<p>Buildings and other human-made structures can exhibit various irregularities due to environmental factors or architectural considerations. These irregularities can alter the structural response to applied forces, leading to the concentration of seismic demands in specific elements, such as shear walls or braces, which may result in irreparable damage or even collapse. As a result, understanding and considering these effects is essential in the analysis and design of irregular structures. While most research on irregularities in height has focused on setback structures, this study investigates the seismic behavior of RC buildings with geometric irregularities in shear wall height. The seismic response and collapse capacity of buildings with varying levels of irregularity are evaluated in comparison to regular structures to assess the impact of these irregularities on structural capacity. The results imply that when this type of irregularity occurs at higher elevation levels, it has minimal impact on the seismic behavior and, in some cases, may even enhance it. However, when the irregularity spans multiple stories and originates from lower elevation levels, its impact becomes significant, leading to substantial increases in structural responses and a higher probability of collapse. Furthermore, it was demonstrated that present seismic standards are ineffective in providing accurate predictions of the seismic behavior of RC shear wall structures exhibiting this type of irregularity. Consequently, this study proposes a new index, ∅_v, which accounts for the vertical position of wall width reduction, addressing a critical gap in current seismic design provisions for these types of structures. Finally, recommendations were provided to improve the existing seismic codes.</p>