For an accurate regional seismic loss assessment, it is essential to quantify the uncertainties and correlations of engineering demand parameters (EDP) of building structures. In previous studies, the mean EDP of each structure was represented with a regression function, which is a function of an intensity measure, and the variability of the EDP, i.e. EDP residual, is represented with the residual of the regression function. The authors recently proposed a new formulation and incremental dynamic analysis-based methods to evaluate the correlation between EDP residuals (Kang et al., 2021). This paper proposes a simplified approach for estimating the variances and correlations of the EDP residuals of building structures. Based on the EDP residuals of various buildings estimated using the proposed approach, primary structural characteristics affecting EDP residuals are identified. In addition, this study proposes regression equations to predict EDP residuals and correlation coefficients based on the structural characteristics. The developed regression equations are expected to facilitate the consideration of the EDP residual correlation in regional seismic loss assessment. Numerical examples demonstrate that the proposed approach can improve the accuracy of a regional loss assessment.