ADU Rules: Bostonia vs Carlsbad

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.

How do I apply for an ADU permit in Carlsbad?

Submit the Carlsbad ADU permit application through the city's digital permit portal with the building permit application, site plan, floor plans, elevations, the ADU checklist, and the Hold Harmless Agreement. Under CMC 21.10.030 and Gov. Code §65852.2(b)(1), staff must act ministerially within 60 days of a complete application — no public hearing is held. Coastal Zone applications also require a Coastal Development Permit under CMC 21.201.

What zoning rules apply to an ADU in Carlsbad?

CMC 21.10.030 allows ADUs in every zone that permits one-family, two-family, multifamily, or mixed-use residential development (R-1, R-2, R-3, R-W, R-A, R-P, V-B/Village-Barrio, and mixed-use). The ADU must comply with the underlying zone's front setback, a 4-foot minimum side and rear setback (when 16 ft or less in height), and the height limits in CMC 21.10.030 — up to 16 ft detached, 18 ft on multifamily lots, 20 ft within a half-mile of transit, or 25 ft for an attached ADU.

Can I build a backyard ADU in Carlsbad?

Yes — a detached backyard ADU is allowed on any lot with an existing or proposed dwelling under CMC 21.10.030. The backyard ADU is capped at 1,200 sq ft on single-family lots, must keep a 4-foot side and rear setback, and is limited to 16 ft tall (or up to 20 ft within a half-mile walk of major transit). The front yard setback of the underlying zone still applies, and Coastal Zone backyard ADUs need a Coastal Development Permit.

Can I convert my garage into an ADU in Carlsbad?

Yes. A garage conversion ADU is processed under CMC 21.10.030 and Government Code §65852.2. Carlsbad cannot require replacement parking when an existing garage is converted, the existing garage's setbacks are preserved for the conversion footprint, and the unit may be permitted as either an ADU or a JADU (JADU capped at 500 sq ft). A building permit is still required to change the use to habitable space.

Does Carlsbad allow ADUs for multigenerational housing?

Yes — CMC 21.10.030 explicitly recognizes that ADUs and JADUs accommodate multigenerational households. A single-family lot can hold the primary residence, one ADU, and one JADU (three units total), letting extended family live independently on the same lot. A JADU can be created within the primary dwelling (including an attached garage) at up to 500 sq ft, with owner-occupancy of either the primary unit or the JADU recorded as a deed restriction.

Is a parking space required for a Carlsbad ADU?

No, in most cases. CMC 21.10.030 follows Government Code §65852.2(d) and waives the parking requirement when the ADU is within a half-mile walk of public transit, created by converting existing space, attached to the primary dwelling, located in a historic district, or where on-street permit parking is required. Where parking is required, one tandem space in the driveway or setback area is sufficient.

What does an ADU permit cost in Carlsbad?

Per the FY 2024-25 Master Fee Schedule, Carlsbad ADU permitting fees typically run $2,000–$4,000 depending on square footage. ADUs under 750 sq ft are exempt from City Impact Fees by state law (Gov. Code §65852.2(f)(3)); ADUs over 750 sq ft pay impact fees scaled proportionally to the primary dwelling. Coastal Development Permit fees apply separately in the Coastal Zone.

Can I rent my Carlsbad ADU on Airbnb?

No. Any ADU permitted in Carlsbad on or after January 1, 2020 carries a recorded deed restriction prohibiting rentals shorter than 30 days, and short-term rental use is separately prohibited under the Short-Term Vacation Rental ordinance (CMC 5.60). Violations can result in deed-restriction enforcement and revocation of the ADU's certificate of occupancy.