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