Marin County · California
Mill Valley ADU guide: local rules, permits & property planning
Mill Valley calls its detached-plan approval “structure only.” Foundation work, trees, fire safety and the usable area of a specific hillside lot remain part of the homeowner’s permit package.
Local planning guide · Reviewed October 2, 2026
What matters for an ADU in Mill Valley
Permitting authority: City of Mill Valley — ADUs
Official local guidanceLocal rules and design checks
| Topic | Local guidance |
|---|---|
| Structure-only approval | Preapproval covers the detached building concept, not its placement or site works. |
| Site package | The City specifically identifies setbacks, foundation work, fire safety and tree removals as property-specific considerations. |
| Occupancy milestone | Outside-agency approvals, inspections and final sign-off remain necessary before occupancy. |
Selected local requirements, not a complete zoning determination. Confirm the current rules for your address with the responsible agency.
Fees and budget checks
Use Mill Valley’s July 1, 2026 Planning and Building schedules. Plan purchase, fire and sanitary review, site engineering and permit fees remain separate from structure preapproval.
Mill Valley current Planning and Building feesHow to start the permit process
Review the buildable area, select a concept and contact its designer. Prepare the site-specific development-permit checklist, apply online, resolve conditions and obtain the building permit before construction.
Plan resource
Mill Valley structure-only plan collection
The City publishes an eight-step homeowner process from concept selection to final inspection and rental planning, with site-specific work called out separately.
View the original sourceMill Valley ADU questions
- Does preapproval include my foundation design?
- No. Mill Valley lists foundation work among the site-specific information the applicant must supply.
- Which fee year should I use?
- The City posts Planning and Building schedules effective July 1, 2026. Confirm any later revision at application.
Sources for this guide
- City of Mill Valley — ADUs
- Mill Valley current Planning and Building fees
- Mill Valley structure-only plan collection
- Mill Valley site-specific ADU checklist
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 Mill Valley 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.