A 3-inch waste line can drop only 9 inches between its upstream end and the stack because of a beam overhead. Take the required slope for that pipe size as 1/4 inch per foot, given. What is the longest developed length that the available fall will support?
- A18 feet
- 36 feet
- C72 feet
- D108 feet
Where to look it up
Explicit exercise assumptions; not a universal code requirement.
Why B is correct
Use the slope explicitly given in this question: maximum length = available fall / slope = 9 inches / (0.25 inch per foot) = 36 feet. Eighteen feet would use 0.5 inch per foot, 72 feet would use 0.125, and 108 feet would use about 0.0833; none uses the stated slope. This calculation does not establish the minimum slope in a particular adopted code or permit an exception to it. Confirm elevations and any additional drops separately when laying out the actual line.