San Mateo County · California
Foster City ADU guide: local rules, permits & property planning
Foster City links a 2026 ADU handbook, a neighbor-notification form and pre-reviewed detached plans. Its planning appointment and eTRAKiT resources provide a practical route from concept to application.
Local planning guide · Reviewed October 2, 2026
What matters for an ADU in Foster City
Permitting authority: Foster City — ADU guidance and 2026 handbook
Official local guidanceLocal rules and design checks
| Topic | Local guidance |
|---|---|
| Current checklist | Use the City’s 2026 handbook and ADU checklist rather than an older regional summary. |
| Plan review | Pre-reviewed drawings still need the City’s property-specific submittal materials. |
| Existing unpermitted unit | The City provides a separate AB 2533 resource for qualifying units built before January 1, 2020. |
Selected local requirements, not a complete zoning determination. Confirm the current rules for your address with the responsible agency.
Fees and budget checks
Ask Building for a current valuation-based estimate. The regional ADU Resource Center reports a historical 2021 detached 564-square-foot example with a $7,600.71 building-permit fee; that sample is not a current rate or total project cost.
San Mateo County ADU Resource Center — Foster City examplesHow to start the permit process
Use a planning appointment to review the proposal, assemble the City checklist and any required neighbor-notification material, then submit through the City-linked eTRAKiT portal.
Historical permit-fee example
564-square-foot detached permit example
The regional Resource Center publishes a 2021 Foster City detached-ADU fee example. It is a permit-cost reference, not a verified completion record or ADU.zone portfolio item.
View the original sourceFoster City ADU questions
- Which Foster City handbook should I start with?
- The City’s ADU page links its 2026 handbook alongside application forms.
- Does a pre-reviewed design remove site review?
- No. Use the separate preapproved-plan checklist and include the property-specific material required by Foster City.
Sources for this guide
- Foster City — ADU guidance and 2026 handbook
- San Mateo County ADU Resource Center — Foster City examples
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 Foster City 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.