An accessory dwelling unit can add an independent home to a property, but the right permit path depends on the parcel, the proposed unit, and the agency with jurisdiction. This guide uses current City of San Marcos and California guidance and avoids generic price or schedule promises. Our team serves homeowners throughout Rancho Bernardo and greater San Diego County.
First confirm the governing jurisdiction
A San Marcos mailing address does not prove that a parcel is inside City limits. Check the parcel with the City zoning lookup and City GIS maps before applying City standards. Properties outside the City may be reviewed by San Diego County or another agency.
The City accessory-dwelling-unit code and the California HCD ADU Handbook, updated March 2026, should be read together. Current state law controls when a local rule conflicts with it.
Choose the correct unit type
- Detached ADU: a separate structure with independent living, sleeping, cooking, and sanitation facilities.
- Attached ADU: an independent dwelling connected to the primary home.
- Conversion ADU: qualifying existing space converted to an independent dwelling.
- Junior ADU (JADU): no more than 500 square feet and created within a proposed or existing single-family residence.
Current San Marcos dimensional snapshot
| Topic | Planning rule |
|---|---|
| Size | City code lists up to 850 square feet for a one-bedroom ADU and 1,000 square feet for an ADU with more than one bedroom. Converted-space and state-mandated categories can follow different rules. |
| Side and rear setbacks | New detached ADUs generally use four-foot side and rear setbacks. Existing-space conversions and qualifying same-location replacements may be treated differently. |
| Height | A detached ADU is generally limited to 16 feet. Specified transit and multifamily circumstances can allow 18 feet, with a possible additional two feet for an aligned roof pitch. Attached ADUs are subject to the lower of 25 feet or the primary-dwelling height limit and may not exceed two stories. |
| Minimum state-law path | Front-yard and lot-coverage rules cannot eliminate the ability to build at least an 800-square-foot ADU with four-foot side and rear setbacks when the state-law conditions are met. |
| Parking | Local requirements cannot exceed one space per unit or bedroom, whichever is less. Exemptions include qualifying transit proximity and existing-space conversions. Removed garage or carport parking generally need not be replaced. |
These are planning checkpoints, not a parcel determination. Easements, fire access, utilities, grading, recorded restrictions, and the selected ADU category can change the applicable review.
Standard permit or permit-ready plan
San Marcos offers permit-ready ADU plans for pre-approved detached, one-story designs. The plans cannot be altered. Each property still needs project-specific information and a detailed site plan, and may require truss, solar, fire, utility, grading, or stormwater documents.
A complete permit-ready application has a 30-day approve-or-deny review period. That is a review rule for this limited program, not a promise of total project duration.
Property feasibility checklist
- Confirm the assessor parcel number, City limits, zoning, and recorded easements.
- Review existing permits and compare built conditions with approved records.
- Measure the proposed footprint, setbacks, access, and usable outdoor space.
- Trace sewer, water, electrical, gas, and communications routes.
- Check electrical-service capacity and likely equipment locations.
- Identify grading, retaining, drainage, stormwater, and fire-access constraints.
- Decide whether the unit is for family use, long-term rental, or another lawful use.
What affects scope without fabricated price ranges
Reliable pricing requires a defined design and property-specific investigation. Major drivers include the structure being converted or built, foundations and site work, utility distances and upgrades, engineering, energy and fire requirements, finishes, permits, agency charges, and correction cycles. Cali Dream Construction does not publish a fixed price or duration for a site it has not evaluated.
Impact fees are generally exempt for an ADU of 750 square feet or less, but school, utility, connection, capacity, special-district, and project-specific charges require direct confirmation with the responsible agencies.
Application and review
ADU applications are reviewed ministerially against objective standards. State law requires a written completeness determination within 15 business days. That is not an approval guarantee. Plans, required supporting documents, agency comments, and corrections still affect the path to permit issuance.
Occupancy, rental, solar, and fire cautions
- Standard ADUs generally cannot carry an owner-occupancy requirement. JADU owner occupancy changed on January 1, 2026 and can depend on whether sanitation is shared; confirm the current rule for the proposed layout.
- JADUs cannot be used as short-term rentals and, if rented, must be rented for more than 30 days. Confirm other rental plans against current City rules.
- New detached ADUs are generally subject to solar requirements, with exceptions. Conversions and additions to existing space can be treated differently.
- Fire sprinklers may be required when they are required for the primary residence, but constructing an ADU does not by itself trigger sprinklers in the existing primary home.
Get project-specific guidance
Cali Dream Construction provides construction services and In-Person Project Planning & Design Guidance. We are not a City agency or architectural firm, and the relevant authorities issue permits and approvals. Use the project-planning form on the Cali Dream Construction contact page to share the parcel location, intended ADU type, and known site constraints.
Next Cost And Scope Planning
Use these related guides and project examples to turn the topic above into a realistic budget, scope, and permit plan.