Chimney Removal to roof level

[boppygloworm]

I am about to have my chimney removed down to roof level due to a problematic leak and lots of money spent. After the chimney has been removed down to roof level the roof will be retiled/sealed and refelted etc.

The chimney in question is not on the side of the house or external wall. My question is what happens to the chimney stack in the loft is it sealed or left open as I have read lots of conflicting information some people say it needs to be sealed and other advise it to be left open as it it.

People who have advised leaving the stack open in the loft say that the attic would then be prone to damp and rot? Does anyone know what the correct procedure is after removal of chimney stack to roof level with regards to the open stack.

 

[Alastairreid]

An internal stack is normally sealed off! as is any flue openings to the stack.

 

[boppygloworm]

If you seal the internal stack won't there be a build up of moisture in the stack with no where for the air to escape?

 

[Alastairreid]

There is no moisture as the openings are sealed off and it is not open to the elements on any side.

 

[smashngrab]

I think the best thing to do is stuff a load of fibre glass down the flue's. This will stop any warm air that comes up the flue hitting the cold and causing condensation.

 

[taz123]

I would be tempted to leave it open to allow air circulation or at least vent it.

 

[kbdiy]

Had a similar job done 20+ yrs ago when we had our roof re-tiled. Flue was just left open and no problems in all that time, so don't worry about it.

 

[tony1851]

If the roof void is an old, draughty one, you shouldn't have a problem in just leaving it open.

 

[dann09]

All flues should be vented top and bottom no matter where bottom starts or top ends.
And all redundant flues should be swept before de-commissioning them.

I hope that you fix the "leaks" and leave the chimney stack alone. They are traditional, and add value and style to the property.

 

[boppygloworm]

The Roofer that is doing the job has advised me to cap the chimney off which he will do when he does the job.

There seems to be a difference of opinion on here some are saying leave as it is others are saying cap it off. So I do not what is the best way to go. I can understand that if left open the warm air from the lounge will go up the flue and into the loft causing lots of moisture. I think what I will do is my roofer will cap it in the loft and I will plug it from the lounge so its basically sealed at both ends?

 

[taz123]

The Roofer that is doing the job has advised me to cap the chimney off which he will do when he does the job.

There seems to be a difference of opinion on here some are saying leave as it is others are saying cap it off. So I do not what is the best way to go. I can understand that if left open the warm air from the lounge will go up the flue and into the loft causing lots of moisture. I think what I will do is my roofer will cap it in the loft and I will plug it from the lounge so its basically sealed at both ends?

It is standard practice to vent cavity walls and a chimney has/is a cavity.

IMHO it should be vented to discourage damp/moisture build up.

 

[Alastairreid]

Its an internal stack and should be sealed both top and bottom! where is this moisture going to come from?

We have removed hundreds of stacks over the years, many from council owned properties..this was the stipulation from the council architects/engineers.

External stacks were vented top and bottom but sealed in the attic.

 

[dann09]

I dont intend to rehearse elementary chemistry.

moisture is in the air (sealed flues contain air), its called RH (relative humidity), temperature affects the RH, and the hygroscopic salts in the soot (even in a swept flue) attracts this RH (air moisture).
Sulpherisation is the consequence.

Air flowing thro vents from bottom to top of a flue, even a limited length flue, will disrupt the above chemical cycle - similar to how an extractor in a bathroom will disperse condensation - roughly speaking, the same dispersal happens in a vented flue.

 

[Alastairreid]

I dont intend to rehearse elementary chemistry.

Thank god for small mercies!

And i wont bother rehearsing building physics.

As i said before if the flues are sealed (top and bottom) and if it is an internal flue then there is no moisture.

 

[dann09]

Repetition is not an argument.

Maybe you will prove me to be wrong or false but first, of course, you will have to provide an argument based on facts.

AAMOI:
What type of air do you consider your sealed chimney flues to contain?
Do you deny the fact of sulpherisation?

Can you refer me to an authority that supports your contention?