Confirm the property and the proposed project.
Begin with the address, parcel information, existing buildings, and the type of work proposed. A mailing address or neighborhood name alone does not settle jurisdiction or approval requirements. Confirm who reviews the property before applying a generic rule.
Record whether you are planning a detached dwelling, a garage conversion, an attached unit, or a JADU. Include known easements, previous additions, and existing unpermitted work in the discussion. The design team needs the actual starting condition.
Local source: City of Costa Mesa ADU resources. Check the current City instructions for your address and proposed work.
Build the submission around the site.
The City uses TESSA for electronic submissions. Its building-permit instructions call for entering application information directly into TESSA rather than uploading a scanned paper application. Follow the current instructions and checklist for your application type.
Before submission, confirm that the documents coordinate the layout, existing conditions, proposed work, and the supporting professional information required for the project. A preparation meeting should assign who gathers property records, prepares each drawing, coordinates engineering, submits, and responds to review comments. Keep the drawing set and priced scope aligned as revisions occur.
Resolve service questions alongside the building.
Costa Mesa's ADU checklist identifies sewer coordination with Costa Mesa Sanitary District and coordination with the water provider. Use the applicable providers and project requirements to confirm what documentation and connection work are needed.
For the construction scope, distinguish a service question that is still open from an upgrade that has been confirmed. Locate equipment and service routes on the design where relevant. This helps the budget describe the work outside the dwelling as well as inside it.
Track review, revisions, and construction separately.
Submission, approval, permit issuance, construction inspections, and final signoff are separate stages. Ask the project team to explain the next milestone and any dependencies before setting a start or move-in date. Do not assume that an initial submission resolves every site question.
When comments change the design, check their effect on pricing, materials, and coordination. During construction, confirm inspection responsibilities and required signoffs through the agreed process. Our construction sequence connects these handoffs.
Preapproved plans and existing unpermitted units.
Costa Mesa provides information for a preapproved ADU plan program and a separate Safe ADU Legalization Program. These are different starting points with different project questions. Read our preapproved plans guide or ADU legalization guide before assuming either route applies.
Rules, checklists, and fees can change. Verify the current requirements with the City and the professionals responsible for your project. Local source review: September 5, 2026.