Encroachment Plane

The encroachment plane is an invisible inclined plane that rises inward at a 45-degree angle from a specified height above the required front and side yard setbacks. A building may not intersect the plane. The result is the slanted upper-floor setback visible on most newer LA City houses — the upper story steps back below an imaginary tilted line drawn from a point above the property setbacks. Roof structures and equipment as listed in §12.21.1 B.3 are exempt from the rule.

ENCROACHMENT PLANE definition at LAMC §12.03. R1 zone application at §12.08 C.5(a) with the plane originating 20 feet above existing or finished grade. R1V, R1F, and R1R variants apply the rule at §12.08 C.5(b), (c), and (d) with origin heights and angles set in Tables 12.08 C.5(b), (c), and (d). Roof structures and equipment exception at §12.21.1 B.3. PC/STR/Corr.Lst.106A Part III.B and Figure 12.03-1 illustrate the rule in plan-check form.

A correction that a second-floor wall, eave, balcony, or window assembly intersects the encroachment plane at one or more points along the perimeter. The correction may include a request for an encroachment plane diagram drawn at scale, showing the 45-degree plane projected from the setback line at the relevant origin height with the proposed building section overlaid. Plan check may also flag roof equipment that exceeds the §12.21.1 B.3 exception parameters, including the 5-foot height-above-limit cap that typically applies to skylights, chimneys, and similar elements.

Drawing a flat, multi-story box on an R1 lot without testing the upper floors against the encroachment plane. The rule typically forces the second story to be smaller in plan than the first, with the wall plane stepped back below the 45-degree line. A second common pattern is treating the encroachment plane and the BHO Maximum Envelope Height as a single rule. The two are independent geometric constraints that may bind separately, and a project could satisfy one while violating the other.

The encroachment plane may be the most common reason the buildable second-story footprint is smaller than the first-story footprint on an R1 lot. The 20-foot R1 origin means the rule begins to govern wall geometry only above that elevation; below 20 feet, front and side wall planes can typically rise straight from the setback line. The standard R1 zone application does not provide a balcony exception, so projecting elements typically need to be designed inside the envelope from the start.

Maximum Envelope Height under the Baseline Hillside Ordinance (which interacts with the encroachment plane on hillside lots), Yards and Setbacks (because the plane originates from the required setback line, and the setback rule determines where the plane begins), and Substandard Hillside Limited Street (where the 24-foot front-line height cap may compound with the plane on the front of the lot).

Verification: ENCROACHMENT PLANE definition confirmed verbatim at LAMC line 3008, including the 45-degree angle, the originating-at-specified-height language, the prohibition on building intersection, and the §12.21.1 B.3 exception clause. Figure 12.03-1 referenced at LAMC line 3014. R1 origin height of 20 feet from existing or finished grade confirmed at LAMC line 5540. R1V, R1F, and R1R variants confirmed at LAMC line 5532 area with origin heights and angles in Tables 12.08 C.5(b), (c), and (d). §12.21.1 B.3 Roof Structures and Equipment exception list confirmed at LAMC line 16447, including the typical 5-foot allowance above the height limit for listed elements.