“Site coverage” means that portion of a lot or parcel that is covered by buildings, measured from exterior face of framing of the exterior walls, excluding open decks and porches, roof eaves, and stoops. Portions of the building which project beyond the foundation wall and enclose floor area, such as bays and basement spaces, shall count toward site coverage. Basements which are completely below pre-construction grade that are used exclusively for the storage of vehicles and for associated storage shall not be counted towards site coverage. However, for basements which are used exclusively for the storage of vehicles and for associated storage that project above pre-construction grade, only that portion of such basements that project above pre- or post-construction grade, whichever is more restrictive, shall count toward site coverage.