GeoffSmith Posted September 9 Share Posted September 9 Hi Everyone, I've got a bit of a problem that I hope I'm posting in the right place. We recently discovered a disused chimney flue in our kitchen that leads to the loft. It terminates in the left, and both ends are open. Up until last week, it was unknown to us, and we only discovered it after the two year old damp patch it created started growing, leading us to cut it away. I'm wondering what the best course of action is, firstly, for sealing this chimney somehow. All of my recent reading is suggesting I should only seal it at one end, and leave the other end open. If anyone can advise on that, it would be great, but my bigger issue is what to do with the side of the chimney that is inside the house. One side is internal, the other side is external, like so: My problem is that all the head in the house is going up the stairs, and I'm pretty sure it's getting sucked into this massive floor to double height ceiling cupboard, and then hitting the exposed brick of the chimney flue. What's my best course of action here in terms of insulating this cupboard? Also, as a bonus question, if the walls of my house are cavity walls, will the chimney be a cavity wall on the external side as well? Thanks everyone! Link to comment Share on other sites More sharing options...
ProDave Posted September 9 Share Posted September 9 Is this the SAME chimney already being talked about in your damp patch in the ceiling thread or a different one? Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 9 Author Share Posted September 9 Sorry, same, I didn't want to mix the threads as I felt they were different issues. I understand what I'm looking at now thanks to you and Joe, so I can focus on more specific questions. Link to comment Share on other sites More sharing options...
Redbeard Posted September 9 Share Posted September 9 Block at the bottom, perhaps with PIR (and air-tight foam and air-tightness/vapour-tight tape) as suggested in the other thread. Backfill with EPS beads. Seal at the top the same as below. There is some risk of interstitial condensation on the skin which is external but careful attention to air- and vapour-tightness should mitigate that to an extent. I cannot remember; can you get your head in to look *down* the flues? If so, you could always engineer an airtight 'dump-valve' in the bottom to allow you to let out some or all of the beads so that you could check for dryness inside the flue at the top end. (If any of the chimney breast is un-plastered (above the bedroom ceilings, for example) you could roughly plaster it to prevent (moist) air ingress. Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 9 Author Share Posted September 9 Hi mate, Thanks for reply. My problem is that since reading more and more on the subject over the last couple of days, I'm hearing repeatedly that blocking both ends would be the worst thing I could do, so I'm confused. In terms of access, it turns out that the mortar is so sandy that I can literally just unseat the bricks with nothing more than a slight lift, so I've now reduced the heigh of the cimney to the point where it's level and easily accessible. None of the chimney breast is plastered, but I didn't even realise that was a possibility. So if I just throw some bonding up, that'll make it airtight in those places. That's great. So if trying to avoid sealing both ends, but taking all the rest of your advice on board, is the following my best bet: 1. Rip out cupboard and get to exposed brick. 2. Bonding coat the entire brick face. 3. Block bottom of flue with PIR + seal with foam 4. Fill entire flue with EPS beads up to loft level 5. bask in the heat of suddenly warm home that doesn't feel like a meatlocker in December? Please please please tell me 5 is also a possibility! Link to comment Share on other sites More sharing options...
Redbeard Posted September 9 Share Posted September 9 OK, others will no doubt comment too, but here's my 2 penn'orth: Back in the days of DIY guides to home improvement the suggestion was that you *always* ventilated unused flues, so you were advised to insert a vent in any rooms which once had a fireplace. So, that gives us warm, moist air from a living environment being pushed into flues which get colder as they get towards the cold roof, bringing with it the risk of condensation. Your flues no longer run out of the roof, but to the ventilated roof void, so if you decide to leave the whole lot open you *may* be OK, whereas if you leave the top open and close the bottom you have closed off the ventilation anyway, with the PIR at the bottom and the EPS in the flues. I suspect that in your *particular* situation ventilation of the flues could be irrelevant. Can't comment on 5 as we do not know all the myriad specifics of your house, but if the *before* status is a situation which sucks heat out of the room and the *after* status is one which doesn't then I'd say you have a recipe for a good outcome. All other shades of opinion welcome. *Note that any filling of existing flues with any sort of insulant is regarded as 'experimental' (hence my suggestion of the 'dump valve' for checking).* Link to comment Share on other sites More sharing options...
joe90 Posted September 9 Share Posted September 9 My two Penney’s worth, block both ends, no warm air movement into a cold space to create condensation. 1 Link to comment Share on other sites More sharing options...
Redbeard Posted September 9 Share Posted September 9 (edited) By the way, is your cavity wall (I think the other thread said you have a cavity wall) insulated? If it is not, is it vented? If the latter, that would further reduce any potential issues in the flue. Looks like @joe90 and I are sharing the same 2 pennies! Edited September 9 by Redbeard 1 Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 9 Author Share Posted September 9 Right I've got what you're saying. The house is cavity wall, with grey EPS insulation inside. And everywhere else, actually, since this stuff seems to get everywhere. I cleared the loft of old 100m insulation today in order to replace it with new 270mm, and there were three bin bags worth of EPS beads in a pile at the back of the loft that had blown in from a void in the cavity wall. I'm guessing if I'm plastering the internal facing side of the chimney, I can also batten and insulate before replacing the cupboard to further mitigate war air hitting it, right? Link to comment Share on other sites More sharing options...
joe90 Posted September 9 Share Posted September 9 1 minute ago, GeoffSmith said: to further mitigate war air hitting it, right? However there will be no cold air blowing in the now closed off chimney. I wonder if the cavity extends along the outside of the chimney ? Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 9 Author Share Posted September 9 Yeah, that's what I can't work out. I don't know how to confirm either way. Link to comment Share on other sites More sharing options...
joe90 Posted September 9 Share Posted September 9 (edited) 20 minutes ago, GeoffSmith said: Yeah, that's what I can't work out. I don't know how to confirm either way. You would have to measure the depth of the breast on the outside and compare to the inside (if you can get in there). Either way blocking it off will massively help control the cold IMO. If you filled it with leftover beads it will be yet another filled cavity 👍 Edited September 9 by joe90 Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 9 Author Share Posted September 9 Yes, that's it, you've just put into words what's been in my head. If I seal both ends, and then fill, how is it any different to the rest of the house? I genuinely cannot find a single post anywhere online suggesting that it's OK to seal a chimney at both ends, but if I do seal it and fill with beads, how is it not that it simply becomes a cavity wall like everywhere else? Surely, in that instance, it simply ceases to be a chimney flue, and is now just one more cavity wall? Makes perfect sense. Thanks Joe, appreciate the advice. Had a huge hole in my understanding of this, but you, Dave, and RedBeard have really put me on the right path - thanks! I'll report back once the job's done. Final question: Am I OK to remove bricks from the left end of the chimney if it makes further access even easier? I'm Link to comment Share on other sites More sharing options...
joe90 Posted September 9 Share Posted September 9 1 hour ago, GeoffSmith said: Am I OK to remove bricks from the left end of the chimney if it makes further access even easier? I don’t see why not, you say they are hardly stuck together anyway. 🤷♂️ Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 9 Author Share Posted September 9 Great, thanks Joe, I'll get on with it. Once again, thanks for taking the time to help. Have a good week! Link to comment Share on other sites More sharing options...
Redbeard Posted September 9 Share Posted September 9 If your cavity is filled the critical risk area could be the inside of the outer cavity skin, though as @joe90 said it depends how the cavity interacts with the flues. However if the insulation in the flues is 2x that in the cavity the inner skin could also be at risk. A WUFI condensation risk analysis, while costing a fair bit, might put your mind at rest. Link to comment Share on other sites More sharing options...
Mike Posted September 9 Share Posted September 9 5 hours ago, GeoffSmith said: I genuinely cannot find a single post anywhere online suggesting that it's OK to seal a chimney at both ends, but if I do seal it and fill with beads, how is it not that it simply becomes a cavity wall like everywhere else? It does, however some condensation can occur in voids in cavity walls. In the case of a flue, its internal faces will be infused hygroscopic salts, which increases the condensation risk. 5 hours ago, GeoffSmith said: Am I OK to remove bricks from the left end of the chimney if it makes further access even easier? Yes. But if you're going to do that, and already plan to replaster, why not just remove the flue, as I suggested in your other thread? Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 9 Author Share Posted September 9 (edited) Removing the flue sounds like an enormous job, though. There's a difference with me removing four bricks to level off the opening, and removing 200+ spread across three floors! I think for my skill level and budget (skint), I need a solution that involves as little faff as possible. Removing the flue, unless I've wildly misunderstood what it entails, sounds like it would be a serious job? On your first point, should I see if a chimney sweep can give it a proper clean? Edited September 9 by GeoffSmith Link to comment Share on other sites More sharing options...
joe90 Posted September 9 Share Posted September 9 Yes three floors of removing a chimney is a lot of work and if it’s not in the way why bother? I think the condensation risk is over egged,!! Filled with beads and draught proof has got to be better than what exists. There is no timber in a chimney to rot and the house is heated. Just my penneth worth. Link to comment Share on other sites More sharing options...
Mike Posted September 9 Share Posted September 9 45 minutes ago, GeoffSmith said: Removing the flue, unless I've wildly misunderstood what it entails, sounds like it would be a serious job? Most difficult and expensive is removing the part above the roof. After that, it's normally easy if you have an aptitude for that sort of thing, and can live with the mess for a few days. But if skill and cash are limiting factors, then filing it as previously described is next best (preferably after sweeping it). Link to comment Share on other sites More sharing options...
Redbeard Posted September 9 Share Posted September 9 Am I wrong in having understood that there is no part above the roof? I thought there was a pic in the other thread of the flues ending at loft floor level. Link to comment Share on other sites More sharing options...
Mike Posted September 9 Share Posted September 9 23 minutes ago, Redbeard said: I thought there was a pic in the other thread of the flues ending at loft floor level. There is, but below the roof (tiles) - so no scaffolding & no water-tightness to worry about. 1 Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 10 Author Share Posted September 10 Yes, that's right, new roof and no exposed chimney - I'll get it swept and filled, and if it still causes problems, I'll remove it. Glad to know that removing it is actually an option, because I hadn't even contemplated that. Can't have a problem with something that no longer exists, so that's a good backup 1 Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 11 Author Share Posted September 11 Just a quick update. So I've removed a few of the bricks to get it level and easier to work with: I decided to test them with a moisture meter while I was there, and the inside of every brick I could reach was a consistent 18% moisture. The other side of the bricks, and all bricks outside of the chimney registered 6-8%. Should I be concerned about that - I'm not sure if that's expected or if it changes anything Link to comment Share on other sites More sharing options...
GeoffSmith Posted September 11 Author Share Posted September 11 Oh, and the bricks could be removed with nothing more than a wiggle Link to comment Share on other sites More sharing options...
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