Sewer smell in home from adding to soil pipe

[cool_dude_2000]

Since working on the soil pipe to plumb in new toilet, shower and basin waste in the loft, I am experiencing problems with sewer smell coming into the house below.

The soil pipe runs vertically up through the house and is boxed in on ground and first floor to protrude through the roof where it is externally vented.

I have converted a storage room in our converted loft into an ensuite wetroom with a shower, wash basin and wall hung toilet. To accommodate their waste outlets, I have cut into the soil pipe at loft level and inserted a push fit slip coupling and branch connector which the toilet and basin connect into. The shower waste pipe connects to the soil pipe via solvent strapped boss connection. There are no water leaks when I flush the toilet and run the taps.

However, in the corresponding room below, there are sewer smells emitted from the boxed off soil pipe which runs into the loft. Adjacent to this room is the bathroom. An examination of the soil pipe here confirms there are no leaks from the bathroom connection.

The loft room basin and toilet both have traps filled with water. The waste outlet for the shower is blocked up with a rag.

I am struggling to understand why the sewer smell continues to emanate? Particularly as there is no smell in the loft wet room, but in the room below? Do I need to add in an air admittance valve to the new waste outlets in the loft?

I have added a diagram below.

I welcome any thoughts?

 

[Chuck]

You haven't mentioned pressure testing the modified stack.

 

[cool_dude_2000]

As an avid DIYer, dont have the tools to run pressure test.

I'm going to add an air admittance valve to the 40mm basin waste pipe and see if that makes a difference.

 

[king of pipes]

Your traps on the lower floors could be loosing their water seal when the bathroom in the loft is used so in theory sucking the water out of the trap or traps allowing sewage smells to enter the property you could change them to a 75mm deep seal trap or a hepvo trap but without seeing it it hard to say cheers kop

 

[cool_dude_2000]

Thanks king of pipes. The pipes and traps on the first floor are concealed and so would be difficult to add the hepvo.

I'll add the air admittance valve to the loft basin waste and hope this eliminates the vacuum.

I'm hoping one 40mm AAV should be sufficient. To be honest I wouldn't have thought it necessary as the soil pipe externally vents through the roof.

 

[ShaunCorbs]

It's vented and it's straight though so won't need an aav

You should be able to see the water in the traps on the 1st floor

Flush the toilet in the loft does the 1st floor traps stay full of water

 

[Chuck]

As an avid DIYer, dont have the tools to run pressure test.

You can hire them. Or employ a plumber to do the test for you. You do not want sewer gas getting into your house.

I'm going to add an air admittance valve to the 40mm basin waste pipe and see if that makes a difference.

Unlikely IMO unless the 'external vent' is blocked or your diagram is misleading.

As an alternative to the other possibilities already suggested: My guess is a leaking joint somewhere in the bottom half of the stack possibly aggravated by a partial blockage, most likely downstream of the existing loo. My idea is that flushing the top loo pressurises the gas below it in the stack and forces it out through a leaking joint.

 

[cool_dude_2000]

The other thing to point out is that if the traps are being siphoned in the 1st floor bathroom, i would expect a strong smell in the bathroom itself. However, there is virtually little smell here - the strongest smell is actually in the adjacent room where the soil pipe is boxed in.

 

[king of pipes]

Only other thing to do is cut access panels in the boxing to find the source of the problem cheers kop

 

[justlead1]

Soil and waste system are far more complex regarding physic's than thought.
This may help.:- single stack system - Google Search

 

[cool_dude_2000]

Really struggling with this now...

The external soil stack vent doesn't appear to be blocked.

I have disconnected the waste pipe from the wash basin in the loft in case that is causing a vacuum. There are now open waste pipes for the shower and wash basin up in the loft and connected to soil pipe.

I have checked the gully trap in the shower on 1st floor. There is a bit of water trapped inside which falls below the outlet hole. Flushing loft toilet has no effect.

 

[Chuck]

There are now open waste pipes for the shower and wash basin up in the loft and connected to soil pipe.

This is not a good idea. Sewer gas is potentially toxic/asphixiant and explosive and you are allowing it into your house.

I recommend that you reinstate the traps, and stop using the new attic bathroom until the problem is sorted out properly. Make sure the rooms that have experienced a smell are well-ventillated and call a plumber who knows how to pressure test your system and perform a smoke test if, as I suspect it will, it leaks.

Further information about sewer gas:

Sewer gas - Wikipedia

 

[cool_dude_2000]

Thanks, will do. Funny thing is that there is no smell coming from the disconnected outlet pipes in the loft.

 

[justlead1]

There is no mention of ground floor. (Soil connection to drain)
Then boxing formed around pipes can act as a duct. The area that smells may not be the area of problem regarding pipes.

 

[cool_dude_2000]

Yes possibly. I have a plumber coming round this morning to check and will hopefully locate the issue. I do suspect a vacuum is the issue as the sink in the loft gurgles as the waste goes down, and the water in the 1st floor bathroom sink is very slow to go down the plughole.

 

[Chuck]

Yes possibly. I have a plumber coming round this morning to check and will hopefully locate the issue. I do suspect a vacuum is the issue as the sink in the loft gurgles as the waste goes down, and the water in the 1st floor bathroom sink is very slow to go down the plughole.

It's possible the gurgling, is a separate issue. Your conversion may have revealed a long-standing issue with the drain at ground level by sealing the top of the boxing. This could have previously been venting the smell into a (draughty?) roofspace where it wasn't noticed.

I'll be interested to learn how your plumber tackles the problem. Do report back and good luck.

 

[cool_dude_2000]

Ok, plumber has taken a look and suspects a drain blockage as his jet wash pipe cant proceed beyond a certain point from the mancover access. Flushing a tissue down brings slow release of water out but no tissue. Has to be rebooked with a camera to investigate further.

Comforting to know its not a venting issue - but has opened up another can of worms!