Everything homeowners need to know about building an accessory dwelling unit in Modesto - size limits, setbacks, permits, and the local financing programs that make building here more affordable.
Last verified: August 2026
8/10 · ADU-friendly
1,000 sq ft*
Max ADU size
16 ft*
Max height
Not required
Owner-occupancy
By-right
Permit type
This page summarizes Modesto Municipal Code, Title 10 (Zoning Regulations), Chapter 4, Article 5 (Accessory Dwelling Units) for general reference only, and it is not legal advice. Regulations change; always confirm current requirements with the Modesto Planning Division before designing or applying for permits. See sources below.
Zoning & size requirements
What you're allowed to build
ADU type
Max size
Max height
Notes
Detached, new construction (state-guaranteed floor)
800 sq ft or smaller, with 4 ft side and rear setbacks
16 ft
This size and setback combination must be approved ministerially regardless of other local standards
Detached or attached (city standard pathway)
Up to 850 sq ft (studio/1-bedroom) or 1,000 sq ft (2+ bedrooms); attached units also capped at 50% of the primary home's floor area
16 ft typical for detached; attached generally follows the primary home
Never reduced below 800 sq ft by setback or percentage limits under state law
Junior ADU (JADU)
Up to 500 sq ft
Within the existing home
Created within the walls of a single-family home; only allowed in single-family zones
Allowed zoning districts
ADUs are permitted in Modesto's single-family and multi-family residential zones (R-1, R-2, R-3, and related districts) under Municipal Code Chapter 4, Article 5. Confirm your parcel's zoning with the Planning Division before designing.
Additional standards
Setbacks, parking & other rules
Setbacks
4 ft side and rear yard for ADUs built under state and local standards; front setbacks follow the underlying zone but can't be used to block an 800 sq ft ADU, per state law.
Parking
Many ADUs and JADUs qualify for a parking exemption (near transit and several other state-defined scenarios); confirm whether your specific project needs a space.
Units per lot
Single-family lots can typically combine one JADU with one ADU, whether converted from existing space or newly built, consistent with state law's by-right combinations.
Owner-occupancy
Not required for ADUs permitted since 2020, and permanently eliminated statewide for all ADUs by AB 976 in 2024.
Building code
Must meet current California Residential/Building Code dwelling unit standards.
Financing help
Modesto is unusual among mid-size cities in offering city-backed ADU financing - see Budgeting below for the Measure H loan fund and CalHFA grant access.
Ordinance history
How Modesto's ADU rules got here
2017Statewide by-right ADU law takes effect. California Government Code §65852.2 begins requiring cities, including Modesto, to approve qualifying ADUs ministerially, without discretionary review.
Apr 2023Modesto adopts Ordinance No. 3762-C.S. The city updates Municipal Code Chapter 4, Article 5 to address the prior round of state ADU reforms.
Nov 2023State review flags compliance gaps. California's Department of Housing and Community Development (HCD) finds several provisions of the new ordinance - including a setback cross-reference, JADU zoning language, and a parking-exemption gap - don't fully comply with state ADU law, and gives the city 30 days to respond.
Nov 2024Zoning code amendment adopted. The city adopts a zoning amendment bringing its ADU ordinance in line with current state law, alongside a $450,000 ADU Revolving Loan Fund funded by the voter-approved Measure H sales tax.
2024Owner-occupancy eliminated statewide. AB 976 permanently bars California cities from requiring owner-occupancy for ADUs, and SB 1211 raises the detached-ADU cap on multifamily lots.
Worth knowing, in the interest of accuracy: Modesto's original 2023 ADU ordinance needed a state-required cleanup pass in 2024 after HCD flagged several provisions as noncompliant - a bumpier history than some larger California cities. That doesn't change what homeowners are entitled to build; the statewide law guarantees a ministerial approval path regardless of local ordinance hiccups, and Modesto has since paired its fix with genuinely useful local financing programs described below.
Permit process
How Modesto ADU permitting works
1
Sketch a site plan & get pre-app advice
Bring a rough site plan to the Planning & Building counter (3rd floor, 1010 10th Street) or email planning@modestogov.com for informal feedback before you design.
2
Choose a design
Pick one of the seven free pre-approved plans from the Stanislaus County regional partnership, or hire a licensed architect or engineer.
3
Assemble your submittal package
Complete plans, energy calculations, and structural/truss calculations, as applicable to your project.
4
Apply through eTRAKiT
Submit your permit application online. If your project needs a new address assigned, budget around $197 for the address application.
5
Plan review & permit issuance
City staff reviews for zoning and building code compliance. The ADU Express program offers same-day, in-person feedback from Building Safety, Fire, Planning, and Engineering by appointment - call (209) 577-5232 ext. 0.
6
Build & inspect
Construct your ADU and schedule the standard inspections before final approval.
State law caps ministerial review at 60 days. Fees and timelines are approximate - confirm current figures with the Planning Division at (209) 577-5267.
Budgeting
What it costs to build an ADU in Modesto
Garage conversion
Roughly $60,000-$150,000, the least expensive path since the shell already exists
New detached ADU
Roughly $130,000-$280,000 for a code-compliant, freestanding unit; Central Valley costs typically run below coastal California
Address application fee
Around $197, only if your project requires a new address to be assigned
ADU Revolving Loan Fund
Up to $50,000 at fixed rates up to 5 points below Wall Street Prime, terms up to 120 months, funded by Measure H and administered by Valley First Credit Union
CalHFA ADU Grant
Up to $40,000 toward pre-development and closing costs (design, permits, surveys), available to qualifying homeowners through the Stanislaus Equity Partners (STEP) program
These are general ranges from local contractor estimates and regional reporting, not quotes - actual cost depends heavily on lot conditions and finishes. Modesto's loan and grant programs can meaningfully offset upfront design and permitting costs if you qualify.
Before you apply
Tips for a smooth approval
Look into the Measure H loan fund before you price out financing. Modesto's $450,000 revolving loan fund can cover up to $50,000 at below-market rates if you qualify.
Grab a free pre-approved plan. Seven Stanislaus County-vetted designs are available at no cost and can simplify your review.
Use the ADU Express appointment. A single same-day meeting with Building Safety, Fire, Planning, and Engineering can catch problems before you submit.
Confirm your setbacks against the current code, not an old printout. Modesto's ADU ordinance was updated in late 2024 after a state compliance review, so older summaries may be outdated.
Ask about the CalHFA grant. Up to $40,000 toward design and permitting costs is available through the STEP program for qualifying homeowners.
FAQ
Common questions
Do I need to live on the property to build an ADU in Modesto?
No. ADUs permitted since 2020 haven't required owner-occupancy, and California's AB 976 permanently eliminated the requirement statewide in 2024.
How many ADUs can I build on one lot?
Single-family lots can typically combine one JADU with one ADU, whether converted from existing space or newly built, per state and city standards.
Do I need parking for my ADU?
Often not - many ADUs qualify for a parking exemption under state and local rules. Confirm with the Planning Division for your specific project.
How long does the permit process take?
State law caps ministerial review at 60 days. Modesto's ADU Express program can give you informal feedback the same day you request an appointment.
What's the maximum size for a detached ADU?
800 sq ft is guaranteed under state law with 4 ft side and rear setbacks. Under the city's standard pathway, detached ADUs can reach 850 sq ft (studio/1-bedroom) or 1,000 sq ft (2+ bedrooms).
How much does an ADU cost to build in Modesto?
Garage conversions tend to run roughly $60,000-$150,000, and new detached units roughly $130,000-$280,000, based on local contractor estimates and regional reporting. Modesto's Revolving Loan Fund and the CalHFA ADU Grant can help offset these costs for qualifying homeowners.
Is financing help available for an ADU in Modesto?
Yes. The Measure H-funded ADU Revolving Loan Fund offers up to $50,000 at below-market rates through Valley First Credit Union, and the CalHFA ADU Grant offers up to $40,000 toward pre-development costs through the STEP program.
Can I rent my ADU out short-term?
Modesto regulates short-term rentals separately from its ADU ordinance. If that's the plan, confirm current short-term rental requirements with the city before you finalize your design.
Did Modesto's ADU ordinance always comply with state law?
Not quite. California's housing department flagged several provisions in the original 2023 ordinance as noncompliant, and the city adopted a fix in late 2024. It's a good reminder to always confirm current standards with the Planning Division before designing.
