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Cavity wall Insulation Options on self-build 2024

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    #32
    listermint
    Registered Users Posts: 33,895 ✭✭✭✭listermint


    https://www.boards.ie/discussion/comment/121631392#Comment_121631392

    I've an acrylic render on mine 6 years now. Perfect finish on top of EWI.

    Still wondering how some builders in the West are getting their detailing so wrong.



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    #33
    mickdw
    Registered Users Posts: 23,348 ✭✭✭✭mickdw


    No, but appearance wise, the majority would be white render finish. You.might be interested to know that the rural housing guidelines call for traditional detailing YET they are not asking for thatch roofs. It's more proportion, appearance and scale.

    A simply detailed dwelling of proportion similar to old cottage with a simple rendered finish is deemed to be suitable..... and yes plan ing department are quite happy with any of the multiple render systems available.

    They will even accept that the front door may not be a wood product as long as it has the appearance of wood. Imagine that.



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    #34
    MakersMark
    Registered Users Posts: 636 ✭✭✭MakersMark


    You should be going externally insulated on a new build.



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    #35
    davegilly
    Registered Users Posts: 683 ✭✭✭davegilly


    https://www.boards.ie/discussion/comment/121623402#Comment_121623402

    Why not #3?

    If you have a house that only has 100mm cavity as it was started 15 years ago and left idle when structure was built until now, what would you suggest?



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    #36
    mickdw
    Registered Users Posts: 23,348 ✭✭✭✭mickdw


    What's in the cavity?



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    #37
    SodiumCooled
    Registered Users Posts: 367 ✭✭SodiumCooled


    https://www.boards.ie/discussion/comment/121631638#Comment_121631638

    Because you want to heat up the thermal mass of the walls which in turn give the heat back to the house (assuming they are well insulated on the cavity side from losing it to the outside world). Putting an insulated slab on the wall prevents this process.

    Plenty of new builds do it and it shows very poor understanding of thermal management in the house by the designers.

    Thats new builds though it might make sense on a retrofit where there isn’t sufficient cavity though external insulation would be a better option there.



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    #38
    Furze99
    Registered Users Posts: 11,012 ✭✭✭✭Furze99


    https://www.boards.ie/discussion/comment/121631447#Comment_121631447

    How will that advice look in 20 years time?



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    #39
    Tefral
    Registered Users Posts: 4,346 ✭✭✭Tefral


    https://www.boards.ie/discussion/comment/121631638#Comment_121631638

    Apples and oranges.


    You don't do it on a new build where you have a choice not to. If its a retrofit we'll... you have no choice but to do it.



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    #40
    Dont Be at It
    Registered Users Posts: 391 ✭✭Dont Be at It


    https://www.boards.ie/discussion/comment/121623077#Comment_121623077

    What's the difference between the k8 and Tw50?



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    #41
    sydthebeat
    Subscribers Posts: 41,477 ✭✭✭✭sydthebeat


    https://www.boards.ie/discussion/comment/121739257#Comment_121739257

    completely different materials

    the K8 is phenolic foam

    the TW50 is polyisocyanurate.

    phenolic has a better thermal conductivity value than the polyiso.

    both require a min 40mm residual cavity



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  • Options
    #42
    Dont Be at It
    Registered Users Posts: 391 ✭✭Dont Be at It


    https://www.boards.ie/discussion/2058331483/cavity-wall-insulation-options-on-self-build-2024

    We went with option 1 with house current under construction. In practice it seems like it's hard to avoid bits of gaps between internal leaf and insulation. Does this cause much of a reduction in insulation performance?



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    #43
    thomas 123
    Registered Users Posts: 2,768 ✭✭✭thomas 123


    https://www.boards.ie/discussion/comment/122045653#Comment_122045653

    I think it would reduce performance significantly. A decent builder in here may advise.
    If it was my house I would not want any holes in it anyway.



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    #44
    Biker1
    Registered Users Posts: 387 ✭✭Biker1


    Unfortunately blocks are not all exactly the same thickness and the blocklayer will be lining them up from the side he is working from so any differences will be on the insulation side. Also if the insulation is not stacked on the flat it can end up with bows. There is a way of ensuring that the insulation is in full contact with the inner leaf and that is to bring up the inner leaf three rows ahead of the outside and fit the insulation as you go. Rarely done this way though.



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    #45
    Dont Be at It
    Registered Users Posts: 391 ✭✭Dont Be at It


    Insulation boards are in very good shape and there's a tongue and groove on them which is good for preventing gaps between boards, at least.

    Any idea if the gaps where the insulation is a bit out from the block causes much of a downgrade in thermal performance of the insulation? Hard to quantify I guess.



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    #46
    mickdw
    Registered Users Posts: 23,348 ✭✭✭✭mickdw


    What I've found over the years is that despite what appears to be an excellent idea re the tongue and groove, in reality, a board with straight cut edges fits better. The ones with the groove tend to climb more and basically if they are climbing, they are not fitting together right.

    Material type is even more important and a board that is alittle soft will tighten much better than a super rigid one.

    The boards without the tongue creat less waste too as they can go in in various orientations.

    Cavity insulation in general in my opinion only reaches a fraction of its theoretical insulation value. Not so much due to uneven block thickness but due to difficulty in fitting around dpc trays, loose fitting at corners, gaps when blocklayer couldn't be arsed etc.

    It's still my preferred method in terms of safety from water penetration and no danger of pressure within the cavity as is a problem with some of the injected systems.



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    #47
    thomas 123
    Registered Users Posts: 2,768 ✭✭✭thomas 123


    https://www.boards.ie/discussion/comment/122047494#Comment_122047494

    Sorry, misread what you said initially, I'd imagine not an issue at all really at a guess. If a bit of heat does get in there it either has to go through the wall plate or back into the wall, or through the insulation.



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    #48
    dathi
    Registered Users Posts: 1,399 ✭✭✭dathi


    https://www.boards.ie/discussion/comment/122047494#Comment_122047494

    https://www.kore-system.com/cavity-wall-insulation-the-devastating-effects-of-thermal-looping/

    a bit about it here



  • Options
    #49
    Dont Be at It
    Registered Users Posts: 391 ✭✭Dont Be at It


    Seems that gaps between boards is the main issue that you want to avoid.

    Had similar concerns re the injection system. Not sure new blocks would deal with it.



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    #50
    joeyanne
    Registered Users Posts: 36 ✭joeyanne


    We are currently building and going with 150mm cavity of full fill beads and insulated plasterboard on external walls.

    I see a number of people saying this is the worst option but after watching both my sister in laws do builds and go with 110mm insulation in 150mm cavity, I can safely say this is not an efficient option. They had two different builders and gaps could be seen in both builds. Which significantly reduces the efficiency of the insulation. It's near impossible to ensure the insulation is being installed correctly and gaps are always going to happen.



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    #51
    SodiumCooled
    Registered Users Posts: 367 ✭✭SodiumCooled


    It’s not that it’s terrible it’s just losing the advantage of the thermal mass (plus the nuisance of having slabs on the wall for hanging things). A bigger pumped cavity is the best option removing the need for the plasterboard while staying away from rigid board which is as you say nearly impossible to get right. Most block layers don’t want to know about it anymore either as pumping is the norm - one of the first things they asked when I was getting quotes was is the cavity being pumped. Now blocklayers aren’t too pleased on the large cavity either as they have to lean out a lot more with blocks but it’s certainly less hassle than putting in board insulation correctly.



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