Question re: IPC drain vent requirement

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DIYERFROMVA

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I live in Virginia, which uses the IPC plumbing code. We're in the process of remodeling a bathroom and the plumbers just completed the drain install. The distance from the toilet flange to the vent is approximately 16 feet and is 3" PVC. The 2" shower trap connects to the same 3" line via a horizontal wye fitting within 12 inches and the distance from the shower trap to the vent along the 2" run and the 3" run is about 12 feet. The IPC says that the distance from the fixture trap to the vent on a 3" line cannot be longer than 12 feet and cannot be longer than 8 feet on a 2" line. The IPC has an exception that says "The developed length of a fixture drain from the trap weir to the vent fitting for self siphoning fixtures, such as water closets, shall not be limited.

My question is this: Are the distances for both the toilet flange and the shower trap to the vent acceptable given the IPC exception? It seems to me that this would be OK only for the toilet, but not for the shower drain since the shower is not self-siphoning. Can a pro lend a hand and offer an opinion?

Thanks in advance!

JP

I'm attaching a photo of the IPC code for reference.
 

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wwhitney

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So the lav and any other bathroom fixtures are separate? I.e. at the point of the dry vent takeoff, the drain is just carrying the shower and the WC?

If so, for a 2" drain, the trap arm (from trap outlet to vent connection) is limited to 8' horizontally and 2" of fall, while at a minimum rate of fall of 1/4" per foot.

Cheers, Wayne
 

DIYERFROMVA

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Thanks. Yes, the drain is only for the water closet and the shower. The lav drains directly into the stack as it is about a foot away.
So it sounds like the 3" line the shower is connected to needs to be re-routed so that the distance from the shower trap to the vent is 8 feet or less. the fact that the 2" shower drain is less than a foot before connecting to the 3" line is irrelevant for purposes of calculating the maximum length from fixture to vent. Do I have that right?

Thanks again!

JP
 

wwhitney

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Yes. Under common venting, which is the only time you are allowed to join two unvented drains, each fixture needs to satisfy the length/fall limits with respect to the common vent, ignoring the other fixture. The WC is unlimited on length and fall to the vent, so that's fine. But the shower is limited to the 8' horizontal and 2" fall, which you determine ignoring the WC and ignoring that the shower trap arm increases in size.

Cheers, Wayne
 

DIYERFROMVA

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Yes. Under common venting, which is the only time you are allowed to join two unvented drains, each fixture needs to satisfy the length/fall limits with respect to the common vent, ignoring the other fixture. The WC is unlimited on length and fall to the vent, so that's fine. But the shower is limited to the 8' horizontal and 2" fall, which you determine ignoring the WC and ignoring that the shower trap arm increases in size.

Cheers, Wayne
Thanks, Wayne. Looks like we'll have some fun when the inspector shows up and says "no can do". I'll try to get the plumber to change it beforehand.

JP
 
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