The statewide 4-foot rule
California Government Code 65852.2 sets a uniform minimum: new detached ADUs need only 4 feet of side and rear setback. Cities cannot impose larger setbacks for new construction up to 800 sq ft. This is one of the most important homeowner protections in current ADU law.
What setbacks apply where
- Side setbacks: 4 feet minimum from each side property line.
- Rear setback: 4 feet minimum from the rear property line.
- Front setback: Must match the existing front setback of the main house (the ADU cannot project further forward).
- Between buildings: Most cities require at least 6 feet between the main house and detached ADU for fire safety.
When you can build closer than 4 feet
- Garage conversions: If the existing garage already sits within 4 feet of a property line, you can convert it without changing the footprint.
- Existing structures: Converting an existing shed or accessory structure preserves its current setback.
When you must build farther than 4 feet
- Larger ADUs: ADUs over 800 sq ft may have to comply with the underlying zoning setbacks, which can be 5, 10, or more feet.
- Coastal zones: Coastal Commission jurisdiction can override the 4-foot rule.
- Fire hazard zones: Designated very high fire hazard severity zones may impose larger setbacks.
- Easements: Utility, drainage, or access easements override setback minimums.
How to measure your buildable area
- Walk your property line and confirm where each line actually is. Order a property survey if you are unsure.
- Subtract 4 feet from each side and rear line. The remaining area is your by-right ADU buildable zone.
- Subtract any easements or utility lines crossing the lot.
The remaining footprint is what an experienced ADU builder will design within.
Related reading
Frequently asked questions
Can my city require a 10-foot setback? Not for detached ADUs up to 800 sq ft. State law overrides local ordinances.
Does the 4-foot setback apply to attached ADUs? Attached ADUs follow the main house's setback rules.
What if my neighbor's house is right on the property line? Your ADU still gets the 4-foot setback. Fire-rated wall construction may be required.