At night, an unpleasant, damp-like smell develops in the corner of our bedroom and in the hall just outside it.
We first assumed it was caused by condensation. So we've been leaving the windows open all day and at night to improve ventilation, we've cleaned the walls with mould remover (they're white and there was no visible mould on them). This helped a bit but didn't solve the problem.
We then started thinking the smell was coming from under the floor. I've just ripped the skirting board off the wall and lifted a floorboard to have a look. There's a thick layer of dust (the floorboards have quite big gaps so it's been collecting there for decades) but I can't see any sign of damp or mould. There's no smell down there now. I guess there could be mould mixed up in the dust but only the upward-facing surfaces are covered whereas I'd have thought mould would go for the vertical or downward-facing surfaces too.
The smell from the floor seems to begin late at night - maybe 11pm - whether we've been in the room or not. That makes me think there's a human source. One wall in that corner has our elderly neighbours on the other side. Perhaps there's an issue in their house and it's coming through the wall to ours? How would we tell?
As a next step I've ordered a humidity detector and surface damp detector to check whether we do have a condensation or other damp problem.
We could also do a proper mould test but I'm not convinced it's worth it?
Will report back with the humidity results but otherwise we're feeling a bit stuck. DP wants to lift all the floorboards in the bedroom and hall and have the dust cleaned out but that will involve dismantling our bed, cost £000s (we're not in good health so couldn't do it ourselves) and, as far as I can tell, the dust isn't what's causing the smell.
Any advice hugely appreciated! @PigletJohn - any ideas?