California · San Mateo
In Half Moon Bay you can build a detached ADU up to 800 sq ft guaranteed (1200 sq ft ceiling), 16 ft tall, set back 4 ft from side and rear property lines. Owner-occupancy is not required. Parking is capped at 1 space and is waived entirely in six situations, including within half a mile of transit. Because the state found Half Moon Bay's ordinance non-compliant, these are state figures and the city's own ordinance does not currently govern.
Gov. Code §§ 66310–66342 · 38 of 51 fields checked against statute textCalifornia's Department of Housing and Community Development reviewed Half Moon Bay's accessory dwelling unit ordinance and found it does not comply with State ADU Law. Under Gov. Code § 66316 a non-compliant ordinance is null and void in its entirety, and state standards apply instead. Every figure below therefore comes from state statute, not from the city's code.
Not in force
All 20 of them, word for word. Nothing here is paraphrased, because paraphrasing a legal requirement is how error gets in.
All 51 fields via API · 38 verified against statute text
Important, and worth checking before you rely on it: the state reviewed Half Moon Bay's ADU rules on 2024-11-06 and said they break state law. When that happens the law says the city's rules stop counting and the state's rules apply instead, which is usually better for you because the state's are more generous. A city is allowed to disagree with the state and keep its rules in place while it argues, so this is a strong position to take rather than a settled fact. The practical move: if a planner quotes you something stricter than the numbers below, ask which rule they are relying on given the state's findings, and confirm with the planning department whether the city has since fixed its ordinance.
What you can build. You can build a separate building in the yard, an addition attached to your house, or a conversion of space you already have, like a garage.
How many. On a normal single-family lot you can have 1 ADU, plus 1 "junior" ADU, which is a small unit carved out of the existing house.
How big. The city has to let you build at least 800 square feet. If you want two or more bedrooms, it has to allow up to 1000 square feet. For reference, 800 sq ft is roughly a one-bedroom apartment, about the size of a two-car garage.
How close to the property line. You need to leave 4 feet on the sides and 4 at the back. That is measured from your property line, not from the fence, and those are not always in the same place. If you are converting a garage that already sits closer than that, you can generally keep it where it is.
How tall. Up to 16 feet, which is a single storey with a normal roof. If your lot is within a half mile walk of a major transit stop, you get 18 feet instead.
Parking. You may need to add 1 parking space, but there are a lot of exemptions. The big one: if you are within a half mile walk of public transit, no parking is required. And if you convert your garage, nobody can make you rebuild the parking you lost.
California's Department of Housing and Community Development found it non-compliant on 2024-11-06. Under Gov. Code § 66316 a non-compliant ADU ordinance is null and void in its entirety and state standards apply instead. The city may disagree and contest the findings, so confirm current status with the planning department.
4 feet from the side and rear property lines (Gov. Code s 66323(a)(2)). No setback at all is required if you convert an existing structure such as a garage that already sits closer (Gov. Code § 66314(a)(7)).
16 feet for a detached ADU (Gov. Code s 66321(b)(4)(A)), rising to 18 feet within half a mile walking distance of a major transit stop, plus 2 more feet to match the roof pitch of the main house. Attached ADUs may reach 25 feet or the primary dwelling's limit, whichever is lower.
No. California bars a local agency from imposing an owner-occupant requirement on an ADU (Gov. Code s 66315). A junior ADU is different: owner-occupancy can still be required there.
At most one space (Gov. Code s 66314(d)(10)(A)), and six statutory exemptions remove it entirely, including within half a mile walking distance of public transit, within a historic district, or with a car share vehicle within one block (Gov. Code § 66322(a)). Converting a garage never obliges you to replace the lost parking.
No. Rentals shorter than 30 days are barred, and for units approved on the by-right track that bar is mandatory rather than optional (Gov. Code § 66323(e)).
How Half Moon Bay's neighbours fared in the same review process.
Across San Mateo County the state has reviewed 8 ordinances and found 8 of them non-compliant.
Rather than list contractors we cannot evidence, this stays empty until Half Moon Bay publishes permit records naming them or licence matching reaches the city. The cities already covered show how the ordering works, and whichever contractor you use, the rules above are the ones that govern the job.