If the ratepayer created a door through the wall between properties A and B, or a staircase through the floor/ceiling between properties D and E, the units would again be one hereditament.
Pe bai'r talwr ardrethi yn creu drws drwy'r wal rhwng eiddo A a B, neu risiau drwy'r llawr/nenfwd rhwng eiddo D ac E, byddai'r unedau unwaith eto'n un hereditament.