Blocking off chimney stack (chimney already removed)

cem

so I moved into a house 2 years which had the chimney taken out completely and only the chimney stack has been left behind which is supported on two large 'L' brackets in the bedroom and is (badly) closed at the bottom with a wooden piece with screws.

When I open the screws, I can see right through so it is open and as you can imagine given the weather now days, it does get rather cold (which I hadn't felt to date).

Would the following be the best way of fixing this:

1 - Chimney Flue up top
2 - Chimney balloon which will go into the stack ?

cyclonebri1

The age old way was simply to lay slate over the void at the top and then flaunch off with sand /cement over. Done as a large convex "mound"

Balloon at base is really only if the stack is being left open as a say a feature etc, ie, it's largely just to stop soot and deteriorated mortar falling out.

Have done them with rebar and asbestos free cement board too. (both at top and bottom).

It is sometimes recommended to put an air brick into the flue cavity to the outside, assuming we are talking a stack on an exterior wall.;)

cem

Yes this is a stack on the roof (I have a flat roof)...I am not sure if either of those options will actually insulate the room in question.

I would like to avoid removing the chimney stack as it means spending a lot of money and getting the council involved which I don't really wish to do but rather just insulate and protect from damp etc too for future.

cyclonebri1

cem wrote: »

Yes this is a stack on the roof (I have a flat roof)...I am not sure if either of those options will actually insulate the room in question.

I would like to avoid removing the chimney stack as it means spending a lot of money and getting the council involved which I don't really wish to do but rather just insulate and protect from damp etc too for future.

You didn't ask about insulation, just sealing the chimney.
BUT, if the stack is sealed top and bottom, it contains nothing but still air.
Second only to a complete vacuum as the best insulator.;);)

cem

haha I was expecting you to read my mind

jokes apart yes that makes sense, so slate with sand/cement up top and at the bottom..in terms of sealing it off from the bottom...what would you suggest

Just sick of the cold coming in through there...

zaax

It will need air flow otherwise you will get damp on the chimney breasts. Best to remove the whole stack

cem

zaax wrote: »

It will need air flow otherwise you will get damp on the chimney breasts. Best to remove the whole stack

Right so until I can afford to do that, what would be the best solution for this?

cyclonebri1

cem wrote: »

Right so until I can afford to do that, what would be the best solution for this?

Not arguing with anyone but as I indicated in the 1st post most people don't vent the stack to outside and do get away with it, I would only go with the vent if damp did become an issue.

Given that the stack is supported, (I don't know at what height), why not fit 2 layers of 50mm poly insulation board cut to fit tightly withing the void. Seal with silicon or similar then apply plasterboard over then decorate.?

spacey2012

It should be RSJ supported or removed in it's entirety, one collapsed recently killing the householder in the news if I recall

vaio

cyclonebri1 wrote: »

You didn't ask about insulation, just sealing the chimney.
BUT, if the stack is sealed top and bottom, it contains nothing but still air.
Second only to a complete vacuum as the best insulator.;);)

I'd have thought that trapped air in a 9 x 9 chimney would be a poor insulator because convection currents will happily move heat from hot area to cold.

I think the same logic is why we insulate cavity walls, what you want is little trapped pockets of air so you don't get the convection currents

cyclonebri1

vaio wrote: »

I'd have thought that trapped air in a 9 x 9 chimney would be a poor insulator because convection currents will happily move heat from hot area to cold.

I think the same logic is why we insulate cavity walls, what you want is little trapped pockets of air so you don't get the convection currents

No, you'r right , convection currents can even start in wide gap double glazing, hence the arrival of triple glazing..

But, cavity walls are open at the top, unlike this chimney issue, which will be sealed top and bottom.

Guessing that the OP chimney is flush with the roof (?????OP), there won't be much exposed stack to conduct heat to the cavity?