Two Detached ADUs in Los Altos Hills (AB 956, 2027)
Plan Two ADUs in Los Altos Hills: Free Site Assessment
Los Altos Hills ADU rules today
Los Altos Hills currently allows one ADU and/or one JADU on a property with a single-family home. From January 1, 2027, state law (AB 956) requires the Town to approve up to two detached ADUs on a single-family lot. With large lots throughout the Town, many properties have the room. Slopes, oaks, creeks and fire access decide where the units can go.
- Units allowed now: one ADU and/or one JADU on any R-A property with an existing single-family home, regardless of lot size.
- Size: an ADU of up to 800 sq ft; up to 850 sq ft (studio or one bedroom) or 1,000 sq ft (two bedrooms) if your Maximum Development Area (MDA) and Maximum Floor Area (MFA) allow; up to 1,200 sq ft with one on-site parking space and 30 ft side and rear setbacks.
- MDA and MFA: a new ADU of up to 800 sq ft is exempt from both. Area above 800 sq ft counts toward them.
- Height: 16 ft, or 19 ft with an on-site parking space and 30 ft side and rear setbacks.
- Setbacks: 40 ft front; 4 ft side and rear.
- Parking: one on-site space (tandem or in a setback is allowed), with exemptions near transit and for conversions. The ADU must use the existing driveway.
- Where an ADU cannot go: inside a Heritage Oak’s critical root zone, on slopes over 30%, within 25 ft of the top of a creek bank, in a recorded easement, or in a geotechnical or seismic hazard zone.
- Design: exterior materials, windows and roof to match the main house; wall colors with a light reflectivity value of 50 or less and roofs of 40 or less; shielded, downward-facing lighting.
- Process: ministerial, with no Site Development Review. It starts with a pre-application meeting with a Town planner, then a building permit application. Planning: 650-941-7222.
State review of the Town's ADU rules
In a January 26, 2026 letter, the California Department of Housing and Community Development (HCD) found that parts of the Town’s ADU and SB 9 code do not comply with state law. The issues included the 16 ft height limit for detached ADUs, which must include the state’s 18 and 20 ft exceptions; requiring sprinklers in the existing house when an ADU is added; and the 650 sq ft JADU option. Where the Town’s code is stricter than state law, state law applies. We check the Town’s current code for every project.
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 raises the number of detached ADUs the Town must approve on a single-family lot from one to two. The Town may limit each to 800 sq ft of living space and apply height limits, and side and rear setbacks can be no more than 4 ft. If two detached ADUs are built, the Town does not have to also approve a JADU. How the Town applies its MDA and MFA exemption to a second ADU will depend on its ordinance update.
Planning two detached ADUs on a hillside lot
- Placement: we map slopes, oak root zones, creek setbacks and easements first, since they decide where two units can sit.
- Driveway and parking: ADUs use the existing driveway, so access and parking for two units have to work from it.
- Sewer or septic: properties near a public sewer must connect, and septic properties need County review. We confirm which applies early.
- Fire safety: parts of the Town are in mapped fire hazard severity zones. Fire access and wildfire-resistant construction shape the design.
- Electrical: two units usually need a load calculation and often a service upgrade. We coordinate PG&E work from the start.
Our Los Altos Hills ADU work
Axiom Renovation builds ADUs in Los Altos Hills and neighboring Los Altos. Read our Los Altos Hills ADU guide, the AB 956 overview, or two detached ADUs in 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.
Los Altos Hills Two-ADU FAQ
Can I build two ADUs in Los Altos Hills?
Today the Town allows one ADU and/or one JADU on a property with a single-family home. From January 1, 2027, AB 956 requires the Town to approve up to two detached, new-construction ADUs on a single-family lot that meets objective standards.
Does an ADU count toward my MDA and MFA in Los Altos Hills?
A new ADU of up to 800 sq ft is exempt from Maximum Development Area and Maximum Floor Area. Any area above 800 sq ft counts toward both.
How tall can an ADU be in Los Altos Hills?
The Town code allows 16 ft, or 19 ft with an on-site parking space and 30 ft side and rear setbacks. HCD has told the Town it must also include the state’s 18 and 20 ft height exceptions.
Where can I not build an ADU in Los Altos Hills?
Not inside a Heritage Oak’s critical root zone, on slopes over 30%, within 25 ft of the top of a creek bank, in a recorded easement, or in a geotechnical or seismic hazard zone.
Does an ADU in Los Altos Hills need Site Development Review?
No. ADUs are approved ministerially, without Site Development Review or discretionary design criteria. The process starts with a pre-application meeting with a Town planner.
Who builds ADUs in Los Altos Hills?
Axiom Renovation designs, permits and builds ADUs in Los Altos Hills 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.