Enought Air Movement in Ancillary Chimney?

[dishman]

I am removing a brick form a disused ancillary (mini) chimney stack to allow it to have some airflow and breathe.

Accessing the small capped of stack at roof level is out of the question (for me), although the loft window is temptingly close.

Would removing one brick at the lowest point possible and one in the loft (just below roof line) create enough air movement within the stack? Or will it rely on the top one being outside to give enough of a pressure differential for air movement.

Last time I got a roofer out he said it was a difficult stack to get to (aka, he did not want to do it) as it was not in-line with the roof line, it is in line with the sloping hip part. Was he just fobbing me off? Would a good roofer be able to access it with the correct ladders.

 

[Jadele]

if the lower point is warmer than the upper point there will be movement of air. Also damp air will be allowed out in to dryer air despite the air flow so it will always help and I think will solve any issues you may or may not have.

 

[dishman]

Taa,

Removed another brick at the top this evening. So it will hopefully have a nice flow of air through it.

The chimney was fully sealed up. It was remove at ground floor level and capped at the roof.

It seems to have just been sweating inside and been the cause of a long standing damp patch in one room.

So hopefully, this will help.

 

[vinn]

A chimney stack is the bit that sticks up above the roof. Everything below the roof is the chimney breast. The chimney flue (or flues) is inside the chimney breast.

Do you know how or if the upper chimney breast was supported when the ground floor c/breast was removed?
Is there a blocked up fireplace opening in the bedroom c/breast?
How many flues are there in the c/breast?
Flue ventilation requires a bottom & a top vent, and the flue to be swept all the way up to the stack terminal.

Where exactly is the "damp patch"?

Why not post pics of the stack on the roof - from the ground and from the "loft window"?
And pics of the damp patch area?

FWIW: a proper roofer would have no problem accessing any domestic roof. If you have any doubts and are a stranger to roofs then stay off it & hire a professional roofer: ask for pics of what he sees up there.

 

[dishman]

This was originally a small secondary chimney for the original 1930s aga. It is about 40cm square (external measurement). It was removed at kitchen level some 40+ years ago but the breast was left intact at first floor and the loft. The stack is still present (it seems to have been reduced in size) but was also capped off.



So it has been like this, capped off and sealed, for 40 years.The damp patch has been present for that length of time too probably. A lot of houses on the street has a similar thing done, some also have a similar damp patch.

It runs internally in the house i.e does not run along an outside wall. The damp patch appears in the bedroom that it shares a wall with (chimney on one side, bedroom on the other). The damp patch itself appears at the top of the wall and onto the ceiling. So exactly at the point the chimney goes from a warm first floor level to colder loft space.

The damp does seem to get worse on either cold and or wet days but there is no sign of a leak. Inside the flue looks dry to look at. The exposed brick in the loft is dry, there does not seem to be any dripping or obvious leak.

Flashing looks OK. The cap is not the best but it is hard to say if is letting water in or not.

Although the damp gets a bit worse in bad weather, with no obvious signs of a leak, it may be just the chimney sweating. We shall see if it improves. I am tempted to make a little platform and put some desiccant crystals de-humidifier pots to see if it will speed the drying process.

 

[vinn]

OP,
With respect, you are prescribing for yourself which rather defeats the object of coming on here and asking for advice.

Your "crystals" idea is useless in the scheme of things.

Why not, as above, post some pics?

 

[dishman]

I'm not prescribing any solution myself. A lot of the responses in other posts I have made on here have suggested creating some airflow within the chimney to stop it sweating. This is what I have done.

See pictures above of stack.

My question was, will removing a brick at loft level, be as effective as creating a vent at stack (i.e outside) level. As per the second post, the answer was that it should, if the loft is well ventilated, which it is in that area.

The majority of the responses I have got on the forum and by plasterers, chimney sweeps and builders is that it is probably sweating due to the salts that are lining the inside of the flue.

I have done my best to exclude a leak as being the cause of the issue. I cannot detect one. If there was one, it contains itself to this small damp patch and does not present itself anywhere else. The stack is dry above the damp patch both externally and internally. There is quite a bit of efflorescence around the stack at loft level. But the stack is dry to touch as are the roof rafters etc.

So, as per the advice on here, I am left to try adding vents to let the chimney breathe.

So we shall see if it gets any better. Only time will tell.

I will not bother with the dehumidifier crystals then.

 

[vinn]

OP,
You are still prescribing for yourself in post #7 only you dont seem to notice. You are also contradicting yourself, and you dont seem to notice that either.

I obviously know what your question was but long experience in Remedial work causes me to question you further in an attempt to get to the bottom of whats going on, and to provide you, or anyone else following this, with a considered technical explanation.
My questions have a technical purpose they are not idle curiosity.

I wish you well with your proposition.

 

[dishman]

Apologies if I have misunderstood you or we have misunderstood each other. As I said, I have posted about this chimney before and discussed it in length, so I can only act on what I have been advised. I am only acting on the prescription of others. I of course welcome any advice you can offer too.

Basically, I was told to add vents to stop it sweating, and that is what I have done.

Here is an image on inside the flue. From the lowest point looking up and the highest vent, also looking up.