A structural irregularity that is observed in the elevation or section of the building (vertical plane). If more than one vertical irregularity is observed, the primary vertical irregularity is that deemed to be the most significant in terms of affecting the building’s seismic performance, and the secondary vertical irregularity is that deemed to be the next most significant. If there is only one structural vertical structural irregularity observed, the term "No Irregularity" will be used by default.