Hi, I have a bad smell problem in my house that I can't seem to resolve, I have had a non-return vaule put in but its still there. The soil pipe is concealed or hiden from view by a tiled roof which was put in on top of a kitchen extention. I have an au-suite with a toilet and a bathroom with a toilet, both soil pipes run into the main one. I get bad smells in my au-suite if someone uses the bathroom toilet and sometimes when no one does, also there is a bad smell up in the loft room if i go into the eves, the plumber just told me that he thinks it is the seal or joint between the old soil pipe and the new is leaking and he could feel a draft from behind the toilet where he thinks it is coming in from but that he can't do this because the tiles need taking off for him to look.
I want to handle this situation in the most reliable and practical way to eliminate this problem rather than get one person after another coming to look but not able to resolve my problem. Is there an expert in this field a bit like a structual surveyor but for pluming who can check out exactly what is going on in this case so that I know when I get the plumber to fix the problem that will be the end of it?

Only way is to visually inspect the end of the pipes and any connections.

If the roof was put over the pipe, does it have an AAAV on the top or is it just an open end.

Whatever, I think you're going to have to wreck at least part of the boxing in, if you have no other access.

Not if you can't cap the vents CW.