ADU Regulations in Portola Valley, California (2026)

Regulations at a glance

Local rules & notes

Fire Safety Prohibitions: The town attempted to prohibit ADUs on parcels smaller than one acre with narrow access roads (<18ft) due to fire risk, which HCD ruled cannot apply to state-exempt ADUs. Easement-Based Setbacks: The town tried to measure setbacks from the edge of easements (roads, trails, utilities) rather than the property line. Triple Unit Combination: HCD clarified that homeowners are entitled to a converted ADU, a JADU, AND a detached ADU on the same lot.

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

Frequently asked questions about ADU regulations in Portola Valley

• What is the maximum ADU size in Portola Valley, California?

  In Portola Valley, the maximum ADU size is typically 1700 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; Portola Valley may follow state defaults or have local limits. Verify with Portola Valley planning for your specific lot.

• What are the setback requirements for ADUs in Portola Valley?

  In Portola Valley, 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 Portola Valley planning for overlay zones or design standards that could affect your site.

• What is the maximum height for an ADU in Portola Valley?

  In Portola Valley, 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 Portola Valley or county planning for your zone.

• Is ADU approval ministerial in Portola Valley?

  In Portola Valley, 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; Portola Valley planning can confirm the exact process.

• Are there parking requirements for ADUs in Portola Valley?

  In Portola Valley, parking for ADUs is generally true. California law often waives parking for ADUs within a half-mile of transit or in certain historic districts. Check with Portola Valley planning for your address.