Number of toilets on 3" drain

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Horst22

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Hello,
I'm getting ready to add a basement bathroom. As far as I know we only have 3" drain lines running under our slab which I had planned to tie into. We already have 3 existing toilets in the house. My question is if I can add a 4th assuming we have a 3" main drain.

From what I've read on this forum and others is with 3" horizontal line, the limit is 3 WC's. However, I live in Iowa and am under 2021 UPC - Note 4 under table 703.2 appears to state "not to exceed fiver water closets or five six-unit traps." This looks like a change from prior code and I am ok with 4 WC's assuming I have 3" main? Can someone confirm?
I also added the other fixtures in the house and looks like with planned bathroom, I would be at 34 DFU's and fall under the 35 max for 3" line.
 

wwhitney

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Yes, that's what it says. I checked the 2021 UPC at iapmo.org, it's a change in the model code, not an Iowa specific amendment.

Cheers, Wayne
 

Montan

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Reviving this thread because I’m facing a similar situation. Looking at Table C 304.2 footnotes, 2021 UPC specifies that a 3” main drain is limited to three WC or bathroom units for single house residential.

Can anyone explain the discrepancy between the footnotes in tables 702.3 and C 304.2, or how they might be applied?
 

Jeff H Young

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I can't find 702.3 only 703.2? it says 5 w/c c304.2 I'm not finding that either interested to know the discrepancy you are talking about.. if there is an error in text no idea if it reverts back to the prior code or how that gets dealt with
 

Tuttles Revenge

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Table C 304.2 footnotes, 2021 UPC specifies that a 3” main drain is limited to three WC or bathroom units for single house residential.

That is the Alternate Plumbing Methods chapter Apendix C.. that is not part of the adopted plumbing code anywhere. *that I know of*

Might be easier to describe the problem you're having rather than look up the weird parts of the code book. The OP was asking if they could install a 4th toilet on a 3" horizontal drain, which the 2021 code now allows in places its been adopted. I've done it in the past by getting a letter from our lead plumbing inspector waiving the 3 wc on 3" rule.
 
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Jeff H Young

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I've gotten verbal permission remodel added a 4th toilet years ago actually done it a few times with out issue just not on new build .
 
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