Accessory Structures in San Marcos, CA: What Residents Actually Need to Know
If you live in San Marcos or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. San Marcos has 5 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.
Tiny Homes
San Marcos permits tiny homes on permanent foundations as ADUs under California ADU law (Government Code 65852.2). Tiny homes on wheels are not recognized as permanent dwellings under SMMC.
Key details: Min JADU Size: 150 sq ft. Max ADU Size: 1,200 sq ft detached. THOWs: Not permitted as dwellings. Permit: Building permit required.
Unpermitted dwelling units subject to code enforcement action. Occupying a THOW as a residence may result in citations. Contact Code Enforcement at (760) 744-1050 x3234.
Carport Rules
Carports in San Marcos require building permits and must comply with SMMC Title 20 zoning setbacks. Carport area counts toward maximum lot coverage for the applicable zone district.
Key details: Permit: Building permit required. Side Setback: 5 ft minimum typical. Front Yard: Generally not permitted. Lot Coverage: Counts toward maximum.
Stop-work orders for building without a permit. Fines and required removal for setback violations. Code Enforcement at (760) 744-1050 x3234.
Garage Conversions
San Marcos allows garage conversions to ADUs per CA Gov Code Section 65852.2. Replacement parking is not required. Parking may be located in setbacks and driveways as tandem parking. Building permits required.
Key details: Parking: No replacement required. Tandem: Allowed in driveways. JADU: Up to 500 sq ft. State Law: Gov Code §65852.2.
Unpermitted conversions are building code violations. Living in a converted garage without permits is a safety and code violation.
ADU Rules
San Marcos allows one ADU plus one JADU per single-family lot per SMMC Chapter 20.410.060. One-bedroom ADUs up to 850 sq ft, two-bedroom up to 1,000 sq ft. ADUs generally cannot be in the front yard. A soils report is required over 500 sq ft.
Key details: 1 BR Max: 850 sq ft. 2+ BR Max: 1,000 sq ft. Front Yard: Generally prohibited. Soils Report: Required over 500 sq ft.
Unpermitted ADU construction subject to enforcement. Short-term rental of ADUs is a zoning violation. Separate sale not permitted.
Shed Rules
San Marcos exempts detached sheds under 120 square feet from building permits. Sheds must comply with zoning setbacks. Larger accessory buildings require permits and must meet building code standards.
Key details: Exempt: Under 120 sq ft. Setbacks: Zone requirements apply. Front Yard: Not permitted. Habitation: Not allowed in sheds.
Sheds over 120 sq ft without permits are building code violations. Structures in setbacks or front yards face removal orders.
If you are coming from a city with tighter rules, you will find San Marcos gives residents more flexibility on shed rules.
The Bottom Line
San Marcos's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming San Marcos is broadly strict or permissive.
This guide is based on San Marcos's current municipal code. Local rules can and do change, so check the individual ordinance pages for the latest details, penalties, and FAQs.