Where could this smell be coming from?

[vpn33]

Quick backstory: I have a basement rambler and for the past several months, I have been noticing a faint odor in certain areas of the house that seemed to be originating somewhere under the stairs. I have switchback stairs with a landing going down to the basement and underneath is a storage area. When I open the folding door to under the stairs, it has a pretty strong smell which I determined has to be coming from the joist channels because they are exposed under there and I took everything out from underneath and found nothing. I originally thought it was a dead smell and was just waiting for it to go away but it has been there for probably 6 months and hasn't changed and the more I go in there, I think it is more of like a stagnant water/sewer smell.

Lately when I go outside the front door (in the picture), I occasionally get a sewage smell depending on the wind. Anyways, yesterday the dishwasher was running and I smelled it more and I leaned down to that vent under the window and could smell it coming from there. I get a pretty faint smell from that vent with no water running but when the water starts running, it comes on stronger. That vent is right beneath the floor level of the main floor so it must be venting the joist channels. The kitchen sink is centered under the window and you can see the roof vent and I know where the pipe is in the basement (it goes straight down inside the wall and into the floor) and from where I measured, it appears that it is a straight shot from the vent all the way down into the basement and the sink drain must go over horizontally into it somewhere (I have the yellow line drawn where I believe the drain pipe is likely run, the yellow circle above the hose bib would be where the drain goes into the wall in the undersink photo). I can definitely hear the water running well when I get down near that grate just like you would hear water running through a pipe in an exposed wall. Where could this smell be coming from? There can't be a leak in this pipe anywhere or else I would have water in the basement or at least leaking through the ceiling or walls down below. What are your thoughts?

 

[Terry]

Below the hosebib there looks to be a crawlspace vent.
A friend of mine was noticing smells in the lower section of his home, turned out to be rats had gnawed through the kitchen drain lines and there was waste water there. It turned into a major cleanup.

The smells outside the home depending on wind? That's the roof vent that disperses sewer gas into the atmosphere.
Or if coming from the foundation vent, maybe water leaking from the sink drain below.

 

[Sponsor]

 

[vpn33]

Below the hosebib there looks to be a crawlspace vent.
A friend of mine was noticing smells in the lower section of his home, turned out to be rats had gnawed through the kitchen drain lines and there was waste water there. It turned into a major cleanup.

The smells outside the home depending on wind? That's the roof vent that disperses sewer gas into the atmosphere.
Or if coming from the foundation vent, maybe water leaking from the sink drain below.

The vent below the hosebib is a joist space vent as there is a basement below. There is definitely a smell coming from that vent, but like I said, if there was a leak somewhere in the drain line, there would be water leaking down into the basement and I would see it, right?

I originally suspected a dead smell coming through the joist space under the stairs because I heard mice or rats in the joist space between the basement and main floor about 6 months ago. Something has been eating bait I had been putting out so I suspected something died in the joist or wall space. Just recently though, I found a small hole where I believe they had been getting in and put traps and ended up catching 6 mice within a week so it looks like they were mice and not rats. But after smelling through that vent below the hose bib, it is definitely more of a sewer smell as opposed to a dead smell which would get stronger with the water running. I mention the under stairs smell because the stairwell is located just to the left of that front door in the picture, so that is only about 10 feet or less from that kitchen drain, so I think whatever that smell is coming from around the drain is making itself over through the joist space to the stairs and you can smell it there because they joists are exposed.

 

[WorthFlorida]

Looks like you'll need to remove the vent cover. It might be a small leak where it won't show itself. A hole on the top part of the drain pipe can be venting into the cavity and not leak any water. Is it galvanized pipe or PVC?

 

[vpn33]

Looks like you'll need to remove the vent cover. It might be a small leak where it won't show itself. A hole on the top part of the drain pipe can be venting into the cavity and not leak any water. Is it galvanized pipe or PVC?

The vertical pipe is galvanized for sure where it comes up through the roof and goes down into the basement. There is a tee in the basement that a laundry room sink connects to and that along with a few feet of underground piping had to be replaced a few years ago because there was a hole in the tee. I don't know what the piping is that would go from the kitchen drain inlet over to the tee in the vertical pipe. It may be PVC as that kitchen was probably remodeled sometime in the last 20 years or so.

From my picture, do you think where the drain goes into the wall under the sink, that the pipe would immediately go straight over horizontally into that vertical pipe as opposed to going down first and then over? Would it be worthwhile to get one of those $100 endoscopes to see if I can see anything inside the wall (or inside the pipes)? I know they won't be as good as a plumber's scope but maybe they will show something?

 

[WorthFlorida]

At the roof you can place a garden hose inside the roof vent and run the water full blast. You can get a spray nozzle that will fit inside the pipe, adjust it for a stay pattern so the wall of the pipe gets most of the water. Lower and raise the hose, let it run and check the basement.

https://www.homedepot.com/p/Orbit-Contractor-Nozzle-Set-26809/300210095#overlay

 

[Terry]

Growing up my parents had remodeled a bathroom, firing out a wall for a wall hung toilet, dropping the ceiling, adding tube lights there.
The boys were getting blamed for the smell in there, even with a wall hung bowl that was easy to see under as to whether it was clean or not.
When I became a plumber, I changed out the bathtub and pulled drywall off the walls. Rats and mice had been running rampant through walls and ceilings peeing everywhere. It was horrible. All I could think was,

"You dirty rats!"

 

[vpn33]

At the roof you can place a garden hose inside the roof vent and run the water full blast. You can get a spray nozzle that will fit inside the pipe, adjust it for a stay pattern so the wall of the pipe gets most of the water. Lower and raise the hose, let it run and check the basement.

https://www.homedepot.com/p/Orbit-Contractor-Nozzle-Set-26809/300210095#overlay

That sounds like it would definitely work, but do you have any other ideas (maybe involving a camera or something) that would not try to get water into the basement? It is a finished basement with a newly remodeled room right under there so I would rather not mess it up if I don't need to, plus I wouldn't see water down there right away anyways.

 

[vpn33]

Growing up my parents had remodeled a bathroom, firing out a wall for a wall hung toilet, dropping the ceiling, adding tube lights there.
The boys were getting blamed for the smell in there, even with a wall hung bowl that was easy to see under as to whether it was clean or not.
When I became a plumber, I changed out the bathtub and pulled drywall off the walls. Rats and mice had been running rampant through walls and ceilings peeing everywhere. It was horrible. All I could think was,

"You dirty rats!"

They definitely are nasty. I have rats in the attic before and also in the crawl space (it is not a full basement). Pulled all of the insulation out of the crawl space and it was nasty. Now I am starting to second guess if this is plumbing related. I have had pipes apart full of sludge and that smells awful and this is not like that smell. I also have a septic tank and it does not smell like that either. It is almost more like a smell of stagnant water, like if a bunch of decaying leaves were left in a small pond or something. But the fact that it gets a little stronger when the water starts running must mean it is plumbing related, unless I am missing something.

 

[vpn33]

Interesting thing.....

I was just walking up to the front door and got a pretty big whiff of the smell and it was a little windy. I went down to smell inside the vent and didn't smell anything. Maybe some of the smell is coming from that roof vent or the toilet or shower vent that are also near that area. But that still wouldn't explain the stagnant water smell inside the vent cover. I will do a little more investigating to see if the smells are the same and try to get on the roof soon and smell the vents.

 

[vpn33]

I just wanted to update that I did go on the roof and smelled all of the roof vents. I did not get any strong smells from any of them. They all had a very faint sewage smell which I would imagine is normal, but the smell was definitely different from what I can smell from that vent below the window. It still does really only come on when the water is running though. I guess I will try to get a camera in the pipe or in the wall and see if I can see anything.

 

[Lucy20]

I just wanted to update that I did go on the roof and smelled all of the roof vents. I did not get any strong smells from any of them. They all had a very faint sewage smell which I would imagine is normal, but the smell was definitely different from what I can smell from that vent below the window. It still does really only come on when the water is running though. I guess I will try to get a camera in the pipe or in the wall and see if I can see anything.

Did you ever figure this out? We are having a similar situation that is related to amounts of water and we're stumped.