions
- Attached ADU: Must not exceed height of primary dwelling
- ADU above garage: 25 feet in many jurisdictions (per AB 2221)
Utility and Systems Requirements
- Separate address: ADUs must have their own address for 911 purposes
- Utility connections: Can share utilities with primary home or have separate metering (detached ADUs often get separate meters for rental purposes)
- Electrical: Must meet current NEC requirements; AFCI and GFCI protection required
- Plumbing: Separate bathroom and kitchen required for ADU (vs. JADU which can share bathroom)
- Fire sprinklers: Required only if primary dwelling is required to have them (San Jose does not require residential sprinklers for most remodels)
- Energy efficiency: Title 24 compliance required; ADUs typically require all-electric systems under current California code
Quartz Construction navigates all California ADU building code requirements for San Jose homeowners. Learn more about ADU construction. CSLB #1003436 | BBB A+ | 4.9⭐. Call (650) 749-7436.
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