Drainage Vent Pipe sizing requires three things that should be known, which are
1- Soil stack pipe size.
2- Drainage fixer units connected to that soil stack pipe
3- Developed length.
So these three things should be known before doing the vent pipe size calculation or before getting the vent pipe size.
What is Developed Length: Develop length is basically the length of the vent stack and is measured from the point of connection to the drainage system at its base point so this is the
base point from here to the point of discharge at the outlet above the roof so from the base point of the drainage system to the point of discharge at the roof level. ICC code defines Developed length as “The length of a pipeline measured along the centerline of the pipe and fittings”.
Step 1: Soil stack pipe size calculation method is shown on the following link. Please click the link to learn more about Soil stack pipe sizing techniques.
Step 2: Drainage fixture units connected to the soil stack. From the plumbing riser diagram find the total drainage fixture units connected to the soil stack pipe