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Permit guides

ADU Permits in Napa: a Homeowner's Guide

What you can build, which permits you need, and how review actually works — in plain language.

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

Who handles your permit

The City of Napa's Community Development Department handles ADUs — planning review through the Planning Division, building permits through the Building Division — from the Community Services Building at 1600 First Street, Napa, CA 94559 (mailing: PO Box 660). The Building Division can be reached at (707) 257-9540, and the city's eTRAKiT site covers current and historical permit and planning records. The city's own ADU process handout lays out the full sequence from feasibility through final inspection. Outside city limits, you're with the County of Napa Building Division and its Online Permit Center instead — a different portal and different reviewers.

What you can build

California state law sets the baseline, and Napa follows it:

There is no minimum lot size for an ADU under state law. Napa also offers a JADU Express Review track — but it requires bringing a sewer permit from the Napa Sanitation District and a signed deed restriction, and paying all fees at that time.

Pre-approved plans

Under AB 1332, the city maintains a list of preapproved and repeatable ADU plans — check the city's website for what's currently posted, since the list evolves. The Napa-Sonoma ADU Center's Standard Plans Program is another regional source of designs. Pre-approved plans clear most of the structural review in advance, but site-specific items — setbacks, utilities, drainage, fire access — are always reviewed against your property.

What goes into the submittal

• Site plan — lot lines, existing structures, setbacks, easements, and utility terminations.
• Architectural plans — floor plans, elevations, sections.
• Structural details and calculations — foundation, framing, shear walls.
• Title 24 energy compliance — required forms and documentation.
• Electrical, plumbing, and mechanical layouts.
• Utility connection plans — including the Napa Sanitation District sewer clearance where applicable.

Where applications usually get stuck

• Flood zones. The Napa River puts parts of the city in floodplain — placement and elevation can become the whole project.
• Historic and design review. Napa has historic properties and design review rules that add review steps a plain building permit wouldn't.
• The Napa San sewer step. For the JADU express track, the separate sewer permit from Napa Sanitation (1515 Soscol Ferry Rd, (707) 258-6000) is a prerequisite, not an afterthought.
• Contractor licensing. Contractors and subs working in Napa must hold an active City of Napa business license — out-of-town crews trip on this.
• Unpermitted existing work. A garage or shed already used as living space without permits adds a legalization layer — inspectors will want to see inside walls.