San Marcos | Lots and Subdivisions

San Marcos, California Lot Size and Subdivisions: Minimum Lots, Slope Rules, Lot Averaging, Parcel and Tentative Maps, SB 9 Lot Splits and Starter Home Maps

This page covers how large a lot must be in San Marcos and how land is divided into new lots. Lot sizes are set in Title 20, the zoning code, and the steps to divide land are in Title 19, the subdivision code, of the San Marcos Municipal Code. A subdivision is any division of land into new lots that can be sold separately; California's Subdivision Map Act requires a map approved by the City for each one. San Marcos is a hill city, so the slope of the land changes the minimum lot size more than in a flat city. The San Marcos overview has the summary.

Minimum Lot Sizes by Zone and Slope

Source: San Marcos Municipal Code Table 20.300-2 (Gross Slope Acreage Analysis Standards). The first column is the "Minimum Lot Area" row, which matches Table 20.215-3.

Table 20.215-3 sets the base minimum lot areas: 20,000 square feet in R-1-20, 10,000 in R-1-10, 7,500 in R-1-7.5 and 3,500 in R-2. Its note 7 says "Minimum lot sizes are net area; reciprocal access easements not included." Net area leaves out land used for a shared access strip. For the R-3 zones, Table 20.215-4 sets 6,000 square feet in R-3-6 and 10,000 in R-3-10.

Each R-1 and R-2 minimum carries note 4: "Subject to gross slope/acreage analysis." Section 20.300.040 says that where slopes vary "from relatively easy (moderate) slopes to excessive slopes, a gross acreage analysis shall be completed by the property owner or the subdivider." The owner computes the size and density of each proposed lot from Table 20.300-2, checks that each lot has at least one home, and checks that no lot is smaller than the zone allows. The effect is large on hillsides: an R-2 lot needs 3,500 square feet on flat ground and 20,000 on a slope of 25 to 35 percent.

Table 20.215-3 lists no minimum lot width and no lot coverage limit for the R-1 and R-2 zones. The subdivision code adds some of these rules. Section 19.16.010(f) says that "Unless otherwise authorized by the provisions of Title 20, lot depth shall be at least 90 feet," and that depth "shall be no greater than three times the average width", except for minor subdivisions where the new ratio is less than that of the existing lot. Section 19.16.010(b) says every lot must meet the zone minimum, "provided, however, if no lot area is established, every lot shall contain a net area of no less than 7,500 square feet."

Section 20.300.020(B) bars any action that reduces a lot below the zone minimum, except a partial taking for public use. Section 20.300.020(E) protects older lots: a developed lot that existed by deed or contract of sale before the City first zoned it is exempt from the minimum lot area if the owner "owns no adjoining land" and the lot did not come from an illegal division.

Lot Averaging and PRD Lots

Two San Marcos tools allow lots below the zone minimum inside a larger subdivision. Neither adds homes beyond the zone density.

• Lot averaging. Section 20.300.030 allows it, with a conditional use permit, when land in R-1-20, R-1-10 or R-1-7.5 is divided into five or more lots. The total area of all lots must equal "the product of the lots in the subdivision multiplied by the minimum lot area required by the Zone." In R-1-7.5 "no lot shall have a net area less than 6,000 square feet."
• Planned residential development. Section 20.435.050 says "there shall be no minimum area requirement for individual lots" in a PRD, but in the R-1 zones the whole site must equal the zone minimum lot size times the number of homes, and 40 percent of the site must be open space.

The lot averaging section has two drafting slips. It names an "R-10" zone, and the zone list has R-1-10. It also says no lot may be smaller than "three-quarters percent (0.75%) of the minimum lot area," a figure that would allow a lot of 56 square feet in R-1-7.5. The R-1-7.5 floor of 6,000 square feet in the same sentence suggests three-quarters of the minimum was meant. Ask the Planning Division for its reading.

Map Steps

Sources: San Marcos Municipal Code 19.04.020, 19.12.080 and 19.12.085, 19.24.020, 19.24.120 and 19.24.140, 19.44.100; Government Code 66411.7 and 66499.41.

Section 19.04.020 defines a minor subdivision as "a subdivision of four or fewer lots" and a major subdivision as "five or more lots." A tentative map is the first, detailed proposal for the new lots; the final map or parcel map is the survey that is recorded with the County once the conditions are met.

Minor subdivisions. The owner files a tentative parcel map with the City Engineer. Within ten working days the City Engineer sends it to other agencies and mails notice to owners within 500 feet, who have 15 days to ask in writing to be heard. Section 19.24.120 gives the City Engineer 50 calendar days to approve, conditionally approve or disapprove the map, with a preliminary decision within 40 days that the owner may ask to have reviewed. Final decisions are mailed to owners within 300 feet. The subdivider or "any interested person" may appeal to the City Council within ten days. An approved tentative parcel map lasts 24 months, with one extension of up to one year.

Major subdivisions. The Planning Commission holds a public hearing on every tentative map and acts "within 50 days following the certification of the Environmental Impact Report, approval of a negative declaration or determination by the City that the project is exempt" from state environmental review. Appeals go to the City Council within ten days. A tentative map expires after 24 months, and the Planning Commission may extend it "for a period or periods not exceeding a total of three years."

Improvements and fees. Section 19.28.060 makes a minor subdivision build the same street and utility improvements as a major one, normally when a building or grading permit is issued. Section 19.08.050 requires drainage and sewer fees before a final or parcel map is filed, and Section 19.08.060 allows bridge and major road fees in areas of benefit. A panhandle or flag lot needs "a minimum frontage of 30 feet," or 20 feet for each of two flag lots placed back to back with a recorded joint easement.

SB 9 Urban Lot Splits

SB 9 lets an owner split a lot in a single-family residential zone into two lots with no public hearing. San Marcos writes it into Chapter 19.44, adopted by Ordinances 2021-1510 and 2021-1511. The City Engineer "shall ministerially approve" the map if it meets all of the following:

• Both new lots are at least 1,200 square feet, and neither is "smaller than 40 percent of the lot area of the original parcel."
• The lot is in a single-family residential zone and not in a historic district, a State Historic Resources Inventory listing or a local landmark site.
• No housing would be demolished or altered that is rent restricted, under rent control, withdrawn from rental within 15 years, or "occupied by a tenant in the last three years."
• The lot was not itself created by an urban lot split, and the owner has not split an adjacent lot this way.
• Each unit has vehicle access to the public street, the lots are for residential uses only, and rentals are longer than 30 days.
• The applicant signs a recorded affidavit "to occupy one of the housing units as their principal residence for a minimum of three (3) years," unless the applicant is a community land trust or qualified nonprofit.

Section 19.44.100 gives the City Engineer "50 calendar days after an application is deemed complete" to decide, which is shorter than the 60 days in Government Code 66411.7(b)(1)(B). Section 19.44.110(B) refuses a split that creates "more than two lots or more than four units total among the two lots", and Section 19.44.140 bars any further division of the new lots. By VanPlex arithmetic, a 7,500 square foot R-1-7.5 lot splits into two lots of 3,750 square feet; the 40 percent floor is 3,000 square feet.

Two San Marcos rules differ from the statute, and the statute controls. Section 19.44.110(D) lets the building official deny a split for an adverse impact "upon public health and safety of the physical environment," while Government Code 66411.7(d) allows denial only for a specific, adverse impact "upon public health and safety for which there is no feasible method to satisfactorily mitigate or avoid" it. Section 19.44.050(L) caps homes on the new lots at 16 feet and one story; the statute bars standards that "would result in a unit size of less than 800 square feet" and limits side and rear setbacks to four feet. The ADUs and SB 9 page covers the unit rules.

Starter Home Maps Under SB 684 and SB 1123

SB 684 and SB 1123 added Government Code 66499.41, which requires a city to consider "without discretionary review or a hearing" a map that creates 10 or fewer parcels for a project of 10 or fewer homes. VanPlex searched the San Marcos code chapters read for this guide and found no local chapter that applies it, so the statute applies on its own terms. The version in force on October 11, 2026 was amended by SB 1090, effective September 30, 2026.

• Which lots. A lot zoned for multifamily use of up to five acres, or a vacant lot zoned for single-family homes of up to one and one-half acres, "substantially surrounded by qualified urban uses."
• Lot size. New parcels of at least 600 square feet, or 1,200 square feet if zoned single-family.
• Home size. An average of no more than 1,750 net habitable square feet.
• No frontage minimum. The project need not meet a minimum "size, width, depth, frontage, or dimensions" for each parcel beyond the parcel size floor.
• Deadline. Approval or denial within 60 days of a complete application, or the map is deemed approved.

In San Marcos the R-2, R-3-10 and R-3-6 zones permit multifamily dwellings, so their lots are candidates. The 90-foot lot depth in Section 19.16.010(f) and the flag lot frontage in Section 19.28.020 would not apply to a qualifying map, because the statute sets aside those dimension rules. A tentative map under this statute still needs a filing with the City, and the City has no published local form in the code; ask the City Engineer how to apply.

Where to Go Next

Related on VanPlex: the San Marcos overview, the California SB 9 page and the California SB 684 and SB 1123 page.

Frequently Asked Questions

Official sources (checked October 2026)