Drainage, Waste & VentQuestion 5 of 120
A fixture drain serving a lavatory is 1-1/2 in in diameter. What is the smallest vent size that may serve it?
a.1 in
b.1-1/4 in
c.1-1/2 in
d.2 in
Explanation
A vent must be at least one-half the diameter of the drain it serves but never smaller than 1-1/4 in. Half of 1-1/2 in is 3/4 in, so the 1-1/4 in floor controls. A 1 in vent violates the absolute minimum, while 1-1/2 in and 2 in are larger than required and are not the smallest permitted size.
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