Damp behind shelves

Interior RH is too high for the level of insulation the walls have. Look at where excess RH is coming from in the house.

NT

One easy way is to make sure there's an air gap between the shelves and the wall, so letting the air circulate and help remove the condensation.

It helped no end in the caravan when I worked the trick out.

Please forgive my ignorance but, what does RH mean? :)

roof height?

Relative Humidity.

Assuming it IS condensation. Strange that the OP notices it after a lot of rain. There is a simple test, namely sticking a tile or a mirror to the wall and seeing if the face gets wet

plus maybe lack of ventilation in the house

NT

No harm in checking the gutters etc. for a possible external source of damp.

Tim

humidity condensing where it's trapped behind CD's - the humidity will be the same over the whole room, but as there's no air movement behind your shelf junk, this is where it's showing up.

Increase ventilation by moving CD's forward and decrease humidity by however way you see fit.

A sheet of aluminium foil will do, taped around the edges.

Impossible to say, but in my house it would be gutters overflowing with heavy rain causing a lot of water to splash onto the masonry.

Tim W

Even if it's not condensation, an air gap helps by allowing any slight moisture penetration to evaporate.

But where does the poster I was replying to say he thinks it's penetrating dampness? He say that he has noticed recently that there is rust on the brackets and dampness inside the CD cases on the shelves and suspects that the recent cold, damp weather has caused condensation.

So, nothing to do with an external wall being colder than the average room temperature and the stagnant, damp, air next to the wall being insulated from the general room temperature by the contents of the shelf, so causing condensation, then?

Gawd knows. Go and stand outside when it's raining heavily. Observe. It ain't rocket science

Um, I don't think that any of us "gutter overflow" adherents are saying it's the only possible cause. Just trying to point out to the RH adherents that it would be daft not to check.

Tim