Buildings on hill slopes sustained considerable damage during past earthquakes owing to elevation and plan layout anomalies. Current building code provisions lack specific design guidelines for these buildings, except for height constraints to estimate the natural period. Occasionally, landslides induced by earthquakes or heavy rainfall intensify the damage. Abrupt alterations in the boundary conditions of these buildings might result in catastrophic failure. This research aims to evaluate the earthquake performance of various building configurations, each with two different heights (five and ten storeys), located on hill slopes in compliance with current code regulations. The analysis is conducted under the assumption of fixed boundary conditions, and the building responses are evaluated when these conditions are abruptly changed (e.g. to pinned or roller supports). The responses from nonlinear pushover analysis (NLPoA) and nonlinear time history analysis (NLTHA) are studied based on capacity curve, performance point, and level of damage in structural elements under maximum considered earthquake (MCE). In ten-storey buildings, when the boundary condition changes, the failure of struts reaches 75% under MCE shaking, indicating that such buildings will not survive under repeated earthquake scenarios. Changes in the boundary conditions are more effected in buildings with ten storeys than five-storey buildings.