Purpose <p>Buildings on hill slopes have very different geometric layout than those on flat land. The uneven topography of mountainous terrains necessitates the buildings’ foundations to rest on inclined slopes, making them horizontally and vertically asymmetric. Step-back building configuration is prevalent in the hill cities of the Indian subcontinent, wherein the foundation of the building follows the natural slope of the ground. Most seismic vulnerability studies of buildings in hilly regions overlook the impact of soil-structure interaction (SSI) on their seismic performance. This study highlights the crucial role of SSI in the dynamic behaviour of step-back buildings constructed on flexible ground for better prediction of their response during earthquakes.</p> Methods <p>The impact of soil flexibility on step-back buildings resting on hill slopes has been investigated numerically using static nonlinear (pushover) analysis to assess the lateral response. Further, a parametric investigation is conducted to explore the impact of soil flexibility on step-back buildings with various level differences between the uppermost foundation level (UFL) and the lowermost foundation level (LFL), along with simultaneous variations of the plan area by changing the number of bays. The current study investigates the comprehensive evaluation of the seismic behaviour of step-back buildings by incorporating Soil-Structure Interaction (SSI) effects.</p> Results and Conclusion <p>As a result, the initial hinge formation relocates from columns to beams, finally failing due to column collapse. The results highlight that step-back building exhibits better seismic resistance along the slope than across. The outcomes for models considering soil flexibility indicate a tendency to underestimate the displacement at a particular performance level. In buildings with a step-back larger than 15 metres between uppermost foundation level (UFL) and lowermost foundation level (LFL), soft soils increase the fundamental period of vibration by 24% to 35% in the first mode, indicating greater soil sensitivity. Under soft soil, buildings between UFL and LFL of less than 10 metres and 10 to 15 metres have a ‘Collapse Prevention (CP)’ performance level, indicating a higher risk of collapse. Ground-supported and road-level columns exhibit brittle failure, and step-back building experiences excessive torsional responses in across-slope direction. SSI study shows that step-back buildings with larger plan areas and floors above UFL are the most vulnerable. The study advises updating building codes to address these criticalities and proposes SSI integration for hillside building design.</p>