In addition to neighborhood characteristics, the structural and physical attributes of residential properties introduce significant biases into the assessment of property values and represent an important source of administrative inequity in the property tax. A model is presented which captures the influence of dwelling characteristics on both the constant and slope parameters in the traditionally employed linear relationship between assessed and market values. The model is tested using a sample of properties taken from three western counties in North Carolina. The results support the hypothesis that different types of properties with equivalent market values may receive significantly different assessments.