The 10-Foot Separation Rule

In the A and R Zones, all accessory buildings must be located at least 10 feet from any main building or accessory living quarters on the same lot. The rule is most often encountered on detached ADU projects, detached garages with habitable space above, and other accessory structures sited near the existing main dwelling. A narrow exception in the same code section permits a 5-foot reduction for non-residential accessory buildings under specific side-yard conditions, but that exception does not apply to ADUs or accessory living quarters.

LAMC §12.21 C.5(d) sets the 10-foot rule and the narrow exception for non-residential accessory buildings. PC/STR/Corr.Lst.20A Part II.H item 6 names the requirement on the ADU correction sheet for the applicable pathways. LAMC §12.22 A.33(c)(7) clarifies that no passageway between an ADU and the main building is required and that §12.21 C.2 and §12.21 C.5(d) do not require additional spacing for the ADU itself, while Building Code separation requirements continue to apply.

A correction that a detached ADU or other accessory living quarters is located within 10 feet of the main building, often paired with a request for a dimensioned site plan showing the wall-to-wall distance between the structures. The correction may also flag eaves or projections that close the gap below 10 feet even where the wall planes are 10 feet apart. On certain ADU pathways, plan check may distinguish between the §12.21 C.5(d) zoning separation and the LABC fire-separation analysis, which are separate rules with separate compliance pathways.

Designing a detached ADU at less than 10 feet from the main dwelling to maximize rear yard space, save a yard tree, or fit a tight lot, then discovering at plan check that the rule applies and the ADU has to be moved, redesigned as attached, or paired with a fire-separation analysis under the LABC. A second pattern is treating the §12.21 C.5(d) exception as more permissive than it is — the exception is conditional, applies only to non-residential accessory buildings, and does not cover ADUs or accessory living quarters.

The simplest fix when a detached ADU is too close to the main house is to move the ADU. The simplest fix is rarely available, because moving the unit typically pushes it into a setback or removes a yard tree the owner wants to keep. The other path is converting from detached to attached, which removes the §12.21 C.5(d) separation rule but introduces the floor-area limit under §12.22 A.33(e) — typically capping the unit at 50 percent of the existing primary dwelling, with statutory floors at 850 and 1,000 square feet under specific conditions.

ADU Pathway Selection (because pathway choice often turns on whether the 10-foot rule can be satisfied), Yards and Setbacks (because rear-yard requirements interact with ADU placement), Lot Cut Date (because lots with multiple existing structures may have unresolved subdivision questions affecting siting), and the Encroachment Plane (where two-story ADUs trigger upper-floor setback rules independently).

Verification: §12.21 C.5(d) ten-foot separation rule confirmed verbatim at LAMC line 14737, including the conditional 5-foot exception for non-residential accessory buildings sited at least the side-yard width from the adjacent lot line. §12.22 A.33(c)(7) clarifying provision (no passageway requirement between an ADU and the main building, with Building Code separation continuing to apply) confirmed at LAMC line 18441. §12.22 A.33(e)(1) 50-percent attached-ADU floor-area cap confirmed at LAMC line 18521. §12.22 A.33(e)(3) 850/1,000 sf floor confirmed at LAMC line 18529. PC/STR/Corr.Lst.20A Part II.H item 6 referenced as the plan-check expression of the rule.