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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.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    • CommentAuthorSilky
    • CommentTimeOct 3rd 2016
    This is just one of those things that has me scratching my head, cellular glass commonly known as foam glass is available as various sheet/bat material and also as granular material ( aggregate ). The aggregate is claimed as a 'breathable' insulation material, i.e. to be placed under 'breathable' limecrete floors. The bat materials that I have checked from the well known brands are claimed to be absolutely impervious to water vapour and have a mu-value of infinity. Therefore I'm guessing that the breathability of compacted foam glass aggregate floors is a bit of a mystery, espcially as the aggregate materials are also described as being impervious to water. I'm guessing the 'breathability' is purely down to gaps between the compacted pieces and therefore the material cannot be both breathable and liquid water/air tight? Therefore I'm also guessing there can be air leakage through the floor when it's exposed internally, i.e. at services or where a padding material is used around the edge of a slab. Anyone able to help out with this?
    I think your analysis is correct. The breathability comes from the gaps between the aggregate.

    As with all insulation materials, you should make sure there's a wind/water barrier on the outside to prevent thermal bypass and an air barrier on the inside to prevent air leakage/interstittial condensation. The latter is especially important at material junctions, eg at the floor-wall junction.

    • CommentTimeOct 4th 2016
    Yes, it's the gaps in the aggregate that allow both water vapour to migrate and liquid water to drain. Thee aggregate is 'impervious' in the sense that it is not hygroscopic and so does form a capillary break, which is useful in some circumstances.

    It's completely open to the passage of air as well and does not form any part of an airtightness plan. There must be an adjacent airtight material if you need airtightness.
    • CommentAuthorSilky
    • CommentTimeOct 5th 2016
    Thank you both for the input and sanity check. Think I will have a layer of eps on top and then some barrier membrane lapped up the wall then. I'm in a flooding zone, where the ground water level could come alongside the insulation on average once a year usually just for a couple of hours before receeding. Hence I'm looking for a strategy that does not trap water anywhere, no dpms, bitumen etc.. Just in case anyone thought I was being pedantic! I'm also going to render the inside and outside of the stone foundations with perlite/lime render.. it would have been good to add some foamglass bats here too as it's quite deep in some places, but now I think that's too much of a risk to drying out.
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