Sink Vent in Attic-"Cheat" Vent


I have added a small second story addition on my house that enclosed a roof vent for my kichen sink. The contractor plans on installing what he called a "cheat vent" because it vents into the attic. He will of course have to extend it up a few feet to get into the new attic space. It does not require him to punch a hole up through the roof. He said it has a spring like flipper on the top that only opens when air is being sucked. His reasoning for this is that he wants to minimize the number of cuts into my roof because of its low pitch. It is almost a 12:4. I already have my chimney, two roof vents and a bathroom vent poking through and have never had an issue.
My question is, do these things work adquetely, this is a kitchen sink and I do not want it to be a slow drainer? Will it add moisture to my attic? I have a very dry attic and have worked hard to vent exhaust fans and other items outside of the attic. Any reason why I should not let him use this type of "cheat" vent?
Thanks for all your help. John
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PeleSajan wrote:

I wouldn't allow it. a 4/12 is not a low pitch, and punching a vent through it is not a big deal. Are you subject to plumbing inspections? I can't imagine a plumbing inspector would let that pass. my understanding is these devices are used as a last resort, when conventional venting is not possible. your situation isn't even close to a last resort.
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PeleSajan wrote:

It's a mechanical vent. Some places allow them, some don't. In any event, I wouldn't put one in an attic. That's poor design. If you get freezing temps where you are, it probably will freeze shut anyway.
Instead of cutting another roof termination, he should TEE into an existing vent.
Back to your question: No they won't add moisture to your attic; they only draw air in. Jim
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Awesome, thanks guys for the quick responses. I will tell that I do not want it.
John
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Just out of curiosity.....I'm wondering why these sink vents need to go through the roof instead of the side of the building (like gable end of attic)?
J.
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Some jurisdictions allow side venting, others don't. Concerns include where vapors go that come up from the sewer -- some idiot pours gas down a drain, the fumes come up your vent stack, do they dissipate outdoors or accumulate in your attic?
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feet, completely unsupported. I took the 6 foot extension off, since it was only a matter of time until it broke off. Now, occassionally, it doesn't smell too good in that area. Would putting a spring loaded damper on it help, or would it just ruin my venting?
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Check your local codes for what's required.
Personally, I suspect you should put the stack extension back on, but with adequate support this time.
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vacuum when the last of the water goes down the stack so you don't suck the traps dry and it also gives backed up sewer gas a way to get up and out. It is methane rich, even without that gasoline mentioned above. You can use a Studer Vent like the OP has for the vacuum break but you still need at least one free vent to air and that should be above the roof line. There are rules about the height, roof pitch etc. The air admittance vent (Studer is a brand) must remain accessible.
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methane sewer vent gas is flammable.
PeleSajan wrote:

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wrote:

Why can't he just stuff the sink vent into the side of the existing bathroom vent before it goes through the roof? (It might be too far away, or inaccessible..)
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wrote:

imho:
Confused, is this a real plumber, who is governed by codes and an overbearing inspector? ;)
I would suggest you get help from your local code enforcement personnel. Many times trades people will take shortcuts to not 'cross-trade', meaning this plumber does not want to do roofing work.
later,
tom @ www.Consolidated-Loans.info
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