Hopefully you can see the patches in the photo.
We pulled out the sofa and found the whole wall has these damp looking patches near the skirting board and in small dots higher up the wall. This is the external wall, the house is 5 years old. Is it just where it is cold and lacking in ventilation? Or something external? We don't use loads of heating, as the house stays warm with minimal heating on. Perhaps we just need to heat for longer? Any ideas gratefully received.