ADU Rules: Bonsall vs Bostonia
How do adu rules rules compare between Bonsall, CA and Bostonia, CA?
Bostonia has fewer restrictions than Bonsall.
Bonsall, CA
San Diego County
San Diego County allows Accessory Dwelling Units (ADUs) on residential properties in unincorporated areas per state law and the County ADU Handbook. Detached ADUs up to 1,200 sq ft. Must maintain 4-foot side/rear setbacks. ADUs up to 800 sq ft are exempt from lot coverage limits.
View full Bonsall rules →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 →Key Facts Comparison
| Fact | Bonsall | Bostonia |
|---|---|---|
| Max Size (Detached) | 1,200 sq ft | - |
| Side/Rear Setback | 4 feet minimum | 4 ft minimum + fire setbacks |
| Lot Coverage Exempt | ADUs up to 800 sq ft | - |
| Height (at property line) | 16 ft max, else 4 ft setback | - |
| Separation | 6 ft from other structures | - |
| 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 |
Highlighted rows indicate differences between cities.
Bonsall FAQ
Can I build an ADU in unincorporated San Diego County?
Yes. State law requires the County to allow ADUs on residential properties. Detached ADUs up to 1,200 sq ft are permitted with a building permit from County PDS.
What are the setback requirements for an ADU?
Both attached and detached ADUs must maintain at least 4-foot side and rear setbacks. Detached ADUs 16 feet tall or less may be at the property line. Front setbacks follow the underlying zone.
Does an ADU count toward lot coverage?
ADUs up to 800 sq ft are exempt from lot coverage requirements, meaning you can build one even if your lot is at the maximum allowed coverage.
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.
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