Wherever a lot is occupied by a nonconforming, commercial or industrial use in an R district, a screening wall, fence, or hedge of the maximum permitted height is required along any rear or interior side lot lines thereof which abut any lot in an R district. This requirement shall not apply to that portion of any such lot line which is within two feet of the wall of a building on the lot and parallel to such line. (Prior gen. code § 8-60.58)