The fixture load of a 4 inch branch interval is based on how many per inch per foot fall?

The fixture load of a 4-inch branch interval is based on a calculation that considers the amount of load per inch of diameter and per foot of fall. In plumbing design, particularly according to the Uniform Plumbing Code, a 4-inch branch interval typically accommodates a fixture load determined to be 1/4 for each inch per foot fall.

This means that for every inch of branch pipe diameter, you expect to handle a certain volume of wastewater or fixture load. In this case, with a 4-inch branch, applying the standard of 1/4 indicates that this would account for a more substantial load, reflecting the necessity for greater diameter pipes to manage larger volumes of wastewater effectively. This designation ensures that the plumbing systems are constructed to safely and efficiently handle the anticipated fixture units without risk of backup or failure.

Choosing 1/16, 1/8, or 1/2 would not accurately represent the standard measures used in most plumbing codes for a 4-inch diameter branch. These measures either underrepresent or miscalculate the load requirements expected in practical applications, leading to potential system inadequacies.