Cold disused chimney breast / condensation

sgoode

I have an external chimney breast running the whole height of my detatched 1930s house. Both upstairs and downstairs fireplaces have been blocked up and the chimney stack has been removed down to below roof level. From within the roof there is none of the stack visible at all, just a gaping hole going down the side of the house. The wall and ceiling in the upstairs bedroom is damp where the chimney breast is, and also behind the bed (the bed is in the centre of the wall). It is not exceptionally damp, but the paper is lifting off. To me the chimney is causing a massive cold area on the wall (the rest of the walls are cavity wall insulated) and therefore causing condensation. The wall is north facing so it is cold.

There was a vent in the upstairs bedroom where the fireplace would have been but I sealed this up when the stack was removed as otherwise the warm air from the bedroom would be vented into the cold roof space. Was I right in doing this?

I thought about installing air bricks on the outside of the chimney breast but then it will still be cold, if not more so. Should I put something inside the chimney to warm it up? I worry about if I put something unsuitable in there it will be near impossible to remove. Would putting wood over the top of the open chimney and covering it with loft insulation help? Or would this block cold/damp air in the chimney?

We do get quite a lot of condensation in the bay windows in the upstairs bedrooms despite opening windows as much as possible for ventilation. The windows are old though and the bays themselves are not insulated at all (I do plan to address this). There can also be condensation at times in the loft despite plenty of insulation and soffit vents.

On the back of the house there is another chimney breast that is only on the top half of the house. The stack has also been completely removed to below roof level many years ago and there are no such damp problems. There are no vents. It looks like there is some wood placed over the top of it in the roof.

I realise there have been previous posts regarding blocked off chimneys but I haven't been able to find anything specific to my problem.

The wall was similarly damp when the chimney stack was still in place. We assumed it was the stack leaking so we had it removed. however the wall is still damp in the same place.

Sorry for the long post.

Thanks.