Multifamily and Duplex Properties for Sale in San Marcos: Zoning and Rent Rules

By Matthew Martinez, Founder, CEO & Managing Broker, Diamond Real Estate Group. California DRE #01869679.

San Marcos zones for duplexes through fourplexes in R-2, apartments in R-3-10 and R-3-6, and denser mixed-use housing in MU-1 and MU-2. Many newer projects sit inside specific plans such as the University District. Apartment rents follow state law, but the city’s 18 mobile home parks fall under a local Mobile Home Rent Review Ordinance.

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What multifamily in San Marcos looks like

The housing stock includes small-lot and attached homes, duplex-to-fourplex buildings, garden apartments and townhome communities, newer mixed-use buildings in specific plan areas, and a large stock of mobile home parks. The city says it has 18 parks housing 3,557 families (City of San Marcos). Specific plans such as University District, Heart of the City and San Marcos Creek set their own residential standards (City of San Marcos). For 2-4 unit purchases, see our financing guide. Larger buildings need apartment building loans.

Where the zoning allows it

Zone	Housing types	Density	Min. lot	Height
R-2	Small-lot and attached single-family, duplex, triplex, fourplex (designed to look like a single home)	12 du/acre	3,500 sq ft	35 ft / 2 stories
R-3-10	Medium-density multifamily near services and bus lines	12.1–20 du/acre	10,000 sq ft	35 ft / 2 stories
R-3-6	Apartments, rowhouses, townhomes, motorcourts, condos	20.1–30 du/acre	6,000 sq ft	45 ft / 3 stories
MU-1	Apartments over storefronts on corridors and near transit	20–30	—	25–48 ft
MU-2	Higher-intensity mixed use	30–45	—	25–60 ft
R-MHP	Mobile and manufactured home parks	Per Ch. 20.245	—	—

Sources: SMC Ch. 20.215, Ch. 20.225, zoning overview.

R-2 limits multifamily to buildings that look like single-family homes unless a Planned Residential Development (§ 20.435) modifies that. R-3-6 requires 30% common open space plus private open space: 250 sq ft at ground level or 50 sq ft balconies above. Rooming houses need a CUP in the R-3 zones (SMC § 20.215.040–.060). MU-3 and MU-4 don’t allow residential at all (SMC Ch. 20.225). Some multi-unit projects in the Ridgeline Protection Overlay need a Ridgeline Development Permit.

ADUs and SB 9. ADU rules are in SMC Ch. 20.410 (zoning overview). SB 9 applies on qualifying R-1 lots. See our SB 9 guide and ADU investment guide.

Rent rules: state law for apartments, local review for mobile home spaces

Apartments and houses. The Attorney General’s chart lists no local rent limit for San Marcos. AB 1482 caps San Diego-area increases at 8.2% from August 1, 2026 to July 31, 2027 (AG rent caps). Exempt: buildings with a certificate of occupancy in the last 15 years, single-family homes not owned by corporations, and owner-occupied duplexes. After 12 months, just cause applies (AG). See AB 1482 for landlords and just cause eviction.

Mobile home spaces. San Marcos has a Mobile Home Rent Review Ordinance. Its stated goal is to protect residents from unreasonable space-rent increases while letting park owners earn a just and reasonable return. A council-appointed Mobile Home Rent Review Commission encourages owners and residents to negotiate space rents, and the Commission revised its procedures in 2023 (City of San Marcos). The city also says designated mobile home park properties carry 30-year deed restrictions keeping units available to low- and moderate-income households (City of San Marcos). Before buying a park, get the ordinance, the Commission’s procedures and any recorded restrictions.

San Marcos rental property rules

Mobile home park buyers. Expect both state Mobilehome Residency Law and the city’s rent review process. AB 1482 generally doesn’t cover space rents.
Specific plan housing. In the University District and other plan areas, the plan’s standards control, including density and parking.
Contacts. Housing & Neighborhood Services, (760) 744-1050 ext. 4517, handles mobile home matters.
I found no rental registration or inspection program, or short-term rental permit system, on official city pages. Confirm with the city.

Floodplain, ridgelines and building issues

The city’s Flood Damage Prevention Overlay and Ridgeline Protection Overlay apply to mapped parcels (zoning overview). Both can limit additions and new units. In older garden apartments, review tuck-under parking for soft-story risk (seismic retrofit). Buildings with three or more units and elevated balconies need SB 721 inspections (SB 721).

Underwriting a San Marcos multifamily purchase

Confirm whether the parcel is under Title 20 or a specific plan, then test the units against the zone’s density (12, 20 or 30 per acre).
In R-2, confirm that a three- or four-unit building was approved under the single-home design rule or a PRD.
Confirm the certificate-of-occupancy date for AB 1482, and use the 8.2% cap.
For a mobile home park, get the rent review ordinance, any Commission decisions and the deed restrictions.
Get estoppels and leases (estoppel certificates).
Check flood and ridgeline overlays, then run the numbers (rental property analysis).

Questions people ask

Does San Marcos have rent control?

Not for apartments. AB 1482 applies there. Mobile home space rents are subject to the city’s Mobile Home Rent Review Ordinance.

Can I build a fourplex in R-2?

Yes, if it’s designed to look like a single-family home, at a maximum density of 12 units per acre. A Planned Residential Development can modify the design limit.

Which zone allows the densest apartments?

R-3-6 allows up to 30 units per acre, and MU-2 allows up to 45 in a mixed-use project.

How many mobile home parks are in San Marcos?

The city reports 18, housing 3,557 families.

Does the University District have its own rules?

Yes. It’s a specific plan, amended in 2022, that sets its own standards near Twin Oaks Valley Road and North City Drive.

Is housing allowed in MU-3 or MU-4?

No. Both are job- and industry-focused and exclude residential.

Sources & notes

General information, not legal or tax advice. Last reviewed October 2026 by Matthew Martinez.

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