Maximum Envelope Height (BHO)

Maximum Envelope Height is the BHO method of measuring building height on hillside R1, RS, RE, RA lots. Unlike the simpler feet-above-grade measurement used outside Hillside Areas, the envelope height is measured as the vertical distance from the Hillside Area Grade — a code-defined reference line that runs underneath the building — to a projected plane at the roof structure or parapet wall directly above and parallel to grade. The numerical limit varies by height district and roof slope.

LAMC §12.21 C.10(d)(1) through (d)(6) for the envelope height framework. Table 12.21 C.10-4 for the height values per district per roof slope. LAMC §12.03 for the Hillside Area Grade definition. PC/STR/Corr.Lst.107A Part II.D for the plan-check items. Table 12.21 C.10-5 for the permitted roof structure projections beyond the envelope.

A correction that the building exceeds the envelope at one or more points along the roof, that the height-district setting on the cover sheet does not match the calculation, that the 1SS Single-Story Height District restriction is not satisfied, that the 24-foot front-line height limit measured from the street centerline is exceeded, or that roof structures and equipment are not addressed under the projection rules. Plan check may flag the issue with a request for an envelope diagram showing the relationship between the proposed roof and the Hillside Area Grade reference.

Measuring height the way it is measured outside the Hillside Area — from a single grade point to the highest roof point — rather than from the Hillside Area Grade reference that runs underneath the building. The two methods can yield substantially different numbers on a sloped lot, and the envelope method typically returns a lower allowable height. Another common pattern is treating cantilevered balconies as falling under the envelope rule, when balconies with visually permeable railings may project up to 5 horizontal feet beyond the envelope under §12.21 C.10(d)(6).

The envelope method may force the upper floor to step down on the downhill side of a sloped lot, which could shape the roof line in ways the owner did not anticipate. Roof equipment locations and parapet heights typically need to be coordinated with the envelope from the start, not added in late. Within 20 feet of the front lot line, the additional 24-foot cap measured from the street centerline under §12.21 C.10(d)(5) may be the binding limit on lots where it applies, not the height-district limit from Table 12.21 C.10-4.

Encroachment Plane (which typically interacts with the envelope on the side and front), Slope Band Analysis (because the slope drives both RFA and the envelope’s reference line), Substandard Hillside Limited Street (where the 24-foot front-line cap may become binding), and Yards and Setbacks (because the height step may interact with the side-yard increments above 18 feet of building height).

Verification: §12.21 C.10(d) height limits and Table 12.21 C.10-4 confirmed at LAMC line 15600 area. §12.21 C.10(d)(4) 1SS Single-Story Height District restriction and §12.21 C.10(d)(5) 24-foot front-line cap confirmed in the BHO height framework. §12.21 C.10(d)(6) cantilevered balcony projection (up to 5 horizontal feet beyond the envelope, visually permeable railings) confirmed in the same framework. §12.03 Hillside Area Grade definition confirmed at LAMC line 3158.