San Mateo County · California
San Mateo ADU guide: local rules, permits & property planning
San Mateo publishes distinct new-unit, remodel and JADU permit fees. Its initial property checks also include FEMA flood mapping and heritage-tree protection, making the parcel review more than a setback exercise.
Local planning guide · Reviewed October 2, 2026
What matters for an ADU in San Mateo
Permitting authority: City of San Mateo — ADUs
Official local guidanceLocal rules and design checks
| Topic | Local guidance |
|---|---|
| Property screening | Use the City’s zoning lookup, FEMA flood information and heritage-tree requirements together. |
| JADU bathroom | When a JADU shares the main home’s bathroom, the City requires interior access. |
| Unpermitted units | The City provides an AB 2533 handout, construction-date affidavit and inspection checklist. |
Selected local requirements, not a complete zoning determination. Confirm the current rules for your address with the responsible agency.
Fees and budget checks
The reviewed City page lists permit fees of $2,831.57 for a new ADU, $2,031.12 for an ADU remodel and $1,454.02 for a JADU. These are published permit line items, not the total of construction, utility and all agency costs; reconfirm at application.
San Mateo ADU/JADU permit fee listHow to start the permit process
Identify the zoning and flood designation, then use the City’s ADU/JADU plan submittal guide. For legalization, assemble the dedicated construction-date and inspection materials instead of treating the work as an ordinary new unit.
Plan resource
San Mateo ADU plans gallery
The City links a plan gallery and a separate preapproved-plan submittal guide. These are design resources; City-listed drawings do not approve a specific lot.
View the original sourceSan Mateo ADU questions
- Does the listed $2,831.57 cover my whole project?
- No. It is the City’s published new-ADU permit fee, not an all-in project price.
- What should I bring for an older unpermitted unit?
- Start with the City’s AB 2533 materials, including its construction-date affidavit and inspection checklist.
Sources for this guide
Local sources reviewed October 2, 2026. Historical examples retain their stated dates. Contact ADU California to confirm project availability; this guide does not establish an office location or property approval.
A useful first review
Separate what is available from what still needs verification.
01
Confirm the property
Start with a complete address and review the available parcel, building, and map context.
02
Identify the unknowns
Keep missing setbacks, easements, utilities, access, hazards, and local requirements visible.
03
Choose the next review
Use the preliminary result to prepare a focused conversation with the required professionals and agencies.
Explore project types
Compare the scope before choosing a solution.
These pages explain the questions each project type introduces. They do not assert that a particular scope is permitted or suitable for your address.
Compare planning footprints
See common ADU sizes before choosing a design.
These model pages are planning references only. They are not a statement that a particular size is allowed or buildable at a San Mateo address.
California directory
Explore more city guides.
The next useful action
Put your address at the center of the conversation.
The online review is preliminary and is not a permit decision, survey, engineering opinion, construction document, final price, or guaranteed schedule.