State Preemption Footnote

The State Preemption Footnote is the asterisked clause that appears on PC/STR/Corr.Lst.20A and identifies the protected baseline ADU configuration that California state law preempts certain local zoning rules from precluding. Under the state-preemption pathway, a local jurisdiction cannot enforce zoning rules that would prevent an 800-square-foot ADU at 16-foot height with 4-foot side and rear setbacks, even where the local rules would otherwise apply. The footnote operates as a floor: local rules below the floor are preempted; local rules above the floor (rules that would permit a larger or differently-configured ADU) continue to apply. The preemption is narrow: it protects a specific configuration, not a general override of local rules.

LAMC §12.22 A.33(c)(1)(iii) restates the protected baseline within the local ordinance, confirming that the 800-square-foot, 16-foot height, 4-foot setback configuration is permitted regardless of certain local rules including size, lot coverage, floor area ratio, open space, and minimum lot size. California Government Code §65852.2, which the LAMC subdivision references as the source of the state ADU framework, carries the underlying preemption authority; the LAMC still predates the 2024 California statutory renumbering of ADU provisions to GC §§66310–66333. PC/STR/Corr.Lst.20A pages 4 and 7 carry the asterisked footnote that names the preemption in plan-check terms. The hub references the protected baseline at hub Concept 10 (ADU Pathway Selection) and Part 3 (the interactions that surprise owners).

A correction that an ADU project claiming state-preemption protection does not actually fit the protected baseline, the proposed ADU exceeds 800 square feet, exceeds the 16-foot height, or proposes setbacks below 4 feet, and therefore cannot invoke the preemption to override the cited local rule. Plan check may also flag a project that has claimed preemption against a rule the preemption does not actually cover (the preemption operates against specific local rules within the four corners of the statutory baseline, not against all local rules). Conversely, plan check may flag a project under a local rule that the preemption does cover; the correct response is to cite the preemption explicitly in the plan-check response and point to the protected baseline.

Treating state preemption as a general override of local rules. The preemption is a narrow protection of a specific configuration, not a blanket exemption. An ADU at 850 square feet does not invoke preemption; it falls outside the protected baseline. An ADU with 3-foot setbacks does not invoke preemption; it falls below the protected baseline. The preemption protects exactly the configuration the statute names. Designers who hear “ADU is by-right under state law” and assume the preemption resolves all conflicts with local rules typically discover at plan check that the protection has limits. A second pattern is forgetting that the preemption applies only to the rules §12.22 A.33(c)(1)(iii) names, size, lot coverage, FAR, open space, minimum lot size, height, and setback, and does not address other local rules such as the 10-foot separation rule or fire-protection requirements.

The State Preemption Footnote functions as a strategic tool when local rules would otherwise preclude an ADU on the lot. On a hillside R1 lot where the BHO setback table would require 5-foot side yards, the State Detached pathway invoking preemption permits the ADU at 4-foot side yards within the 800-square-foot protected size. On a lot where local height rules would limit the ADU below 16 feet, preemption permits the 16-foot protected height. The strategic question at the feasibility stage is whether the program fits the protected baseline (in which case preemption is a useful tool) or exceeds it (in which case local rules apply and preemption does not help). The decision typically determines pathway selection: Ordinance Detached for projects above the baseline, State Detached for projects at or within the baseline.

ADU Pathway Selection (because invoking the preemption requires selecting a state pathway and is the gating decision on whether the preemption is available), Yards and Setbacks (because the preemption operates most often against setback rules), Maximum Envelope Height under the Baseline Hillside Ordinance (because preemption against height rules turns on the 16-foot protected height), and the 10-Foot Separation Rule (a separate local rule the preemption does not address: detached ADUs invoking state preemption still must satisfy the 10-foot separation from the main dwelling under §12.21 C.5(d)).