Contra Costa County · California
Alamo ADU guide: local rules, permits & property planning
Alamo is an unincorporated County market. Contra Costa County even publishes a redacted Alamo ADU permit as a worked example, making local fee categories and project scope visible without exposing owner details.
Local planning guide · Reviewed October 2, 2026
What matters for an ADU in Alamo
Permitting authority: Contra Costa County — unincorporated Alamo
Official local guidanceLocal rules and design checks
| Topic | Local guidance |
|---|---|
| Jurisdiction | Use County planning and building services for an unincorporated Alamo parcel. |
| Sewer or septic | The County identifies Central Contra Costa Sanitary service in Alamo; a septic-served parcel needs Environmental Health-approved plans before building submission. |
| Application materials | Use the separate County ADU planning and building checklists. |
Selected local requirements, not a complete zoning determination. Confirm the current rules for your address with the responsible agency.
Fees and budget checks
The County’s redacted Alamo example lists $4,934.80 for an 842-square-foot detached ADU permit issued January 4, 2023. This is a historical permit example, not a current fee quote or total construction budget.
County’s redacted Alamo approved-permit exampleHow to start the permit process
Confirm the parcel in the County property lookup, resolve sanitary or septic approval, and submit the planning and building materials through County ePermits.
Public permit example — issued
842-square-foot Alamo ADU permit
The County’s official example describes a new detached unit and a 2.11 kW photovoltaic requirement from its energy report. The record proves permit issuance, not completed construction.
View the original sourceAlamo ADU questions
- Should I use Danville’s permit application?
- For an unincorporated Alamo parcel, begin with Contra Costa County and confirm jurisdiction by address.
- Can I copy the example’s solar size?
- No. The 2.11 kW requirement belongs to that project’s energy report. Your design needs its own energy calculation.
Sources for this guide
- Contra Costa County — ADU permitting
- County’s redacted Alamo approved-permit example
- County agency and sanitary approvals
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 Alamo 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.