ADU Regulations in Hillsborough, California (2026)

Regulations at a glance

Local rules & notes

Illegal Income Reporting & Deed Restrictions: The Town requires deed restrictions, income reporting, and neighbor noticing as conditions for ADU applications. HCD explicitly states these are unauthorized by State Law and must be removed. Excessive Front Setback: The Town imposes a 25-foot front setback. HCD flags this as non-compliant if it prevents the construction of an 800 sq ft unit with 4-foot side/rear setbacks. Multifamily Zone Restriction: The Town currently restricts ADUs to single-family zones. HCD mandates the ordinance be amended to allow ADUs in multifamily residential zones as required by State Law.

For the official ordinance and latest updates, check your city or county planning department.

Frequently asked questions about ADU regulations in Hillsborough

• What is the maximum ADU size in Hillsborough, California?

  In Hillsborough, the maximum ADU size is typically 1200 square feet, depending on whether the unit is attached or detached. California state law allows up to 1,200 sq ft for detached ADUs and 800 sq ft for attached in many jurisdictions; Hillsborough may follow state defaults or have local limits. Verify with Hillsborough planning for your specific lot.

• What are the setback requirements for ADUs in Hillsborough?

  In Hillsborough, typical setback requirements are 4 feet from the side property line and 4 feet from the rear. These may be reduced to 4 feet under California Government Code § 65852.2 where applicable. Check with Hillsborough planning for overlay zones or design standards that could affect your site.

• What is the maximum height for an ADU in Hillsborough?

  In Hillsborough, the maximum height for an ADU is generally 16 feet. State law often allows up to 16 feet for detached ADUs and up to 25 feet when within 4 feet of the property line in some cases. Confirm with Hillsborough or county planning for your zone.

• Is ADU approval ministerial in Hillsborough?

  In Hillsborough, ADU approval is typically Ministerial (by-right) per Gov Code §65852.2. Ministerial (by-right) review means the city must approve qualifying applications without discretionary review, per California Gov Code § 65852.2. Your project must still meet objective standards; Hillsborough planning can confirm the exact process.

• Are there parking requirements for ADUs in Hillsborough?

  In Hillsborough, parking for ADUs is generally Often waived per state law; check local ordinance. California law often waives parking for ADUs within a half-mile of transit or in certain historic districts. Check with Hillsborough planning for your address.