Wouldn’t like to jump to conclusions after just 1 month other than we seem to be moving in the right direction. We might have been away for longer and left the house unheated for more days. Leap day in 2024 of course! And the known weaknesses of the degree days approach. We do have 8 rooms with fireplaces though
Oh dear. Do not buy this house without a full specialist moisture survey!
Oh, too late. Then I suggest a cowl for now. It should stop rain getting in and still allow the flue to vent off excess moisture. If the chimney is on an outside wall then fit a vent at the bottom of the chimney to allow a through draught to dry it out and then revisit the problem in a couple of years. You could fit a vent inside but then you need to allow for the lost air in your heating calculations.
I compared only the first 28 days of February 2024 
And the 8 fireplaces might account for a lot…
Thanks again Tim, for making me look about things slightly differently.
The chimney serving the front living room and bedroom above has no visible vents above or below floor, inside or out.
Whereas the chimney serving the ‘middle’ room & bedroom above has a curious circular opening below the floor, with a pile of earth(?) on the ground in front of it, plus a vent at floor level in the ‘middle’ room, plus a vent at floor level in the bedroom above.
Following the Great Rains at the turn of the year, surface water was seen below the living room floor, but none below the middle room floor (at least none that I could see).
The front living room has damp issues, but the ‘middle’ room has no apparent damp issues.
This set of sensors haven’t been in place very long but show humidity under ‘middle’ room lower than under front living room. Perhaps the chimney is ventilated and there is some kind of stack effect going on?
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Your pile of earth like material is probably decayed ash and other detritus from the chimney. It seems likely that your chimney is indeed keeping the subfloor dry. This is important additional information when it comes to insulating your floor. If you block off that vent, which may originally have been to provide air to the fire, then the chimney becomes unvented and you will need to take measures to protect or remove it.
Just mentioned in a different feed. But i thought important to remember.
Chimneys on the external wall as opposed to in the middle of the house are more suseptable to moisture ingress, through the masonary. They might require more critical consideration.
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It should be remembered that combustion of coal gives off hydroscopic salts. Therefore unused flues can draw humidity from the air and into the bricks. In addition removing three sides of the flue and incorporating the front or back into your wall leaves an area vulnerable to damp from the salt contamination. Salt treatments are available and usually end with plastering/rendering with special products.
If the same applies to other fuels please would someone add the information in another post.
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I’m about to order leca beads to fill my chimneys. How was the amount needed calculated?
After filling the chimneys with dry leca, if the alcoves and chimneybreasts are taken back to brick then insulated with woodfibre (100mm in alcoves, 40mm around chimneybreast), and lime plaster over the woodfibre, what effect will that have on salt contamination?
The damp remediation people have fixed some kind of damp proof membrane up to 1.2m in the alcoves which keeps salts at bay, but not around the chimneybreasts themselves.
I’m afraid our contractor estimated that. The hardest bit must be the fireplaces, the flue space is susceptible to some basic arithmetic
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Where will your airtightness layer be in the proposed construction? Is that the lime plaster, at a suitable thickness?
My first reaction to insulating over bare brick is that it isn’t smooth and air will circulate between parts of the wall and the insulation. That brings potentially humid air into contact with the hydrophilic salts. There are salt resistant plasters available. The only lime based one I know of, having never researched the subject, is in the Diathonite range. A parge coat of that would give a smooth surface to insulate against, blocking air and salt. Your club sandwich of construction would then be brick, salt resistant plaster it manufacturer’s specification, wood fibre insulation, lime plaster, mineral or clay paint.
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Thanks.
Fair enough 
. I know the height of the chimney, but not much idea what’s going on inside it!
Ah we removed the tops of some of our chimney stacks and got a feel for the shape of the flue void. Even so i think it was trial and error and possibly multiple orders for our builder, they had 8 flues to fill in total
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Yes the airtightness layer will be the lime plaster base coat plus finishing coat on top of the woodfibre. But there will also be a thinner layer of the same lime plaster used as adhesive behind the woodfibre. Seciltek Isovit has been specified for both adhesivve and base coat, and will check with suppliers whether it’s salt resistant.
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Hi chaps,
I will just chime in here to ask about a few details you maybe able to help with.
My chimney has now been removed on the ground floor and first floor up into the loft.
It is currently all open and while I have washed the ground floor wall a bit it is still quite dark.
Here are some before pictures: GF
First Floor (all plastered in):
Some GF during removal:
During FF removal:
Unlined chimney that will need some cleaning…
Current status with structural piers intels in on GF and GF wall (wall was washed as much as was possible with soap and wire brush):
Removal up until the loft, but piers kept for structural support:
As you can see above, my structural engineer wanted piers to be kept to hold up the chimney in the loft. She said you can’t rely on brackets in the loft to hold this anymore, especially as this was a party wall and the neighbour still uses his chimney.
The whole thing required a significant amount of lintels, which my builder thought were unnecessary as the brick piers are toothed into the wall. However, I thought these piers would be quite interesting to keep and wanted to be safe rather than sorry.
A surprise moment was that the right side of the old First Floor chimney pier did not sit flush on the pier below. It just finished on the floor boards… and in order to make that work with today’s regulations we put in a steel lintel below that pier which cantilevered on the ground floor pier. Hence that steel is sticking out on the GF, which will be a pain to box in without wasting the space below.
If you have some good ideas on how to make this look decent let me know. Thanks.
My actual 1st question for you, triggered by your discussion on salts in the wall, was about how you would treat the bricks that were in the chimney?
I was going to wash off as much soot as I can, then point up any loose areas with lime mortar.
Then maybe parging with lime mortar to get the airtightness and finally plasterboard it. As it is a party wall I don’t really feel it needs insulation, so I mainly want to ensure airtightness.
And then I have a second question on how you would best handle the openings in the floors and ceilings left by the removed chimney?
Thanks.
Brackets in the loft are actually OK while the neighbouring chimney is in use (but no longer permitted by building regs) the problem is when it is no longer used and it is decided to remove it. Suddenly there is no longer support on your side and the house of cards comes tumbling down. I have such brackets where my rear chimney used to be and I have told my neighbours that if ever they wander to remove their chimney I would like to do so with them. That would provide a safe removal option.
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Exposed brick and piers.
Airtightness is essential so that you don’t get fumes from your neighbour’s combustion. Also you need to block salts and discolouration from the bricks. I would wet plaster rather than dry line, so that the plaster is both of these, using a suitably certified plaster.
I am thinking of removing the front of my remaining chimney on the first floor and incorporating it into the existing fitted wardrobe. That should provide enough shelf space for Mrs. G’s shoe collection. I am retaining the downstairs fireplace as it is very attractive, sealed up and cannot be used.
Edit: The plaster needs to be continuous from slab to roof void.
The jumble of bricks in the first of these pictures is obscured by the steel and lintel in the second.
Had you penetrated the neighbour’s flue? How was it fixed?
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The steel lintel I can understand but why the concrete one below it? One lintel should be enough and gives you more space below.
Just box in the steel at ceiling height. Put a cornice on it if you want. There’s no need for anything fancy.
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