Permit guides

ADU Permits in Antioch: a Homeowner's Guide

Antioch tiers its ADUs by size and type — cross 800 square feet of new construction and you're in a different permit track.

Last updated October 2026. Rules change; always confirm current requirements with the city before you build.

Who handles your permit

ADU permits in Antioch go through the Community Development Department, Planning Division (200 H Street, PO Box 5007, Antioch, CA 94531-5007, (925) 779-7035). Applications are filed digitally through the EnerGov / EPL Civic Access Portal. ADU permits are approved ministerially — no discretionary review or hearing.

What you can build

Antioch's tiered system:

≤800 sq ftSmall new-construction ADUs: simplest path

>800 sq ftADU Permit required + must match main house

850 / 1,000Size caps: studio/1BR 850, 2BR 1,000

16 ftHeight (18–20 ft near transit)

60%Max total lot coverage

60 daysDeemed approved if the city misses the deadline

Antioch's categories: JADU, Conversion ADU, Small Detached/Attached (≤800 sq ft new), and Large/ADU-Permit ADU (>800 sq ft new). Cottage communities are allowed in the IH Overlay District.

The 800-square-foot line

This is the number that matters in Antioch: new construction over 800 square feet needs an ADU Permit on top of the building permit, must match the appearance of the main house, and faces the full objective-standards checklist — including a 60% total lot coverage cap.

Stay at or under 800 square feet of new construction (or convert existing space) and the path is much simpler. Antioch's code even provides that applications are deemed approved if the city doesn't act within 60 days of a complete application.

Design around 800. In Antioch, the difference between 800 and 801 square feet of new construction is a different permit, design standards, and coverage math.

What goes into the submittal

Antioch's digital submittal asks for:

ADU Permit Form (for ADUs over 800 sq ft of new construction)
Development plans uploaded to the EnerGov portal, fully dimensioned on consistent sheet sizes
Objective Design Standards Checklist
Stormwater Control Plan addressing C.3 requirements
Property owner authorization form

Where applications usually get stuck

The 800-sq-ft threshold. Crossing it triggers the ADU Permit, appearance matching, and coverage math.
60% lot coverage. An independent cap that constrains larger designs.
Stormwater C.3. Contra Costa Clean Water Program requirements add a report to the package.
Soils reports. The city can require a preliminary soils report based on borings.

Not sure where to start? That's the part we do. We look at your property, map the requirements, coordinate the plans and specialists, and manage the submittal and corrections — one point of contact.

Tell us what you need help with.

Not sure where to start? That's what we're here for.

Send your project

Erik — (916) 540-8960 · Vall — (916) 956-8106
office@pcg-engineering.pro