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Housing - Renovation: EPS for breathable internal wall insulation

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    I am internal wall insulating my Victorian maisonette with 400mm solid brick walls (EWI is definitely not possible)
    So far for the top floor I used Phenolic insulated plasterboard on battens, although this seemed a less than ideal solution due to the condensation risks and gaps in the insulation.

    So now I have been looking at moisture open insulation solutions, one material I have seen come up for this is EPS.
    I have seen some manufacturers offering specifically breathable Graphite EPS (Jub and Baumit), but cannot see any mention by them of using it for internal wall insulation.

    For the build-up I was thinking of using a breathable lime adhesive applied to the walls to stick 80 or 100mm eps onto the walls (hopefully this should prevent air leakage through the bricks as well.
    Then followed by either plasterboard and gypsum plaster, or alternatively insulated lime plaster applied onto a mesh mechanically fixed through EPS (think this would be more breathable?)

    The other alternative to EPS I was looking at was wood fibre insulation, although this performs worse per mm thickness and costs far more. So was just wondering if anyone had any advice on using EPS in a moisture open IWI system?

    Thanks in advance
    • CommentAuthorbhommels
    • CommentTimeAug 2nd 2022
     
    Fire risk is probably the main reason not to use EPS indoors. As discussed here on a well known forum:
    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=15819
  3.  
    If the iwi is too vapour-open it will let moisture easily through, which risks condensing onto the (now colder) inner surfaces of the brick. The brick only has finite capacity for a moderate amount of moisture to permeate out.

    Some approaches to this are:

    1) don't use vapour open system, instead use vapour barriers (retarders) such as foil faced insulation or a plastic sheet, to reduce amounts of moisture reaching the brick so that it can cope.

    1a) use fairly vapour-closed insulated linings, mounted on battens to create a void between insulation and brick. Make the void open to the loft or underfloor (pref both) so fresh outside air circulates to remove the moisture.

    2) use hygroscopic insulation such as woodfibre, which has a large capacity to adsorb moisture during high humidity and wick it back to the inside surface to dry back into the room later.


    This is a complex system because an unknown amount of moisture is being absorbed into the wall from rain, usually more than is condensing on the inside, and an unknown amount is permeating out through the mortar joints. Attempts to model this in the early 2000s (eg Wufi) had to make conservative estimates about how much rain would be absorbed, which led to doom laden predictions of mould. This gave IWI a bad name and many properties were poorly insulated to be 'safe'. However some better systems were proven effective in practice, usually you have to follow the manufacturers' recipe to be sure of replicating the success.
  4.  
    Seems I may be better of just sticking with the phenolic insulation on battens then which followed the manufacturers guidelines for installation.

    Wood fibre would potentially be the other option but it works out needing to be very thick to get equivalent u-values and also very expensive.
    • CommentAuthorMike1
    • CommentTimeAug 3rd 2022 edited
     
    Posted By: jackmccabe80 or 100mm eps.
    That would drop the U-value to 0.33 or 0.27 respectively. I'd probably do the same, provided I was happy that the external face of the wall isn't very exposed to high rainfall and is readily able to dry, and if I was using a natural insulation (other than wool) to help control relative humidity.

    There are some useful studies (particularly Historic Environment Scotland Refurbishment Case Study 4) where similar IWI U-values have been achieved without problem, but beware that values below 0.5 have 'traditionally' been viewed as risky, from the condensation perspective.

    Posted By: jackmccabebreathable lime adhesive... should prevent air leakage through the bricks as well.
    Use a parge coat first, to be sure.
    • CommentAuthortony
    • CommentTimeAug 3rd 2022
     
    For me, no battens, stick or fix to wall.
    • CommentAuthordathi
    • CommentTimeAug 4th 2022
     
  8.  
    I've seen a that study before but seems like quite a few of the solutions would have issues with thermal bridging through the timber frames.

    I don't think I really want to use wood fibre as the cost is pretty high and also ends up needing to be very thick to get decent u-values. We used it on our party wall for sound proofing and it was a bit of a pain to work with as well.

    I've not seen much about breathable insulation that does not absorb moisture well like EPS so makes me a little cautious about using it.
    If I did use it sounds like I would need a vapour barrier on the inside then?
    Also would I not need battens as moisture can migrate through it?
    • CommentAuthorSimonD
    • CommentTimeAug 5th 2022
     
    This might help. EPS IWI using 2 layers, 1st between battens, 2nd layer lapped to reduce thermal bridging, then vapour control layer and finally plasterboard fixed to the battens.

    https://www.sundolitt.com/globalassets/sundolitt/01.-international-market/03.-documents/climate-internal-wall-insulation.pdf
    • CommentAuthorJeff B
    • CommentTimeAug 11th 2022
     
    Posted By: SimonDThis might help. EPS IWI using 2 layers, 1st between battens, 2nd layer lapped to reduce thermal bridging, then vapour control layer and finally plasterboard fixed to the battens.

    https://www.sundolitt.com/globalassets/sundolitt/01.-international-market/03.-documents/climate-internal-wall-insulation.pdf


    This is what I have done too. Works well. (With PIR rather than EPS but same principle).
    • CommentAuthorTimSmall
    • CommentTimeAug 22nd 2022
     
    Maybe use an externally applied water repellent like Stromdry to reduce water absorbed from driving rain?
    • CommentAuthorwookey
    • CommentTimeOct 9th 2022
     
    I don't think I really want to use wood fibre as the cost is pretty high and also ends up needing to be very thick to get decent u-values. We used it on our party wall for sound proofing and it was a bit of a pain to work with as well.


    The k-value for woodfibre and EPS are not that different so it doesn't make much difference to the thickness - about 10%. There is a fair variation across products so the very best EPS will be quite a lot better than the very worst woodfibre. The main advantage here is that it is well-tested as an internal insulator and known to make robust systems not dependent on an undamaged internal membrane So you can happily continue to screw things to walls for the next 50 years without degrading the system.

    It's a lot more solid than EPS so is good for noise, thermal mass, decrement delay (not that important for IWI), fire performance, and the aforementioned attaching things to walls.

    In what way did you find it 'a pain to work with?' I rather liked it. Chopping it up makes a mess, but a harmless, natural mess and in fact I used the resulting fluff as stuffable insulation in various places. EPS is much worse unless you've got a big hotwire cutter, and it still stinks. Woodfibre is quite heavy, but for IWI thicknesses and working heights that shouldn't be a problem.

    Also much lower carbon to produce unless you search out low-carbon EPS, and easy to dispose of at EOL (maybe there will be a thriving per-house polystyrene recycling mechanism by then - there certainly isn't now).

    It does cost more, but not dramatically so. It would no doubt help a lot if there was a UK manufacturer but I don't think we have one yet.

    For solid wall IWI woodfibre is a pretty good option IMHO.

    EPS can clearly be used instead, although hardly anyone does SFAIK. Interesting question what happens as you get to the higher levels of insulation where people start to worry about condensation risks (~80mm of either). EPS has quite a low vapour transmission rate so whilst it could work as a 'breathable' insulation, that's only going to be true if the moisture load is sufficiently low. I don't have any numbers. How much water is coming up from the foundation (what's the DPC like?), getting in from the internal air and getting in from the rain, and how much is evaporating off again on the outside and through the EPS? The main advantage of woodfibre here (IMHO) is that you don't need to worry about this stuff too much - just do what is known to work. (80mm woodfibre unless known to be damp in which case less).

    If not going the 'breathable' route then you might as well just put PUR/PIR up, sealed as well as possible, for the better U-values.

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