California ADU rules · San Diego County
Can I Build an ADU in El Cajon?
Yes — you can build an ADU in El Cajon. California's statewide ADU law requires every city, including El Cajon, to approve a qualifying accessory dwelling unit by right, plus a junior ADU (JADU) on a single-family lot. What varies city to city are the local specifics below.
Can you build one?
ADUs allowed
CA state lawYes — by right
ADUs and JADUs are allowed by right in all residential and mixed-use zones; ministerial approval, no hearing.
Units on a single-family lot
CA state law1 ADU + 1 JADU
At least one ADU and one JADU per single-family lot (a conversion ADU may also be possible).
Units on a multifamily lot
Local ruleconversions (>=1 or 25% of units) + up to 8 detached or as many as there are primary units (whichever is less)
Detached ADUs on multifamily lots capped at 8 or number of primary units, whichever is less.
Junior ADU (JADU)
CA state lawAllowed
Up to 500 sq ft, within the walls of an existing single-family home (single-family lots only).
Size & height
Max detached ADU size
Local rule1,200 sq ft
Detached ADU cannot exceed 1,200 sq ft or the size of the primary dwelling (including attached non-habitable spaces).
Max attached ADU size
Local rulenot more than 1,200 sq ft and not larger than the primary dwelling (including attached non-habitable spaces)
Attached ADU cannot exceed 1,200 sq ft or the size of the primary dwelling (including attached non-habitable spaces).
Guaranteed minimum size
CA state law800 sq ft
An 800 sq ft ADU must be allowed regardless of FAR/lot-coverage caps; a city also cannot cap an attached ADU below 850 sq ft (1,000 for 2+ bedrooms).
Max JADU size
CA state law500 sq ft
Max height
Local rule20 ft
20 ft with 5 ft setback; 16 ft with 4 ft setback; 12 ft with 3 ft setback; 18 ft if near transit or on 2-story lot; up to 2 ft more for roof pitch alignment.
Setbacks
Side setback
Local rule3 ft
Minimum 3 ft; may be 4 or 5 ft for greater height.
Rear setback
Local rule3 ft
Minimum 3 ft; may be 4 or 5 ft for greater height.
Front setback
Local ruleDetached ADUs must be outside the front and exterior setback unless this would prohibit an 800 sq ft ADU
Front setback applies unless it would prohibit an 800 sq ft ADU.
Separation from main house
CA state lawNone required
No statewide separation requirement between the ADU and the primary dwelling.
Parking
Parking required
Local ruleUp to 1 space
1 paved off-street space per ADU, with multiple exemptions.
Transit parking exemption
CA state lawYes — no parking required near transit & for conversions
No parking may be required within ½ mi walking distance of transit, in a historic district, for an ADU within an existing structure, within one block of car-share, or in certain permit-parking areas.
Garage-conversion replacement parking
Local ruleNot required
No replacement parking required when garage/carport/covered parking is converted.
Approval, timeline & cost
Approval path
CA state lawMinisterial (by right)
No public hearing or discretionary design review for a qualifying ADU.
Approval timeline
CA state law60 days
The agency must act within 60 days of a complete application — and the ADU is deemed approved if it does not.
Owner-occupancy
Local ruleOnly for a JADU
Owner-occupancy required only for JADUs if there are shared sanitation facilities.
Impact-fee waiver
CA state lawWaived under 750 sq ft
An ADU of 750 sq ft or less pays no impact fees (the 750 sq ft threshold itself is exempt under § 66311.5); larger ADUs pay fees proportional to the primary dwelling. JADUs (≤ 500 sq ft) are exempt.
Permits required
CA state lawBuilding permit
Only a ministerial building permit — no conditional use permit or discretionary design review for a qualifying ADU.
El Cajon-specific factors that can change the answer
State law sets the floor, but these local conditions often decide whether a specific parcel works.
Very High Fire Hazard Severity Zone (VHFHSZ)
Movable tiny homes (used as ADUs) not allowed in VHFHSZ unless approved by fire marshal with extra conditions.
Historic/Architectural Districts
Parking and demolition notice exemptions apply for ADUs in historic districts.
El Cajon caps both attached and detached ADUs at 1,200 sq ft or the size of the primary dwelling, and allows up to 8 detached ADUs on multifamily lots (or as many as there are primary units, whichever is less). Minimum side and rear setbacks are 3 ft, increasing for taller ADUs.
Frequently asked questions
Can I build an ADU in El Cajon?
Yes. California's statewide ADU law requires El Cajon to approve a qualifying accessory dwelling unit ministerial (by right), plus a junior ADU (JADU) on a single-family lot.
How big can an ADU be in El Cajon?
A detached ADU of at least 1,200 sq ft must be allowed, and an ADU of 800 sq ft can never be zoned out by floor-area or lot-coverage limits. A JADU can be up to 500 sq ft.
What are the setback requirements for an ADU in El Cajon?
Side and rear setbacks are limited to 3 ft. Detached ADUs must be outside the front and exterior setback unless this would prohibit an 800 sq ft ADU.
Is parking required for an ADU in El Cajon?
Up to 1 space. No parking can be required within ½ mile of transit, for conversions, or for units inside the primary home. When a garage is converted, replacement parking is not required.
How long does ADU approval take in El Cajon?
A complete application must be acted on within 60 days, with ministerial (by right) — no public hearing or discretionary design review for a qualifying ADU.
Do I have to live on the property to build an ADU in El Cajon?
Owner-occupancy: only for a jadu. ADUs under 750 sq ft are also exempt from impact fees.
Sources
- El Cajon Municipal Code § 17.140.180 (Ord. 5142, 5/28/2024; Ord. 5148, 1/28/2025; Ord. 5173, 2/10/2026)
- § 17.140.180(B)
- § 17.140.180(C)(2)
- § 17.140.180(E)(2)(b), (E)(3)(b)
- § 17.140.180(E)(2)(a)-(c)
- § 17.140.180(D)
- § 17.140.180(D)(2)
- § 17.140.180(F)(1)
- § 17.140.230(J)
- § 17.140.180(D)(1)(b)
- Cal. Gov. Code §§ 66310–66342 (ADU Law)
- HCD 2025 Accessory Dwelling Unit Handbook
- Cal. Gov. Code § 66317 (ministerial approval, 60-day deadline)
- Cal. Gov. Code § 66323 (by-right ADU/JADU, 800 sq ft, 4-ft setbacks)
- Cal. Gov. Code § 66333 (junior ADUs)
- Cal. Gov. Code § 66321 (size minimums & height)
- Cal. Gov. Code § 66322 (ADU parking; § 66334 covers JADU parking)
- Cal. Gov. Code § 66311.5 (impact fees: none for an ADU ≤ 750 sq ft or JADU ≤ 500 sq ft)
Last updated February 10, 2026. This is an AI-assisted summary of El Cajon's ADU rules, drawn from its published ordinance and California ADU law — general information, not legal advice, and it may be incomplete or out of date. Verify the controlling rule for your specific parcel with El Cajon Planning before relying on it.
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