Permit guides

ADU Permits in Fairfield: a Homeowner's Guide

Fairfield starts with a planning step before the building permit. Here's the two-stage path and how to work it — in plain language.

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

Who handles your permit

In Fairfield, ADU permits run through the Building Safety Division at 1000 Webster Street, 2nd Floor, Fairfield, CA 94533 — 707-428-7451, Building@fairfield.ca.gov. Submittals go through the city's BUILD portal, where PDF uploads must not be password-protected or secured. But there's a step before Building: most projects need an ADU Permit from the Planning Division first — a ministerial approval with a 60-day decision timeline.

What you can build

1,200 sq ftMax for a detached ADU under state law

16 ftHeight limit for most detached ADUs

4 ftMinimum side and rear setbacks, detached ADUs

2 stagesPlanning ADU Permit first, then the building permit

60 daysMinisterial decision timeline on the ADU Permit

JADU shortcutJunior ADUs skip Planning and go straight to Building

The two-stage process

Stage one is the Planning Division's ADU Permit — ministerial, meaning no hearing and no discretionary conditions, decided within 60 days. Stage two is the building permit through BUILD. Two shortcuts exist: projects that qualify under Government Code Section 65852.2(e)(1) are exempt from the ADU Permit entirely, and Junior ADUs skip the Planning Division and go straight to the Building Division. Public kiosks at City Hall are available if you need to submit or pay in person.

Don't start at stage two. The most common Fairfield delay is submitting a building permit to BUILD before the Planning ADU Permit is approved. Intake bounces it, and the clock restarts when you come back in the right order.

What goes into the submittal

ADU Permit application to the Planning Division (stage one)
Site plan: lot lines, structures, setbacks, easements, utilities, drainage
Architectural plans: floor plans, elevations, sections
Structural plans and calculations, Title 24 energy documents
Unsecured PDFs only in the BUILD portal — remove password protection before uploading

Where applications usually get stuck

Skipping the planning stage. Building submittals without an approved ADU Permit get returned at intake.
Secured PDFs. Password-protected uploads are rejected by the BUILD portal — a trivial error that costs a full intake cycle.
Historic and flood overlays. Fairfield's older downtown and low-lying areas carry extra review layers; check overlays before design.
Exemption confusion. The (e)(1) exemption is real but narrow — confirm your project actually qualifies before skipping Planning.

Not sure where to start? That's the part we do. We sequence the planning and building stages for your parcel, prepare the submittal packages, and manage 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