Merced & Stanislaus Counties
California law guarantees your right to build an ADU. Here’s every rule, every city, and every law that applies to your property — free from Jantz Group.
Updated June 2026 · California State LawFor years, homeowners were told they couldn't add units — too small a lot, wrong zone, HOA says no. Most of that is no longer true. Here's what California guarantees you:
You are entitled to 1 ADU + 1 Junior ADU on any single-family residential lot statewide. No minimum lot size required by state law.
You may add up to 2 detached ADUs, or convert up to 25% of existing units into ADUs on multi-family properties.
HOAs for single-family homes cannot prohibit ADUs. They may apply reasonable design standards but cannot flat-out block them.
Cities and counties must approve a compliant ADU application within 60 days — and cannot sit on your application indefinitely.
Not all ADUs are the same. Understanding which type fits your property is the first step. Each has different size limits, setback rules, and approval processes.
A completely separate, free-standing structure on the same lot. New cottage, prefab unit, or modular home placed in your backyard.
An addition physically connected to your existing house — a new suite with its own entrance, kitchen, and bathroom.
Converting your existing attached or detached garage into a livable unit. Often the least expensive path — the structure is already built.
A small unit carved out within your existing home or garage — converting a bedroom suite or part of a floor into a mini-apartment.
Converting existing livable space inside your home — basement, bonus room, or large bedroom suite — into a separate unit.
Converting a legally existing non-garage structure — barn, workshop, studio — into a dwelling. Common on larger rural and ag lots.
These are the core statewide standards that apply across all of Merced and Stanislaus counties. Local cities may be slightly more permissive but cannot be more restrictive than these.
| Requirement | Standard ADU | Junior ADU (JADU) |
|---|---|---|
| Minimum Size | 150 sq ft | No stated minimum |
| Maximum Size | 1,200 sq ft new; 800 sq ft guaranteed minimum for detached | 500 sq ft maximum |
| Height (Detached) | 16 ft; 18 ft within ½ mile of transit; 25 ft if attached | Same as primary home |
| Setbacks (New Construction) | 4 feet from rear and side lot lines | None — stays within existing structure |
| Setbacks (Conversions) | None required for existing structures | None |
| Parking | 1 space per unit; waived near transit, for conversions, or on certain lots | No additional parking required |
| Kitchen | Full kitchen required | Efficiency kitchen only (sink, cooktop, refrigerator) |
| Bathroom | Full bathroom required | May share with primary home |
| Separate Entrance | Required — exterior access | Required — may also connect to primary |
| Fire Sprinklers | Not required unless primary home has them | Not required |
| Owner Occupancy | NOT required (permanent as of 2025) | Owner must live on property |
| Rental Term | 30+ days minimum (no Airbnb/VRBO) | 30+ days minimum |
| Impact Fees | Waived for units under 750 sq ft; proportional above | Waived |
| Solar Required? | Yes — new construction subject to Title 24 solar mandate | Generally no for conversions |
| Approval Timeline | 60 days max — ministerial (no public hearing) | 60 days |
Stanislaus County Cities
| City | Key Notes | Where to Apply |
|---|---|---|
| Modesto | Free pre-approved ADU plans; ADU loan program via Valley First CU; online permit system (eTRAKiT); up to 1,200 sq ft detached | Community & Economic Development modestogov.com |
| Turlock | Free pre-approved plans (same 7 designs); standard state rules apply | Building & Safety Division cityofturlock.org |
| Ceres | Free pre-approved plans available; standard state rules | Building Division ci.ceres.ca.us |
| Oakdale | Free pre-approved plans available; standard state rules | Building Safety Division oakdalegov.com |
| Riverbank | Free pre-approved plans available | Development Services riverbank.org |
| Waterford | Free pre-approved plans available | Building Dept. cityofwaterford.org |
| Patterson | Standard state rules apply | Building Division ci.patterson.ca.us |
| Newman | Standard state rules apply | Building Dept. cityofnewman.com |
| Hughson | Standard state rules apply | Building Dept. cityofhughsonca.gov |
Merced County Cities
| City | Key Notes | Where to Apply |
|---|---|---|
| City of Merced | Follows CA Govt. Code §65852.2 fully; single-family: 1 ADU + 1 JADU; standard setbacks; aligns with state minimums for guaranteed approval | City of Merced Planning Dept. cityofmerced.org |
| Los Banos | Standard state rules apply | Building Division — Los Banos |
| Atwater | Standard state rules apply | City of Atwater Building |
| Livingston | Standard state rules apply | City of Livingston |
California has passed a wave of pro-ADU legislation since 2019. Here's every major law you need to know:
The core statute governing all ADUs in California. Requires local agencies to ministerially approve ADUs that meet state standards. Mandates 60-day review, prohibits excessive setback/size requirements, and establishes baseline rights every homeowner has statewide.
Eliminated minimum lot size requirements for ADUs, reduced setbacks to a maximum of 4 feet, allowed both an ADU and JADU on the same lot, and prohibited cities from requiring passageways to ADUs.
Prohibited cities from requiring setbacks exceeding 4 feet, eliminated impact fees for ADUs under 750 sq ft, expanded parking waivers, and initially removed owner-occupancy requirements.
Prohibited permit denials based on existing non-conforming conditions. Waived impact fees for ADUs under 750 sq ft. Combined with AB 68 and AB 881, SB 13 created the modern California ADU framework.
Authorized urban lot splits on single-family parcels. A homeowner may split a qualifying lot into two parcels and build 2 units on each — up to 4 units total. Original lot must be at least 2,400 sq ft.
Increased maximum ADU height to 18 feet near transit, 25 feet for attached ADUs. Required that all local ADU standards be "objective" — no personal judgment by city officials.
Clarified height limits, simplified conversion of existing spaces into ADUs, allowed ADUs to be proposed alongside new multi-family buildings, and reduced arbitrary decision-making in the approval process.
Made the prohibition on owner-occupancy requirements permanent — removing the original 2025 sunset date. No local agency can require you to live on the property to rent out an ADU. JADUs still require owner-occupancy.
Authorizes local jurisdictions to optionally allow ADUs to be sold separately as condominiums. If your city or county opts in, your ADU becomes a separate, sellable real estate asset.
Effective January 1, 2025. Extends amnesty to unpermitted ADUs and JADUs built before January 1, 2020. Cities cannot deny permits based solely on code violations. No impact fees or connection charges. See Section 06 for full details.
A city cannot require correction of non-conforming zoning conditions as a condition of approving an ADU permit. Old fences, pre-code structures — none of that can be used to block your application.
Newly created ADUs — including conversions — are exempt from state and local Rent Stabilization Ordinances for 15 years after the certificate of occupancy is issued. This applies even to buildings otherwise subject to rent control.
How the Amnesty Process Works:
The unpermitted unit must have been built before January 1, 2020. It can be a garage conversion, an added room, a casita, a converted shed — any dwelling unit constructed without permits.
Submit an application to your local building department. Cities cannot deny this application solely because the unit violates building codes or doesn't meet current zoning — only if it presents a genuine health or safety hazard. Application fees typically run $570–$800.
An inspector evaluates the unit against California Health & Safety Code Section 17920.3 — a basic "habitability standard," NOT full modern building code compliance. They check structural integrity, electrical safety, plumbing, egress, ventilation, and serious hazards only.
The inspector gives you a specific list of what needs to be fixed. You only fix what's on the list. Typical correction costs: $10,000–$70,000+ depending on condition.
Hire licensed contractors to complete the required corrections. Schedule your final inspection. Upon approval, you receive a Certificate of Occupancy or Certificate of Compliance. Your unit is now legal.
A legalized ADU adds assessed value to your property, can be legally rented, protects you from code enforcement, may unlock refinancing/HELOC options, and gives your tenants proper legal protections.
Stanislaus County partnered with Modesto, Ceres, Turlock, Oakdale, Riverbank, and Waterford to develop 7 pre-approved ADU designs (260–1,192 sq ft) available completely free. Cuts architecture costs and speeds up permits significantly.
Stanislaus County and Modesto have a revolving ADU loan program through Valley First Credit Union. Deferred loans available to property owners willing to rent to households at or below 120% AMI.
Central Valley ADU rents typically run $1,200–$2,200/month depending on size and city. A local Modesto investor built a 900 sq ft cottage and rents it for ~$2,000/month — enough to significantly offset a mortgage payment.
New ADUs are exempt from rent control for 15 years after your Certificate of Occupancy is issued. This protects your ability to adjust rents to market rate even in areas with rent stabilization ordinances.
New construction ADUs must comply with California's Title 24 energy code, which includes a solar requirement. Budget for solar panels ($5,000–$15,000) before you start. Garage and interior conversions are generally exempt.
State law requires ADU rentals to be 30+ days minimum. ADUs cannot legally operate as Airbnb or VRBO short-term rentals under state ADU law.
ADU applications are ministerially approved — no Planning Commission hearing, no neighbor notification, no public comment period. Your neighbors cannot object.
Finance an ADU through a HELOC, cash-out refinance, construction loan, or renovation loan. The CalHFA ADU Grant (up to $40,000) is currently paused — check calhfa.ca.gov for updates.
Both Merced and Stanislaus counties allow ADUs in agricultural zones. Even on an A-2-10 parcel (10-acre minimum), you can add 1 ADU + 1 JADU.
Before committing to any ADU project, verify your sewer connection capacity or septic system size. Adding a second unit may require a septic expansion — one of the top hidden cost surprises in the Central Valley.
AB 1033 allows local jurisdictions to optionally permit ADUs to be sold as condominiums separately from the main home. If your city adopts this, you could build and sell your ADU outright.
Stanislaus County offers a free online Interactive Permit Guide at stancounty.com. Enter your address or APN and it tells you exactly what's permitted on your parcel.
In Stanislaus County, before your building permit is issued, you must sign and record a restrictive covenant confirming the ADU cannot be sold separately. Budget for recording fees.
You can develop an ADU simultaneously with a new primary home. Excellent for developers and investors buying vacant infill lots in the Central Valley's urban areas.
Always confirm your specific situation with the relevant planning or building department. Most offer free pre-application consultations.
Jantz Group · Design · Build · Atwater, CA
Whether you’re starting from scratch, converting a garage, or legalizing an unpermitted unit — Jantz Group handles the full project from permits to final inspection. Licensed, local, and Central Valley based.
CSLB# 1139545 · Serving Merced & Stanislaus Counties