Cities | Modesto

Modesto Multiplex Rules 2026: R-1 Duplexes, ADUs, SB 9, Mixed Use Corridors and Fees

Modesto publishes one Municipal Code on Municode. Title 10 holds the zoning rules, including the zones, the R-1 duplex rule, the ADU article, parking and the density bonus. Title 4, Chapter 4 holds the subdivision rules, and Title 9 holds the floodplain and landmark chapters. This page sums up the routes to two, three, four or more homes on a Modesto lot, what each allows, and where City text and state law differ. The code was read in Supplement 72, whose history table lists ordinances through No. 3813-C.S. of May 12, 2026. The seven guide pages below cover each topic in depth.

Modesto Guide Pages

Start With State Law

Four state laws set the floor Modesto must allow. SB 9 (2021) allows two main homes on a lot in a single-family zone, a split into two lots, or both, approved by staff with no hearing. ADU law sets the accessory dwelling units (ADUs), which are second homes on a lot, and junior ADUs a city must allow; a junior ADU is a unit of 500 square feet or less inside the house. SB 684 and SB 1123 allow maps of up to 10 lots with 10 homes. SB 79 raises zoning near qualifying rail and bus stops, but only in an "urban transit county," which Government Code 65912.156 defines as "a county with more than 15 passenger rail stations."

HCD's SB 79 advisory lists Alameda, Los Angeles, Sacramento, San Francisco, San Mateo, Santa Clara and San Diego Counties as the places where the upzoning took effect on July 1, 2026, and adds that "the geographic scope of SB 79 is dynamic and will modify over time." Stanislaus County is not on that list, so SB 79 does not change zoning in Modesto today. SB 9, ADU law and SB 684 all apply now.

Modesto has written ADU rules into Title 10, but no SB 9 rules. The City's adopted Housing Element says "The City has not adopted an SB 9 ordinance or objective standards," and its Program A-15 promised one "By Q1, 2025." Supplement 72 still has no SB 9 section, so the statutes apply as written. They apply to every city "whether general law or chartered," and Modesto is a charter city: its Charter took effect on January 14, 1963.

Modesto in Numbers

The US Census Bureau's Vintage 2025 city file estimates 219,652 people in the City of Modesto on July 1, 2025, up from a 2020 estimates base of 218,485. In that file Modesto is the twentieth largest city in California, after Fontana (221,223) and ahead of Moreno Valley (214,263). Stanislaus County has 557,719 people in the same file.

Section 500 of the Charter makes the City Council "the Mayor and six Councilmembers." Most housing decisions sit below the Council. Table 9.1-1 of the zoning code gives the Community and Economic Development Director development plan review, second-story review and small exceptions; the Board of Zoning Adjustment conditional use permits and variances; and the Planning Commission tentative maps. The Council decides rezonings, Planned Development zones and General Plan amendments. Staff approve ADUs and duplexes with a building permit.

The Routes to More Homes Compared

Sources: Modesto Municipal Code 10-3.217, 10-4.503, 10-4.104, 10-7.103, 10-7.604 and 10-9.1002; Government Code 65852.21, 66411.7 and 66499.41.

Zones That Allow Homes

Section 10-1.401 sets up three residential zones: R-1 Low Density, R-2 Medium Density and R-3 Medium-High Density. Density, the number of homes allowed per acre, is counted per net acre, the land without streets. Section 10-4.104 caps R-1 at 10.9 homes per net acre, sets R-2 at 10.9 to 22 and R-3 at 22 to 45. The R-2 and R-3 minimums bind: a project must reach them unless the Director finds the lot cannot hold them, or that a lower number will not harm the City's share of the regional housing need.

In December 2023 the City added two mixed use zones, MU-P and MU-H, for apartments at 22 to 45 homes per acre on commercial corridors. The Housing Element page names McHenry Avenue, Sisk Road, Oakdale Road and Yosemite Boulevard. Downtown has six form-based zones with nine building types, including a Du-Tri-Quadplex, and every downtown project needs development plan review. Section 10-7.103 permits condominiums only in a Planned Development (P-D) zone. The zoning districts page has the full table.

House Lots: Duplexes, ADUs and SB 9

Modesto's biggest change for house lots came in 2025. Section 10-3.217 now says "A duplex is allowed on any lot in the R-1 Zone subject to all other standards of the R-1 zone including but not limited to lot coverage, setbacks, height, parking, and fencing but not including density." Before Ordinance No. 3797-C.S., which took effect on July 24, 2025, only corner lots could have one. A lot with a duplex can also have ADUs.

ADUs follow Article 5 of Chapter 4. A detached ADU may be up to 1,200 square feet but no larger than the main home, 16 feet tall or 18 near major transit, with 4 foot side and rear setbacks and at most one parking space. A junior ADU is up to 500 square feet inside the house. The City must decide a complete ADU application within 60 days, and its ADU Express program offers same-day plan review. Where the City text is stricter than state law, for example its cap of two added units on a house lot, Government Code 66323 controls. See the ADUs, duplexes and SB 9 page.

Lots in R-1 must be 5,000 square feet and 50 feet wide (5,500 and 60 on a corner), and R-2 and R-3 lots 6,000 square feet and 60 feet wide. An SB 9 lot split can make two lots of 1,200 square feet or more, and Modesto may not require street dedication or offsite work for it. The lots and subdivisions page covers flag lots, parcel maps and SB 684.

Three or More Homes

A triplex or fourplex is a multiple-family building, which Table 3.1-1 permits in R-2, R-3, MU-P and MU-H and bars in R-1. By VanPlex arithmetic, four homes at the R-2 cap of 22 per net acre need 7,920 square feet of land, and a 6,000 square foot R-3 lot can hold 6.2 homes at 45 per acre. Five or more homes in R-2 or R-3 add development plan review by the Director and 1 guest parking space for every 4 homes. The state density bonus, which Modesto carries out in Chapter 8, starts at five homes, and the City Council decides the incentives. See the three or more homes page.

Parking, Setbacks and Height

Table 4.1-1 sets a 15 foot front setback, 20 feet for a garage facing the street, 5 foot sides for one story and a 10 foot rear. Height is 2 stories or 30 feet in R-1 and R-2 and 3 stories or 42 feet in R-3. Lot coverage is 50 percent on an interior R-1 lot. A new two-story home or second-story addition in R-1 goes through a second-story review, with notice to owners within 150 feet. Table 5.1-1 asks for 2 spaces per single-family home and, for apartments, 1 per studio or one-bedroom home and 2 per larger home. State law removes minimum parking within one-half mile of public transit. See the parking, setbacks and height page.

Flood Zones and Landmarks

In FEMA's mapped flood zones, Title 9, Chapter 4 requires a building permit for any development and a lowest floor at or above the base flood elevation, the height of the flood with a 1 percent chance each year. Work costing 50 percent or more of a building's value must meet the same rule. Chapter 10 requires Landmark Preservation Commission approval before a permit issues to alter or demolish a designated landmark, with a 45 day limit, and SB 9 does not apply to landmark sites. See the flood zones and landmarks page.

Fees

Fees come from City schedules for July 1, 2026 through June 30, 2027. Inside the city, the capital facilities fee is $18,146 per single-family home and $12,250 per multi-family home, due at permit issuance, with lower rates in the Sphere of Influence and the Downtown Economic Incentive Program area. Sewer capacity is $2,643 per single-family home and $2,151 per multi-family home. A tentative parcel map costs $2,961 in planning fees and development plan review $3,930. The fee page does not say which capital facilities rate applies to a duplex, so ask before you budget. See the permits and fees page.

Changes in Progress

Three things are moving. First, the City is preparing General Plan 2050, a comprehensive update of the Urban Area General Plan, last comprehensively updated in 1995. Second, the Housing Element's SB 9 program has not yet produced code text, so the statutes apply directly. Third, the City's 2026 ordinance book, through Ordinance No. 3816-C.S. with an effective date of August 13, 2026, replaces the City's building code chapters, adopting the 2025 California Building Code, and amends a specific plan and rezones one lot, but none of its ordinances amends the text of Title 10. Every rule on these pages is the code in force on October 9, 2026.

Where to Go Next

Related on VanPlex: the California impact fees page and the duplex to fourplex guide.

Frequently Asked Questions

Official sources (checked October 2026)