I have a dry vent in a basement. Is it true that no revent is needed if the appliance is within 8 feet of the vent? I have a (28 gallon capacity) sink with a 1.5" PVC drain that I thought would need a PVC revent, but since this sink is less than 6 feet from the main (dry) vent it could save me a little work/expense to do without. TIA
you could install one of those indoor vents, one way vents to prevent vacuumn
I'm pretty sure the IRC allows 5' for vent to trap length. It's probably a good idea to have a vent on a laundry tub or slop sink anyway. Try one of the Studor air admittance valves. The IRC allows individual vents to terminate with a connection to an air admittance valve.
R
I generally think it would be better to revent if it is only a little work/expense.
As to the plumbing codes, the length of the trap arm (the drain between the trap and the vent take off) is governed by the rule that the vent opening shall not be below the weir of the trap. The trap arm is sloped at the usual 2%, so this limits the trap arm length, depending on the diameter of the trap arm. Basically, if you draw a level line from the point in the trap at which water would first spill over into the trap arm (the weir of the trap), it needs to hit the vent opening rather than hit the top of the trap arm. The purpose of this rule is to prevent the trap arm from being siphoned dry.
Having said that, apparently the two plumbing codes, the IRC (International Residential Code) and the UPC (Uniform Plumbing Code) come up with different maximum trap arm lengths. For a 1.5" trap and drain, the maximum IRC length is 6', and the maximum UPC length is
3.5'. So you'll need to find out which plumbing code is operative in your location.One option for greater length is to upsize the trap and trap arm to 2" (they have to be the same size). Then the IRC allows 8' for the trap arm, and the UPC allows 5'. Of course, this would require a 2" drain. Under the UPC, you'll have to increase the drain to 2" anyway before it turns horizontal: a 1.5" horizontal drain (other than the trap arm) is only good for 1 fixture unit under the UPC, and your sink/laundry tub is a 2 fixture unit sink.
Yours, Wayne
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