In all Residence Districts, on corner lots, enclosed accessory off-street parking spaces shall be considered permitted obstructions in any portion of a side yard which is within 30 feet of both side lot lines, provided that, in an R1 or R2A District, on a corner lot whose mean width is 45 feet or more, no structure used for such purposes shall be less than five feet from any side lot line. In R2A Districts, detached garages shall be included in lot coverage.