How to deal with a draughty redundant chimney?

[ScottC]

I have discovered a significant and cold draught at floor board level around the chimney breast of an upstairs bedroom and am after some advice on how to best deal with it.

The chimney originally served this room and the room below however it no longer serves either. The entire chimney breast has been removed from the lower room, the chimney stack has been removed just below the roof line and although the original cast iron fireplace still exists in the bedroom the damper flap has been removed and sealed (with plaster by the looks of it). I suspect the chimney flue which served the down stairs room has been left open below the bedroom floor boards and the draught is coming from the cold loft space into the void between the down stairs ceiling and upstairs floor. Both these rooms are significantly colder than the rest of the house.

My thinking is to simply block off/seal the redundant chimney in the loft (which would be a lot easier than doing anything at the chimney bottom). Is it this simple or is some sort of ventilation for the chimney still required?

Thanks in advance

 

[Feltwell]

It is advisable to always ventilate redundant flues, which I realise is not really the answer you're after. Normally there should be ventilation from the original site of the fireplace and from the chimney pot, even if it is capped off then it should be done with a ventilated cap.

In your case, if what remains of the stack is entirely internal and so unlikely to get damp, you may get away with just ventilating into the loft space.

However, with no chimney breast at ground floor level but still remaining in the bedroom above, first thing I'd want to check is has it been adequately supported at first floor level on some steels. I've seen one that was left supported only by a couple of bits of 4x2 timber! :shock:

 

[worms]

In your case, if what remains of the stack is entirely internal and so unlikely to get damp, you may get away with just ventilating into the loft space.

But keep an eye out for issues of condensation caused by the warm, moist air entering the unheated attic.

However, with no chimney breast at ground floor level but still remaining in the bedroom above, first thing I'd want to check is has it been adequately supported at first floor level on some steels. I've seen one that was left supported only by a couple of bits of 4x2 timber! :shock:

That was my first thought too! :shock: indeed!

 

[ScottC]

Thanks for the advice.

I have been pondering this problem a bit more and am leaning towards blocking off the flues in the loft, my reasoning being:
1) I am sure the chimney alterations were done in the mid 80's so it has been 30 years since the chimney was exposed to the elements. Therefore there will be no dampness from rain to consider/ventilate for
2) I can't imagine the fire in either room was used that much as they are both very small rooms compared to the rest of the (Edwardian) house. My thinking is there would be a lot less salt build up within the bricks (compared to the main living rooms say). Also wouldn't it be better to stop the warm air getting to this salt?? (not to mention the loft as was pointed out)
3) As I mentioned one of the flues is already blocked off at the back of the cast iron fireplace and no sign of any issues even after 30 years.

Does this seem reasonable or is my logic flawed?

 

[discobarry]

We also have a redundant chimney which we have recently boarded off at the bottom and insulated in a wooden frame at the bottom. We then plaster boarded and skimmed. The chimney is still vented from it's pot and it hasn't had damp problems nor shown signs of it in the past. The kitchen should be warmer now.

 

[a twig]

We also have a redundant chimney which we have recently boarded off at the bottom and insulated in a wooden frame at the bottom. We then plaster boarded and skimmed. The chimney is still vented from it's pot and it hasn't had damp problems nor shown signs of it in the past. The kitchen should be warmer now.

Isn't best practice to have some sort of vent at the bottom as well?

 

[Penners]

We also have a redundant chimney which we have recently boarded off at the bottom and insulated in a wooden frame at the bottom. We then plaster boarded and skimmed. The chimney is still vented from it's pot and it hasn't had damp problems nor shown signs of it in the past. The kitchen should be warmer now.

Discobarry may be fine, but I wouldn't be comfortable relying on ventilating an entire chimney stack from just a vented pot. Throughflow of air the ideal, so if you can arrange this in some way consistent with elmininating the majority of the draught, this would be advisable.

However, as Feltwell has suggested, you might get away with allowing a substantial amount of air into the stack from the loft, provided - as worms says - you don't get condensation.

I absolutely concur with the advice to ensure that the remains of the stack are properly supported. Better still, how would you feel about dismantling the entire redundant structure? That would be a permanent and effective solution (if the property is listed you would, of course, require LBC).

 

[Feltwell]

I've got my own draughty chimney problem to resolve now. The corner of my dining room, which is where the family PC is located, has a positively viscious draught at floor level - it really freezes your feet! The window next to it has well-sealed secondary glazing now, which has improved matters, but you still end up with frozen feet after a while.

I've been putting off crawling under the suspended floor to check the insulation for a while, but finally got around to it last night and found that the insulation, which I put in about 4 years ago, is still all in place with no major gaps anywhere, insulation well stuffed up around the edges etc.

So, the only culprit I can think of now is the chimney. It's "sort of" a live flue - not capped at the top, unlined, but the original fireplace has long gone and previous owners have tiled the builders opening, added a wooden surround, for a fire basket ("dog basket") to go in the hearth. This doesn't work very well as there's not enough draw for the size of opening, so it smokes the room out, hence we don't use it. Job no. 3076 is to fit a new fireplace I have sat in the garage.

Anyhow, I've always been reluctant to block the flue off, but I think I will now for the winter at least. I don't really see the point in paying for a chimney balloon, I'll cut a bit of celotex to size.