ADU permits in Mountain View, CA
A plain-English starting point for ADU contractors working in Mountain View (Santa Clara County). This is general California guidance — it does not replace the requirements published by the city.
Short answer
Yes — every ADU (new construction, garage conversion, or a JADU within the existing home) requires building permits in California. State law (Government Code §65852.2) constrains how cities may regulate ADUs and sets a mandatory review period for a complete application, but each jurisdiction still sets its own development standards, fees, and submittal format. ADUs are generally permitted and built under a B (General Building) contractor coordinating the trades.
Mountain View-specific fees, forms, and timelines are set by City of Mountain View Community Development — Building Division. Verified data — portal, fee schedule, adopted code — is sourced below.
The general picture
An Accessory Dwelling Unit (ADU) is a project type rather than a single trade — it bundles building, electrical, plumbing, and mechanical work, so it always requires permits from the local building department. California state law (Government Code §65852.2, and §65852.22 for Junior ADUs) sets a baseline framework that limits how local agencies may regulate ADUs and requires them to act on a complete ADU permit application within a state-mandated review period; the specific local development standards, fees, and submittal format are still set by each city or county. Confirm those specifics with the jurisdiction below before you file.
Code basis
2025 California Building Standards Code (Title 24), which applies to permit applications filed on or after per the California Building Standards Commission. Sections checked against the published code; cities may add local amendments.
California Residential Code (Title 24, Part 2.5) §R105.1 — Any owner or agent who intends to construct, enlarge, alter or change the occupancy of a building must first obtain a permit; creating a dwelling unit always does. The 120-square-foot detached accessory-structure exemption in §R105.2 does not cover a dwelling unit.
California Energy Code (Title 24, Part 6) §150.2 — Energy Efficiency Standards for Additions and Alterations to Existing Single-Family Residential Buildings: a garage conversion or attached ADU follows §150.2; a detached new ADU follows the single-family new-construction standards (Subchapters 7 and 8).
California Green Building Standards Code (CALGreen) (Title 24, Part 11) Chapter 4 — Residential Mandatory Measures apply to newly constructed dwelling units, including ADUs.
California Plumbing Code (Title 24, Part 5) §104.1 — Permits Required: the unit's plumbing system needs its own plumbing permit; the mechanical permit comes from the same section number in the California Mechanical Code (Part 4, §104.1).
Typically needs a permit
- New detached ADU
- Garage or accessory-structure conversion
- Junior ADU (JADU) within the existing home
- Attached / addition-style ADU
Usually doesn't (general norm)
- There is effectively no no-permit path for an ADU — by definition it creates a dwelling unit and requires permits
- Only minor cosmetic work inside an already-permitted, legal ADU is treated like any existing dwelling
- Anything that creates or converts living space requires a permit
Documents & plans generally required
- Site plan showing the existing dwelling, the ADU footprint, setbacks, and parking
- Floor plans and elevations
- Structural plans/calcs for new construction or conversions
- Title 24 energy documentation
- Electrical, plumbing, and mechanical plans for the new unit
- School/impact fee and utility-connection forms where applicable
Common reasons ADU applications get bounced
These are general, code-rooted patterns across California — not a Mountain View rejection rate.
- Site plan missing required setbacks, dimensions, or the existing structure
- A local ordinance that conflicts with state ADU law and hasn't been updated — resolve with the AHJ
- Incomplete structural or Title 24 documentation
- Fire-separation or egress details missing for a conversion
- Utility/sewer capacity or connection details not addressed
The inspection sequence
A typical order — the number of stops and exact sequence vary by jurisdiction and scope.
- 1Foundation / underground rough for new construction
- 2Framing, then rough electrical/plumbing/mechanical before cover
- 3Insulation and Title 24 / HERS verification where required
- 4Final inspections across trades and a final building sign-off before occupancy
Licensing — who can pull it
An ADU is generally built under a licensed B (General Building) contractor who coordinates the C-10 (electrical), C-36 (plumbing), and C-20 (HVAC) subtrades. State ADU law is statewide; the local building department is still the Authority Having Jurisdiction for the permit itself.
Mountain View permit data
Sourced from public City of Mountain View documents — every field carries the source URL and verification date. Full dataset last re-verified .
- Permit portal
- ePermitsMV (Avolve)
verified Aug 10, 2026 · source · "The permit process is handled exclusively on this platform" — city pages link ePermitsMV to the Avolve-hosted portal; account sign-in is required to apply
- Adopted code edition
2025 California Building Standards Code (Title 24, with Mountain View amendments)
verified Aug 10, 2026 · source · Effective January 1, 2026, all Building and Fire permit applications must comply with the 2025 California Building Standards Code and certified standards, adopted by reference with local amendments
- Fee schedule
- Building Permit Fees — effective August 22, 2026 (valuation-based fee table)
verified Sep 13, 2026 · source · The city applies a 5% technology fee on the total permit cost of each building and fire permit issued
Frequently asked questions
Do I need a permit to build an ADU in California?
Yes, always. An ADU creates a dwelling unit and requires building, electrical, plumbing, and mechanical permits. State law (Gov. Code §65852.2) limits how cities may regulate ADUs and sets a mandatory review period for a complete application, but the city is still the permitting authority. Confirm local standards with the department below.
Does a garage conversion to an ADU need a permit?
Yes. Converting a garage or accessory structure into living space is an ADU and requires permits, including fire separation, egress, and Title 24 compliance. Confirm the local process with the AHJ below.
How long does an ADU permit take in California?
California law requires local agencies to act on a complete ADU application within a state-mandated review period set by statute. The clock depends on the application being complete and on local process — confirm current timing and completeness requirements with the city's building department below. getPermit does not publish city-specific timelines it hasn't verified.
What is a JADU?
A Junior ADU (JADU) is a smaller unit, size-capped by state law, created within the walls of an existing single-family home with its own entrance. It still requires a permit and has its own state-law rules (Gov. Code §65852.22). Confirm local specifics with the department below.
Other trades in Mountain View
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