Odor in basement
 

House is less than 2 years old. Propane heat, septic system that does not require a pump. In the last month (yup, during the coldest weather) we have noticed an odor in the unfinished and perfectly dry basement. At first, I thought the cats, when they invariably escape to investigate twhat's in the basement, had maybe pooped in a corner or in a box. But, that's unlike them. I am now of opinion that we have a frozen trap or something going to septic system and what we are smelling is odor from that. This is 3BR 2.5BA house, with only 2 adults and 2 cats, so I don't think the septic is overly full. The odor doesn't seem to be worsening, but it does linger. Any suggestions are appreciated.

Washer Connection
 

Do you have a laundry in the basement? Check for a dry trap at the washer drain connection.

Is it kind of a fishy/musty smell? Unpleasant but not over powering, like a septic might be?

I'm asking because we found where the drains in out basement (root cellar, really) were growing some sort of weird science project. We sprayed down the rocks in the crawl space with a Lysol and water mixture. Then, we bought some baking soda and placed it near the drain. I put a little bleach and water at the opening of the drain, just to kill the bacteria, but didn't want to kill the septic system.

Infrequenty used drains?
 

If you have any drains that are infrequenty used the water in the traps eventually dries out and can open a path for sewer gases to back up. You mentioned the cold (cold air is also very dry, speeding evaporation) but along with the cold has come some very windy days that can pull some water out of traps. If a drain is in occasional use, no problem, the trap fills right back up. But if it isn't used much and the trap is drying out, the wind can be the finishing touch, sloshing water out of the trap and also pushing sewer gas in when a strong gust comes along. We had a seldom used shower in the basement of a house that opened up exactly this way with the accompanying odor. The fix, pour some water in to refill the trap. If the drain is NEVER in use (like a just in case floor drain) I don't know if the sink antifreezes (NOT car) are more resistant to evaporation which would make the problem less likely to reoccur.

Yup,I would suspect a dry trap also.Check any place you have water going to the waste line.All sinks,toilets,clothes washer,floor drains, laundrey sink,etc.

I agree with the dry trap people. No trap/Missing trap I have seen as well over the years. The other one that I saw recently is a vent tube that was not hooked up. It could be coincidence with the winter weather. I am not sure how much you use your house but in the summer we would normally have windows open and get fresh air.....

Jon

Dry trap.

It only takes about four months for an unused drain to evaporate and allow gases inside the house.

Odor in basement
 

We've seen this happen before. It can vary. We've seen dry traps and we've seen rodents cause these smells. It's worse in the winter months. The heated air rises through the house. The heated air eventually works its way out through the walls, windows, attic, etc. This causes a negative pressure in the lower levels. This negative pressure will draw odors in from the dry traps, joints in the basement slab and other opening in the lower levels.

I recommend checking all the traps. Make sure they have water in them. I would also take a close look at the foundation walls and the basement slab. Any penetrations in the walls and slab should be sealed.

Dead Rodents
 

Dead rodents can cause this smell. Sometimes the mice/rodents hide between the floor and insulation and die there. Not a pleasant smell.

I had the smelly trap problem. My washer & dryer are in the basement and the washer drain is very high- just under the floor joists. I shut off the heat in the living space above when the home is not in use. Water in the trap froze and caused a hairline crack along the threads in the trap drain plug. There was no noticable leak. I found the leak by tying a paper towel around the drain plug and over time noticed it was always damp and water stained.

Anyone aware of a trap that can withstand freezing without damage?

Loony, check your plumbing supply store. There is an industrial grade rubber boot trap with clamps on both ends that should work. Not difficult to install. Remove or cut away old section and slip in new. You may want to check to make sure it meets the code.

You might as well winterize it with RV antifreeze just like the toilet and sink traps should have done.

Thanks for info on the rubber trap.

I do winterize plumbing in the the living area. The washer drain is rather difficult to get at, otherwise I would have put antifreeze in it. The temperature at knee height in the basement never goes below freezing. The washer drain is slightly below the sill which is above ground level- probably why it froze. I should place a thermometer with min/max reading next to the trap to see how low the temperature goes. We're probably past the average low temperature for this year. Maybe next year.....

I have poured a small amount of oil (mineral oil works fine) into an infrequently used trap at home to prevent evaporation. I am not sure if this would be detrimental to a septic system and have not done this at the camp. Any opinions?

What it might be
 

Thanks everyone. The odor has lessened. We believe it may be the vent that is put in by the builder (by code) in case you want to expand and build additional bathroom(s) at later date ... can't recall what the proper name is for this. We called the builder, who called the plumber, who never called anyone back. The builder is not exactly a reliable guy anyway. We had Lakeside Heating/Plumbing come over and try to find the spot, to no avail. However, in the last few weeks the odor has definitely lessened. So, now I just try to run water in each sink/bath every now and then. The toilets are always used.... so I don't think that's the problem. Thank you everyone for all your input.