New Home sewer odor master bath.

[Paradiceau]

First of all, thank you to the forum for all the great information.
I have read many posts on various threads dealing with sewer odors in bathrooms etc..
I built a house in the mountains which is on septic and the owner notified me of the following after two months of use:
Very strong sewer odor in master bath.
The bathroom has twin lavatories, toilet and shower.
All fixtures are installed with traps and vented per the UPC.
All traps are filled with water.

When he closes the lavatory drains with a popup plug and tapes off the shower drain the odor stops, (I find this interesting because the lavatory overflow is still drains into the P trap.) Because of the overflow there is still a path for gas from the inlet side of the trap to the interior of the bathroom.

He has opened the two way clean out immediately outside the bathroom in an attempt to relieve any "back pressure" from the tank. This had no effect on the odor.

The DWV system was tested per code during the rough plumbing stage. I don't think any drain or waste piping was damaged during construction, the smell being stopped by closing and sealing drains would support that I think.

I am wondering if a change in atmospheric pressure could provide enough resistance to the venting to create this situation? But the traps are working as they should apparently......

I did extend the fixture vents another sixteen inches above the roof, 6:12 pitch.... Maybe this will help.

There are no windows in the bathroom.

I discussed this with the plumber who did the house and he is puzzled as is my partner who has decades of home building experience...

Thanks for reading this and I really appreciate any constructive advice!

 

[WorthFlorida]

No windows? Do you have a high flow bathroom exhaust fan causing negative pressure? Raising the roof vent is a good idea, I would temporarily raise it past the peak if possible. Is there only one roof vent? Is it on the down side of the prevailing wind? Does your plumber or builder have a smoke tester? They can be rented.

Tape off all drains except one and wait, then another. Right now you taped off all of them. I'll guess it is the shower drain.

 

[Sponsor]

 

[Paradiceau]

The fan is on a timer and will shut off after a few minutes if left on per Ca energy requirements..
There are two vents through the roof for that bathroom, a 2' and a 1 1/2'. They were raised about 18".
The lot is on a cut hill and there is a hill on the west side which is about the elevation of the vents, the wind is generally from the west. Today when we arrived at 7:30 am there was no wind and there was no odor.
After raising the vents and leaving the sinks and shower drain open the owner was going to leave the house for a few hours and let me know if the smell had returned when they got home..... I have not heard from him yet.
I am considering a peppermint oil test next if necessary..
Thanks for taking the time to respond, much appreciated.

 

[WorthFlorida]

Two roof vents will cause odor problems especially if it's on the down side of the prevailing wind and each are at a different height. Just look at it as an aircraft wing. The lower vent will have lower pressure than the upper one. The lower vent will pull air out and the upper one will feed air in. This can cause the traps to slosh around a bit. Also a constant wind will change the indoor air pressure to be lower as air get sucked out on the down wind side.

Extending the roof vents I'm confident it will take care of the issue.

 

[Reach4]

If other things don't pan out, I would consider running a camera to see if there is a belly in the path to the septic. I am not a plumber. My theory supposes that pressure develops as water gets put into one drain, and gas bubbles up on the other. I am not sure this is the case. I will have trouble coming up with a model. So again, if nothing else works...

If you do the peppermint test, the person pouring the peppermint oil and hot water down a roof vent stays outside during the whole test.

 

[Paradiceau]

Worth, the problem is present even with no wind. This is an interesting problem for sure, I am still wondering how the odor is present if the shower and lavatory traps are full of water.
I have seen an automotive situation where a fuel line was sucking air in but there was no fuel leaking out.... Repaired the fuel line and the problem was solved. Still considering a peppermint oil test.

Reach4, I don't think pressure from the tank can happen as the inlet side has a clear airway to the atmosphere via the fixture venting system.
Thanks for your input

 

[Paradiceau]

I just got photos of the trap arm for the lavatory which was emitting the smell. The photos show a grey green deposit on the bottom of the pipe. It appears that the trap arm may not have adequate fall allowing material to settle and bacteria to grow...
I have asked the plumber to replace the trap arm and increase the fall on the pipe.... We shall see what that does.
Thanks for your responses....

 

[Reach4]

Good deal. Consider shrinking one of the photos and posting it, for those following. Max limits 900 pixels and 200kB AFAIK.

The plumber can increase the water seal, perhaps with a reversible trap. He may have to cut a slot in the base to clear a deeper trap.