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HCD March 2026State-law path screen

California ADU
Setback Screen

Identify the state-law setback path for a project configuration you have already verified. This screen does not determine parcel boundaries, local standards, Coastal Zone requirements, fire separation, or entitlement.

Who it's for: California architects and homeowners screening the ADU setback path at pre-design, before permit application.

State-law setback path
Confirm the project path before selecting it

How to use this calculator

1
Verify the legal project path
Distinguish new construction from a qualifying conversion or same-location, same-dimension replacement.
2
Identify Coastal Zone status
HCD states that additional setbacks may apply where required by a local coastal program.
3
Read the bounded state-law result
Use it as a starting point, then verify the current local ordinance and parcel constraints.

The formula

March 2026 HCD guidance states: new attached or detached ADUs may be subject to side and rear setbacks of no more than four feet. No setback is required for an ADU or JADU within a qualifying existing living area or accessory structure, or for a new ADU in the same location and to the same dimensions as an existing structure. A local front setback may apply to the general path but cannot preclude an ADU of at least 800 square feet.

Worked example

Example
A verified new attached ADU outside the Coastal Zone receives the state-law baseline: local side and rear setbacks cannot exceed four feet; a local front setback may apply but cannot preclude an ADU of at least 800 square feet. This is not a parcel approval.

When this estimate will be off

  • The user must verify which statutory path applies; the screen does not establish eligibility.
  • Local objective standards, the protected 800-square-foot configuration, property boundaries, easements, building and fire code, utilities, overlays, and title restrictions are not evaluated.
  • Additional Coastal Zone setbacks may apply where required by a local coastal program.
  • State law does not establish the distance between an ADU and other structures; applicable local and building/fire-safety requirements still require review.

Frequently asked questions

A common mistake: The user must verify which statutory path applies; the screen does not establish eligibility.

Yes. HCD’s March 2026 guidance says a side and rear setback of no more than four feet shall be required for an attached or detached ADU.

No. It reports that result only after you select a qualifying existing-envelope or same-location, same-dimension replacement path. Eligibility and other safety requirements must be verified.

Yes on the general path, but HCD states that it cannot preclude an ADU of at least 800 square feet. Other statutory paths may restrict local standards differently and need separate eligibility review.

Sources

  • California HCD ADU Handbook, March 2026 — Setbacks — official state guidance on four-foot side/rear limits, existing/replacement footprints, front-setback protection, Coastal Zone caveat, and structure separation
  • California Government Code §§66314, 66321 and 66323 — current statutory framework; verify the applicable section and current text for the project path

Sources and review record

Sources and method basis

Limitations

  • State-law path screen only; user must verify path eligibility, parcel and Coastal Zone status, local objective standards, protected configuration, boundaries, easements, building/fire code, utilities, overlays, and entitlement.

This free California ADU Setback Calculator is built and maintained by DataDrivenAEC, using the relevant codes and standards. It does not substitute for professional judgment.