San Marcos, CA Accessory Structures: Shed & Carport Rules (2026)

040 sets development standards for accessory structures such as sheds, garages, workshops, greenhouses, and cabanas, separate from ADUs. Subsection B caps the combined gross floor area of all completely enclosed accessory structures on a single-family lot at 40 percent of the primary dwelling's living area or 800 square feet, whichever is less, counting every accessory structure that requires a building permit, even ones that individually don't, but excluding structures open on at least three sides. Subsection C limits height to one story and a maximum of 15 feet at the peak of the roof, and the structure can never exceed the height of the primary dwelling.

Subsection D sets the setbacks: a detached accessory structure needs a minimum 10-foot separation from the primary dwelling or any other accessory structure (a breezeway may bridge that gap), a minimum 5-foot rear property line setback, and an interior side setback matching either the applicable zone's standard or the primary building's existing setback, whichever is less. No accessory structure may sit in a required front or street-side setback, and none may be closer to the right-of-way than the dwelling itself. Subsection A bars using an accessory structure as a dwelling: bathtubs, fireplaces, and kitchens are prohibited outright, though air conditioning, heating, a shower, toilet, washtub, or washer/dryer are allowed if the owner records a deed restriction confirming the structure won't be used for sleeping quarters. Freight containers, railroad cars, and similar storage-type structures are prohibited unless altered to match the primary dwelling's architecture.