Four sewage smell coming from shower trap

[Kaps86]

Hi all

I really need some help or advise…..

Back story…..



Some years ago my dad had an extension to his house which included a newly built downstairs shower room. Recently he had this downstairs shower room re-fitted/decorated. Quite a simple set up consisting of a sink, toilet and shower. However after my plumber/fitter completed the job we started to notice a real foul sewage smell coming from the shower trap. I’ve noticed in addition to the smell there was a fairly decent pressure of smelly air/gas coming out of the trap. After multiple attempts and messing with the trap and basket (that holds the water) I think I have stopped the smell/gas from coming into the room. Obviously if I take the sliver lid of the trap off for cleaning etc I notice the smell/gas again as it’s still coming into the trap pipes.



So my questions are as follows…..

1. Is this pressure of smelly air normal to come up through the waste pipe? I assume it’s coming from the soil pipe that the toilet is also connected to. But guessing there shouldn’t be any foul smelling pressure coming back up in the wage pipes?
2. Am I correct in thinking that the small amount of water in the trap/basket should stop smelly gas coming into the room? I’ve checked and with all the trap components fitted, the only way for the gas to come through is through the water, but I’m assuming the water will completely block out the gas?
3. The water in the waste trap basket is only around 38mm deep. I read somewhere that a shower trap water should be around 70mm deep as shallow water won’t block the gas……is this true? Or is the water depth irrelevant as long as the only way in or out of the trap is via the water?
4. My assumption is that there should not be a back pressure of smelly foul gas coming back through the waste pipe, as I’ve read all soil pipes (which the shower waste pipe flows into) must be connected to a vent pipe to rid of gasses? Is this correct?
5. My biggest worry is that I or my plumber don’t know how the builders who created the shower room extension originally layed out the soil pipes and where they eventually lead to? A vent or straight to the sewage drain/pipe outside? The new shower room extension is at the front of the house, but the original vent pipe which sits outside and connects the kitchen and upstairs bathroom is at the back of the house. Therefore the soil pipe which my builder connected to the toilet waste and shower waste pipes we don’t know if it is connected to a vent pipe or simply just connected directly to the waste drain/pipe outside? Is this even allows as I assumed all soil pipes should be connected to a vent pipe? Is there any way of telling?

Extra information



I’ve flushed the toilet in the shower room, run the taps and also run the taps in kitchen and flushed toilet upstairs and none of these seem to pull water from the shower trap. There is still the correct level of water sitting in the shower trap. Neither is there any gurgling or feeling of suction from the shower.



Would honestly appreciate any advise to my questions as it would give me a better idea of what I’m dealing with



Thanks

 

[Activate Trade Training]

The presence of foul-smelling air and pressure from your shower trap isn't normal and indicates a problem. The water in the trap is designed to create a seal that prevents sewer gases from entering the room; however, a depth of 38mm might be insufficient for this purpose. The standard requirement for effective gas blocking is closer to about 50-70mm, depending on local regulations and trap design. This is because a deeper water seal is more effective at preventing gas escape.

Yes you're right - the water in the trap should stop gas from coming through, but if the smell persists, this indicates either the water seal is not deep enough or there's a venting issue. Proper venting is crucial for allowing gases to escape through a vent pipe rather than back through your fixtures. Every soil pipe should indeed connect to a vent system to prevent the build-up of pressure and ensure gases escape safely to the atmosphere.

Your concern about the soil pipe's connection to a vent pipe or direct connection to the waste drain is valid. It's not just about being connected to a vent; the venting system must be correctly designed and installed to balance air pressure within your drainage system. Improper venting can lead to the issues you're experiencing.

The fact that using other fixtures doesn't affect the water level in the shower trap is a good sign, indicating no significant suction or back-pressure issues at a basic level. However, the problem seems to be with the venting or trap design.

For a definitive answer, probably best to get a detailed inspection by a qualified plumber. They can assess the trap depth, ensure it meets the required standards for effective gas blocking, and check the venting system's design and connection. Adjustments or corrections in the venting system or trap may be required to solve the problem permanently.

Good luck!

 

[Rtplumb]

Could you post a picture of the shower trap with the 'hair catcher' (the shallow bit with the the holes around the top) removed so we can see the bottom of the trap. thanks.