📒 This research first examines the current condition of the building drainage system design in Taiwan, including an investigation 51 apartment buildings. The second part is to experiment on the air pressure in the vertical stack drainage system . An experimental device that simulates a medium-height apartment was set up to provide empirical parameters and model verification at NTUST. A considerable progress has been made in predicting the air pressure distribution within vertical drainage stacks.The third part focuses on a 2-pipe vertical drainage stack for conducting the empirical parameter and evaluation method of air pressure of building drainage systems. Next, the air pressure prediction in 2-pipe vertical drainage stacks from the predicted results of a single drainage stack has been illustrated.The study also conducts the comparison between the measured data and calculated values. It reveals that these prediction and evaluation methods can reproduce the mean air pressure distribution value in a vertical drainage stack. Meanwhile, the prediction method of air pressure in the 2-pipe stack drainage system has been successfully established in the study.