Accessory Structures in San Marcos, CA (2026)
6 verified accessory structures rules for San Marcos, California, sourced directly from the municipal code and official government pages.
Verified from official government sources
ADU Rules
San Marcos caps accessory dwelling units under Municipal Code § 20.410.060 at 850 square feet for a one-bedroom unit and 1,000 square feet for two or more bedrooms, or 50% of the primary home's living area, whichever is smaller. Detached ADUs top out at 16 to 20 feet in height depending on transit proximity.
San Marcos ADU Size and Height Rules
Some RestrictionsSan Marcos Municipal Code § 20.410.060.C.1
C. Size and Height Limitations. The building size for all ADUs shall be limited to the smallest square footage applicable to the parcel:1.Size of attached or detached ADU shall be:a.The total floor area of an ADU shall not exceed fifty percent (50%) of the living area of the proposed or existing primary dwelling, provided, however, that the maximum square footage allowed must be at least eight ...
ADU Impact Fees
San Marcos charges no utility fees or capacity charges on ADUs, and Municipal Code § 20.410.060.G exempts any ADU under 750 square feet from public facilities fees entirely. Larger units pay fees sized only to their actual burden on services, based on the primary home's size.
San Marcos ADU Impact Fee Rules
Few RestrictionsSan Marcos Municipal Code § 20.410.060.G
G. Public Facilities and Utilities Fees.1.The City does not assess utilities fees or capacity charges.2.All public facilities fees required by this chapter shall be proportionate to the burden of the ADU on the public facility, shall be based upon the size of the primary dwelling unit, and shall not exceed the reasonable cost of providing the service. No public facilities fees shall be imposed ...
ADU Owner Occupancy
San Marcos requires an owner-occupancy deed restriction before any Junior ADU gets a building permit. Municipal Code § 20.410.060.O.5 mandates that either the primary home or the Junior ADU be owner-occupied, recorded against the property with the County Recorder.
San Marcos Junior ADU Owner-Occupancy Rule
Some RestrictionsSan Marcos Municipal Code § 20.410.060.O.5
O. Deed Restriction. Prior to the issuance of a building permit for a Junior ADU, a Deed (Land Use) Restriction shall be recorded with the County Recorder that includes all the following:1.Prohibiting of the sale of the Junior ADU separately from the sale of the single-family residence, including a statement that the deed restriction may be enforced against future purchasers; ... 5.Requiring th...
ADU Rental Restrictions
San Marcos bans short-term rentals of accessory dwelling units outright. Municipal Code § 20.410.060.H allows an ADU to be rented only for terms of 30 days or longer, and bars selling it separately from the primary home except in narrow state-law circumstances.
San Marcos ADU 30-Day Rental Minimum
Heavy RestrictionsSan Marcos Municipal Code § 20.410.060.H
H. Rental or Sale of ADU. The ADU may be rented for terms 30 days or longer. The ADU may not be sold separately from the primary dwelling unit except when pursuant to Government Code Section 66341. An ADU may be approved and built at the same time as the primary dwelling unit is approved and constructed. This section shall not apply to Junior ADUs.
Shed & Carport Rules
San Marcos caps a detached shed or other accessory structure at 15 feet in height and one story, and limits total enclosed accessory floor area to 40% of the primary home's living area or 800 square feet, whichever is less, under Municipal Code § 20.410.040.
San Marcos Shed and Accessory Structure Rules
Some RestrictionsSan Marcos Municipal Code § 20.410.040(B)-(C)
B. Accessory Structure(s) Size. The maximum allowable gross floor area for all completely enclosed accessory structures in conjunction with an existing single-family residence, excluding ADUs, shall be equal to forty percent (40%) of the living area of the primary dwelling unit, or eight hundred (800) square feet of gross floor area, whichever is less. ... C. Height. Height of the accessory str...
Garage Conversions
San Marcos lets a garage be converted to an accessory dwelling unit without adding new setbacks and without replacing the lost parking under Municipal Code Section 20.410.060, but bars converting the required third garage stall on larger homes into living space under Section 20.340.050(H).
San Marcos Garage Conversion Rules
Some RestrictionsSan Marcos Municipal Code §§ 20.410.060(E)(1),(J)(3); 20.340.050(H), Table 20.340-5
1.No setbacks are required for an existing living area or accessory structure that is converted to an ADU or is in the same location and to the same dimensions as the original structure.2.A setback of four (4) feet from the side and rear lot lines is required for an ADU that is not converted from an existing structure or a new structure constructed in the same location and to the same dimension...
Looking for San Diego County county-wide rules?
County ordinances apply to unincorporated areas and may supplement San Marcos city rules.
Accessory Structures in San Diego County →