San Mateo County · California
Hillsborough ADU guide: local rules, permits & property planning
Hillsborough distinguishes State Exempt, ADU Planning Permit and optional Exception paths. Selecting the correct category determines whether Town planning approval precedes the building application.
Local planning guide · Reviewed October 2, 2026
What matters for an ADU in Hillsborough
Permitting authority: Town of Hillsborough — ADUs
Official local guidanceLocal rules and design checks
| Topic | Local guidance |
|---|---|
| State Exempt screening | The Town’s summary describes an 800-square-foot scale with four-foot side and rear setbacks, subject to the applicable height exceptions. |
| Larger or different designs | An ADU Planning Permit uses additional objective standards; proposals outside those standards may enter the optional Exception process. |
| Fire access | The Town asks owners to prepare a site plan showing access before consulting its ADU specialist. |
Selected local requirements, not a complete zoning determination. Confirm the current rules for your address with the responsible agency.
Fees and budget checks
Use the Town’s planning application resource and its fee schedule effective July 1, 2026. Ask which planning category applies and request the separate building and outside-agency charges for the same scope.
Hillsborough planning applications and feesHow to start the permit process
Prepare an initial site plan and contact the Town’s ADU specialist. Establish the review category; obtain planning approval first where the selected path requires it, then submit for building permits.
Plan resource
Hillsborough ADU Plans Gallery
The Town links an ADU gallery alongside Ordinance 777. A listed plan still needs the correct local review path and fire-access evaluation.
View the original sourceHillsborough ADU questions
- Does every Hillsborough ADU need the same planning permit?
- No. The Town publishes three different paths. Discuss the proposed size and placement with its ADU specialist.
- What helps the first fire review?
- Bring a site plan showing the access route, as requested in the Town’s ADU guidance.
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 Hillsborough 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.