ADU builders and rules in El Cajon

El Cajon ADU rules

El Cajon's ADU rules live in Municipal Code § 17.140.180, part of the residential zones chapter. The city hasn't published a plain-language ADU handout we could reach, so the table below reflects the code as amended by Ordinance No. 5151 in 2025 and the state's review of it. These are the city of El Cajon ADU requirements most homeowners ask about.

Two details set El Cajon apart. First, the size rule ties the ADU to the house: a detached ADU can't be bigger than the primary home. The 2025 amendment added that any lot may still include an ADU that state law guarantees, regardless of the size of the primary dwelling, lot coverage or open space limits. That guaranteed unit is a detached ADU of up to 800 sq ft with 4-ft side and rear setbacks, or a conversion of existing space.

Second, the code carries design standards. In 2024 the city granted an administrative zoning permit to reduce window transparency on one wall of a proposed 1,127 sq ft ADU under § 17.140.170, so expect design review details such as window placement to come up in plan check. For the state rules behind El Cajon ADU laws, see California ADU laws, and for layout choices, attached vs. detached ADUs.

HCD review and the 2025 update

In February 2025 the state housing department found that El Cajon's ADU ordinance, adopted May 28, 2024, failed to comply with state ADU law on ten points. Among them: it allowed only one ADU and one junior ADU on a single-family lot, capped attached ADU height by setback, left out a parking exemption, and didn't treat an attached garage as part of the house for a junior ADU.

The city responded with Ordinance No. 5151, adopted May 13, 2025, which rewrote the sections HCD flagged on unit counts, parking exemptions, detached ADU standards, fire sprinklers, attached ADU height and junior ADUs.

El Cajon ADU loan program

El Cajon runs an ADU Loan Program for homeowners who build an ADU on property they live in. It's a deferred loan, meaning you repay it later, and it covers construction costs only. The ADU must stay affordable for at least five years. Priority went to homes in the city's Environmental Justice Areas and Racially and Ethnically Concentrated Areas of Poverty during the first application period; since April 1, 2024 the city has taken applications first-come, first-served. Questions go to the Housing office at 619-441-1710 or housing@elcajon.gov.

The city didn't publish a loan limit or interest rate we could confirm, and funds are limited, so ask Housing whether money is still available before you plan around it. Our ADU financing guide and California ADU grants cover other ways to pay.

El Cajon ADU fees

Both school districts' fee pages include instructions for projects in the City of El Cajon, and both fees are paid before the building permit is issued. A 700 sq ft ADU would owe about $3,180 in school fees at those rates. El Cajon didn't publish a total ADU fee estimate, so ask the Building Division for plan check and permit fees. For build costs, see what an ADU costs in San Diego or try the ADU cost calculator.

Getting an El Cajon ADU permit

ADU permits go through El Cajon's Community Development Department at 200 Civic Center Way. Once your application is complete, state law gives the city 60 days to approve or deny it. El Cajon doesn't publish its own pre-approved ADU plans that we could confirm; our pre-approved ADU plans guide covers the County's free plans and other regional options.

Before you sign, read how to hire an ADU contractor, check a contractor's license, and compare verified ADU builders in San Diego County.

Common questions