Western PA Luann (I am in w pa too!) If the wax seal is bad 1) how would I know? 2) why would it sometimes have a smell but usually not? 3) what would you do as a first step to find out if it is the problem? The reason I guessed it might be animals is 1) it does not smell like sewer to me 2) it will go away whether I do anything or not 3) it seems to come from the wall that is against the garage and might be open to the garage above the ceiling. The toilet is cleaned and flushed once a week. Inbetween it is not (ie never) used. There is an unused shower that everyone blamed but I pour water down it and it makes no difference. The sink is used off and on.

If your local plumbing code is based upon the IRC(Inernational Residential Code) it could be a problem with your DWV layout. The IRC requires that all structures must have one "Main Vent" that must run undiminished in size from the house "Main Drain" through the roof. Once that is achieved when auxiliary vents are required, the may terminate through the roof, in the attic space or in some instances, through a side wall. The IRC also permits an unlimited use of AAV's (air admittance valves, commonly called cheater vents or studor vents). While it may be code approved, terminating a vent in the attic space is never a good idea for two reasons: 1. the excess moisture discharged from the vent may collect in your insulation which would then greatly reduce the value of the insulation, not to mention that it creates a high risk of mold. 2. Many of the components in sewer gas are heavier than air, so if it is terminated in the attic space, the heavier than air gases will go downward and can permeate through your ceiling material causing the odor. Very few homeowners, and sadly, even many professional insulation installers are not aware that there may be plumbing vents in the attic, and when installing insulation often those vents get covered, which then increases the chances of the sewer gases settling into the living space.

The post does not say where you live so I cannot tell which plumbing code you are under, however this house is new to you and if you are under the IRC (International Residential code) or the IPC (International Plumbing Code) there is a very strong likelyhood that you may have an "AAV" (air admittance valve), AKA "Studor Vent" or "Cheater Vent" instead of a true vent pipe in your bathroom. One quick way to get an good idea if you have an AAV is open the cabinet under the sink when you smell the odor. If you have a defective AAV the odor should be much stronger under the sink. AAV's have a spring loaded plunger that will allow air to enter the drain line to prevent a negative pressure that would suck the water out of your traps, but, when working properly they are closed to prevent sewer gasses from escaping from the pipe. Given that it is a mechanical device, it also stands that it is subject to malfunctioning. AAV's must be installed at a location where they can be periodically inspected and allow access for repair. Typically for a bathroom they are installed on the lavatory bowl waste arm in the cabinet under the sink. Look at the sink drain line. If you have an AAV you will see a Tee fitting on the horizontal line coming out of the wall and before it connects to the P-trap from the sink bowl. You will then see a vertical line attached to that tee which rises a minimum of 6" above the horizontal line and generally it will rise up behind the sink bowl. You will then see a Cap on the top of the line, but if you look close you will see either some slots or a square opening on that cap fitting. That cap fitting is the AAV. AAV's are mounted by means of ordinary pipe threads. On the top of the vertical riser there is a female thread adapter and the AAV is simply screwed in. To replace it you simply unscrew the existing AAV, than apply teflon tape to the threads of a new AAV and screw it back in place. You can get the AAV's at any hardware store or home supply center. Personally I prefer to go to a True Value or ACE hardware and you will be more likely to find a clerk that really knows what their talking about to help you.

Can I get in on this conversation with a question? I have something similar in my 22 year old house. It is three stories. We do not have city sewer. We sometimes have a sewer gas odor that comes up the vents in two bathrooms only. They are exactly on top of each other. We have had a plumber out to the house three separate times. At first he said make sure to keep traps wet. We did that, smell sometimes comes back. He came out again, same thing and checked everything. Last time he said that all fixtures go into one large vent pipe on roof. Husband got up there and sure enough only one for 4.5 baths, washer, etc. The smell is only in these two bath areas. There is one bath below these two exactly as well. He said tub downstairs is not used much and trap could be dry. He extended the vent pipe up several feet in the air. He said sometimes when weather system moves in, it can hold gases down. We have absolutely no idea what this could be. It only happens every couple of weeks, but when it does, it smells so bad. We have also smelled this outside once or twice and it was so bad, I was so embarrassed. We were gone one week and our friends walked by the house to make sure everything was okay. They said they thought something BIG had died there and they actually walked around the back of the house but could not find anything. Please any thoughts. Desperate in NC