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Permit guides

ADU Permits in Mountain View: a Homeowner's Guide

What you can build, which permits you need, and how Mountain View’s preapproved ADU program actually works — in plain language.

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

Who handles your permit

ADU permits run through the city’s Community Development Department, 500 Castro Street, First Floor, Mountain View, CA 94041. Building Division — (650) 903-6313, building@mountainview.gov; Planning Division — (650) 903-6306. Every application and resubmittal is filed online through the city portal, ePermitsMV. After you submit, staff prescreen the file and send you the fee amount with online payment instructions before review starts.

What you can build

California state law sets the baseline, and Mountain View follows it:

There is no minimum lot size for an ADU under state law. Converted garages and other existing structures keep their current footprint — no new setbacks apply to the conversion itself.

Mountain View’s preapproved ADU program

The city runs a preapproved ADU program built around speed: the published process puts the typical time from submittal to permit at about 30 days, with each review round coming back in about 7 business days. Preapproved still isn’t permit-free — reviewers verify placement, setbacks, foundation, utilities, and fire access for your property, and the site plan is always site-specific.

What goes into the submittal

• Building permit application through ePermitsMV with the full plan set: site plan, floor plans, exterior elevations, foundation and framing details, structural calculations, Title 24 energy compliance, and MEP layouts.
• Fire sprinkler permit if the ADU needs a new or modified sprinkler system — obtainable after the building permit, during construction.
• Demolition permit before any construction or demolition activity starts.
• Excavation permit for new or upgraded utility connections or work in the public right-of-way — must be obtained in tandem with the building permit.
• An account in the city’s Construction and Demolition Waste Tracking system (Public Works: (650) 903-6311).

Where applications usually get stuck

• Incomplete prescreens. The 7-business-day cycle starts only once the application is deemed complete — missing materials trigger another full cycle.
• Right-of-way utility work. The excavation permit is a separate Public Works track with its own reviews — plan for it early.
• Sprinklers discovered late. If review requires them and they weren’t scoped, the separate sprinkler permit and inspections land mid-project.
• C&D waste tracking. Easy to overlook; the permit won’t finalize without the account set up.