Venting an orphan chimney breast

5 Feb 2022
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United Kingdom
Hi all. I live in a house with 3 floors. The previous owners of our house removed a chimney breast in the loft (floor 3), and they also removed the chimney stack from the roof.

However, on the lower floors (1 and 2) they left the rest of the chimney breast standing. This means we have a chimney flue which can't vent to the outside at the top --- instead, it terminates at the ceiling of floor 2, and this causes damp as warm air condenses there.

Apart from removing the chimney breast at lower floors, what could I do to avoid damp? I thought that a vent in the breast near the ceiling of floor 2 might fix this, but what do you reckon? Would this be a sticking plaster or would it probably work?

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Your lower floors(1&2) fireplaces have separate flues that might need sweeping, and venting at the bottom if the fireplaces are blocked off?
But if what appears to be damp is showing on the wall then it could be chemicals from the old flue?
IOW's the soot from the old flues was not properly cleaned off the wall before plastering over.
However, why not post pics showing the damp marks?

Is the c/breast on an outside wall or a party wall?
Thanks for the reply. Some answers to your questions:
  • That's right - the lower floors' fireplaces are blocked off, so do also need venting at floor level.
  • Sorry, recently stripped the wallpaper in the affected room ready for decorating (once I've solved this chimney issue) so there's not much to see in a photo. I have had a damp survey done though, and they confirmed it was wet, particularly around the ceiling of floor 2 next to the chimney breast. Problem gets worse in Summer when the warm air holds more moisture. I think it's rising in the chimney, cooling and condensing.
  • The breast forms an internal wall between two rooms.
Will make sure to get the flues properly cleaned and vented at lower levels. Will that be enough though? I'm concerned that the air drawn in at lower points will have nowhere to go once it hits the top of floor 2.
Still, please post pics of the stripped off wall plaster area, & floor.
And pics of the new claim of damp marks showing on floor 2 ceiling.

Carefully examine all remaining c/breast(s) & adjacent walls for damp signs or dark smudges.
Given this is an internal c/breast then trace the other side from ground floor to where it enters or had entered the loft - look for damp signs.
Would it be easy for you to lift any floor boards above the ceiling in floor 2?

The possibility is that you will have to hack off affected plaster back to brick, & render with a sand & lime render 3:1 mix - dont use gypsum plaster.
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Seal the redundant flues off top and bottom...Its an internal wall it doesn't need venting.

Ignore the foolish and ignorant suggestion that you seal off the redundant flues on the basis that flues - that already appear to be a cause for complaint - dont need venting.
Your flues are already sealed off at the bottom blocked fireplaces - and we dont know if they are open or sealed at the top.

The ignorant advice above seems to think that being on an internal wall will somehow prevent Hygroscopic chemical reactions taking place in sooty flues.
The counter logic being that only c/breasts located on an outside wall will cause Hygroscopic chemical reactions in flues?

Look at more of the nonsense:
1. there's no advice ref what to do about existing & potential damage.
2. nothing about sweeping the flues.
3. no advice about the adjacent wall and ceiling.
4. not even a confused explanation about what is the cause of the damage you report.
Troll80, can you explain to the op how all this moisture laden air is is entering the redundant flue? You should know as you said you have been to builders school.
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Op seal the redundant flue off in the attic if the room vents have been sealed no moisture can enter the flue cavity.
I'm sure you would have benefited from even a short time as an apprentice at "Building School"?
Unfortunately you dont seem to have been either an apprentice or learned anything - I'm sorry for you,
a little learning would have done you some good.
Ree the flue is open in the attic and you are telling the op to vent from the rooms below.
Explain your reasoning .
Popcorn at the ready oh man of many names.
"all this moisture laden air" - please quote where i said that.
You even big up your made up quote with the superlative "all" - I am so sorry that you lack a little learning.
"the flue is open in the attic" - where did the OP say that? He didn't.

The OP said the flue "terminates at the ceiling of floor 2" - your foolishness does show through can't you even read what the OP says or lacking the simple ability to read do you just make it up?
Anyhow, I'll let the OP decide what he wants?
Regardless where the redundant flue terminates installing vents to the rooms below would only make matters worse.
The remedial works you suggest the op undertakes is just pathetic.

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