Rialto | Lot Size and Subdivisions

Rialto, California Lot Size and Subdivisions: Lot Minimums, Tentative Maps, SB 9 Lot Splits and Small-Lot Maps

To subdivide is to divide one lot into two or more lots that can be sold separately. In Rialto the lot size rules sit in Title 18 (Zoning) and the map rules in Title 17 (Subdivisions) of the Rialto Municipal Code. There are three ways to divide a lot: a regular parcel or tract map under the state Subdivision Map Act and Title 17, an SB 9 urban lot split under Chapter 17.51, and a small-lot map under state law. This page covers the minimum lot sizes, who approves each kind of map, how long approvals last and how Rialto's SB 9 chapter compares with the statute. The Rialto overview has the summary.

Minimum Lot Sizes by Zone

Sources: Rialto Municipal Code Sec. 18.08.030, 18.10.030, 18.12.030, 18.14.030, 18.16.030, 18.18.060, 18.22.030 and 18.24.030 (Supplement 39).

Four general rules affect these numbers. Section 18.54.010 says no parcel "may be reduced in any manner below the minimum standards established by this title for the district within which the lot is located." Section 18.54.020 lets an owner count "one-half of the width" of an abutting alley as part of the lot when working out lot area. Section 17.44.010 requires new lots in residential zones to meet the zoning minimum and says "corner lots shall be five feet wider than the minimum required lot width." And each zone keeps a rule for older lots: a lot smaller than the zone requires, which was separately owned or on record when the title took effect, may still be used.

The R-3 site minimum of one acre and 150 feet of width applies "when developed pursuant to this chapter." Section 18.22.030 also says a smaller R-3 lot that was separately owned or on record when the title took effect "may be developed or occupied by any use permitted in the zone." The zoning districts page lists what each zone allows.

Parcel Maps and Tract Maps

Section 17.12.010 says "A tentative and final tract map or parcel map shall be required for all divisions of land in accordance with the provisions and requirements of the State Subdivision Map Act." Under Government Code 66426, a division that creates five or more parcels needs a tentative and final map, often called a tract map, unless one of the listed exceptions applies; the other divisions use a parcel map. A tentative map is the first approval, showing the planned lots and streets; the final map is the surveyed map recorded with the county once conditions are met.

• Who decides. Section 17.04.020 makes the Planning Commission "the advisory agency of the city council" with power "to approve, conditionally approve, or disapprove" tentative maps. Section 17.16.040 requires a public hearing with notice under the Map Act. Section 17.18.090 refers to "the approval of the final map by the city council."
• What to file. Section 17.16.020 asks for "twenty copies of the tentative map," topography at contour intervals of no more than five feet, existing buildings, flood areas, streets and easements, and a geologic soils report unless the Community Development Department waives it. The City's entitlement checklist asks for the tentative map application items as PDF files, including "the tentative map and conceptual grading plan."
• Timing. Section 17.16.030 says the Commission reports on a map "within fifty days after the tentative map has been filed," approving, conditionally approving or denying it.
• Denial. Section 17.16.070 lists the findings that require denial, such as a map that is "not consistent with applicable general and specific plans" or a site that "is not physically suitable for the proposed density of development."
• Appeals. The subdivider may appeal any Commission action on a tentative map to the City Council under Section 17.16.060. Other people affected by the decision may file a complaint "within ten days after the action."

Two 2025 agenda items show the process. The November 5, 2025 Planning Commission agenda listed Tentative Parcel Map No. 2023-0004, a request to divide "one 1.71-acre parcel of land at 605 East Etiwanda Avenue in a R-1B zone" into two parcels, with a new house on one of them. The August 26, 2025 City Council agenda listed Resolution No. 8394 to approve Tract Map 20685, dividing one parcel "within the Single Family Residential (R-1C) Zone into 20 Single-Family Lots."

How Long a Tentative Map Lasts

Section 17.16.050 says that "Unless otherwise prescribed by the Subdivision Map Act, an approved or conditionally approved tentative map shall expire twenty-four months after its approval or conditional approval." When a subdivider must spend $125,000 or more on public improvements outside the map, each phased final map extends the tentative map by 36 months, up to ten years in total. The subdivider may also ask for an extension before the map expires; filing the request extends the map "for sixty days," and the Planning Commission may grant extensions "not to exceed a total of thirty-six months." A denied extension can be appealed to the City Council within fifteen days. The City's planning fee schedule lists an "Extension of Time for Land Divisions" fee of $705.10.

Streets, Water and Parks

• Street design. Section 17.44.010 calls for local streets "not less than sixty feet in width," alleys of at least twenty feet in industrial, commercial and multiple family areas, dead-end turnarounds "not less than seventy-six feet in diameter," and blocks no longer than 1,300 feet.
• Water fee. Section 17.21.040 requires a fee, set by City Council resolution, "For each additional lot created by subdivision or lot split," paid into the City's water development fund.
• Parks. Chapter 17.23 requires land, a fee or both for parks whenever a residential project divides land, based on "3.0 acres of property for each one thousand persons." Developments of fifty parcels or fewer pay a fee in place of land. The City's impact fee schedule lists a Quimby in-lieu fee of $6,515.17 per single-family home and $6,142.98 per multi-family home, and notes it applies "only to residential project that contain 50 or more dwelling units."

SB 9 Urban Lot Splits (Chapter 17.51)

An urban lot split under SB 9 divides one lot in a single-family zone into two, approved by staff with no hearing. Rialto wrote its rules into Chapter 17.51, adopted by Ordinance No. 1665 on February 8, 2022. Section 17.51.050 defines a single-family zone as "a zone where the only residential use that is allowed as a primary use is a single residential dwelling on a lot," which covers the R-1 zones.

Sources: Rialto Municipal Code Sec. 17.51.030, 17.51.040 and 17.51.050 (Supplement 39); Gov. Code 66411.7 (as amended effective June 30, 2026).

Beyond the table, Section 17.51.050 bars a split on a lot that was itself created by a split, or next to a lot the same owner split. It bars splits that would demolish or alter rent-restricted housing, housing withdrawn from rent under the Ellis Act (the state law that lets an owner take rental housing off the market) within fifteen years, or "Housing that has been occupied by a tenant in the last three years." The owner must sign easement agreements with each utility and record them before the final map; an easement is a recorded right to use part of a lot, here for utility lines. No street dedication or offsite improvement may be required. The applicant must sign an affidavit, a sworn written statement, to live in one of the homes "for a minimum of three years," and a deed restriction, a recorded limit on how the property may be used, must bar rentals "for a period of less than thirty days" and any non-residential use.

Each new main home on a split lot may be 500 to 800 square feet, and a house built before the split that is larger than 800 square feet "may not be expanded." On a resulting lot larger than 2,000 square feet a new home may be one story and 16 feet. The ADUs and SB 9 page covers those building rules and the matching two-unit chapter.

Where Chapter 17.51 and the Statute Differ

• Deadline. Government Code 66411.7(b)(1)(B), as amended effective June 30, 2026, says an application "shall be considered and approved or denied within 60 days" of a complete application, or "shall be deemed approved." Chapter 17.51 sets no such deadline; it says only that the City will report incompleteness within thirty days. The statute controls.
• Who may apply. Section 17.51.030 limits applicants to "individual property owners" and names partnerships, LLCs and corporations as excluded. The statute's applicant rule is the three-year occupancy affidavit in subdivision (g), and subdivision (g)(3) says a city "shall not impose additional owner occupancy standards." Ask the City how it applies Section 17.51.030 before a company buys a lot to split.
• Three-month map. Section 17.51.040 says the tentative map "shall expire three months following approval." The statute sets no expiration period for an urban lot split map.

Small-Lot Maps Under SB 684 and SB 1123

A search of Titles 17 and 18 in Supplement 39 found no section on these maps, so Government Code 66499.41 applies directly. In the version in force until January 1, 2027, a city must consider ministerially, meaning by staff against fixed written rules with no hearing, a map that creates 10 or fewer parcels for 10 or fewer homes on a lot "Zoned to allow multifamily residential dwelling use" of up to five acres, or a vacant lot "zoned for single-family residential development" of up to one and one-half acres. New parcels may be as small as 600 square feet, or 1,200 where zoned single-family, and the average home may not exceed 1,750 net habitable square feet. The City must act within 60 days of a complete application. In Rialto the multifamily rule applies to R-3, R-4 and HOD sites; see the SB 684 and SB 1123 page.

Where to Go Next

Related on VanPlex: the Rialto overview, the SB 9 page and the SB 684 and SB 1123 page.

Frequently Asked Questions

Official sources (checked October 2026)