Our house has a conservatory built onto it. Standing in the conservatory, looking at the kitchen door, you have the kitchen sink downpipe on the left (boxed in) and the bathroom wc & sink (boxed in) to the right. Bothe sets of pipes go underneath the consevatory floor. We don't know where, as we have only been there for a few months and the conservatory was built 3 years ago.
The problem is that the kitchen sink water drains very slowly and the washing machine backflows into the kitchen sink on some cycles. When we use the kitchen sink, we would get a foul smell coming into the house.
This is only coming from the dining room through the floorboards, as it is next to the kitchen.
I have checked under the dining room floorboards and could not see any signs of water pooling there, so the smell must be coming rom elsewhere.
We decided to lift the laminates in the conservatory inbetween the two sets of boxed pipes at the kitchen door, in the hope of inspecting what goes on underneath. Unfortunately we have only managed to lift two as when we did, we found the underlay & what I assume to be cement boards, to be wet. That area must have been like that for some time, as the underlay has mould/fungus on it. It seems that it might only be the area between the kitchen downpipe & bathroom downpipe.
We are uncertain as to what constructionmethods were used to build the conservatory, but it has brick wall, so I assume that it is on a concrete foundation.
Could it be that there is a blockage in the drain that allows the water to overspill and cause the smell, as well as the moisture in the underlay/laminates & cement boards?