San Mateo | Lot Size and Subdivisions
San Mateo, California Lot Size and Subdivisions: Parcel Sizes, Parcel Maps, Tentative Maps, Lot Design Rules, SB 9 Urban Lot Splits and Small-Lot Maps
Dividing land in San Mateo means meeting two titles of the Municipal Code. Title 27, the Zoning Code, sets the size and width each new parcel must have. Title 26, the "San Mateo City Subdivision Code," sets the type of map, who approves it and how lots must be shaped. State law adds two more ways to divide land: the SB 9 urban lot split, which the City has written into Chapter 27.21, and the SB 684 small-lot map, which applies directly from the statute. This page covers all four. The San Mateo overview has the summary.
San Mateo lots and subdivisions in six facts
- A new R1 parcel needs 10,000 square feet and 75 feet of width in R1-A, 6,000 square feet and 60 feet in R1-B, and 5,000 square feet and 50 feet in R1-C. Source: Zoning Code 27.18.040
- A division into four or fewer lots may use a parcel map, which the Zoning Administrator approves; other divisions need tentative and final subdivision maps. Source: Subdivision Code 26.12.040 and 26.56.060
- Every new lot needs at least 30 feet of frontage on a street, an average depth of no more than three times its average width, and no panhandle shape. Source: Subdivision Code Chapter 26.20
- An SB 9 urban lot split in San Mateo creates two parcels of at least 1,200 square feet each, and the smaller one must be at least 40 percent of the original parcel. Source: Zoning Code 27.21.140
- A tentative map approval expires two years after its date of approval, and the Zoning Administrator may grant up to three two-year extensions. Source: Subdivision Code 26.48.135
- The Public Works fee for a parcel map is $8,411.50 per map and for a final map $10,630.35 per map in the fee schedule for July 1, 2026 to June 30, 2027. Source: Adopted Comprehensive Fee Schedule 2026-2027
How Large a New Parcel Must Be
Section 27.18.040 says "Dwellings developed after the effective date of this title shall be developed on recorded parcels which meet the following prescribed standards," and lists an area and a width for each R1 district. A footnote says "Parcel width is measured at the front setback line." A second width rule applies at the street: "All parcels shall provide a minimum width of thirty (30) feet on a recorded public street frontage."
| District | Minimum parcel area | Minimum width | Street frontage |
|---|---|---|---|
| R1-A | 10,000 sq ft | 75 ft at the front setback line | 30 ft of width on a public street frontage |
| R1-B | 6,000 sq ft | 60 ft at the front setback line | 30 ft of width on a public street frontage |
| R1-C | 5,000 sq ft | 50 ft at the front setback line | 30 ft of width on a public street frontage |
| R2, one house | R1-C standard: 5,000 sq ft | 50 ft | 30 ft of frontage, held for 120 ft of depth |
| R2, two-family dwelling | 5,000 sq ft; 4,400 sq ft if recorded before March 3, 1947 and northeast of El Camino Real | Not stated for this row | 30 ft of frontage, held for 120 ft of depth |
| R3, R4 and R5 | 5,000 sq ft; 4,000 sq ft if recorded before March 3, 1947 and northeast of El Camino Real | 50 ft; 40 ft for the older parcels | Larger and wider parcels earn more homes |
Source: San Mateo Zoning Code, 27.18.040, 27.20.050, 27.22.040, 27.24.040 and 27.26.040.
- Parcels older than the code. A house may be built on an R1 parcel below these sizes "if the parcel was recorded under separate ownership from adjoining parcels prior to March 3, 1947, if the subdivision map was approved with exceptions or if a recorded parcel has received a certificate of compliance."
- After a division. Section 27.02.075 says that when land is divided or sold "all resulting zoning plots or parcels shall conform with all regulations of the zoning district," and "There shall be no reduction in yards, open space, parking or other zoning requirements which causes or increases non-conformity."
- Apartment districts. In R3, R4 and R5 the smallest standard parcel is 5,000 square feet and 50 feet wide. Parcel size also sets the home count: see the tables on the zoning districts page.
Which Map a Division Needs
Title 26 applies to "the subdivision or other division of land for any purpose whatsoever within the City." Section 26.12.040 sorts divisions into two kinds. A map is the surveyed drawing of the new lots, recorded with the County once approved. A parcel map is decided by staff. A subdivision map has two stages, a tentative map decided at a hearing and a final map approved by the City Council.
| Application | When it applies | Who decides |
|---|---|---|
| Tentative parcel map | Four or fewer lots, four or fewer condominiums, or any number of lots on less than five acres with no new streets or dedications needed | Zoning Administrator; Planning Commission if an exception is asked for |
| Final parcel map | After the tentative parcel map is approved | Director of Public Works reviews it and has it recorded |
| Tentative subdivision map | Every division that a parcel map or lot line adjustment does not cover, and every condominium conversion | Planning Commission; City Council on appeal or when the project needs Council action |
| Final subdivision map | After the tentative map is approved | City Council |
| Lot line adjustment | Lines between two or more lots move and the number of lots stays the same | Director of Public Works and Director of Community Development |
| Merger | Lots are combined into four or fewer lots | Zoning Administrator, through the Director of Public Works |
| SB 9 urban lot split | One R1 parcel becomes two | Zoning Administrator, with no hearing and no appeal |
Source: San Mateo Subdivision Code, 26.12.040, 26.48.090, 26.52.090, 26.56.060, 26.57.010 and 26.58.010; Zoning Code 27.06.020, 27.06.040 and 27.21.030.
One rule overrides the lot count: "in all conversions of a dwelling, community apartment project, or a stock cooperative to a condominium, regardless of the number of lots, parcels, condominiums, or dwelling units involved, a tentative and final subdivision map shall be required." Chapter 26.65 has the rest of the condominium conversion rules, which this guide did not read in full. One City document differs from the table: the Planning Application Guide of April 3, 2026 lists a "Tentative Map without exceptions" among the applications the Zoning Administrator decides, while Chapter 26.48 has the Planning Commission act on a tentative map. Ask the Planning Division which applies.
The Steps and Deadlines for a Map
- Who prepares it. A tentative map is "prepared by a licensed land surveyor or registered civil engineer licensed by the State to perform such work."
- Completeness. The Zoning Administrator checks the filing and reports to the applicant in writing within thirty days. "If the written determination is not made within thirty days of receipt, the application shall be deemed complete."
- Tenants on the site. The date the application is complete "shall also vest relocation rights in the tenants then residing on the project site who will be displaced by it and who have not given voluntary notice of termination."
- The decision on a tentative map. The Planning Commission "shall take action on the map within fifty days of the application being complete," and "Failure to act within such period of time shall be deemed approval of said map" under the state Subdivision Map Act.
- Grounds to deny. Section 26.48.060 lists seven findings, any one of which requires denial. Among them: "That the site is not physically suitable for the proposed density of development."
- The decision on a parcel map. The Zoning Administrator "shall, if compliance with this Title is found, approve, or conditionally approve the tentative parcel map," guided by the same findings. If the project also needs a Planning Commission or Council approval, the map goes to that body with it.
- Notice. For hearings under Title 26, notice is published in a newspaper and posted in three public facilities at least ten days before the hearing, in addition to notice by mail.
- Appeals. A staff decision may be appealed to the Planning Commission, and a Commission decision to the City Council, "within ten (10) days of the action or decision." An appeal about a time extension has fifteen days.
- How long approval lasts. "The approval of a tentative map expires two years after its date of approval, unless extended," and the applicant "may apply to the Zoning Administrator for up to three two-year extensions."
- The final map. The City Council "will approve the map if it conforms to the tentative map and all applicable provisions of the Subdivision Map Act and this Title." A final parcel map goes to the Director of Public Works instead.
A subdivider may also file a vesting tentative map, which gives the project the right to proceed under the rules in force when the application is complete. The Planning Commission approves one only if it finds the vested rights "will not endanger the health, safety, or welfare of the City or its inhabitants."
How New Lots Must Be Shaped
Chapter 26.20 sets design rules that apply on top of the zoning sizes.
- Frontage. "All lots created, shall have not less than thirty feet of frontage on a public or private street."
- Depth. "The average depth of any lot shall not exceed three times its average width," unless a planned unit development allows it.
- Panhandle lots. A panhandle or flag lot is a lot reached by a narrow strip of its own land. "The creation of new panhandle lots shall not be permitted."
- Double frontage. "Lots with more than one frontage, other than corner lots and those designed for other than single family use shall be avoided."
- Leftover land. "No remnants of property shall be left in the subdivision which do not conform to lot requirements."
- Steep land. "Subdivisions that result in new parcels with slopes of twenty-five (25%) percent or more are prohibited unless" each parcel has a connected area below that slope "which equals or exceeds the minimum required parcel size for the applicable zoning district." Chapter 27.83 repeats the rule for R1 and R2, and in apartment and commercial districts only land below 25 percent slope counts toward floor area and density.
- City boundary. "No lot shall be divided by a city boundary line."
The Planning Commission may grant an exception to a Title 26 rule under Chapter 26.68 if three facts exist. The first is that the land "is of such shape or size, or is affected by such topographical conditions" that it is "impossible or impractical for the subdivider to comply." A map that asks for an exception goes to the Commission even when it has four or fewer lots.
Improvements, Park Fees and Affordable Homes
A subdivider builds the public improvements the division needs. Ordinance No. 2026-09, adopted on September 8, 2026 and "effective 30 days after its adoption," rewrote the list in Section 26.60.020. It now covers "the subdivision's public right-of-way frontage" as well as the land inside the map, and it includes sidewalks with "a 10-foot minimum sidewalk width," stormwater treatment, "Undergrounding of existing overhead utilities" and street trees. Ask Public Works which items apply to a two-lot map.
- Park land or fee. Chapter 26.64 requires land or a fee for parks, based on "two acres" for "each 1,000 estimated population." "Only the payment of fees is required in subdivisions of 50 parcels or less." The fee schedule for July 1, 2026 to June 30, 2027 sets the park in-lieu fee, the fee paid in place of land, at $29,971.00 per single-family home, $29,461.00 per home in a building of 2 to 4 units and $21,408.00 per home in a building of 5 or more.
- Existing homes. Homes "in existence for five years or more on the date of approval of the tentative subdivision or tentative parcel map shall be excluded from the calculations."
- Map fees. The fee schedule lists Public Works mapping fees of $8,411.50 per parcel map, $10,630.35 per final map or condominium conversion, and $4,241.43 for a lot line adjustment certificate. The planning application itself runs on a deposit; see the permits and fees page.
- Below Market Rate homes. The City's Below Market Rate Program applies to "all development projects that include five (5) or more residential units or parcels." A subdivision "resulting in eleven (11) or more parcels shall provide BMR units equivalent to at least fifteen percent (15%) of the density permitted on the subdivided lots." A division into four or fewer parcels is below the program's threshold.
SB 9 Urban Lot Splits
SB 9 is the 2021 state law that lets the owner of a house lot split it in two with no hearing. San Mateo's rules are Article II of Chapter 27.21, adopted by Ordinance No. 2022-10. The statute is Government Code 66411.7, last amended effective June 30, 2026, which is after the City text was written.
- The application. A survey by a licensed land surveyor, a parcel map under Title 26, a title report, and an affidavit on tenants and owner occupancy. The applicant "shall prepare, file, and record a final parcel map with the Department of Public Works."
- Notice, with no hearing. The City sends "an informational notice" to "all property owners and tenants within a 500-foot radius." The permit "is not appealable."
- Size. "Each newly created parcel shall be at least 1,200 square feet in gross area," and "The smallest subdivided parcel shall not be less than forty percent (40%) of the lot area of the original parcel."
- Access. Flag lots are allowed here, and so is access by easement, a recorded right to cross another lot. "A minimum 10-foot-wide strip of land owned in fee (i.e. flag lot 'pole') or 10- foot wide access easement shall be provided for all flag lots or landlocked parcels," and 20 feet where the strip "is greater than 150 feet in length."
- Homes. "In no case shall more than two dwelling units on a single lot in any otherwise allowed combination of primary units, SB 9 units, ADUs and/or JADUs be permitted."
- No street work. "Unless required to accommodate an urban lot split or provide access to a parcel, no dedications of rights-of-ways or the construction of offsite improvements" are required.
- Deed restriction. Recorded limits: residential use only, no rental of less than 30 consecutive days, and no further urban lot split of either parcel.
- Lots that cannot split. A parcel made by an earlier urban lot split, and a parcel next to one that the same owner, "or any person acting in concert with said owner," already split this way.
- Excluded housing and land. Section 27.21.050 excludes a parcel where the project would demolish or alter rent-restricted housing or "Housing that has been occupied by a tenant within the last three years," and land in the hazard and resource areas the statute lists.
| Topic | San Mateo Chapter 27.21 | Government Code 66411.7 |
|---|---|---|
| Lots that qualify | R1-A, R1-B and R1-C parcels, except those on the exclusion lists | A parcel "located within a single-family residential zone" |
| Size of the new parcels | At least 1,200 sq ft each; the smaller at least 40 percent of the original | The same two tests |
| Historic property | No parcel "designated an historic district or property" | No landmark site, and no demolition or alteration of a contributing structure in a historic district |
| Grounds to deny | Impact on "public health and safety or the physical environment" | Impact "upon public health and safety" |
| Owner occupancy | Affidavit of intent to live in one home for three years from approval and recordation of the final map | Affidavit of intent to live in one home for three years "from the date of the approval of the urban lot split" |
| Deadline | None stated in Chapter 27.21 | 60 days from a completed application, then "deemed approved" |
| Homes per new parcel | Two of any kind | A city need not allow more than two |
Sources: San Mateo Zoning Code, 27.21.030, 27.21.050, 27.21.110 and 27.21.140; Gov. Code 66411.7 as amended by Stats. 2026, Ch. 56 (SB 1426).
A city rule that is stricter than the statute allows is void to that extent, and the statute controls. Three rows of the table matter in practice. The City text lets the Building Official deny a split for an impact on the physical environment; the statute names public health and safety. The City text excludes any parcel in a historic district, and the City's historic project review page says SB 9 "does not apply to historic properties or districts"; the statute now excludes landmark sites and bars only work that alters a contributing structure or an exterior structural wall in a district. And Chapter 27.21 names no deadline, while the statute gives 60 days. Ask the Planning Division which text it applies.
Chapter 27.21 also conflicts with Title 26 on flag lots and on the 30 feet of frontage. Section 27.21.070 settles it: "If such standards conflict with this Chapter, the standards in this Chapter shall prevail."
Small-Lot Maps Under SB 684 and SB 1123
SB 684 and SB 1123 created a second state route, in Government Code 66499.41. A city must decide, with no hearing, a map for a project where "The proposed subdivision will result in 10 or fewer parcels and the housing development project on the lot proposed to be subdivided will contain 10 or fewer residential units." The lot must be "zoned to allow multifamily residential dwelling use" and "no larger than five acres," or be "A vacant lot zoned for single-family residential development" that "is no larger than one and one-half acres." New parcels may be as small as 600 square feet, or 1,200 square feet in a single-family zone, and the city must act "within 60 days from the date the local agency receives a completed application."
A search of Titles 26 and 27 found no mention of this statute or of either bill, so San Mateo has no local form or standards for it in the code. The Legislature's database holds four versions of the section, all effective September 30, 2026; this page quotes the one in force through December 31, 2026. Ask the Planning Division how it accepts such a map.
Limits of This Page
Titles 26 and 27 were read from the City's bulk copy of the code, whose index page prints "Current through" October 8, 2026. Chapters 26.16, 26.24, 26.28, 26.32 and 26.36 (design standards, blocks, streets, utilities and drainage) and most of Chapter 26.65 (condominium conversions) were not read. The City's urban lot split checklist, the interim objective design standards for SB 9 projects and the engineering standards were not read. The General Plan designation of a lot can change how many homes fit on it after a split; see the Measure T page. City Council agendas were read for September 8, September 22 and October 5, 2026 only.
Best For
- ✓ R1 parcels that can yield two lots of 1,200 square feet or more through an urban lot split, with two homes on each.
- ✓ Divisions into four or fewer lots that meet the district parcel size and need no exception, decided by the Zoning Administrator.
- ✓ Parcels with 60 feet or more of street frontage, which can give each new lot its own 30 feet.
Usually Fails When
- ✕ A regular parcel map depends on a flag lot, which Section 26.20.100 does not permit.
- ✕ A new lot would have a slope of 25 percent or more with no flatter area of the minimum parcel size.
- ✕ An urban lot split is planned on a house that a tenant occupied within the last three years.
What To Verify Before Spending Money
- → Whether the City applies its historic district exclusion or the narrower test in Government Code 66411.7.
- → Which frontage improvements Public Works requires after Ordinance No. 2026-09.
- → The park in-lieu fee and any Below Market Rate fee for the number of lots planned.
Where to Go Next
Related on VanPlex: the San Mateo overview, the California SB 9 page and the SB 684 and SB 1123 page.
Frequently Asked Questions
What is the minimum lot size for a house in San Mateo, California?
How do I split a lot into two in San Mateo?
When does San Mateo require a parcel map and when a tentative map?
Who approves a subdivision map in San Mateo?
Can I create a flag lot in San Mateo?
How small can a lot be after an SB 9 lot split in San Mateo?
Do I have to live on the property to do an SB 9 lot split in San Mateo?
How long is a tentative map good for in San Mateo?
Can I subdivide a steep lot in San Mateo?
Does a small subdivision in San Mateo pay park fees or owe affordable homes?
Does San Mateo have rules for SB 684 small-lot subdivisions?
Official sources (checked October 2026)
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