Two Detached ADUs in San Martin (AB 956, 2027)
Plan Two ADUs in San Martin: Free Site Assessment
San Martin ADU rules today (2026)
From January 1, 2027, state law (AB 956) requires counties, including Santa Clara County, which issues permits for San Martin, to approve up to two detached ADUs on a lot with a single-family home. San Martin is an unincorporated community between Morgan Hill and Gilroy, so ADUs there follow the County Zoning Ordinance rather than city rules. Here is how the new law and the current local ADU rules fit together.
- Who issues permits: Santa Clara County. ADU rules are in County Zoning Ordinance Sec. 4.10.015, last amended by Ord. NS-1200.383 (January 24, 2023).
- Units allowed now: the County’s ADU code allows one ADU plus one JADU per legal lot. One movable tiny home may take the place of one ADU.
- Detached ADU size: the County’s ADU code allows up to 1,200 sq ft, and up to 400 sq ft of attached garage or carport can be included within that.
- Height: 16 ft if setbacks are not met; otherwise the district’s single-family height limit applies.
- Setbacks: 4 ft side and rear, the front setback of the main home, and at least 6 ft from the main home.
- Parking: one off-street space unless exempt, such as within half a mile of transit or in an existing structure. None for a JADU, and no replacement parking.
- Process: a ministerial ADU building permit, decided within 60 days of a complete application.
State review of Santa Clara County's ADU rules
On June 24, 2025, HCD sent Santa Clara County findings on its ADU and SB 9 rules (Ord. NS-1200.383). HCD found that the one ADU plus one JADU limit does not comply, and that the County must allow every state combination, including converted, detached and JADU units together. It also asked the County to allow the state 16, 18, 20 and 25 ft heights, drop size caps on conversions and make septic and water standards objective. The County’s response was due July 23, 2025. 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 Santa Clara County to approve up to two detached, new-construction ADUs on a lot with a single-family home. Each of the two may be limited to 800 sq ft of living space, local height limits can still apply, and side and rear setbacks can be no more than 4 ft. Where two detached ADUs are built, a JADU on the same lot does not have to be approved. Owners in HOAs also gain protections.
The County’s ADU code allows one ADU plus a JADU today, and HCD has already said that limit is too low. AB 956 adds a clear right to two detached new-construction units. The County’s 1,200 sq ft detached limit is above the 800 sq ft cap it may set for each of two units. The County will need to update its ordinance, and we confirm current rules with County Planning as it does.
Planning two detached ADUs on a San Martin lot
- Septic and water: ADUs remain subject to County septic (OWTS) or sewer and water-supply requirements. On a septic lot, the system and leach field must handle the added units, so we check capacity before design.
- Overlays: lots in the County’s -d, -sr and -h1 overlay districts have reflectivity or design rules for ADUs.
- Roof form: the County’s ADU code calls for a hip or gable roof on detached ADUs over 16 ft. HCD has flagged this rule.
- Electrical: two units plus the main home usually need a load calculation and often a service upgrade.
Building ADUs in San Martin with Axiom
Axiom Renovation designs, permits and builds ADUs in San Martin and across unincorporated Santa Clara County. Read our San Martin ADU builder page, see our San Martin service area, or start with the AB 956 overview. Neighbors can read the guides for Morgan Hill and Gilroy.
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.
San Martin Two-ADU FAQ
Can I build two detached ADUs in San Martin?
From January 1, 2027, AB 956 requires Santa Clara County to approve up to two detached, new-construction ADUs on a lot with a single-family home in San Martin, if the project meets objective standards. Today the County’s code allows one ADU plus one JADU.
How large can each ADU be in San Martin?
The County’s ADU code allows a detached ADU of up to 1,200 sq ft. Under AB 956, the County may limit each of two detached ADUs to 800 sq ft of living space.
How tall can a detached ADU be in San Martin?
A detached ADU that does not meet setbacks is limited to 16 ft. Otherwise the district’s single-family height limit applies. HCD has asked the County to allow the state 16, 18, 20 and 25 ft heights.
Who approves an ADU in San Martin?
Santa Clara County. The ADU building permit is ministerial and is decided within 60 days of a complete application.
Can my septic system handle two ADUs?
It depends on the system and the lot. ADUs in San Martin remain subject to County septic or sewer and water-supply rules, so we review septic capacity and leach-field area before design.
Who builds two-ADU projects in San Martin?
Axiom Renovation designs, permits and builds ADUs in San Martin 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 County for every project.