Where a building line has not been established, and where 50% or more of the aggregate street frontage between 2 successive intersecting streets is occupied by buildings of the type and use permitted in the district before the effective date of the Zoning Code, the average setback distance of conforming buildings located within 100 feet on either side of a given lot shall be the minimum front yard setback for that lot; provided, however, the depth of the front yard resulting therefrom shall be not less than one-half of the dimensions set forth in Sections 1129.13 and 1129.14.
(1980 Code 151.29)