A homeowner in Agoura Hills wants a second home on the property and gets two answers in the same week. The architect measures eight feet off one side fence and says that is as close as anything can go. A friend who just did the same thing says four feet. Neither is wrong. They are quoting different chapters of the same city code, and which one applies depends on a choice made before anything is drawn.
Short answer: On an ordinary lot under ten thousand square feet in the RS district, Agoura Hills requires eighteen feet of combined side yard with at least eight feet on any one side, and caps buildings at fifty percent of the lot (9243.4). A project filed under the city's SB 9 rules instead owes only a four-foot minimum side and rear setback (9293.4) — but that same section bans an accessory dwelling unit on a lot split this way.
The property in this example
| Item | Value |
|---|---|
| City | Agoura Hills |
| Lot area | 6,713 square feet |
| Lot width | About 74 feet |
| Lot depth | About 108 feet |
| Zoning district | RS, single-family residential |
| Existing house | About 1,924 square feet, built 1978 |
At 6,713 square feet the lot is comfortably below the ten thousand square foot line that splits the RS standards in two, so the smaller-lot column governs.
Key numbers, side by side
| Standard | Ordinary RS rules | Under the city's SB 9 rules |
|---|---|---|
| Minimum side yard | 18 feet combined, at least 8 on one side (9243.4) | 4 feet (9293.4) |
| Minimum rear yard | 20 feet (9243.4) | 4 feet (9293.4) |
| Minimum front yard | 20 feet (9243.4) | not stated for this district in the section |
| Maximum building coverage | 50 percent (9243.4) | not stated in the section |
| Parking | district standards | 1 space per home, waived near transit (9293.4) |
| Accessory dwelling unit | allowed under the city's separate rules | not permitted on a lot split this way (9293.4) |
What the ordinary rulebook asks
The RS district splits its standards at ten thousand square feet. For everything below that line the city sets a twenty-foot front yard, a twenty-foot rear yard, a fifteen-foot street side yard, and side yards totalling eighteen feet with no single side narrower than eight (9243.4). Building coverage — the share of the lot the buildings sit on — is capped at fifty percent.
On a 74-foot-wide lot, eighteen feet of combined side yard leaves about 56 feet of buildable width. The fifty percent coverage cap allows roughly 3,356 square feet of building on 6,713 square feet of land, against an existing house of about 1,924 square feet — so on paper there is room, and width is the tighter constraint.
Two exceptions soften this for people extending what they already own. A single-story addition may keep the existing distance from the side property line where that is less than the district requires, provided it stays out of the front and rear yards and the total floor area does not exceed the district's building coverage. A second-story addition may follow the first story's line, but the district's combined side yard total still has to be maintained — and it may all be taken on one side (9605.1). Neither exception applies to new construction or a substantial remodel that removes and rebuilds floor area.
What the SB 9 rulebook asks
SB 9 is the state law that lets an owner add homes on a single-family lot or split it in two. Agoura Hills wrote its own standards for projects filed under it, and the setback line is short and blunt:
Side and rear setbacks shall be a minimum of four (4) feet, except that no setback shall be required for an existing structure
— Agoura Hills Zoning Code 9293.4
Four feet on each side leaves about 66 feet of buildable width on this lot, roughly ten feet more than the ordinary rules allow. On a lot 74 feet wide that is a large share of the usable frontage, and it is the single biggest reason a project chooses this route.
Parking loosens too: one off-street space per home is required, but none at all if the parcel is within half a mile walking distance of a major transit stop or a high-quality transit corridor, or if a car-share vehicle sits within one block (9293.4).
The cost of the swap
The same section takes something back, and it is easy to miss because it is buried among the design standards. Accessory dwelling units are not permitted on parcels that have been created, or are proposed to be created, through an urban lot split, nor on proposed developments of no more than two homes under this part (9293.4). If your plan was a lot split now and a backyard unit later, the city's own rules close that door.
The landscape standards are unusually specific, and they are conditions of approval rather than suggestions. At least fifty percent of new planting must be native, drought-tolerant species drawn from the California Native Plant Society's list for Agoura Hills. Nothing on the California Invasive Plant Council's list may be used. New landscape areas need at least five different shrubs and groundcovers. Planted berms and slopes may be no steeper than two to one. Palm trees are prohibited outright in new landscape areas (9293.4).
Protected oaks come with their own limit: no more than ten percent of the total estimated canopy or root structure of the protected oaks on a property may be removed (9293.4). Full public right-of-way improvements along the project frontage are required unless state law prohibits requiring them, and nothing may overhang a known drainage course.
If the ground slopes
There is a third rulebook underneath both. Any parcel with an average slope greater than ten percent picks up a separate set of standards for projects filed under this part (9293.8). Height is measured against the lot rather than the building: no structure may exceed fifteen feet above the average finished grade of the rear lot line where the rear is higher, or above the average front lot line elevation where the front is higher. Structures must sit at least twenty feet back from the top of any slope steeper than ten percent, slopes over thirty-five percent are excluded from the average and closed to development except for access roads, and stilt or cantilevered structures are banned in the very high fire hazard severity zone.
Slope is not in the assessor record, so nothing here says whether this particular lot is above or below that line. In this part of Los Angeles County it is a real possibility and worth measuring before the setback comparison above means anything.
What this does not settle
Whether a project qualifies under the state law at all is a separate test with its own eligibility screens, and this analysis does not reach it. Height limits in the RS district, the accessory building rules for anything detached (9606), overlay districts, oak tree locations, and the actual slope of the ground are all outside what a parcel record can show. Setback numbers also do not tell you whether the resulting home is one you would want to live beside. Confirm everything with Agoura Hills planning before drawing; the Agoura Hills overview collects the rest.
Sources
- Agoura Hills Zoning Code 9243.2 to 9243.4 — RS district minimum lot sizes and development standards
- Agoura Hills Zoning Code 9293.4 — SB 9 development standards for all projects
- Agoura Hills Zoning Code 9293.8 — SB 9 development standards for hillside lots
- Agoura Hills Zoning Code 9605.1 — side and rear yards, requirements and exceptions
- Agoura Hills Zoning Code 9606 — accessory buildings
