Chimney breast damp - any ideas please?

[Frogfleet]

This has been a problem for a while, but I have avoided thinking about it because the room is mostly unused. This is a photo of the damp on the chimney breast in the attic. Apologies that the photo isn't as clear as I wanted because of the lighting. It doesn't feel wet, though it does feel very cold. The damp is not in the bedroom or living room below. This room isn't used regularly, so I don't think there is much humidity, but there is an occasionally used en suite shower on the other side of the wall.

I have also attached a photo of the outside chimney - it seems to have caps on the tops.

I think it seems insurmountable so I've put it off, but I'd love to be able to sort it. Any advice much appreciated!

I don't think you can assume that there is low humidity just because the room isn't used. Presumably that means it isn't heated at all, and if there is water getting in from somewhere, then there will be condensation.

I would get the roof checked as well as the chimney. In the picture, on the left where the roof slopes just below the TV aerials it looks like there might be a potential leak issue.

Also rain could have penetrated the wall if the pointing / brickwork is faulty. Does that wall get the full brunt of the weather? It has been so wet this year that it may not have had time to dry out.

Once you have checked for any ways water can get in, you need to get a dehumidifier in there and leave it running, as well as making sure the room isn't significantly colder than the rest of the house, and remove the mould. If you dry the room effectively having fixed any issues, it shouldn't come back.

As others have said on other threads, I would avoid getting a damp proofing company in. Get a general builder and / or roofer if you can.

Thank you for your help. I know the part of the roof you mean and need to look to fix that. Annoyingly, the damp problem has persisted since before that damage occurred though, so I don't think it will be solely that.

The damp is there all year around - it never goes away, but it does seem more intense in the winter. It's been exactly the same pattern for several years and I'm ashamed to say that I've ignored it as we don't really use the room. The heating does come on in there when the rest of the house is heated, though. There is no mould - I know it looks like it in the picture, but it's just darker (I think my phone may have enhanced the image somehow). It's just darker patches which aren't wet to touch, if that makes sense.

In that case it's likely to be something to do with the chimney. It looks from the picture as though it is directly above the window and not used for a working fireplace. Unused chimneys are often a source of trouble. If rain isn't penetrating the brickwork, it could be condensation inside the actual wall, depending on how it is constructed.

Even if it isn't mould / condensation I think it is still important to ventilate as much as possible so that mould doesn't develop in future. Does the window open? I would leave it open as much as possible (whenever heating not on).

...also this link was posted on another thread, which may be of help:

https://www.heritage-house.org/damp-and-condensation/managing-damp-in-old-buildings.html