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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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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
    • CommentTime6 days ago
    Fire risk is probably the main reason not to use EPS indoors. As discussed here on a well known forum:
    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.
    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
    • CommentTime5 days ago 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
    • CommentTime5 days ago
    For me, no battens, stick or fix to wall.
    • CommentAuthordathi
    • CommentTime4 days ago
    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
    • CommentTime3 days ago
    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.

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