The text of section 314.1 of the Uniform Plumbing Code has been updated.
314.1 Trenches. Trenches deeper than the footing of a building or structure, and paralleling the same, shall be located not less than 45 degrees (0.79 rad)
there from from the bottom exterior edge of the footing, or as approved in accordance with Section 301.0 of this code.
Why It Changed
The text in this section was not clear and was commonly misunderstood. This led to many installers and inspectors performing this measurement from the wrong point. The new text clarifies the intent of the section.
What It Means
The code now gives a clear understanding that the measurement starts the bottom edge of the footing. Installers must be sure that they are measuring appropriately. Due the frequency in which this section was misapplied previously, inspectors are going to have to be aware that this is likely to be the source of frequent violations until the standard practice is well understood.
If the measurement that this section calls for is done incorrectly, it is compromising the integrity of the ground supporting the load transferred through the footing. This could lead to foundation failure, not pipe failure. The main point is to protect the foundation of the building.
Since the relation of the 45 degree angle to the vertical height of the trench creates an isosceles triangle where the two legs are equal, we know that the height from the bottom of the trench to the bottom edge of the footing will equal the horizontal distance from the bottom edge of the footing to the closest edge of the trench. Therefore, if the horizontal distance is equal to or greater than the vertical distance, then the trench is at an approved distance from the footing.
You can see more of these updates in 2015 Guide to Important Code Changes.