In the seismic design and assessment of earthquake resistant buildings, the horizontal ground motion component is given priority, while the vertical component is often given little importance. In some special cases, the vertical spectral acceleration value is considered equal to the reduced level of the horizontal component. However, this common approach may not always accurately reflect the effects of vertical earthquake motion adequately. Particularly in the context of performance assessment of substandard buildings vertical accelerations may become critical. In this regard, both the arrival time of peak vertical shaking as well as its amplitude are critical. Vertical ground motion components can reach high intensities, especially under near field conditions of high magnitude earthquakes in the case of short period structures. Essential factors influencing vertical to horizontal spectral ratios involve the source to site distance, the natural vibration period of the structure, and local site conditions. Existing regulations assume that vertical seismic motion carries relatively low energy and that structures designed accordingly have adequate vertical load carrying capacity. However, most of the existing building stock in Türkiye suffers from poor material quality and inadequate column cross sectional areas. For such buildings, the arrival of the vertical peak ground acceleration before the peak horizontal component has the potential to weaken the building’s capacity to subsequent horizontal earthquake demands. This effect further reduces the already very low resisting capacity of the structures under earthquake action. In this study, we evaluated how early or late the peak vertical acceleration demand of the February 6th, 2023 Kahramanmaraş earthquake sequence occurs compared to the peak horizontal acceleration demand. The results indicate that high vertical acceleration intensities and the occurrence of the peak demand in the vertical component before the horizontal lead to widespread damage in the buildings. This suggests that the seismic resistance capacities of substandard buildings may be significantly reduced when subjected to a strong vertical acceleration before peak horizontal shaking.