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Question DetailsAsked on 6/22/2015

very strong sewer gas odor in the living room but all drains have been cleared, no clue?

I live in a semi detached house, new built (2 years old). Recently it started reeking of sewer gas (sulphur kind of smell). It is stronger in the living room, near the exit door and in the top of the stairs. It does not smell outside, does not smell in the bathrooms and the neighbours don't have that problem. My landlady called a plumber and a builder and all the drains have been cleared, the back yard was digged to check for leaking pipes, the floor was inspected to check for leaks or dead animals, the gas company came over and everything is fine. The smell comes and goes randomly but lately it is getting stronger and taking longer to disappear. I am getting worried as I have small children and I don't know what is causing the smell. I am wondering if it could be the fire sprinkler system water or the central heating radiators water? Any suggestions? Thanks in advance.

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I presume you are confident that you are smelling sewer/biodegradation gases, not natural gas/propane odorant ? If in doubt, you can get sniff strips at gas utility to scratch and sniff to compare with your smell to be sure you are not smelling a fuel gas leak.

Things that can commonly cause this - item 0) is probably the most common cause - and of course even though smell in in only your unit, source might be in the adjacent unit and migrating to yours, so it should be checked too at same time:

0) floor drain through concrete slab that has gone dry (typically take 2-3 years except in very dry desert area much less) so is letting sewer gas up through - fill with a gallon of water. Can also be floor drain that has gone stagnant in the trap - flush with some vinegar and baking soda and let sit a few minutes, then flush with a gallon of hot water to clear out the mixture and refill the drain. (Should flush them with a gallon or so of water with a bit of bleach in it annually as a preventative measure). Same thing can happen with any drain that is unused - like an old overflow drain for an A/C or utility room, unused washer drain riser, disconnected dishwasher drain, etc.

1) sewer pipe leak or septic tank/leach field leak or backup to the house - also check for any drain/cleanout plugs in the sewer line in the house (commonly in basement/crawlspace, and also sometimes under sinks) that might be leaking - they commonly (especially the metal ones and most especially metal plug in plastic pipe or vice versa) tend to leak around the threads after a few years - removing and putting on thread compound or teflon tape can solve that problem. If that is issue, will have brown discoloration around the plug, plus commonly corrosion or mold.

2) broken or leaking or open joint on the sewer vent pipe that goes through the roof to vent fumes from the system

3) iron bacteria growth in the water pipes - morer common in hot water than cold, and most common in water heaters that are set below about 150 degrees (so residential heaters especially) that are not used for an extended period of time - though of course that smell occurs only at sink, shower, tub, laundry, toilet etc and only when you run water

4) fire sprinkler system can go stagnant, especially in iron or organic material rich water (much more commonly with well systems) - should e flushed about annually to every two-three years depending on your water, not only because if system activates your house is sprayed with stinky water rather than clean water, but it also promotes corrosion in the pipes with eventual (typically 5+ years) pinholing or "rotting-out" of pipe threads or joints. Would stink only if leaking. Ditto to hot water heating (baseboard or in-floor).

5) organic water flow to your house from adjacent slough or pond or boggy area, or from neighbor's broken sewer or leach field, seeping up under slab or foundation

6) built in organic area like peat bog or swamp or such, and organic material is decaying and generating "swamp gas" which is rising from under your slab - can also happen if house was built in a low place and contractor dumped clearing debris where house was to be built to fill in, and is now decaying

7) naturally occurring organic gas from natural gas or oil field seeping to surface through ground fractures or along well casing

8) cleanout open or plug/cover cap has been removed - usually a foot to three right outside the house where the sewer pipe exists the house

9) unused capped-off sewer pipe in unfinished bathroom or laundry room that is leaking - commonly these are just covered with taped-on plastic sheeting or a slip-on plastic cover during construction, assuming sink, shower/tub, toilet etc will be connected up to it - but if bathroom is left unfinished they can then leak gases.

10) air inlet vent under cabinet or kitchen island letting sewer gases out

11) rarely, but there is a fungal growth that can grow in wet floors/walls that puts out a rank sewage-type smell with strong sulfur smell - occurs in walls with slow, constant water leaks (pipe or siding or steam/hot water heating) that gradually rots away the studs or floor joists and wood siding. IF from that, you should probably be able to detect by looking for water staining under that area in the basement, or by getting on hands and knees and sniffing along the baseboards and at all outlets in the area while all the household exhaust fans are on (to pull outside air in through walls). If basement under living room is finished, might require taking light fixtures out of ceiling and smelling there for rot smell. Rotting floor/wall due to leak can also be detected by drilling small holes and inspecting (in uninsulated areas) with fiber optic inspection camera/scope, or by use of a thermal infrared camera to detect zones of different temperature in the hidden wall/floor cavities. Significant rot/fungus areas show up also because they are damp, and funguses generate heat.

How to track down - sometimes not at all easy:

A) google on how to do this - do a sewer test using concentrated smell - commonly pure vanilla extract is used - poured down drain at the "head" of the piping (furthest from where sewer leaves house), in each branch of drain lines if multiple branches, being VERY careful it goes straight down drain and is not splashed all around inside the fixture. Then immediately tightly cover or tape that drain so the smell does not come up from the trap and confuse you. Best if done in place with exhaust fan to pull out smell so it does not filter through house from where you put it down. Then sniff around the house to see where the smell first occurs, and what pipes are near there. This can tell you if your smell problem is coming from sewer pipes or somewhere else. Generally works best if you turn off HVAC system, all outside openings under or alongside entry (including garage connecting) doors are masking taped to limit air sources, and all household exhaust fans are run - this puts a negative pressure on the house so it pulls air out of the sewer system into the house through any broken/leaking drain pipes.

B) if living room and exit door are over where the sewer pipe leaves the house, my first suspicion would be a cracked pipe, either under slab due to house weight on it (improperly installed) or very commonly right at the foundation where the differential settlement of the foundation or the backfill around it causes vertical relative displacements, commonly cracking the pipe there or at the commonly close-by cleanout connection.

C) if on septic, check for overfilled tank or leach field backing up, including a couple of hand auger holes dug to a foot below basement floor level, located between tank/leach field and house, to see if sewage is flowing back toward house

D) have sewer and drain contractor run a sewer camera through system looking for cracks or broken/open joints

E) if camera shows nothing, have sewer and drain contractor run a smoke test on sewer system to check for leaks

F) thermal IR camera run on house looking for wet floors/walls/attic

G) if all else fails, give notice to landlord that conditions are unacceptable and unsafe so you are terminating your lease, and move - because this sort of issue is ultimately, in most leases, the landlord's problem.

Answered 5 years ago by LCD

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