Half Moon Bay Has 4,280 Single-Family Homes. Most Could Qualify for a JADU.

What a JADU Is

Of the 4,280 single-family parcels in this market's parcel record, the median home measures 1,970 square feet of interior space. That means most Half Moon Bay houses have a bedroom, a bonus room, or an attached garage that could, on paper, become a legal junior accessory dwelling unit—without adding a square foot to the building envelope.

A junior accessory dwelling unit (JADU) is defined under California law as a unit that is no more than 500 square feet of interior livable space, contained entirely within a single-family residence, and may include separate sanitation facilities or share them with the existing structure. That 500-square-foot ceiling is measured in interior livable space—a definition that was tightened by AB 1154, which made various changes to state JADU law and went into effect on January 1, 2026.

The unit has to be inside the house. JADUs are not allowed in detached accessory structures; the creation of a JADU must be within the single-family residence. An attached garage counts as part of the residence for this purpose, so converting one is generally permitted under state law.

Half Moon Bay's homes, from the record

5,104 of 5,942 parcels in this market's record have a known build year.

How a JADU Differs from a Standard ADU

The two unit types are frequently confused, but they operate under different statutes and carry different requirements.

ADUs can be up to 1,200 square feet and may be detached, attached, or converted from existing space. In contrast, JADUs are limited to 500 square feet and must be created within an existing or proposed single-family home.

The kitchen standard is also different. ADUs must include a full kitchen with a sink; JADUs only require an efficiency kitchen and are not required to have a private bathroom. That lower threshold is what makes JADUs cheaper to build—no full plumbing gut, no separate utility connection required in most cases.

One of the most consequential differences involves who can be on the property at all. On a single-family lot, state law allows up to three accessory units: one detached ADU, one conversion ADU, and one JADU. The JADU and a detached ADU can coexist on the same lot, which is relevant to Half Moon Bay owners who want to maximize their options.

Another key distinction: a local agency cannot impose an owner-occupancy requirement on any ADU. JADUs carry a different rule, described below.

Owner-Occupancy: The Rule That Changed in 2026

This is where JADU law is more restrictive than standard ADU law—and where it shifted materially at the start of this year.

Under AB 1154, effective January 1, 2026, the owner-occupancy requirement for JADUs is now tied directly to whether the unit shares a bathroom. If the JADU has shared sanitation facilities with the existing structure, owner-occupancy is required in the single-family residence in which the JADU will be permitted; the owner may reside in either the remaining portion of the structure or the newly created JADU. Owner-occupancy shall not be required if the JADU has separate sanitation facilities, or if the owner is another governmental agency, land trust, or housing organization.

In plain terms: add a private bathroom to the JADU and you—the owner—do not have to live on the property. Leave it sharing the main house bathroom, and you do. For a Half Moon Bay owner converting a bedroom into a rental unit while planning to move elsewhere, that distinction matters before a single permit is pulled.

JADUs cannot be used as short-term rentals and, if rented, must be rented for longer than 30 days. That rule applies regardless of sanitation configuration, and it is a change from prior law.

The Deed Restriction

Every JADU requires a recorded deed restriction. The restriction must run with the land, be filed with the permitting agency, and include a prohibition on the sale of the JADU separate from the sale of the single-family residence. The restriction must also include a limitation on the size and attributes of the JADU that conforms with state law. This deed follows the property when it sells, so future owners are bound by the same rules.

Note that this requirement is specific to JADUs. A local agency cannot impose a deed restriction on a standard ADU.

Half Moon Bay's Ordinance—and Its Current Status

The City of Half Moon Bay adopted ADU Ordinance No. 2021-01 in August 2021, which covers JADU provisions under Municipal Code Section 18.33. HCD reviewed that ordinance and found it fails to comply with state ADU and JADU laws in several respects. Among the specific findings: the city's ordinance improperly restricted JADUs in garages in the Ocean Colony area, and it limited lots to one ADU where state law allows more combinations. HCD required the city to respond to its findings no later than December 6, 2024.

It is not confirmed in this session's searches whether Half Moon Bay has adopted a revised ordinance since that HCD review. Until the city updates its code, state law controls. The local agency shall apply the standards established in state law for the approval of JADUs unless and until the agency adopts an ordinance that complies with state requirements. Confirm current local requirements with the City of Half Moon Bay Community Development Department before submitting any application.

Parking

Local agencies may not require parking as a condition to permitting a JADU, even when the JADU is converted from an attached garage. This means converting your garage into a JADU does not trigger a requirement to replace the lost parking space under state law.

What to Do Before You Start

Permits for JADUs are processed ministerially—no public hearing, no discretionary review. The permitting agency must determine whether a JADU application is complete and provide written notice not later than 15 business days after receiving the application; the agency must then approve or deny the application within 60 days from the date it receives a completed application if there is an existing single-family dwelling on the lot.

Before submitting, owners should sort out three things with the appropriate professionals: whether the proposed space meets the interior livable space limit (a licensed contractor or designer can measure this), whether adding a private bathroom is practical given existing plumbing (a licensed contractor), and what the deed restriction will mean for any future sale (a real estate attorney). The building permit is issued by the City of Half Moon Bay Building Division.

Where to Check

• California HCD ADU Handbook (March 2026) — Full state requirements for JADUs, owner-occupancy rules, deed restrictions, and recent law changes
• HCD Review Letter: City of Half Moon Bay ADU Ordinance (November 2024) — HCD's specific findings on Half Moon Bay Ordinance No. 2021-01
• California Government Code § 66333 (JADU Article 3) — The current statutory text governing JADUs, including owner-occupancy and deed restriction requirements
• HCD ADU/JADU Housing Law Fact Sheet (April 2026) — Plain-language summary of current state ADU and JADU rules
• California State Fire Marshal Information Bulletin 25-004 on ADUs/JADUs — Fire and life safety standards applicable to JADUs

Tim McMullen · CA DRE #02016832
[email protected] · (415) 691-9272