Design & SizingQuestion 31 of 110
A drainage stack sizing table lists a 4 in stack at 500 DFU maximum and a 3 in stack at 48 DFU maximum for the total to a stack. A stack collects 240 DFU. What is the minimum stack size, and what secondary rule also applies?
a.3 in, and a cleanout is required
b.3 in, and no water closets allowed
c.4 in, and no size reduction downward
d.6 in, and a vent stack is required
Explanation
240 DFU exceeds the 48 DFU limit of a 3 in stack, so a 4 in stack is required, and a stack may never be reduced in size in the direction of flow as it descends. Downsizing a stack lower down would create a restriction that floods the branches above it. The stack must stay 4 in or larger to its base.
Law Reference: IPC §710.1Practice all 110 questions free — no signup required.
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