The cottage is in a coastal town, has a flat roof, solid walls and was originally converted from a much older building in the late 60s. The internal wall on the rear elevation is about a foot below the level of the road. There is a worn gulley across the base of this rear elevation but the road is cracked and has clear holes in it. We bought the property last year. Originally the smell seemed to be confined to the kitchen but now it permeates throughout. We have just two electric panel heaters which we keep on at the lowest setting possible 24 hours a day. We also leave all the vents above the windows open. It’s not our permanent home at the moment and so we’re probably there one week in four. There are no signs of mould. The survey originally alerted us to a high reading in one corner of the bedroom (against the rear elevation) – we’ve since lifted the carpet, had the surveyor re-examine the floor and still there are no obvious sources of the smell. On our last visit just on one day we had water visible all along the base of this wall, about 18inches high, which seemed to dry out on the surface after a day suggesting it had been excessive condensation. We are extremely concerned that there could be a problem that we’re not diagnosing correctly and have very little money to spend on speculative investigation. Any suggestions on a taking a structured approach to diagnosis would be very much appreciated please.