ADUs in San Marcos, CA
✓ Verified November 1, 2026 Rules, fees, and timelines below were verified November 1, 2026. Anything marked “confirm” or “to verify” is still open.
AB 956 allows two detached ADUs per single-family lot from January 1, 2027 under state law. No San Marcos statement on how it will apply the change — including any second-unit size cap — was found. How San Marcos applies it is to confirm.
A mailing address that says “San Marcos” does not guarantee the parcel is under City of San Marcos rules — some addresses, including Lake San Marcos and parts of Twin Oaks Valley, are unincorporated County territory (builder guide). Confirm jurisdiction before relying on anything on this page.
The City has its own ADU ordinance (San Marcos Municipal Code Chapter 20.410, repealed and replaced by Ordinance No. 2024-1551; city standards effective October 24, 2024). City Hall is at 1 Civic Center Drive, (760) 744-1050.
Does it apply to my lot? — address check
Enter a San Diego County street address. The checker geocodes it and checks public transit stops nearby. Privacy: your typed address goes directly from your browser to OpenStreetMap's free Nominatim geocoder and the public SanGIS transit-stops layer. It never touches an ADUKey server — ADUKey has no server endpoint for this, so there is nothing to send it to.
Parking-exemption rule: no parking required within a 1/2-mile walking distance of public transit (bus stops included). Straight-line distance is measured first: a straight-line miss is definitive, a straight-line hit is provisional until the walking route is checked.
What you can build
| Rule | What applies | Note |
|---|---|---|
| Attached ADU size | 850 sq ft (1 bedroom) or 1,000 sq ft (2+ bedrooms); cannot exceed 50% of the primary dwelling's living area | |
| Detached ADU size | 1 bedroom: 850 sq ft on lots under 1 acre, 1,000 sq ft on lots of 1 acre or more; 2+ bedrooms: 1,000 sq ft | Whether the 1-acre distinction also conditions the 2+ bedroom cap is to confirm — the city FAQ table is unclear there. |
| State mandatory ADU | At least one detached new-construction ADU of 800 sq ft must be allowed even if local standards cannot be met | |
| Height | Detached: 16 ft, or 18 ft within one-half mile of a major transit stop or high-quality transit corridor, up to 20 ft to match the primary roof pitch; attached: two stories and 25 ft, or the primary height limit, whichever is lower | |
| Setbacks and placement | Detached: 4 ft side and rear, rear 50% of the lot, at least 10 ft eave-to-eave from other structures; attached: 4 ft side and rear; no setback for conversions or same-footprint rebuilds | |
| Junior ADU (JADU) | Up to 500 sq ft, entirely within the primary dwelling; either the primary dwelling or the JADU must be owner-occupied | |
| Minimum size / lot | Minimum 150 sq ft; no minimum lot size for an existing legal lot; lot coverage/FAR not applicable unless zoning or a Specific Plan says otherwise; exterior must match the primary dwelling's materials, features, and colors | |
| Parking | One onsite paved space per ADU unless exemptions apply; no parking required for JADUs; garage conversions must maintain preexisting driveway parking | Exemption list is builder-guide only — the city FAQ states exemptions exist without enumerating them. |
| Minimum rental term | 30 days or longer | The short-term-rental ban itself is third-party-reported; the 30-day minimum is city-published. |
| Impact fees | Public Facilities Fees apply unless the ADU is smaller than 750 sq ft; Community Facilities District fees may also apply, plus plan check, permit, and outside-agency fees | Dollar figures for CFD charges are builder-guide only and are not published here. |
| Permit fees | Project-specific — contact the Building Division; no published schedule | No fee schedule published by the city; builder estimates of $10–$14/sq ft are not city fees and are not published here. |
| Multifamily lots | Two detached ADUs, plus conversion of existing attached nonlivable space up to 25% of existing units | The FAQ's “one additional ADU” wording is unclear in extraction, and the up-to-8 detached framing is state-law/builder-guide only — confirm with the city. |
| Overlays to check | No coastal zone (inland city); Very High Fire Hazard Severity Zone: Chapter 7A fire-resistive construction, 150 ft fuel modification; FEMA flood zones along San Marcos Creek tributaries — check per parcel | Fire construction rules below are general single-family requirements, labeled as such — not ADU-specific city rules. Hillside ADU rules: to confirm. |
Permit path
- Confirm jurisdiction and overlays with the Planning Division (planningdivision@sanmarcos.net) or Building Division (buildingdivision@sanmarcos.net, (760) 744-1050 ext. 3244).
- Submit. ADUs and JADUs require only a building permit, processed within 60 days of a complete application; the clock is tolled when the city sends corrections and restarts on resubmittal. Plans must be prepared by a licensed design professional.
- Build. Builder guides estimate 5–7 months for a standard timeline — label those as builder estimates, not city timelines.
Digital submission through the city's Clariti permitting system is reported by a builder guide — portal name and full digital availability are to confirm with the city.
Permit Ready ADU (PRADU) program
Under state law, the city Permit Ready ADU (PRADU) program offers a selection of pre-approved, detached one-story ADU building plans. Plans are mostly complete; applicants fill in project-specific information including a detailed site plan. No alterations to city-provided plan sets will be considered — a customized structure requires a standard ADU building permit. Deferred submittals (roof trusses, solar panels, possible fire sprinklers) are required with the city plan, and a building permit is issued only to the property owner or a licensed California contractor.
Review track: approve or deny within 30 days of a complete application (fresh 30-day review on resubmittal). Plan sizes, plan count, and cost were not stated in the city text available — to confirm.
Separate sale (AB 1033)
Not adopted. The 2024 ordinance staff report states staff recommended the city not adopt an AB 1033 separate-conveyance ordinance, and the revisions do not permit separate conveyances. The city FAQ agrees: an ADU may not be sold separately except under Government Code Section 66341, and a JADU may not be sold separately. Re-confirm before relying on this — no later adoption was found, but a 2025–2026 change was not exhaustively excluded.
Transit context — and what it is not
San Marcos is served by NCTD's SPRINTER rail line (stations in the city: Palomar College, San Marcos Civic Center, Cal State San Marcos) plus BREEZE bus routes — relevant because the state parking exemption uses one-half mile walking distance of public transit including bus stops, and the site's SanGIS layer covers NCTD stops county-wide. This is not a Transit Priority Area determination: TPA status is a separate layer and is not claimed here. The city's 2026 SB 79 transit-oriented-district zones are likewise not ADU parking-exemption zones.
What it costs (county range, not San Marcos data)
Cost band $300,000–$450,000+ is a San Diego County range, not verified San Marcos data. Use the calculator below with your own numbers.
Rent calculator
Defaults below are EXAMPLES — editable placeholders, not verified local rent or cost data. Type your own numbers.
Verified builders in San Diego County
One metro-level profile per builder, linked from every city page they serve. Profiles are never duplicated per city, so a correction lands everywhere at once.
Frequently asked questions
Do I need parking for an ADU in San Marcos?
One onsite paved space per ADU unless an exemption applies — the city FAQ states exemptions exist without enumerating them in the text available, so the exemption list (half-mile walking-distance transit, historic district, conversion) is builder-guide only and must be confirmed as a city rule. No parking is required for JADUs. With a garage conversion, preexisting driveway parking must be maintained.
How big can an ADU be in San Marcos?
Attached: 850 sq ft (1 bedroom) or 1,000 sq ft (2+ bedrooms), no more than 50% of the primary dwelling. Detached: 1 bedroom 850 sq ft on lots under 1 acre, 1,000 sq ft on lots of 1 acre or more; 2+ bedrooms 1,000 sq ft — whether the 1-acre distinction also conditions the 2+ bedroom cap is to confirm, as the city FAQ table is unclear there. At least one 800 sq ft detached ADU must be allowed even if local standards cannot be met.
Does San Marcos offer pre-approved ADU plans?
Yes — the city Permit Ready ADU (PRADU) program offers pre-approved, detached one-story plans under state law. Plans are mostly complete, no alterations to city plan sets are considered, and the city approves or denies within 30 days of a complete application. Plan sizes, plan count, and cost were not stated in the city text available — to confirm.
Can I sell an ADU separately from the house in San Marcos?
No. The 2024 ordinance staff report recommended the city not adopt an AB 1033 separate-sale ordinance, and the proposed revisions do not permit separate conveyances. Re-confirm, as no later adoption was found but a 2025–2026 change was not exhaustively excluded. JADUs can never be sold separately.
Sources
- City of San Marcos ADU FAQ — city standards effective October 24, 2024 (city-published)
- Ordinance No. 2024-1551 legislative record (city-published)
- City of San Marcos Permit Ready ADUs page (city-published)
- PRADU program information, Fall 2024 (city-published)
- City of San Marcos Building Division (city-published)
- San Marcos ADU regulations — SnapADU (builder guide)
- San Marcos ADU guide — Lars (builder guide)
Not legal advice. This page is a starting point, not a parcel approval. Confirm your lot with the city before you build, buy, or sign anything.
Report an outdated rule
Rules change. If something on this page no longer matches the city's current rules, tell us what changed and where you saw it. Reporting is not wired to a destination yet — your note stays on this page and is not sent anywhere.