Santa Clara County · California
Los Altos Hills ADU guide: local rules, permits & property planning
Los Altos Hills evaluates ADUs alongside maximum development area and floor area. Geotechnical review and shared driveway access are practical starting points for a hillside or large-lot property.
Local planning guide · Reviewed October 2, 2026
What matters for an ADU in Los Altos Hills
Permitting authority: Town of Los Altos Hills — ADUs
Official local guidanceLocal rules and design checks
| Topic | Local guidance |
|---|---|
| Development-area accounting | The Town identifies the first 800 square feet as exempt from maximum development area and maximum floor area calculations; additional area needs a separate check. |
| Geotechnical information | The Town’s preapplication process can identify a required geotechnical report and supporting documents. |
| Driveway | The published guidance calls for the ADU to use the primary residence’s driveway. |
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 current fee schedule, including its 2026 materials, and request a scope-specific calculation for Planning, Building and Engineering. Ask about school and utility charges separately from Town review.
Los Altos Hills fee scheduleHow to start the permit process
Meet with a Town planner before the permit submittal to receive a project checklist. Show the ADU in the property’s development-area calculations and resolve required geotechnical material before finalizing drawings.
Municipal fee example
Town’s 900-square-foot fee example
The Building Department publishes a sample fee structure. Use it to understand fee categories, not as a current quote for a different parcel or design.
View the original sourceLos Altos Hills ADU questions
- Does an ADU count against MDA and MFA?
- The Town distinguishes the first 800 square feet from additional area. Have Planning check both calculations for the proposed project.
- Can I design a separate new driveway for the ADU?
- The Town’s ADU guidance calls for shared use of the existing primary driveway; discuss unusual access conditions before designing a new approach.
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 Los Altos Hills 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.