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 Why would a 50" drain run include a separate leg to vent?
Author: ArthurPeabody (NM)

The vanity has a 30" horizontal pipe (all 1.5" ) to a tee; a 10" pipe down to an elbow, another 10" pipe to the main drain. At the tee a 14" pipe runs up to an elbow, 10" to the vent. It's less than 60" over all, so doesn't require a separate vent leg, as I understand it. Why was it done this way? This was about 1975.

The tub and toilet share the same drain and vent. The toilet is plumbed directly to the drain/vent, the tub similarly to the vanity, on an even shorter run.



Edited 1 times.

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 Re: Why would a 50" drain run include a separate leg to vent?
Author: bernabeu (SC)

because it was built/installed SURPASSING MINIMIM code as per BEST versus MINIMUM CODE practice

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Retired U.A. Local 1 & 638
"Measure Twice & Cut Once"

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 Re: Why would a 50" drain run include a separate leg to vent?
Author: steve (CA)

There's more to the venting requirement then just the distance. Elevation drop and usage of the pipe, that the sink's drain pipe connects to, must also be factored in.

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 Re: Why would a 50" drain run include a separate leg to vent?
Author: sum (FL)

if I understand correctly the "10 inch down to an elbow", was probably done to avoid some obstruction, and that downward offset breaks the air between the p-trap outlet and the lower tee connection after the offset and thus a vent is required. The trap arm must go from fixture to tee with 1/4" per foot with no offset in the vertical direction.

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 Re: Why would a 50" drain run include a separate leg to vent?
Author: bernabeu (SC)

sum,

thanx for the jabberwocky translation

you are correct .... again


grinning smiley

- - - -

Retired U.A. Local 1 & 638
"Measure Twice & Cut Once"

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 Re: Why would a 50" drain run include a separate leg to vent?
Author: packy (MA)

so if the sink drain drops 10" to and elbow requires an additional vent, if it drops another 10" to another elbow does that require another additional vent?
heaven forbid the drain drops another 10" to a third elbow requiring another vent then the sink drain would resemble an octopus.

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 Re: Why would a 50" drain run include a separate leg to vent?
Author: bernabeu (SC)

Quote

The trap arm must go from fixture to tee with 1/4" per foot with no offset in the vertical direction.




@ packy,

? correct ?





- - - -

Retired U.A. Local 1 & 638
"Measure Twice & Cut Once"

Post Reply

 Re: Why would a 50" drain run include a separate leg to vent?
Author: steve (CA)

Is that a trap arm or trap leg?

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 Re: Why would a 50" drain run include a separate leg to vent?
Author: ArthurPeabody (NM)

It doesn't avoid anything in the way. One could connect the trap directly to the drain with a slight slope with about 42" horizontal pipe. I can see no purpose of the separate vent leg other than to make it closer to the trap, as though the rule was different in 1975 or 30" is enough better than 40" to make it worth a separate leg.

The tub's trap connects to the eventual drain at the drain's level; a vent leg runs up about 20" from the tub's trap far enough to meet the vanity's vent leg in a tee at the main vent.

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 Re: Why would a 50" drain run include a separate leg to vent?
Author: steve (CA)

If the drain didn't drop down that 10" and instead just stayed horizontal to the stack and the stack doesn't receive waste from above, then the vent wouldn't be necessary if the stack above the tie-in is used as a vent.

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 Thanks clap
Author: ArthurPeabody (NM)

Thanks. That answers my question. Because this plumbing has to be exposed (it can't go under the floor or into the wall; I could build a false wall to hide it but I don't want to lose the space in a small bathroom.) I'd prefer to have it drop as low in the vanity as I can to keep the exposed part as low as possible to keep it out of the way. I'll install a shelf above it both to protect it and for storage.



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