ADU permit process in Modesto, California

Stanislaus County, California

Prepared by GetYourPermit editorial teamReport an error

We haven’t written Modesto’s permit guide yet.

We publish permit process guides one city at a time, and we would rather publish nothing than guess at Modesto’s rules using another city’s process. Permit steps, submittal requirements, and review timelines are set locally, so a guide copied from a neighboring city would be wrong in ways that cost you time.

Here is what is useful for Modesto right now.

See the fee estimate for Modesto

Start here instead — official and primary sources for Modesto

CityCity of Modesto Capital Facilities Fees Policies and Procedures
The policy was adopted August 13, 2024. It states that ADUs below 750 square feet are exempt from local impact fees and that larger ADUs are charged proportionately to the primary dwelling, capped at the multifamily CFF rate. Its numeric example explicitly uses a single-family rate only through June 30, 2020, so that example amount is not treated as current.
Accessed August 28, 2026
CityBuilding Permits
The official City page confirms that the live Building Permits page directs users to the Development Fee Schedule, whose Building Safety tab links the FY 2025-26 Building Safety Division fee PDF.
Accessed August 28, 2026
CityBuilding Safety Division Fee Schedule — Fiscal Year 2025-26
The live-linked schedule is effective July 1, 2025 through June 30, 2026 and publishes a $2,429 permit fee per ADU or small dwelling up to 1,200 square feet, including mechanical, plumbing, and electrical work.
Accessed August 28, 2026

What to ask the Modesto building department

The current building permit fee schedule, and the date it took effect.
Whether development impact fees apply at your square footage — many California cities waive them for ADUs of 750 sq ft or less.
Plan submittal requirements: what drawings they expect, in what format, and whether submittal is online or in person.