Half Moon Bay Accessory Dwelling Unit (ADU) Standards

        New laws were recently passed, and updates will be coming soon


Community Development Department – 650.726.8270

ADU Ordinance

Zones allowed

All residential zones (R-1, R-2, R-3) and mixed use zones with a single-family dwelling (use permit required)
Lot restrictions

Must be developed with a be single-family dwelling

Minimum lot size

None, but minimum site area for zoning district applies

Min / Max ADU size

150 sf / 700 sf

ADU building height

Attached two story: 28 feet

Attached one story: 20 feet

Detached two story: 22 feet

Detached one story: 13 feet


5 feet side, 10 feet rear, front same as primary dwelling which is either 20 or 25 feet depending on zoning district

Parking requirements

One parking space is normally required unless state exemptions are met (ADU is within 1⁄2 mile of transit, in existing structures, in historic districts, within one block of car share locations, or in an area with residential parking permit rules that do not allow second units to get a permit). Tandem parking and parking in setbacks are allowed. Exceptions to parking requirements are provided for.

Owner occupancy

Owner must live in the main dwelling or the ADU

Sample fees from recently built projects*

ADU 1 (609 sf, attached): $4,612 (does not include water fee)

ADU 2 (682 sf, detached): $4,512 (does not include water fee)

Other requirements
  • If the existing single-family dwelling has fire sprinklers, the ADU must be sprinklered regardless of whether attached or detached; and similarly, if the single-family dwelling is not sprinklered the ADU is not required to be sprinklered.
  • Generally siding, trim, roofing shall match those of the single-family dwelling in terms of color, material, roof pitch, etc. Some variations may be allowed for detached structures in so far as the building form is smaller.
  • No separate sewer or water connections required, although a separate water meter is required by the water district.
  • The City has a standard tree preservation ordinance; proposals for removals must be approved through that process. The City works with applicants to preserve trees through site planning and also allows for removals if necessary to facilitate reasonable development.
  • Daylight Plane applies only to two-story residential structures, and if changes are necessary they can usually be met with changes to roof type.
  • Only one ADU per property is allowed, however a guesthouse is also permitted.
  • ADUs must comply with all requirements of the underlying zoning district.

If the ADU conforms to the zoning code (setbacks, height, etc.), the approval letter is drafted, notice is provided, and the ADU is approved by the Community Development Director pursuant to the notice. If an ADU does not conform such that a variance is required, it is processed through the Planning Commission. A Coastal Development Permit is required, which is a discretionary permit subject to public notice but not public hearing. Making an appointment to meet with a planner in the initial stages of the project can help avoid challenges and is highly recommended.


Exceptions to parking requirements are provided for.

Disclaimer: standards and process may vary. Consultation with the contact is recommended before starting any project.

*Fees are specific to each project and will vary. Fees change regularly. These are provided as examples only.

Download ADU Standards PDF

Updated: 12/11/2017