Two Detached ADUs in Los Altos (AB 956, 2027)
Plan Two ADUs in Los Altos: Free Site Assessment
Los Altos ADU rules today (2026)
From January 1, 2027, state law (AB 956) requires cities, including Los Altos, to approve up to two detached ADUs on a lot with a single-family home. Los Altos lots, many of them around a quarter acre, are often large enough to fit two backyard units. Here is how the new law and the city’s current ADU rules fit together.
- Units allowed now: one attached ADU, one detached ADU and up to two JADUs on a single-family lot (Ordinance 2024-512).
- Detached ADU size: up to 850 sq ft (one bedroom) or 1,200 sq ft (two or more bedrooms). ADUs are excluded from floor area ratio and lot coverage.
- Height: 18 ft for a detached ADU.
- Setbacks: 4 ft side and rear; 5 ft between buildings.
- Parking: one uncovered space, with exemptions such as within a half mile of transit or in a historic district.
- Process: ministerial building permit only, decided within 60 days. Plans are submitted by email to the Building Division, and inspections are booked through eTRAKiT.
- City plans: Los Altos offers free permit-ready detached ADU plans in three sizes (525, 854 and 1,190 sq ft).
What changes on January 1, 2027
AB 956 raises the number of detached ADUs the city must approve from one to two. The city may limit each of the two to 800 sq ft of living space and keep its height limits, and side and rear setbacks can be no more than 4 ft. If two detached ADUs are built, the city no longer has to approve a JADU on the same lot. Los Altos will need to update its ADU ordinance, so we will confirm exactly how the two-unit option combines with its attached-ADU and JADU rules as the city adopts its changes.
Recent Axiom work
Professional photos from a recent Axiom Renovation full remodel and addition in Los Gatos.
Planning two detached ADUs on a Los Altos lot
- Trees: trees of 12 inches or more in diameter, and native trees of 10 inches or more measured at 48 inches, are protected. A Tree Removal Permit comes before the building permit, and an arborist report is needed for work inside the inner two-thirds of a dripline.
- Electrical: new or relocated electrical services in Los Altos must be underground. Two ADUs usually need a load calculation and often a service upgrade. Separate or shared meters are allowed.
- Sewer: a detached ADU connects to the main lateral downstream of the house. Two units need a layout that works for both.
- Fire access: an ADU more than 200 ft from fire access or 600 ft from a hydrant gets fire review. A Cal Water fire-flow letter is part of the submittal.
- Larger units: an ADU over 750 sq ft adds civil and grading plans and stormwater measures.
- Construction hours: 7 am to 5:30 pm weekdays and 9 am to 3 pm Saturday, with no work on Sundays or holidays.
Our ADU work in Los Altos
We are building ADUs in Los Altos now, including a 1,200 sq ft detached ADU with a new 200-amp underground service and a backyard ADU with a heat pump and wide-plank oak floors. Read our full Los Altos ADU guide, the AB 956 overview, or the guide for neighboring Los Altos Hills.
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.
Los Altos Two-ADU FAQ
Can I build two detached ADUs in Los Altos?
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. Until then, Los Altos allows one detached ADU, one attached ADU and up to two JADUs.
How large can each ADU be in Los Altos?
Today Los Altos allows a detached ADU of up to 850 sq ft with one bedroom or 1,200 sq ft with two or more. Under AB 956, the city may limit each of two detached ADUs to 800 sq ft of living space.
Do Los Altos ADUs need public notice or design review?
No. ADUs in Los Altos are approved ministerially through a building permit, without public notice. The city decides within 60 days of a complete application.
Do I need a tree permit for an ADU in Los Altos?
If a protected tree would be removed, yes. Trees of 12 inches or more in diameter, and native trees of 10 inches or more, are protected, and the Tree Removal Permit must be approved before the building permit.
Can two ADUs share my existing electrical service?
Sometimes. Los Altos allows shared or separate meters, but two units usually need a load calculation and often a service upgrade. Any new or relocated service must be underground.
Who builds two-ADU projects in Los Altos?
Axiom Renovation designs, permits and builds ADUs in Los Altos 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.