Adding shower to horizontal wet vent (IPC)

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Mycorrado

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Hi, Converting an existing half bath to full by adding a shower. Not sure if I can join the existing horizontal wet vent the lav provides the toilet. can the shower be downstream of the toilet under IPC rules? the drawing below if view from above.

1651678627370.png
 

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wwhitney

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Yes, IPC allows the shower to come in downstream of the WC. If the picture is showing the WC on the left, the lav coming in, and a turn down into the lower horizontal drain (running up/down the page), looks tight for adding another wye for the shower.

Bear in mind: the new shower trap arm runs from the trap outlet to the wye where it joins the lav (and WC) drain. That trap arm has to fall at least 1/4" per foot, but the total fall is limited to one nominal pipe diameter. So if its's a 1-1/2" tub drain, that can go at most 6', if you get the slope at the exact minimum Or for a 2" drain, 8'.

Cheers, Wayne
 

Mycorrado

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Thanks Wayne, the photo shows the old drain, which as you say doesn't have room for a second Y but the toilet was moved closer to the lav so the new segment does appear to have the length. I am planing to run a 2" to the shower and the run back should be less than 8'.

The shower Y can be flat or under 45 degrees up correct?
 

wwhitney

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The shower wye inlet needs at least 2% slope (1/4" per foot). More than that makes it harder to comply with the "max trap arm fall is one pipe diameter" rule. That fall should be measured to the "crotch" of the wye, I believe. The fall is what is regulated; the length limit is just a consequence of the fall limit and the minimum rate of fall.

Cheers, Wayne
 
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