Quick Answer: There is no minimum lot size required to build an ADU in San Jose, California as of 2025. California state law (AB 68, SB 9, and related ADU bills) prohibits local jurisdictions from imposing minimum lot size requirements for ADUs. This means even a small San Jose lot (4,000-5,000 sq ft) can have an ADU added if it meets the setback requirements (typically 4-foot rear and side setbacks for ADUs under 16 feet in height) and the ADU complies with size limits (maximum 850 sq ft for 1-bedroom, 1,000 sq ft for 2-bedroom, or 50% of the main house size up to 1,200 sq ft). However, small lots may have little or no space remaining after accounting for the main house footprint and required setbacks — the practical constraint for small lots is often buildable area, not a minimum lot size rule.
ADU Site Requirements in San Jose 2025 (No Minimum Lot Size)
Helpful Resources:
| Requirement | San Jose Standard (2025) | State Minimum (applies if city is more restrictive) |
|---|---|---|
| Minimum lot size | No minimum | No minimum (state preempts local minimums) |
| Rear setback (ADU under 16 ft) | 4 feet | 4 feet |
| Side setback (ADU under 16 ft) | 4 feet | 4 feet |
| Front setback | Match primary dwelling front setback | Match primary dwelling |
| Height limit (detached ADU) | 16 feet (may be up to 25 ft with setback increase) | 16 feet (25 ft near transit, 18 ft for 2-story garage conversions) |
| Maximum ADU size (studio/1BR) | 850 sq ft | 850 sq ft |
| Maximum ADU size (2+ BR) | 1,000 sq ft | 1,000 sq ft |
| Maximum ADU size (% of main house) | 50% of main dwelling, up to 1,200 sq ft | 50%, up to 1,200 sq ft |
| Owner-occupancy requirement | Required for JADU (not for standard ADU as of 2020) | Cannot require for standard ADU |
How to Check if Your San Jose Lot Can Fit an ADU
- Step 1 — Get your lot dimensions: From your property deed or the Santa Clara County Assessor’s website (assessor.sccgov.org). Typical San Jose R-1 lots are 50×100 to 60×120 feet
- Step 2 — Calculate your rear yard setback area: From the rear property line, measure 4 feet forward — this is where the rear wall of the ADU must be. From the side property lines, measure 4 feet — this is the side wall location
- Step 3 — Subtract the main house footprint: The ADU must be outside the main house footprint (unless it’s a garage conversion or JADU within the house). Identify how much rear yard remains after the main house and any required setbacks
- Step 4 — Check utility easements: Many San Jose lots have 5-10 foot utility easements along the rear property line. Permanent structures cannot be built within utility easements
- Step 5 — Free feasibility review: Quartz Construction offers free ADU site feasibility reviews to determine what size ADU is possible on your specific lot
Quartz Construction has built ADUs on small and standard San Jose lots — we assess your site for free and design to maximize livable space within the rules. Learn about ADU construction. CSLB #1003436 | Call (650) 749-7436.
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