Structural irregularity is a feature of a building's structural arrangement, such as one storey significantly higher than other storeys, an irregular building shape or a change of structural system or material, that produces a known vulnerability during an earthquake. The user can choose a maximum of two vertical and two plan irregularities for a building. However, if a building has two irregularities of the same type (plan/vertical), the user needs to prioritize them by identifying the primary irregularity first and the secondary irregularity next.