A bathroom group (water closet, lavatory and bathtub) totals 6 DFU. Using the UPC's drainage sizing table and fixture rules, what minimum drain pipe size is required for the horizontal branch serving it?
Not quite. The answer is C: 3 inch
By load alone, 6 DFU would fit a 2-inch horizontal drain (rated 8 DFU). But Table 703.2's footnote excludes water closets and six-unit traps from the 2-inch row, and Table 702.1 sets the minimum trap and trap arm for a water closet at 3 inches — so a branch carrying a water closet cannot be 2 inches. The smallest size that works is 3 inches, which is rated for 35 DFU horizontal.
Reference: UPC 2021 Table 703.2 (note 3); Table 702.1 (Maximum Unit Loading and Maximum Length of Drainage and Vent Piping)
Checked against the official text
Table 703.2 is not supplied at the exam desk and must be memorized. The 2015 edition's grid and note 3 were not read directly for this question; confirm against your 2015 book.
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