Sewage smell from bathrooms

[Richie]

Hi everyone, Hoping someone can shed some light on an issue we have with a sewage smell from our new built house. 
Smell comes from the 2 bathrooms but comes and goes also inside hot press where the internal soil stack is located. Had builder up recently none of the traps are dry and the smell isn’t coming from any of the toilets, sinks or showers.  All manholes checked and no blockages, septic tank checked and seems to be working fine. Builder did a smoke test ( several )   and smoke is extracted at roof vent where the 2 soil vents extract from. Also no smoke came into the bathrooms/hotpress  when tests were done. Very baffled at this stage would appreciate any advise or something else we could try at this stage ? The builder is bringing his plumber up next to check toilets are sealed correctly but with no smoke showing in bathrooms after smoke test not sure that’s the issue. The smell comes and goes from each of the 2 bathrooms. We have an upstairs bathroom and there is zero smell upstairs. 
 

[Mr Punter]

Could be a durgo valve stuck.  It is not easy to work out where a smell is coming from.  Does the soil system hold an air test as per building regs?

[Kelvin]

We had this in a previous house with one bathroom. Turned out the pipe wasn't connected properly and it was leaking  into the void behind the wall every time the loo was flushed. At first there was a musty damp smell which grew into a more sewerage smell generally in the room so also not coming from the sink, loo, or shower. We didn't use this bathroom much so it came and went. The smell also appeared in the cupboard above this bathroom as it was rising up the void in the internal wall. This was actually how I found it as I cut a hole in the wall in the cupboard and the smell was much stronger. I happened to have a bullet camera so made up some long cables and dropped it down the wall and could see it was soaking wet. Your problem doesn't sound the same type of problem but worth ruling it out. 

Edited Monday at 22:23 by Kelvin

[Richie]

Thanks Mr Punter, if you mean was it air tested I’m not sure to be honest, ( apologies as you can tell I’m not a builder or plumber ) everything has been signed off by building control however. The soil stack has been boxed in with plasterboard maybe it should be removed to see the entire pipe ?  Thanks for the reply Kevlin, just off the phone to a chap who recently built his own house he said to definitely check the toilet seals again. It just seems strange that after doing a smoke test it didn’t show any smoke at the base of the toilets or anywhere else. 

[Richie]

Sorry Mr Punter,  just had to check what a Durgo valve was, I see it’s another name for an air admittance valve, apparently I don’t have one of these having spoke to the architect when this problem arose. He said ours is a direct pipe that is vented out at roof level, flush with the slates. 

[Kelvin]

12 minutes ago, Richie said:

Thanks Mr Punter, if you mean was it air tested I’m not sure to be honest, ( apologies as you can tell I’m not a builder or plumber ) everything has been signed off by building control however. The soil stack has been boxed in with plasterboard maybe it should be removed to see the entire pipe ?  Thanks for the reply Kevlin, just off the phone to a chap who recently built his own house he said to definitely check the toilet seals again. It just seems strange that after doing a smoke test it didn’t show any smoke at the base of the toilets or anywhere else. 

 

Some plumbers can self-certify the air test so building control accept what they send them (in Scotland anyway). In our case the BCO had to come and watch the test. 

 

You could cut a hole in the boxed in section to see if the smell is stronger. 

[saveasteading]

A smell in a cupboard suggests a leaking junction, so maybe all the pipe connections are suspect.

Where does the drainage go? Sewer or treatment tank?

[Richie]

Hi, it goes to a septic tank/treatment tank within  our site, builder checked all pipes to septic tank and the pipe that exits the tank and all are free from any blockages. 

[ProDave]

You can do an air test yourself, I did mine all myself twice for BCO to witness.  You do need to get up on the roof to put a blanking plug in the top of the vent, then you pump it up from the nearest access in an inspection chamber.

 

My guess is you will find it won't pump up at all let alone hold pressure.

 

As it's new, get the builder to come and do this, surely there is some form of warranty?  Did you buy it from as developer or get it built for you?

[saveasteading]

2 hours ago, Richie said:

builder checked all pipes 

Including the vent pipe from the tank?

[Richie]

Hi Saveasteading, yes he actually spoke to the suppliers of the septic tank when he was onsite who told him the vent pipe should be lower to the ground to help with air flow ( he originally had it about 3 foot high ) now it’s about 1ft from ground but still no difference.
There is a stronger smell today from outside the house today at inspection chambers so I opened them up again but everything is clear. It almost seems as if the smell is lying in the ground pipes and not getting away fast enough. I know these chambers will obviously always smell but seems stronger today. Also the smell has moved back into the hotpress where the internal  soil vent is boxed in and not as stronger in bathrooms. ….very strange and frustrating!! 

[saveasteading]

6 minutes ago, Richie said:

as if the smell is lying in the ground pipes

The smell will be created within the tank. That should vent out of the pipe you describe, but imagine a great burp from the depths ...it will go back up the drain as well as the vent. Is there a manhole between the tank and the house? if that has air holes then that might help.

But bottom line is that the pipes in the house should not release any smell.

 

Ahhh.   also check that all basin, bath and shower drains have water in the trap.

[Richie]

Yes, there are several man holes 3 in total from septic tank and house, all are clear. We checked all traps too and all have water in them. 

[saveasteading]

So we are back to the @ProDavescenario. 

 

The gases will go out of the vent but also towards the house so the joint seals must be checked.

I've had some very poor quality seals at times, from very cheap pipes (I've also had great ones cheap). The rubbers were hard and fitting was difficult without forcing.

So it is a likely source...it could be tight enough to keep water inside but allow gas through,, especially under pressure.

 

Is it safe to leave one of the outdoor covers off as a interim trial to vent the drain? It will also encourage a permanent draught.

 

As a positive, digester thanks settle down after a while. But that is all the more reason to get it sorted now, before the nuisance reduces for a while.

[ProDave]

I sometimes curse Scottish BC for being so pedantic about drain tests (they witnessed 3 separate drain tests here) but there is no way this sort of issue would have not been resolved if the OP's house had been tested as diligently.

 

The time to find and fix a leak, is BEFORE it's all covered in plasterboard, skim and painted.

[saveasteading]

22 minutes ago, ProDave said:

there is no way this sort of issue would have not been resolved

Test would have spotted the leak.

 

It's such an easy thing too, especially in sections as the work progresses. Not so easy with the apprentice balancing  3m above the roof.

[Richie]

Yes, I did remove one of the inspection chambers nearer the house to allow the gas to release and the smell definitely wasn’t as bad but when I put it bad on the smell returned to the usual stench. It’s also seems to move from one bathroom to the other randomly, then occasionally the hot press where the soil stack is located. Is there any possibility the issue could be in the ground below floor screed ? 

[dpmiller]

post a photo of the top of the soil stack at the roof

[Richie]

Hi Dpmiller, see attached pic of top soil stack, the vents are flush with roof tiles if you can zoom in. The builder says he always fits them this way and has no issue. However he has mentioned he might change them to 2  pipes extended so they are beyond the roof in case the wind is pushing the gas back down. 

[saveasteading]

A small extension would allow wind to whip over the surface and suck out air, purging the pipes.

What about a chimney spinner or "granny" ?  Modern ones spin on ball-bearing silently.

 

But I'd think of a way to vent before the house, at that cover. Bigger holes or a pipe.

 

But. Air test first. Remember the builder is keen for it to pass. There are ways to fiddle it.

[Kelvin]

Which treatment plant do you have? How long is the run to it from the house? 
 

With ours we had a fit a vent after the pipework exits the treatment plant. Our SVP is at the opposite end of the pipework exiting the garage roof. All we have in the house is an AAV in the roof void. I called the supplier to ask about the secondary vent after the treatment plant and they recommend to do it as best practice. 
 

It does sound like a leak somewhere though which an air test will find. However if it’s leaking enough for it to smell like this I doubt you’ll be able to pressurise it at all. 

[ToughButterCup]

Pressure test, pressure test, pressure test.

[ProDave]

Those roof vents connect with a flexible connection so that is a potential place for a leak.  Is there any loft space at all and if so any access?  If so does the loft smell?

[Richie]

From the septic tank to house is approx 15/ 20 metres Kelvin but not sure the exact type. 
The builder and plumber have just left there and changed the seals on both toilets. ( he did say one wasn’t that tight a fit that was replaced ) 

Still doesn’t explain the smell in the hot press when the SVP is. Yes Saveasteading extending those 2 pipes beyond roof is next on list of the toilet seals don’t help. 
Prodave ….we have an upstairs with a small bathroom  that the  hotpress  SVP extends to  but there is zero smell upstairs or when i open the inspection hatch to the eaves of the house beside the bathroom  i can see that same SVP but again zero smell.