Horizontal vent slope - which way?

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Old 02-13-09, 10:37 AM
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Horizontal vent slope - which way?

I'm doing all the plumbing in a house I'm building but am confused about an issue with horizontal vent slope. I believe code states that the slope (1/4" per foot) needs to be away from the fixture (bathroom sink in this case) rather than back towards the fixture. Is this correct? It seems to contradict reason in that if enough rain water or condensation got into the vent pipe it would end up creating a trap in the vent near the 90 degree turn up toward the roof and thus not allow air to pass out to the roof. It seems it should slope back toward the fixture where rain water or condensation would flow down the drain rather than away from the fixture. What am I missing or am I completely wrong on the code regarding slope? TIA for any help on this.
 
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Old 02-13-09, 11:37 AM
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I'm not convinced yet I have answered my own question but after digging around here I found a statement that a vent 'must have no negative elevation'. So maybe my initial information was incorrect? If vents always need to have an upward slope that would seem more reasonable. Any confirmation?
 
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Old 02-13-09, 11:43 AM
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No plumber here...but I think the "1/4" per foot away" statement you made in the first post, applies to DRAINS...not vents.
 
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Old 02-13-09, 12:28 PM
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Thanks for the reply. I do know that is standard for drain plumbing but I've got a book that says "Horizontal vent pipes should maintain the same slope as drainpipes (1/4 inch per foot) so that trapped moisture will drain away from the fixture" which sounds like they are saying it should be like this:



If this is correct it would seem rain water or condensation could build up in the area where the vent turns 90 degree up to a point where it would completely block the vent assuming the horizontal run is over 8 feet for a 2" inside diameter vent pipe.
 
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Old 02-13-09, 12:32 PM
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Yeah...doesn't make much sense...maybe a typo/editing problem with the book? Never saw a vent like that.

WTH are all the plumbers today? Out collecting their payments I guess. Or on calls for the folks who were waiting for payday to call for repairs. lol


Heres something quoted from this site...

Plumbing Vent Pipes - Can They Be Relocated?


"These vent pipes have certain requirements with regards to their size and length. They also must be installed in such a manner so as to continually slope toward the drainage lines. Water or debris must not be allowed to collect in vent pipes. Blocked vent pipes can create a scenario as described above. If one of your existing drains bubbles or gurgles when another fixture is draining, you may have a blocked vent pipe."


And heres a pic from another site...
http://www.inspect-ny.com/plumbing/1625ss.jpg
 
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Old 02-13-09, 01:25 PM
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drains slope away from the fixture and vents slope to them. a vent is ran exactly backwards from the drain. so if the drain goes down the vent goes up. if they were ran horizontal and met at a point it would look like
 
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Old 02-13-09, 02:13 PM
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Thanks all for the help - sounds like the book I've got is booboo and fortunately when things sound backwards to logic I'll question it even if it's in print The info on that came out of an Ortho's Home Improvement Encyclopedia which does have a lot of good info but that tidbit just sounded wrong or I'm misunderstanding their statement
 
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