ADU Regulations in Los Altos Hills, California (2026)

Regulations at a glance

Local rules & notes

Operable Door Restriction: The Town prohibits operable doors within 10 feet of any property line, effectively creating a 10-foot setback for entryways that exceeds state-mandated 4-foot setbacks. Primary Size Constraint: The Town defines the primary dwelling as the larger unit, which HCD notes cannot be used to preclude ADUs or restrict them below 800 square feet. Subjective Heritage Tree Standards: The Town requires replacement trees for 'damage' to heritage oaks during SB 9 construction without providing an objective standard for measuring such damage.

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

Frequently asked questions about ADU regulations in Los Altos Hills

• What is the maximum ADU size in Los Altos Hills, California?

  In Los Altos Hills, the maximum ADU size is typically 800 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; Los Altos Hills may follow state defaults or have local limits. Verify with Los Altos Hills planning for your specific lot.

• What are the setback requirements for ADUs in Los Altos Hills?

  In Los Altos Hills, 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 Los Altos Hills planning for overlay zones or design standards that could affect your site.

• What is the maximum height for an ADU in Los Altos Hills?

  In Los Altos Hills, 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 Los Altos Hills or county planning for your zone.

• Is ADU approval ministerial in Los Altos Hills?

  In Los Altos Hills, 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; Los Altos Hills planning can confirm the exact process.

• Are there parking requirements for ADUs in Los Altos Hills?

  In Los Altos Hills, 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 Los Altos Hills planning for your address.