There has been this smell in my house for over a year now and I have been putting it off because it is not in the area where we are the most and I don't know where to begin. I have a basement rambler (finished basement) and under the stairs, there is a smell. I don't think I would necessarily call it musty, but maybe some sort of sewage type smell. I don't know, just some sort of damp smell and if you open the door to the under stair storage, it is strong. It is just used for storage and I have taken everything out of there before and it is totally dry. Right above that area, on the main floor, I also can detect a smell. Since I don't see anything in that area under the stairs, it is almost like it is either coming from in the walls nearby or maybe in the joist space of the basement. While the basement is finished, the small space under the stairs is not so it is open to the joist space above. There are no water leaks or anything anywhere that I have seen, but this smell has been lingering in that area for over a year. I don't even know where to begin because I am not going to just go randomly tearing apart the walls and ceilings in the house. It doesn't seem to change whether it is the summer or winter. Do you think this could be coming from somewhere in the plumbing? And if so, how can it be detected? Do I need to get a plumber to run a camera in all the drain lines? I would appreciate any suggestions so I don't just keep ignoring the problem.

 

Hard telling. First thing, look for any open drains. Sinks, floor drains, unused toilet or shower. They all have traps that can go dry. Pour some water/pinesol in them to rule out sewer gas. And see if that helps.

Honestly I would suspect a dead animal too. Is the space empty and clean?

 

Have you tried ventilating the area? An unventilated enclosed unfinished area could just be accumulating smells from dampness that migrates through the floor. Leave the door open and blow air into the space with a fan. If there is a window nearby use a second fan to exhaust stale air outside.

 

I wouldn't suspect a dead animal as the decaying process rarely goes on for more than a few weeks and then the odor is gone.

I agree checking the drains is a good place to start.

 

Depends how big the animal is! LOL

 

The area is not currently empty, I have emptied it a couple of times in the past just to see what happens and the smell is still there. It is just a small space under the stairs with concrete floor, but I made a removeable raised wooden floor that I have in there in case there was ever a flood, the stuff wouldn't get damaged. Maybe I will try that again and leave it open like you said. The thing is though, this only started in the last couple of years. In the basement, there is a laundry tray (that gets used all the time because the washer drains into it) and a bathroom. The sink and toilet get used all the time and the shower gets used every couple weeks so the traps are not dry. There is no floor drain. I thought of the dead animal too but I have had dead mice and even rats before in places and it doesn't smell like that. Plus, that wouldn't remain constant for this long. A couple times in the past I left it open and ran an ozone generator and that got rid of it for a couple days but then it came back.

I will clear it out and leave it open for a week or so and see what happens, but if it doesn't resolve anything, is there a way someone can check all the drain lines without tearing up everything? How does that work?

 

A plumber can send a camera down your drains but I'm not sure he would find anything. Sewer problems usually manifest as slow clogging drains... usually with tree roots to boot.

Is there a crawl space in any part of the basement?

 

No crawl space in the basement. I know where the drain pipes run under the slab. About 6 or 7 years ago, some water was coming up from the slab when a sink was running and they ran a camera and found a big hole in one of the T's under the slab. The tore it up and replaced that piece and ran a camera down the rest of the lines under the slab and said they looked fine. A couple years later, there was a backup and they found the clog in the old cement pipe that ran from the cast iron under the slab to the septic tank. That was all falling apart at the joints and was replaced and when they did it, they ran a camera from that end and it looked fine. There is only about a 10 foot run from the house to the septic tank and no roots around there. About a year ago, a bathroom sink backed up on the main floor and there was a 90 degree bend that was completely clogged with sludge and that was replaced. That pipe is actually accessed from this space under the stairs, but I am pretty sure I noticed this smell before that. It is very frustrating not knowing where to look.

 

I had a similar mystery smell a couple of years ago. I found that a sewer vent stack had not been connected by the plumber when the house was built. I am the original owner and have numerous pictures of the house being built & yet did not notice it then. We never had that smell for the first 12-14 years after we built the house and yet it started showing up after all those years, some days worse than others. Definitely a sewer gas smell for mine. It took a lot of looking / sleuthing but I happened to notice an unconnected pvc pipe just below my main floor 1/2 bathroom. It was mostly buried between joists & studs. My guess it was supposed to connect to a main vent line in the basement that was around 6' away. I ended up splicing it in to that vent line & all smells went away immediately.

With the drain clogs you mention and other drain issues, I would check regarding the vent lines. Something could have changed or become dislodged when they corrected the drain clogs / blockages. Before I found my problem myself, I was looking into having a plumber come & do a vent check. Essentially it is a "smoke" test where they close off all possible known vent locations & then pump some "smoke" into the vent lines & see if it shows up somewhere in the house. If so, then you have a vent disconnect in that area.

In a related situation, my sister had a similar smell in her main floor 1/2 bath. Ended up being a punctured vent pipe in the wall from that sink drain. The drywallers punctured it with a nail or screw. She was lucky in that the drywall nail popped at that spot, when they investigated it further, the smell was greater right there & found the hole in the vent pipe. Old cast iron pipes are hard to puncture, but PVC certainly is easy for that to happen.

Investigate the vent lines, that might be the source.

 

Thank you for that information. I couldn't figure out how I could get a smell if there was never any water, but that makes sense about the vents. Now that you mention it was worse some days, I find that to be the same too. For example, the other morning when I woke up, it was really strong. In fact, I could smell it a little farther down in the house than normal. After everyone was up and took showers and later in the day, it wasn't as bad. Then this morning, it wasn't as bad either. Maybe if water is being used, it is giving the smell less time to escape up the vent? The house was built in the 60s and has cast iron and the ABS replacement was all down low (it has water running through so if it leaked, I would know), but it could be in the vents higher up like you said. It makes sense that since there is no drywall under the stairs, and there is even some exposed pipe from the bathroom under there, it could even be higher up on that line. If there is a break in a pipe under the slab though, that shouldn't cause any smells, right? I did not know about this smoke test, but that sounds like it would do the trick. I thought about buying one of those inexpensive endoscopes from Amazon to try to run down the pipes but that probably wouldn't work well and if there were a smaller crack or hole, I probably wouldn't see it. I have putting this off because I typically do everything myself and don't want plumbers coming out and just randomly tearing up the walls. If this smoke test can help locate if there is a leak, at least I can only tear out the walls that need to be torn out. I will look into this. Thanks.

 

SHORT- use a box-fan or two to create positive pressure in the house, let it run for an hour or so
THEN track down the smell.
A handheld 'carpet-furniture cleaner/shampooer" that does WET cleaning can also help- use it to check out suspect areas of carpet for pet stains or toddler vomit- usually corners and thresholds.


LONG- this is a trick 'technique' I've learned from years as a Realtor and prepping houses for showing.
1) Close all the windows / vents / chimney flues
2) turn off the HVAC
3) blow air into the house using a box fan from sunny window(s) for an hour or so to push in fresh air.
4) spot test carpet corners / thresholds by doors with a hand-held WET carpet/upholstery shampooer. As you check portions of the carpet, when you DO find a place with an under-the-carpet-down-in-the-padding smell, you'll immediately smell it because of the carpet shampooer exhaust.
5) then deep-clean / steam-clean as needed.

 

So here is something interesting I may have discovered. I happened to open the door under the stairs the other day in the morning and I could smell it, but then later in the day I didn't. What I think I noticed is for the past week, it has been hot here so the AC has been running all afternoon and when I checked under the stairs after it has been running all day, there was hardly any smell. That can't be related, can it? Why would the AC running make the smell go away? Maybe I am imagining things.

 

Lack of air movement with the door closed and AC not running allows smell to accumulate. The AC could be drawing return air from the house through the structure (as well as through the return air duct/plenum) and dilutes/dissipates the smell.

 

That makes sense! The return duct is actually right in the vicinity of where the smell is and the furnace is in the basement near the stairs as well. Oh well, I guess there still is a source of smell then but it is just dissipated like you said.