In any R district where the average depth of at least two existing front yards on lots within 100 feet of the lot in question and within the same block front is less or greater than the least front yard depth prescribed elsewhere in this chapter, the required depth of the front yard on such lot shall be modified. In such case, this shall not be less than the average depth of such existing front yards on the two lots immediately adjoining or, in the case of a corner lot, the depth of the front yard on the lot immediately adjoining. However, the depth of a front yard on any lot shall be at least 25 feet. This does not apply to lots fronting on major or collector thoroughfares where the front yard depth shall be measured from the proposed right-of-way side line and shall adhere to the requirements of this chapter.
('65 Code, § 1323.05)