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HCD March 2026State-law screen

California ADU
Height Screen

Identify the minimum height limit a compliant local ordinance must allow for the entered, verified path. State law itself does not establish a universal maximum, and local rules may permit more.

Who it's for: California architects and homeowners screening the state-law ADU height floor at pre-design, before confirming the local ordinance.

How to use this calculator

1
Verify the project path
Distinguish detached, attached, and qualifying conversion work.
2
Verify controlling facts
For detached work, verify transit/HQTC and multifamily-multistory status. For attached work, enter the current primary-dwelling zoning height limit.
3
Read the minimum local limit
The result is not a universal project maximum; verify the current local ordinance and all building standards.

The formula

Detached: 16-foot baseline; 18 feet for the verified transit/HQTC path, with an additional 2 feet only to accommodate roof pitch aligned with the primary dwelling; 18 feet on a lot with an existing or proposed multifamily, multistory dwelling. Attached: the lower of 25 feet and the primary-dwelling height limit in the local zoning ordinance. Conversion: original structure dimension.

Worked example

Example
A detached ADU with verified transit/HQTC eligibility and an aligned roof pitch returns 20 feet as the minimum height limit the local agency must allow. If transit eligibility is unknown, the screen returns a range and refuses one exact result.

When this estimate will be off

  • The screen does not establish transit/HQTC eligibility; HCD directs applicants first to the metropolitan planning organization and then the local agency where needed.
  • State ADU Law contains no universal height maximum; the result is a floor below which a compliant local limit may not be imposed.
  • Building standards, grade and height measurement, local allowances, Coastal Zone rules, site constraints, and entitlement are not evaluated.
  • A conversion remains limited to the original structure dimension and must satisfy applicable building, health, safety, and fire standards.

Frequently asked questions

A common mistake: The screen does not establish transit/HQTC eligibility; HCD directs applicants first to the metropolitan planning organization and then the local agency where needed.

No. HCD describes the extra two feet within the qualifying transit/HQTC path and only to accommodate roof pitch that aligns with the primary dwelling.

No. The minimum local height limit is the lower of 25 feet and the height limit applying to the primary dwelling in the local zoning ordinance.

No. It is the state-law minimum a compliant local height limit must allow for the entered path. Local rules may allow more.

Sources

  • California HCD ADU Handbook, March 2026 — Height Requirements — official guidance for detached, transit/HQTC, multifamily-multistory, attached, conversion, and story treatment
  • California Government Code §66321(b)(4) — minimum height-limit framework; verify current statutory text and applicable project path

Sources and review record

Sources and method basis

Limitations

  • Minimum local height-limit screen only; does not establish transit/HQTC eligibility, a universal maximum, local allowances, height measurement, building/fire code, Coastal Zone requirements, site constraints, or entitlement.

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