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Question DetailsAsked on 5/11/2016

I've removed the bathroom floor tiles, sink, toilet, opened walls and the foul smell hasn't changed. What next?

I noticed a foul smell coming from my bathroom when we came back from holidays. I removed the sink and capped the drain pipe. I removed the toilet and capped the the drain. I removed the floor tile and cut the dry wall opening the walls to expose the pipes, no cracked ABS pipes. I had a plumber come over and check the pipes and he found nothing. I'm not sure what to check next.

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I hope for your sake this is not a simple thing like an evaporated shower/tub trap, after all the effort you have gone to - and unless this is totally a DIY repair job after you find the cause, don't forget to get your insurance company involved for the repair cost as applicable.

When you said foul smell, you did not say if you recognized it as a sewer or urine or mold/mildew or rotten meat/rancid grease (dead animal) type smell or not - which if one of those would simplify the search.

Common causes of this type of smell - some related to leaks, some specifically related to lack of use for awhile:

0) water in drain traps gone stagnant due to lack of use - sink, toilet tank, toilet bowl, shower/tub drain, floor drain if so equipped (bottom level on concrete slab) - flushing with 1/2 gallon or so of scented detergent like lemon scented Mr Clean or Dawn in full hot water usually clears it right up - or you can just squirt a goodly shot in the bottom near the drain and run the hot water to mix with it and go down. If mold in toilet tank needs bleach cleaning to remove / kill it - avoid soaking plastic parts/seals in it - use soaked sponge to extent possible, flushing with poured water on the parts frequently to avoid damaging them. While you can pour a few capfulls of bleach in the tank to kill the mold, can really cause leaks and cracked plastic/rubber with some thypes of materials.

1) evaporation or high winds blowing over sewer vent pipe pulled water out of the traps (sink, toilet, shower/tub, floor drain etc), letting sewer gases into the room - refilling drains with water will stop the smell

2) toilet seal leaked, causing leakage of flushed water in under the toilet and into the subfloor under the toilet, and sometimes creeping in under the flooring as well - though the latter you should certainly have noticed if you pulled the tiles up. Usually accompanied by urine smell. For this to occur concurrent with your vacation would be pure coincidence, though might have been in effect before but normal household activities and fan/HVAC use kept the odor level down to low or non-detectible levels, especially if forced-air HVAC.

3) dead animal or occasionally animal or insect nest in fan ducting or roof hood or in flooring - check attic too if above this bathroom, because could be critter nest or dead animal up there with the smell coming down around the fan housing - so climb up on a ladder or chair and scent close up there after pulling the surface concealing ring or glillage down/off - ditto around any ceiling light fixtures.

4) leakage from pipes in walls or floors causing fungus growth in framing/subfloor - again, would be coincidental to happen during your absence

5) non-visible DWV pipe break - plumber can do a smoke and/or scented tracer test to see if that shows a leaking point, though usually for a significant smell with no visible break you would also have leakage. Coincidence in timing again if that is the cause.

6) if a moldy/mildewy smell, check floor above/attic for possible leak causing wetness from window, siding, roof leak - coincidence in timing again if that is the cause.

7) would be rare, and rarer still for it to be noticed in only one room, but mold growing in HVAC ducting that did not have air flowing through it for an extended period of time would be a possibility. Ditto to possibility of an animal crawling into the ducting while house was vacant and dying in there - smelling close up to the vents (inlet and return) should tell you real quick if that is the point.

8) leaking shower base, with water not draining out of the underlying pan fully, and due to lack of shower use and soapyh water it went stagnant under the shower floor. Might or might not be able to detect readily by scenting at the drain - you might have to use light painter's sheet plastic dropcloth and tape off to the walls and ceiling and shower sill - or from sill angled to side and back walls and taped there to make an airseal over the shower floor/base, then air out the bathroom, let sit for an hour or two, then if scent in room has diminished poke a hole in plastic and smell the air inside for comparison. Commonly stagnant pond or stagnant water in old tire smell but can occasionally smell almost like sewage if enough organic material has accumulated in there. Can also small acidic or like rotten vegetables if algae is growing in there. Here is a diagram of typical tile floored shower showing the liner under it - which is supposed to drain freely to openings below the shower floor in the drain pipe, but if not fully draining or not refreshed with soapy watrer can go stagnant -

Treatment with mild bleach or hydrogen peroxide solution can kill the smell, but not great for liner and concrete under the grout and hard to get in there.


I would go around, nose close to each area and deliberately go around the room smelling. Also check adjacent rooms. If you think you find a possible culprit location, pour scented detergent down it if a drain, or scrub the area with bleach and baking soda if a surface.

To smell in drywalled walls or subfloor use a vacuum stuck down to a hole in the floor/wall and smell at the air outlet from the vacuum. At walls smell at each stud bay opening - or use vacuum at a small hole in each bay if not opened up. (When I say vacuum - a clean household vac will work - with new bag or cleaned cyclone chamber, or a clean shop vac, or even a handheld vacuum pump for pulling out brake fluid and pulling a vacuum on power brake lines and such - about $10 at auto parts store, and would only require a hole smaller than fiber optic camera needs - 1/2" or less - at each stud/joist bay.

For subfloor areas, since tile is off and drywall is opened up in walls, you can get a COLOR (B&W pretty useless) fiber optic camera - about $20-40/day rental at tool rental place or under $100 to buy from Amazon or Harbor Freight and similar places and look into the subfloor and walls for signs of animals, wetness, fungal growth, etc. If you want to get aggressive and avoid paying another person, you could use fiber optic camera or open up underlying ceiling under tub/toilet and check from there visually and with sniffing/vacuum.

If that does not find it, then I would suggest calling around to home inspectors and explain what your problem is and what you have done to investigate - and get one that will give it a try for probably $100-150. Otherwise, a Mold Testing and Remediation (your Search the List category) contractor would probably be your next best place to go.

Let us know what the cause is - it is so frustrating to give advice on this type of thing and not find out the ultimate cause.

You can also find more extensive lists of possible sources of odd smells in houses by individually putting the words SMELL and SMELLS into the Ask box - it will give links to other related questions with answers.

Answered 4 years ago by LCD

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