In Los Angeles what are the exceptions to front setback calculation (20% of lot depth or 20'). Can I average adjacent neighbor’s setbacks or prevailing setback on the block?

According to City of Los Angeles Department of Building and Safety (LADBS) Zoning Section 12, Zones R1 and R2 have a Front Yard requirement is 20% of the depth of the lot not to exceed 20', but not less than prevailing setback.

LADBS provided a detailed manual for determining the front yard setback when subject to “Prevailing Setback Regulation” at the following link:

Prevailing Setback

“Prevailing Setback” is a phrase used to define the front yard regulations for RA, RE, RS, R1, and R2 zoned lots. The Zoning Code reads in part “… that where all of the developed lots which have front yards that vary in depth by not more than 10 ft comprise 40 % or more of the frontage, the minimum front yard depth shall be the average depth of the front yards of such lots. Where there are two or more possible

combinations of developed lots comprising 40% or more of the frontage, each of which has front yards that vary in depth by not more than 10 ft, the minimum front yard depth shall be the average depth of the front yards of that combination which has the shallowest average depth. In determining the required front yard, buildings located on key lots, entirely on the rear half of lots, or on lots in the C or M Zones, shall not be counted; provided, however, that nothing contained in this paragraph shall be deemed to require front yards which exceed 40 ft in depth.”

Due to the fact the above definition requires an average of such lots, there must be a minimum of 2 lots that have setbacks within 10 feet of each other in order to establish a prevailing setback.