Bay Area ADU Setbacks, Height, and Lot Coverage Rules Explained

California's statewide ADU law overrides most local zoning. If your city's rules are more restrictive than the state minimums below, the state minimums win. Here's what actually applies in 2026 to a detached ADU on a single-family lot in the Bay Area.

Setbacks

• Side and rear setback: 4 feet minimum. Cities cannot require more.
• Front setback: follows your underlying zoning (usually 15 – 25 ft).
• Existing structures: if you convert an existing garage or accessory structure, no new setback applies, even if it's already at the property line.

Height

• 16 ft, anywhere in California by right.
• 18 ft, single-story ADU within ½ mile of a major transit stop or on a multi-family lot.
• 25 ft, two-story ADU on a lot with an existing multi-family or single-family home, capped by underlying zoning.

Lot coverage, FAR, and open space

The state explicitly prevents cities from using lot coverage, floor area ratio (FAR), or open-space requirements to block an 800 sq ft, 16-ft tall ADU with 4-ft setbacks. That single sentence is why almost every Bay Area lot, even small ones in Sunnyvale and San Jose, can fit at least one ADU.

Parking

No replacement parking required if the ADU is within ½ mile of public transit, in a historic district, part of an existing structure, or in an area where on-street permits are required but not offered to ADU tenants. In practice that covers most of the peninsula and South Bay.

What this means for your lot

If anyone tells you your Bay Area lot is "too small for an ADU," they're almost certainly wrong. The state floor of 800 sq ft at 16 ft tall with 4-ft setbacks fits on the overwhelming majority of single-family lots in the region.

See Bay Area ADU cost & city rules →