ADU setbacks in Southern California:
what to check before you design.

Start with what state law says

For a new ADU, a local agency may require no more than four feet from the side and rear lot lines. For a conversion of an existing living area or accessory structure, or a structure rebuilt in the same location and to the same dimensions, no setback may be required (Gov. Code § 66314(d)(7)).

Front setbacks work differently. A local agency may not use a front setback, lot coverage or a similar limit to prevent an ADU of at least 800 square feet of interior livable space with four-foot side and rear yard setbacks, so long as it meets all other local development standards (Gov. Code § 66321(b)(3)). That does not mean every ADU can go in the front yard. The other local standards still apply.

How the local rules differ

City of San Diego

The City’s code is more lenient than the state’s four feet in some cases (San Diego Municipal Code § 141.0302, edition marked 9-2026). The front setback follows the base zone, with one exception: one attached or detached ADU of 800 square feet of gross floor area or less is not subject to the base zone’s front yard setback, lot coverage, floor area ratio or open space requirements (§ 141.0302(b)(4)). The street side setback is 4 feet or the base zone’s street side setback, whichever is less.

• 16 feet or less, outside a High or Very High Fire Hazard Severity Zone: no minimum interior side or rear setback.
• 16 feet or less, inside one of those zones: 4 feet.
• Taller than 16 feet: the same, except that where the side or rear line abuts residentially zoned or residentially developed land, the minimum is 4 feet or the base zone’s setback, whichever is less.

In each case the code lets the Fire Code Official require a greater setback. HCD, the state housing department, wrote to the City on October 6, 2025 that this should be framed as a fire separation distance rather than a setback, which is a different standard. Read the letter. Treat the zero figure as a minimum the Fire Code Official can raise. See our San Diego guide.

Unincorporated San Diego County

The County requires a new detached or attached ADU to meet the front yard setback of its zone and a minimum side and rear setback of 4 feet. On a corner lot, the exterior side setback is at least 4 feet from the edge of any easement, street and property line. An ADU may encroach into the front yard if the setback would otherwise prevent an ADU of 800 square feet or smaller. Converting an existing permitted accessory structure needs no setback except for fire safety, private wells and installed septic systems (Zoning Ordinance § 6156.x, items 13, 15, 16 and 17, as published with the County’s 2026 amendment). The zone’s front yard is set by a setback designator in the County’s Schedule C (§ 4810), measured from the street centerline, and its note warns that fire code setbacks may be more restrictive. HCD’s July 7, 2026 findings on the County’s ordinance concern unit counts, interior livable space wording and junior ADUs; they make no finding on these setbacks. See the County guide.

Unincorporated Ventura County

For the non-coastal area, a new detached ADU needs at least 4 feet on the side and rear. For a conversion of space in an existing home or accessory structure, setbacks must still comply with building and fire code, even if the existing setbacks are legal non-conforming (County of Ventura). The same page says amendments for the coastal area were still being prepared when we read it. HCD wrote to the County about its ADU ordinance in a letter whose file name is dated 26 August 2026, and reported that County staff said they would process applications consistently with state ADU law rather than adopt a new ordinance, so check which text the County is applying. See the County guide.

City of Ventura

A new detached ADU must be at least 4 feet from the side and rear property lines and keep the front yard setback of the zone. An ADU attached to the main residence follows the same setbacks as the main residence. Setbacks do not apply when converting an existing accessory structure such as a garage, but enlarging or modifying that structure means meeting them (City of Ventura FAQ). The City’s ordinance, as we read it in its September 2023 edition, adds that setbacks must be large enough to account for utility easements and recorded setbacks (Sec. 24.430.060). See the City of Ventura guide.

City of Los Angeles

The code requires no more than 4 feet from the side and rear lot lines for a new ADU, and no additional setback for a qualifying conversion (LAMC § 12.22 A.33(c)(8)). That is in Chapter 1 of the zoning code. The City’s code library also carries a newer Chapter 1A, so ask City Planning which chapter governs your parcel. HCD’s findings letter of 19 November 2024 on the City’s ordinance (No. 186481) says the City may not apply a size limit or setback that would stop an 800 square foot ADU with four-foot side and rear setbacks, a front setback included. We have not confirmed whether the City has amended its code since. Unincorporated Los Angeles County is a separate jurisdiction with its own code; check which one governs your parcel.

Five things to check on your lot

1. Who has jurisdiction. A mailing address does not always tell you. Confirm whether you are in a city or an unincorporated area.
2. Whether the unit is new or a conversion. The two are treated differently, and expanding a conversion can bring the new portion under the new-construction rules. In the City of Ventura, for example, enlarging an existing structure means meeting the setbacks.
3. Height. In San Diego, going over 16 feet can change the side and rear setback.
4. Fire and coastal zones. Either can add requirements, so look these up early.
5. Anything recorded on the property. Easements and utility lines are not setbacks, and meeting the setback does not clear them. Your title report and a survey will show what is there.

Where ParcelForm fits

I have spent 24 years taking residential projects through agency review, and I built ParcelForm because this research should not wait until after someone has paid for plans. Take that into account as you read this.

The free California Site Report gives you a preliminary screen of the statewide ADU framework for any California address. In San Diego, Ventura and Los Angeles counties, the $12 Zoning Snapshot lists the setbacks, size, height and parking standards for the parcel, with the ordinance section each one came from. If something cannot be confirmed, the report says so. In a small number of jurisdictions, the Buildable Envelope Report also draws the setbacks on your parcel; the pricing page lists where. All of these are automated research from public records: no one reviews them before they are delivered.

A report is not a feasibility study. Whether a unit fits still takes a survey of what is actually on the lot.

Check an address on ParcelForm →