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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthordelprado
    • CommentTimeMar 6th 2018 edited
    I originally decided IWI because I couldnt run EWI all the way cos of the diagram attached. Anyone got an advice as to how to attack this?

    • CommentAuthorgravelld
    • CommentTimeMar 6th 2018
    Are you asking whether EWI is still an option, or just the questions on the sheet? Is the pitch really that flat?

    Depending on your exposure and other building specific things I would argue a proper job of the cavity is to properly seal it, yes. Consider something like a foam, but EPS is ok so long as it is continuous. I would also argue for a sealing of the top of the cavity.
    • CommentAuthordelprado
    • CommentTimeMar 7th 2018 edited
    Yeah the pitch really is that flat! I have 3-4 courses of brick internally which are effectively single skin.

    My plan is to use 80mm wood fibre internally, then something else externally, to about 60mm, which added to the 70mm eps gives me 210mm of insulation, I just dont know what I do with this funny area and, although I can lift the slates to seal cavity for even better performance, and everything else, its going to be hard to make that little triangle area air tight
    • CommentAuthorgravelld
    • CommentTimeMar 7th 2018
    This is another reason why your sandwich raises a lot of questions (that I'm not qualified to answer). You almost have a hybrid E/C/IWI solution. If the different layers do not connect you're going to have bridges and that's a bad thing.

    I think that means you should convert the roof to a warm one, long term, and tie it to the EWI although appreciate budget might not cover that right now. That inner leaf is going to be a TB.

    If there's more space than is suggested in the drawing you could try something very high performance to envelope the top of the cavity and tie your EWI into the rest (e.g. aerogel) but there'll be a lot of it.
    • CommentAuthordelprado
    • CommentTimeMar 7th 2018
    I can't see any problem with a sandwich in principle though?

    How do you tie EWI into warm roof without creating counter battens or something onto roof rafters? At the moment I've been stuffing the area from the inside with wool (knocking out every other brick).

    I wonder if I could pump lcynene in the area or something?
    • CommentAuthorgravelld
    • CommentTimeMar 7th 2018
    Icynene in which area? Must be a lot of work knocking out those bricks.

    If you have enough EWI you might be ok but it's interstitial condensation that most worries me, both through the main wall makeup and also at the junctions. Allied to that, vapour control and AT. I think you should have someone do some calcs, or do it yourself.

    Where will you put the windows?
    • CommentAuthordelprado
    • CommentTimeMar 7th 2018
    I'm putting the windows on the exterior skin, but with insulated reveals of 30mm, on both sides (internal and out).

    I dont think interstitial is a worry having spoken to a couple of people familiar with WUFI. Vapour control is in the wood fibre boards. AT is wet plaster everywhere.

    Lycene shot into the eaves. But I suspect it cannot happen as it cannot butt up to the membrane on the roof? Might call a contractor
    • CommentAuthorgravelld
    • CommentTimeMar 8th 2018
    When you install it, you allow it to expand then cut it back, if I understand correctly.
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