The paper considers torsion effects that occur during the building response to seismic action. Computation and parametric analysis are conducted for various values of building eccentricity induced by mass and stiffness variation. Such a model accounts for the actual dynamic effect of accidental eccentricity, usually considered in building design by quasi-static value of the torsion moment. Two types of models are employed to explore dynamic parameters of the building. The models are formed using Wolfram Mathematica software in which the mass and stiffness properties are parametrically related to the basic dynamic characteristics of the building. The commercial software package CSI ETABS ver.17 is used for validation of the model. Seismic performance of the building is evaluated, and the results of the parametric analysis are presented using the shear forces and torsion moment. The analysis showed that the nature of eccentricity has a major influence on distribution of seismic forces due to the torsion.