ADU Rules: Bostonia vs San Marcos
How do adu rules rules compare between Bostonia, CA and San Marcos, CA?
Bostonia has fewer restrictions than San Marcos.
Bostonia, CA
San Diego County
Bostonia is an unincorporated CDP in San Diego County (adjacent to El Cajon) governed by the San Diego County Zoning Ordinance §6156 (Accessory Dwelling Units and Junior Accessory Dwelling Units), not a city ordinance. The County allows one ADU plus one JADU on single-family lots; non-conforming multifamily complexes may have up to two detached ADUs OR conversion ADUs created within the existing complex.
View full Bostonia rules →San Marcos, CA
San Diego County
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.
View full San Marcos rules →Key Facts Comparison
| Fact | Bostonia | San Marcos |
|---|---|---|
| Governing Code | San Diego Co. Zoning Ord. §6156 | - |
| Max Attached ADU | 1,200 sq ft (50% rule applies) | - |
| Max Detached ADU | 1,200 sq ft | - |
| Max JADU | 500 sq ft | - |
| Side/Rear Setback | 4 ft minimum + fire setbacks | - |
| 1 BR Max | - | 850 sq ft |
| 2+ BR Max | - | 1,000 sq ft |
| Front Yard | - | Generally prohibited |
| Soils Report | - | Required over 500 sq ft |
Highlighted rows indicate differences between cities.
Bostonia FAQ
Who regulates ADUs in Bostonia?
Bostonia is unincorporated San Diego County, so the San Diego County Department of Planning & Development Services regulates ADUs under Zoning Ordinance §6156, not the City of El Cajon.
How big can my Bostonia ADU be?
Under §6156, detached ADUs may be up to 1,200 sq ft and attached ADUs up to 50% of the primary dwelling capped at 1,200 sq ft (at least 800 sq ft must always be allowed). JADUs are capped at 500 sq ft within the existing single-family dwelling.
Can a Bostonia multifamily complex add ADUs?
Yes, but only one approach per property: up to two detached ADUs OR conversion ADUs created within the existing multifamily complex, not both, per §6156.
San Marcos FAQ
Can I build an ADU on my property in San Marcos?
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.
What are the size limits for an accessory dwelling unit in San Marcos?
1 BR Max: 850 sq ft. 2+ BR Max: 1,000 sq ft. Front Yard: Generally prohibited. Soils Report: Required over 500 sq ft.
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