Sewage gas - advice on steps to take

[Borgia]

Hi all

I am a first time poster, and would be very grateful please for advice.

We purchased and moved into a property two weeks ago. I am experiencing a worsening sewage smell which was originally isolated to an ensuite in the main bedroom and the extension, but now appears to be moving. This is what I know:

• The ensuite on the first floor smelt a bit when we moved in but this has now become much worse to the extent that we cannot use the bedroom. The pipework appears to be segregated and has an intermittent valve which we have changed. When it was changed, one could see sewer gas coming out of the pipe. The valve might be a bit lower than the sink trap. When we put drain chemicals into the ensuite bathroom toilet, we could detect the same chemical smell under the floor on the ground floor near the stairs, so it appears that some issue with the ensuite is creating the smell of sewage in the house. The main drain pipe used by the other two bathrooms is vented at the roof.
• The back and side extension are collectively built over four manholes (three manholes along side extension and one to the back). The extension was built over twenty year ago with planning permission and building regs sign off. The smell was probably noticeable at the ground floor when we moved in but has got much worse since. It seems to be coming from under the floor where there are gaps in the subfloor damp proof underlay (e.g. gap between wall and floor). As mentioned, it has smelt of chemicals here when we used drain cleaner in the ensuite.
• There are two lateral flow pipes going into the back extension manhole that an probably not used and need to be cleaned and capped.

I have done a smoke test and a drain flush testing for both the upstairs ensuite and other bathrooms, no indications of blockages.

Grateful to get your advice on our thinking about what might be causing this.

• A leak in the ensuite waste pipe. We are concerned about this given that the problem has worsened significantly since it was used (and we have since stopped using!). However the smell is of sewage rather than used toilet. Also, we could smell chemicals downstairs. Fumes might be coming from the ground up through the sink as the trap water is drained (trap is about 20cm higher than the valve).
• The dirty unused lateral drain feeding in to one of the manholes is possibly with a dried out gully. We will get the drain cleaned and capped, but do not think that it is the only problem given that the smells has got a lot worse and started moving in rooms;
• A partial block of the main drains somewhere in the network. This seems possible but it would a big coincidence that the smell started when we began using the ensuite.

I am therefore thinking to get a CCTV survey of the ensuite waste pipe, and also clean and cap the lateral drain.

I would be very grateful for your thoughts and advice, please. This all new to me so I am concerned that I am missing something.

Thank you in advance

 

[exedon2]

A accurate sketch of drain layout plus clear pictures of what you have would be useful before commenting.