IPC Table 906.1 / IPC 906.2
What it means on the job
A 1-1/4" vent is the minimum size for an individual vent serving a lavatory with a 1-1/4" trap. The vent size must be at least one-half the diameter of the drain it serves, with a minimum of 1-1/4". This installation meets the requirement.
Tested in 1 CraftIQ puzzle
- code-checkVent Pipe Sizing
Related IPC sections
IPC Table 709.1
Kitchen sinks require a minimum 1-1/2" drain. The 1-1/4" size is only permitted for lavatory (bathroom) sinks. An undersized kitchen drain will clog frequently from food waste.
IPC Table 710.1(1)
Per IPC Table 710.1(1), a 3-inch horizontal building drain at 1/8" per foot slope can handle up to 36 drainage fixture units (DFU) (42 DFU is the capacity at the steeper 1/4" per foot slope). With only 12 DFU on this line, it is well within the capacity of the 3-inch pipe. The critical factor is that no single branch carries more than its rated capacity, and no more than two water closets discharge into a 3-inch horizontal branch. This installation is compliant.
IPC Table 906.1
For a 1-1/4" trap arm, the maximum distance to the vent is 5 feet. Exceeding this distance risks siphoning the trap seal. The trap arm distance is measured from the trap weir to the vent connection.
CraftIQ explanations are original educational commentary written in trade language and verified against the cited standards. Always confirm requirements against the code edition adopted by your jurisdiction — this is training material, not a substitute for the code book or your AHJ.