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Housing - Renovation: Insulating cut off chimney

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    Hi, I realise that chimney insulation has been covered extensively on here but I am not sure if the general advice applies to our situation.

    We have 3 storey Victorian maisonette (4 floors total) that has a Fireplace in each of the 6 rooms on the party wall.
    We have insulated the roof and are going to be doing IWI insulation throughout and fitting an MVHR system.
    Airtightness is obviously a big concern so ensuring the chimney breast is insulated and draught free would be great.

    So the few differences I see to the usual are:
    The chimney breast has been completely removed below us.
    There is no loft space as the ceiling is vaulted.

    I am thinking of sealing each flue with either a chimney balloon or rockwool shoved in a bag,
    then thinking of filling each flue with EPS beads and capping with a rain cover?

    Does that sound reasonable or should I seal at roof level and add air bricks in the top 2 rooms?
    • CommentAuthortychwarel
    • CommentTimeJun 1st 2022
     
    If there on a party wall just remove them once and for all
    • CommentAuthortony
    • CommentTimeJun 1st 2022
     
    Not so easy, no point in eps inside the heated envelope. I would do insulation in line with the ceiling insulation. Airtightness crucial. I would try to add an air brick to each flue just above roofline externally.
    • CommentAuthorjackmccabe
    • CommentTimeJun 1st 2022 edited
     
    Posted By: tychwarelIf there on a party wall just remove them once and for all


    It's not a possibility unfortunately.
  5.  
    Posted By: tonyasy, no point in eps inside the heated envelope. I would do insulation in line with the ceiling insulation. Airtightness crucial. I would try to add an air brick to each flue just above roofline externally.


    What purpose would the air bricks serve if they are above the insulation?
    Would there be enough movement of vapour through the insulation to the air bricks to prevent condensation?
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      CommentAuthordjh
    • CommentTimeJun 2nd 2022
     
    I'm not sure what you're trying to achieve. A chimney balloon or similar won't be airtight. It will stop major draughts but isn't a way to make something airtight. If the chimneys are going to be part of your external wall when finished, then you're right to think about insulating them, although the brickwork will be a major thermal bridge so it would be much better to remove them as suggested. Why can't you?

    Where and what is your airtightness barrier going to be? Until you decide that you can't decide how to treat the chimneys.

    Are the chimneys exposed to a lot of weather or reasonably sheltered? That will also affect how you treat them.
  7.  
    The freeholder really doesn't want us removing the chimney breast and neither does our neighbour.
    The chimney stack is also shared so zero chance of removing that as it is an end of terrace property.

    I forgot to mention but we will also be sealing each fireplace up so that would presumably help with airtightness.
    The chimney stack is fairly exposed to the elements so would presumably lose a lot of heat.
    For the airtightness layer we were just using polyethylene on the internal wall insulation, although can also do a parge coat.

    We could apply insulation to the chimney breast but then not sure how to deal with condensation within?
    Maybe spraying something like Icynene in each flue at a level below the internal insulation, then just using rain cover to ventilate the top?
    •  
      CommentAuthordjh
    • CommentTimeJun 2nd 2022
     
    Posted By: jackmccabeThe freeholder really doesn't want us removing the chimney breast and neither does our neighbour.
    The chimney stack is also shared so zero chance of removing that as it is an end of terrace property.
    I'm confused. You say the chimney is on a party wall - i.e. one shared between two properties. So how can it be an external wall? And what does the neighbour have to do with it? Come to that, why does the freeholder care if they've already allowed the property downstairs to remove theirs?

    The chimney stack is fairly exposed to the elements so would presumably lose a lot of heat.
    For the airtightness layer we were just using polyethylene on the internal wall insulation, although can also do a parge coat.
    Exposure is bad because of the cold, yes, but also because of possible driven rain. Whereabouts are you?

    If the airtightness layer is on the inside, then it also usually needs to be a vapour control layer, which polyethylene is, so you will need a taped membrane or a plaster parge coat over the inside of whatever you do.

    The internal membrane covers one possible source of condensation. The other possible source of moisture is rain, either driven through the external wall (if it is external rather than a party wall) or dropping in through the top if that is open.

    You need to clarify the arrangement (maybe a drawing or photo?) before we can help much further.
    • CommentAuthorjackmccabe
    • CommentTimeJun 12th 2022
     
    Sorry I may not have been supper clear, so it is an end of terrace maisonette with a commercial premises below.
    I've attached floorplans that shows the 6 rooms with chimney breasts in them and an image of the chimney stack.
    The roof construction has 75mm Kingspan phenolic insulation on top of rafters and 150mm Icynene foam between the rafters.
      Capture.JPG
    • CommentAuthorjackmccabe
    • CommentTimeJun 12th 2022
     
    chimney stack
      Capture2.JPG
  11.  
    Can you run an MVHR system through the chimney?
    • CommentAuthorjackmccabe
    • CommentTimeJun 14th 2022 edited
     
    Posted By: Dickie_in_YorkshireCan you run an MVHR system through the chimney?


    Yep that is exactly the plan, I am thinking EPS beads around the ducting in the chimney to avoid heat loss through the ducts supplying the rooms.

    Right now I am thinking of filling the flues with EPS beads, continuing IWI onto the party wall on the top floor and sealing the fireplaces on each floor.
    • CommentAuthorcjard
    • CommentTimeJun 15th 2022 edited
     
    > the chimney stack is also shared

    But do the other side use it? If they already had their fireplaces removed then now would be a good time to help them out by demolishing the stack
    • CommentAuthorMike1
    • CommentTimeJun 15th 2022 edited
     
    Posted By: Dickie_in_YorkshireCan you run an MVHR system through the chimney?
    In principle yes, if all the other flues are irreversibly sealed, if you can thread it with suitable insulated duct, if you can keep intake and exhaust a suitable distance apart, if the distance from the MVHR unit isn't excessive...
    • CommentAuthorjackmccabe
    • CommentTimeJun 21st 2022
     
    So I think the plan is to continue the internal wall insulation across the party wall and chimney breast, this should ensure air tightness on the face of the chimney and prevent any cold bridging.
    We are running the MVHR ducts down the chimney flues and the plan will be to fill around and above the ducts (about 1.2m to roof level).

    I was then thinking of sealing the flues at roof level with something airtight but breathable, maybe Icynene or wood fibre insulation cut tightly?

    Finally all flues will be capped off with a rain guard.

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