Two Detached ADUs in Belmont (AB 956, 2027)
Plan Two ADUs in Belmont: Free Site Assessment
Belmont ADU rules today (2026)
From January 1, 2027, state law (AB 956) requires cities, including Belmont, to approve up to two detached ADUs on a lot with a single-family home. Belmont’s ADU ordinance dates from 2020, and the state flagged it for an update in December 2025. Here is how the new law and the city’s current rules fit together.
- Code: Belmont Zoning Ordinance Section 24, adopted as Ordinance 2020-1150 on August 25, 2020. We did not find a later amendment.
- Units allowed now: the ordinance allows one ADU and one JADU. State law also allows a conversion ADU plus a detached ADU plus a JADU.
- Size: an attached ADU can be 850 sq ft, or 1,000 sq ft with more than one bedroom, and no more than half the home’s living space.
- Height: 16 ft for a one-story detached ADU.
- Setbacks: 4 ft side and rear, 5 ft from the main house, and special rules on reverse-corner lots.
- Pre-approved plans: Belmont accepts detached ADU master plans from qualified professionals, followed by a site-specific permit. Plans over 800 sq ft must meet the main home’s gross floor area rules.
State review of Belmont's ADU rules
On December 1, 2025, the state housing department (HCD) sent Belmont a letter with 13 findings, with a response due December 31, 2025. HCD flagged the unit combinations, JADUs missing as a permitted use, deed restrictions, owner occupancy, the sprinkler language, size caps and the 50% limit, design matching rules, the 5 ft separation, reverse-corner setbacks and the 16 ft height. We did not find the city’s response. 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 raises the number of detached ADUs the city must approve on a single-family lot to two, both new construction. The city may limit each of the two to 800 sq ft of living space and apply its height limits, and side and rear setbacks can be no more than 4 ft. Where two detached ADUs are built, the city does not have to approve a JADU on the same lot. The law also limits how homeowners associations can restrict these units.
Belmont will need to update Section 24, which it is already being asked to revise. Detached master plans of 800 sq ft or less fit the cap the law allows for each unit. The 5 ft separation from the house was flagged by HCD and will matter for two units. We will confirm Belmont’s new rules as it adopts them.
Planning two detached ADUs on a Belmont lot
- Trees and landscape: the master plan checklist calls for a landscape plan showing existing trees by size and species, plus site photos.
- Soils: a soils report is required where the building official sees a geologic hazard. On sloped lots we plan for it early.
- Sprinklers: an ADU does not need sprinklers unless the main house has them.
- Electrical: two ADUs usually need a load calculation and often a service upgrade.
- Corner lots: reverse-corner setback rules can shift where units fit.
Building ADUs in Belmont with Axiom
Visit our Belmont ADU builder page and Belmont service area, or read the AB 956 overview. Nearby, see the guides for San Mateo and San Carlos.
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.
Belmont Two-ADU FAQ
Can I build two detached ADUs in Belmont?
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. Belmont’s current ordinance allows one ADU and one JADU.
How large can each ADU be in Belmont?
Under AB 956, the city may limit each of two detached ADUs to 800 sq ft. Belmont’s master plans over 800 sq ft must also meet the main home’s gross floor area rules.
How tall can a detached ADU be in Belmont?
The current ordinance sets 16 ft for a one-story detached ADU. HCD flagged this height in its 2025 letter, so we confirm the limit with the city.
Does Belmont have pre-approved ADU plans?
Belmont accepts detached ADU master plans from qualified professionals. Once a plan is accepted, each lot still goes through a site-specific permit.
Will I need a soils report for an ADU in Belmont?
Possibly. The city requires one where the building official sees a geologic hazard, which is more likely on sloped lots.
Who builds two-ADU projects in Belmont?
Axiom Renovation designs, permits and builds ADUs in Belmont 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.