Two Detached ADUs in Mountain View (AB 956, 2027)
Plan Two ADUs in Mountain View: Free Site Assessment
Mountain View ADU rules today (2026)
From January 1, 2027, state law (AB 956) requires the City of Mountain View to approve up to two detached ADUs on a lot with a single-family home. Mountain View already allows two-story ADUs up to 28 ft, which is generous for the region. Here is how the new law and the city’s current ADU rules fit together.
- Units allowed now: the city’s ADU page does not state how many ADUs a single-family lot may have. Confirm the count with the city before design.
- Size: 850 sq ft for a studio or one bedroom, 1,000 sq ft for two or more bedrooms. An attached ADU is capped at 50% of the main house. A JADU may be up to 500 sq ft, within the walls of the house.
- Height: up to 28 ft for a one- or two-story ADU, attached or detached. Basements count as a story, and roof decks are not allowed.
- Setbacks: 4 ft side and rear; front per zone. Stairs must meet ADU setbacks. Balconies on detached units have larger setbacks and a 75 sq ft cap.
- Parking: none for a no-bedroom unit; one space for one or more bedrooms, with exemptions under Section 36.12.95. None for a JADU.
- Process: building permit only, with no planning permit. Planners offer a free informal pre-review. First plan check takes about 2 weeks, and the city says permits typically take 4 to 6 months.
State review of Mountain View's ADU rules
On May 11, 2026, the state housing department (HCD) sent Mountain View a technical-assistance letter on its 2023 ordinance. HCD asked the city to update its units-per-lot rules, limit JADU owner occupancy to units with shared sanitation, use 15-business-day completeness checks, drop ADU owner occupancy, and review its sprinkler and design standards. Where local rules are stricter than state law, state law applies.
Recent Axiom work
Professional photos from a recent Axiom Renovation full remodel and addition in Los Gatos.
What changes on January 1, 2027
AB 956 requires the city to approve up to two detached new-construction ADUs on a single-family lot. The city may cap each at 800 sq ft of living space and apply height limits; side and rear setbacks can be no more than 4 ft. Where two detached ADUs are built, a JADU need not be approved, and HOA rules cannot block or unreasonably restrict the units. In Mountain View, the current 850 and 1,000 sq ft sizes are above 800 sq ft, so the city may set a smaller cap when two detached units are built. The 28 ft height limit may make two-story ADUs a way to fit more space on a smaller footprint. The city will need to update its ADU code, and we confirm current rules as it does.
Planning two detached ADUs on a Mountain View lot
- Two-story units: a 28 ft height allows a second floor, but balconies have their own setbacks and roof decks are not allowed.
- Entrances: each ADU needs a separate entrance.
- Fire sprinklers: a fire sprinkler permit may be needed, depending on scope.
- Parking: one space applies to units with bedrooms unless an exemption applies, so check transit distance early.
- Electrical: two units usually need a load calculation and often a service upgrade.
Building ADUs in Mountain View with Axiom
See our Mountain View ADU guide and Mountain View service area, read the AB 956 overview, or compare neighboring Sunnyvale and Los Altos.
Process
Our ADU Process
Step 1
Initial Consultation
We begin with a thorough initial consultation to understand your needs, assess your space, and discuss your vision, budget, and timeline.
Step 2
Planning and Design
At Axiom Renovation, we understand that the planning and design phase of an ADU project is crucial to its success. Our dedicated project managers will work closely with you to understand your goals, design ideas and budget for the project.
Step 3
Material Selection
We guide you through selecting high-quality materials that fit your design and budget, ensuring durability and aesthetic appeal.
Step 4
Demolition and Preparation
Careful demolition and preparation work are performed to ready the space for construction, minimizing disruptions and ensuring a clean work environment.
Step 5
Construction and Installation
Our skilled craftsmen handle the construction phase, including obtaining permits, scheduling appointments, and the actual construction and installation with precision, building the new space according to the approved design.
Step 6
Electrical and Plumbing Work
Licensed professionals conduct all electrical and plumbing work, ensuring everything is up to code and seamlessly integrated into the new ADU.
Step 7
Painting and Finishing
We pay close attention to detail during the painting and finishing stage, ensuring all surfaces are properly prepared and beautifully finished.
Step 8
Fixture and Appliance Installation
We expertly install all fixtures and appliances, ensuring they function correctly and fit perfectly with the overall design.
Step 9
Final Touches and Clean-Up
Final touches are added, and a thorough clean-up is performed, leaving your new space pristine and ready for use.
Step 10
Final Walkthrough and Client Satisfaction
We conduct a final walkthrough with you to ensure every detail meets your expectations and address any remaining concerns, ensuring your complete satisfaction.
Mountain View Two-ADU FAQ
Can I build two detached ADUs in Mountain View?
From January 1, 2027, AB 956 requires the city to approve up to two detached, new-construction ADUs on a lot with a single-family home, if the project meets objective standards. The city’s ADU page does not state the current per-lot count, so confirm with the city for projects before then.
How large can each ADU be in Mountain View?
Today up to 850 sq ft for a studio or one bedroom and 1,000 sq ft for two or more bedrooms. Under AB 956, the city may limit each of two detached ADUs to 800 sq ft of living space.
Can I build a two-story ADU in Mountain View?
Yes. Mountain View allows one- and two-story ADUs up to 28 ft. Basements count as a story and roof decks are not allowed.
How long does an ADU permit take in Mountain View?
The first plan check takes about 2 weeks, and each resubmittal about 2 weeks more. The city says permits typically take 4 to 6 months. No planning permit is needed.
Do I need parking for a Mountain View ADU?
A unit with no bedroom needs none. A unit with one or more bedrooms needs one space, unless an exemption such as transit proximity applies.
Who builds two-ADU projects in Mountain View?
Axiom Renovation designs, permits and builds ADUs in Mountain View and is planning two-unit projects for 2027. Call 408-702-2022, Monday to Friday, 9 am to 5 pm.
Sources: AB 956 (Quirk-Silva), signed September 29, 2026, effective January 1, 2027, as summarized by Brownstein Hyatt Farber Schreck and California YIMBY. This page is general information, not legal advice. Local rules change; we confirm current requirements with the city for every project.