County directory

San Mateo County ADU rules

Each place name links to that city or county's own ADU page. Places with a 'See our rules summary' button also have our plain-language summary of the local ADU rules, with sources. Each place below says whether we show local rules or California state rules.

Places in San Mateo County

Atherton (opens the government site in a new tab)
Showing California state rules
We don't have Atherton's own ADU rules on file, so this shows the California state rules that apply across the state. Check with Atherton for local details.
Belmont (opens the government site in a new tab)
Showing California state rules because Belmont's local rules may conflict with state law or are being challenged
We show the state rules for a 2020 ADU ordinance with a one-ADU limit and owner-occupancy rules that the state found out of compliance in December 2025. Check with Belmont about how it handles this today.
Brisbane (opens the government site in a new tab)See our rules summary
Showing Brisbane city rules
These are Brisbane's own ADU rules on file, shown with the California state rules they build on. Each item says which is which.
Where a Brisbane rule may conflict with state law or is being challenged, we show the California state rule instead. This covers a one-ADU limit outside the state ADU types, limits on pairing a junior ADU with an ADU, front setbacks, lot coverage and floor area limits, detached ADU height, parking in the R-BA and PD districts, and owner occupancy for all junior ADUs.
Burlingame (opens the government site in a new tab)See our rules summary
Showing Burlingame city rules
These are Burlingame's own ADU rules on file, shown with the California state rules they build on. Each item says which is which.
Where a Burlingame rule may conflict with state law or is being challenged, we show the California state rule instead. This covers a 50% size cap, front setbacks and lot-coverage limits that may block an 800 sq ft attached ADU, and parking exemptions that leave out some state exemptions.
Colma (planning page) (opens the government site in a new tab)
Showing California state rules
We don't have Colma's own ADU rules on file, so this shows the California state rules that apply across the state. Check with Colma for local details.
Daly City (opens the government site in a new tab)
Showing California state rules
We don't have Daly City's own ADU rules on file, so this shows the California state rules that apply across the state. Check with Daly City for local details.
East Palo Alto (opens the government site in a new tab)
Showing California state rules because East Palo Alto's local rules may conflict with state law or are being challenged
We show the state rules for owner-occupancy rules for junior ADUs, parking exemptions that leave out some state exemptions, and a 2024 ordinance that cites repealed state law sections. Check with East Palo Alto about how it handles this today.
Foster City (opens the government site in a new tab)See our rules summary
Showing Foster City city rules
These are Foster City's own ADU rules on file, shown with the California state rules they build on. Each item says which is which.
Half Moon Bay (opens the government site in a new tab)
Showing California state rules because a local rule change is pending
A local rule change is pending. The whole city is in the Coastal Zone, where ADUs must also meet the City's Local Coastal Program. The City is amending its ADU ordinance after state review, and draft changes are with the state and the Coastal Commission. We'll add the new local rules after they take effect and we've reviewed them.
Hillsborough (opens the government site in a new tab)See our rules summary
Showing Hillsborough city rules
These are Hillsborough's own ADU rules on file, shown with the California state rules they build on. Each item says which is which.
Where a Hillsborough rule may conflict with state law or is being challenged, we show the California state rule instead. This covers a 20 ft front setback and lot-coverage and open-space limits that apply even when they would block an 800 sq ft ADU, and yearly rent reporting by ADU owners.
Menlo Park (planning page) (opens the government site in a new tab)See our rules summary
Showing Menlo Park city rules
These are Menlo Park's own ADU rules on file, shown with the California state rules they build on. Each item says which is which.
Where a Menlo Park rule may conflict with state law or is being challenged, we show the California state rule instead. This covers a 50% size cap for attached ADUs that applies even when it would block an 800 sq ft ADU.
Millbrae (opens the government site in a new tab)
Showing California state rules because Millbrae's local rules may conflict with state law or are being challenged
We show the state rules for owner-occupancy rules for ADUs and junior ADUs, and a code that cites repealed state law sections. Check with Millbrae about how it handles this today.
Pacifica (opens the government site in a new tab)
Showing California state rules
We couldn't read this city's ADU code yet, so we're showing California state rules. Check with the city before you plan.
City ADU page: https://www.cityofpacifica.org/departments/community-development/accessory-dwelling-units
Portola Valley (opens the government site in a new tab)
Showing California state rules
We don't have Portola Valley's own ADU rules on file, so this shows the California state rules that apply across the state. Check with Portola Valley for local details.
Redwood City (opens the government site in a new tab)See our rules summary
Showing Redwood City city rules
These are Redwood City's own ADU rules on file, shown with the California state rules they build on. Each item says which is which.
Where a Redwood City rule may conflict with state law or is being challenged, we show the California state rule instead. This covers a 50% size cap for attached ADUs with no stated minimum size.
San Bruno (opens the government site in a new tab)See our rules summary
Showing San Bruno city rules
These are San Bruno's own ADU rules on file, shown with the California state rules they build on. Each item says which is which.
Where a San Bruno rule may conflict with state law or is being challenged, we show the California state rule instead. This covers front setbacks that are not reduced to fit an 800 sq ft ADU, and parking exemptions that leave out some state exemptions.
San Carlos (opens the government site in a new tab)
Showing California state rules because a local rule change is pending
A local rule change is pending. The City is updating its ADU ordinance to match state law, with a Planning and Transportation Commission hearing scheduled for November 16, 2026. We'll add the new local rules after they take effect and we've reviewed them.
San Mateo (planning page) (opens the government site in a new tab)
Showing California state rules because San Mateo's local rules may conflict with state law or are being challenged
We show the state rules for owner-occupancy rules for junior ADUs, a junior ADU size limit above the state maximum, front setbacks and parking rules for new ADUs, and an ordinance that cites a repealed state law section. Check with San Mateo about how it handles this today.
South San Francisco (opens the government site in a new tab)
Showing California state rules because South San Francisco's local rules may conflict with state law or are being challenged
We show the state rules for a deed restriction requirement for ADUs. Check with South San Francisco about how it handles this today.
Woodside (opens the government site in a new tab)See our rules summary
Showing Woodside city rules
These are Woodside's own ADU rules on file, shown with the California state rules they build on. Each item says which is which.
Where a Woodside rule may conflict with state law or is being challenged, we show the California state rule instead. This covers owner-occupancy rules for junior ADUs (required even when the junior ADU has its own bathroom) and parking exemptions that leave out some state exemptions.
Unincorporated San Mateo County (opens the government site in a new tab)
Showing California state rules because a local rule change is pending
A local rule change is pending. The County says it is updating its non-coastal ADU rules to match recent state laws, including 2026 changes. We'll add the new local rules after they take effect and we've reviewed them.

All counties in the ADU directory