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Old 12-07-2009, 08:50 AM   #1
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Should I change the venting if possible?


Friend called me over yesterday because her basement has been overcome with sewer smell over the last few days. Only a 2 year old house, the smell seems to be coming from behind the washer, which drains into a laundry tub and away. After the trap in the drain there is a 1' vertical pipe with a Studor on it, I assumed this to be the culprit. I replaced it with a generic AAV but the she said the odor has not ended two days later. There are no other open drains in the area. Two questions:

1. Is it possible for pressure to push gas back through an AAV and into the room? This is in Detroit (not a suburb) so nothing about their sewage system would surprise me.
2. There is a main 3" drain line coming down a wall 4' away from the bathrooms above which I can see vents through the roof. Any reason I shouldn't run PVC from where the AAV is and splice it into the main line? I figured this would be a more permanent fix.

Thanks all!

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Old 12-07-2009, 11:03 AM   #2
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Should I change the venting if possible?


Anything's possible, but as long as there's a roof vent that freely communicates with the atmosphere, then chances are the AAV isn't the culprit. If there's a floor drain in the basement that doesn't get much use that may explain the smell; or likewise if there's a guest bath that isn't used a lot, water can evaporate out of the trap in the shower etc.. Finally, it could even be a crack in a pipe - check especially where the pipe goes through the slab or foundation.

The soil stack coming down through the basement ceiling is a drain for all the fixtures above, so you definitely don't want to tie the laundry vent into the stack there. By Massachusetts code, a vent must be tied in (to a vent stack, or another vent pipe) a minumum of 6" above the "flood-level rim" of the highest fixture. Since the laundry is (presumably) the only fixture in the basement, you then have to run the vent up to the first floor level and tie it in 6" above the rim of a sink on the first floor.

I don't know what the code in your state, or the national codes would say...


Last edited by Ishmael; 12-07-2009 at 11:05 AM.
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Old 12-07-2009, 11:28 AM   #3
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Should I change the venting if possible?


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Originally Posted by Ishmael View Post
as long as there's a roof vent that freely communicates with the atmosphere, then chances are the AAV isn't the culprit...... it could even be a crack in a pipe - check especially where the pipe goes through the slab or foundation.
That's what I figured, but hoped the AAV could have been the problem. The slab is plumbed for a bathroom about 10' away but all of the drains are covered. Laundry tub is the only above-slab drain in the basement. The crack is definitely a good idea, I'll have to check that out. If it is, are we automatically talking about busting up concrete around it to get a fitting over it and reconnect?

Quote:
Originally Posted by Ishmael View Post
The soil stack coming down through the basement ceiling is a drain for all the fixtures above, so you definitely don't want to tie the laundry vent into the stack there. Since the laundry is (presumably) the only fixture in the basement, you then have to run the vent up to the first floor level and tie it in 6" above the rim of a sink on the first floor.
Again my fear....! Since the slab is plumbed for a bathroom would they have incorporated a vent for those drains, or would that have to be done when it is finished? Trying to fix this for her, she had a plumber come out and he said $1000 and wanted to bust up the entire utility room slab.... of a two year old Habitat-for-Humanity house.
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Old 12-07-2009, 12:43 PM   #4
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Should I change the venting if possible?


I would delay the busting up of concrete as long as possible.

As far as all the drains covered, do you mean with caps or do you mean covered over completely by the poured concrete floor and meant to be busted open when needed for remodeling?

Tie a plastic bag over the AAV (interior drain vent) for several hours or maybe even a few days to get a feel for whether it is sucking in or blowing out air/gases.

If there is a crack in the floor you might try sealing it up to at least judge whether the bad odors are coming from below for example a pipe has indeed cracked. If a pipe undrground has cracked you will need to sooner or later dig it up but you want to find out for sure first.
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Old 12-07-2009, 01:31 PM   #5
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Should I change the venting if possible?


Great idea on the plastic bag, I'll try that. Heading over their this afternoon to check for crack at the base. All of the drains for the future bathroom are cut off at floor level and have male/female threaded caps on them, and don't really have any odor in that area so I'm not concentrating there.
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Old 12-07-2009, 01:40 PM   #6
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Should I change the venting if possible?


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Originally Posted by moneymgmt View Post
That's what I figured, but hoped the AAV could have been the problem. The slab is plumbed for a bathroom about 10' away but all of the drains are covered. Laundry tub is the only above-slab drain in the basement. The crack is definitely a good idea, I'll have to check that out. If it is, are we automatically talking about busting up concrete around it to get a fitting over it and reconnect?


Again my fear....! Since the slab is plumbed for a bathroom would they have incorporated a vent for those drains, or would that have to be done when it is finished? Trying to fix this for her, she had a plumber come out and he said $1000 and wanted to bust up the entire utility room slab.... of a two year old Habitat-for-Humanity house.
Ahhhh...a bathroom already roughed-in under the slab; that sort of changes things IF (and only if) the waste pipes tie into the sewer under the slab. If the pipes all drain into an ejector basin and none of the vents are connected yet, then it wouldn't matter. But if it's the former (already connected to the sewer), then the prime suspect would be whatever caps/plugs are covering the pipes that are stubbed up through the slab. If they capped the pipes w/PVC caps, are they glued? If they capped the lines with rubber "test caps" w/large hose clamps, and are the hose clamps tightened? If they used test plugs, are the wing-nuts tightened? Did they just stuff rags into the pipes to keep sewer gases out?

There's no need to bust up the slab if the sub-soil piping was inspected before it was buried and you can do an air test and determine there are no leaks. Often what happens with plumbing that's been installed for future use - especially where it comes up from a concrete slab - is that someone (like the guy who smoothed the slab with the power trowel) may inadvertantly hit the PVC pipe and crack it. If that's the case, you'll most likely have to chip around the pipe enough to cut off the broken piece and couple a good piece onto it.

If she ever does want to finish-off that bathroom, she should check and make sure it was on the plans, approved and inspected/signed-off before she takes it any further. I'm guessing since it was Habitats-for-Humanity they dotted all the i's and crossed all the t's, but it's better to be safe than sorry.
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Old 12-07-2009, 04:53 PM   #7
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Should I change the venting if possible?


I forgot to mention that here in MA, a 2" "future vent" is required so that any future fixtures added in the basement can be vented without the difficulty you're currently faced with. I'm not sure if it's required in other states, but it seems strange that in a house where they piped the laundry connection in the basement, and roughed-in the drains for a future basement bathroom, that they wouldn't have provided a vent to handle these fixtures?
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Old 12-11-2009, 07:44 AM   #8
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Should I change the venting if possible?


Turns out the smell isn't coming from the vent to the washer drain. I took off the Studor vent and smelled the pipe, it smells like detergent, not sewage. The pic I'm attaching is the main drain coming down, two bathrooms feed into it and it vents through the roof. I checked every inch of this thing for a crack and I can't find anything! I looked at the floor above and there is no sign of leakage anywhere. Any thoughts on what is causing this? It is definitely getting worse!

Side note, this started 1-2 weeks before we got below freezing and we haven't had any snow to speak of so I somewhat ruled out a frozen vent.

Thanks all!
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