We have a tri-level home, built in 1980. My husband bought the home in 1990. There has been an on and off sewer gas smell since right after he bought the home. This smell never occurs in winter. It doesn't happen every day. Sometimes we go weeks without smelling it. On those occasions that it does crop up, sometimes you can just barely smell it and sometimes it can just about knock you down. The smell is generally concentrated right along the vent stack from the basement up to the kitchen. We never actually smelled it in the kitchen until we took some baseboard up while remodeling, and this was on the wall that the vent stack runs through. The laundry room is on the level above the basement and the kitchen is on the level above the laundry room. The smell never seems to reach the top floor of the house unless it is really strong and has just permeated the entire house. In those cases, the concentration of smell is still along the vent stack. We have no dry traps. Everything that SHOULD have a p-trap on it, does as far as I know. Both toilets have been recently reset with new wax gaskets and neither toilet shifts or rocks. When my husband bought the house, the basement had plumbing roughed in for a full bath which he had finished by licensed professionals. They jack-hammered out concrete in order to set the tub, but this is the one place I haven't been able to check for a p-trap. There is a closet that runs behind the bathroom and I was able to take some of the sheet rock loose from the bottom of the wall that backs the tub. The tub is sitting directly on the concrete (porcelain coated steel tub), and I finally located the floor drain. It's under the tub and capped off. We've smoke tested and everything seems to be as it should be. Any ideas? I've just about decided I'm going to have to run a camera inch by inch down the stack to see if there are any breaks/cracks or nail holes. I'd REALLY rather not have to do that. Thanks in advance for any advice and/or insight!

Your smoke test should have shown up any cracks in the stacks or joints. The floor drain that capped off. How's it capped? Any odor around it? Any more floor drains in the basement? Are you on city sewer or a septic tank? How many vent pipes do you have coming out of your roof? Any more information you care to share? Back to you, Tom

Can you confirm that your vent stack goes through the attic and out to daylight above the roof? We have found a few that were installed to terminate in the attic or some remodler cut one off in the attic. Is this happening on windy days or calm days?

ballengerb1, thanks for the reply. Haven't checked the attic to make sure it is all attached. The stack does come out the roof, but of course, that doesn't necessarily mean it isn't separated somewhere in the attic, right? We'll check that out. Happens both on windy and calm days,but more often on days when the wind (or even a slight breeze) is out of the east. House faces south.

Thanks for the reply, Tom. The floor drain is capped off with a clean out cap. Not sure that's the right name for it? This is the only floor drain in the basement. No smell coming from under there. We're on city sewer. 2 stacks coming out the roof. One vents the kitchen, the other is the rest of the house. More info: When we use the attic fan, we get that smell every time. It's obviously pulling it from somewhere. When the odor first starts and is just barely there, it is strongest in the laundry room which is on the ground floor. There is definitely a p trap on the laundry. I put that one in. It had an "s", and I thought maybe it was siphoning so I changed it out. No help there. The smell happens in warm, humid weather only. Never in winter. Smell will generally go away if we turn the a/c on and get the house cooled down. Window units, not central air. Smell is never in either bathroom. It is always centrally located in the house until it gets really strong, of course, then it permeates the entire house. Thanks again for the reply and I'll look forward to hearing back.

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2 stacks coming out the roof. One vents the kitchen, the other is the rest of the house.

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I asked that question to learn what you have up in your attic.
Sounds like you're revented back to a single roof vent on the rest of the house. Correct?
When you ran the smoke test was the attic checked?
Your laundry room. Does the washer discharge into the sink or does it have its own washer station and standpipe? You gave me great information. Anything more to add? Regards, Tom

Tom, the attic wasn't checked when we smoke tested, and obviously, should have been. Can you tell we're not plumbers? Re-vented back to a single roof vent? I don't know, but would assume so? Washer has it's own standpipe. As mentioned before, washer is on the ground floor. Behind and below is the basement closet that runs behind the basement bathroom. All of the plumbing for the house, except for the kitchen, culminates in this closet. Not sure if that is needed or helpful information, but trying to give you the best mental picture I can. Thanks again!

This may be helpful; Odors & Smells: How to Find & Remove Odors, Gases & Smells in Buildings
Or you may wish to call in a Odor Detection Service: Home Odor Detection Service
You've certainly have gone the extra mile in attempting to locate the source perhaps a Odor Detection Service is just what you need. Good luck, Tom

Tom, thanks for all your help. Interested to get busy reading the article you sent a link for. Planning on checking the attic today, and if all seems well up there, then I guess we have no choice but to call in a detection service. Thanks again!