Wherever a C-1 district terminates at the boundary of an R district or of any other C district except a C-2 district in the same block, the depth of front yard in that block shall be not less than is required in such abutting district. Wherever the use of a building site is for a motel, hotel or boarding house, the depth of front yard shall be not less than twenty (20) feet. (Prior gen. code § 8-48.6)