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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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    • CommentAuthorluz13827
    • CommentTimeAug 27th 2021 edited
    Hello, we plan to use either 40mm or 60mm wood fibre insulation on the internal side of external solid Victorian walls (we are limited to what we can do on the outside). I've read a few things about wood fibre insulation needing to start 300mm from the floor - is this true, and why - is it to avoid water splashed from the outside of the building coming through and reaching the wood fibre? If this is the case, what insulation is best to put on the bottom 300mm? Trying to avoid anything that offgasses too much, and prefer natural as much as possible.
    • CommentAuthortony
    • CommentTimeAug 27th 2021
    EPS would be my choice, but i cant see how you are meeting regulations
    • CommentAuthorluz13827
    • CommentTimeAug 27th 2021
    @tony would you apply EPS on the bottom part of the wall, and then wood fibre above? Because it's an existing Victorian wall and meeting the u value would take away too much internal space, building reg said as long as we're not making things worse, we don't have to hit the target u value
    • CommentAuthorMike1
    • CommentTimeAug 27th 2021
    I suspect that you may have been reading the recommendations for external insulation.

    Internally, it would be normal for the insulation to start at floor level, joining up with the underfloor insulation. If you have a damp problem that needs addressing first.
    I only use a 'plinth' of something else for IWI when, for example, external ground levels are less than 150 (pref 300) below internal floor level. Yes, EPS. Can use the same lime finish and mesh.

    +1 to Mike1
    • CommentAuthorluz13827
    • CommentTimeAug 27th 2021
    Thanks everyone! It sounds like I should be ok as the internal floor level is about 200mm above external ground level. We do have some rising damp, that we'll be hopefully resolving prior to this being fitted
    • CommentAuthortony
    • CommentTimeAug 28th 2021
    Try lime pointing 🙂
    If you have 'some rising damp' you really need to cure it first (perhaps dropping levels further - the rain where I live splashes up 300mm at times, not the 150mm that Bldg Regs assume - and/or 'softening' the surface - French Drain, perhaps). If you think you perhaps have not, try again, then finally use an EPS plinth as 'belt and braces'. EPS has a degree of breathability.

    What depth of IWI do you propose? Some say max 60mm, some 80mm and many have used 100mm. I would push you towards 100mm, which on a 225mm brick wall should give you around 0.35W/m2K, but I'd definitely suggest a Condensation Risk Analysis, preferably a dynamic one such as WUFI. One of the suppliers offers WUFI calcs for 'free' (they are otherwise, I believe, quite expensive and, more importantly, quite hard to find). Whisper me if you want the name of the supplier.

    Is the external wall 'naked' or rendered?
    • CommentAuthorluz13827
    • CommentTimeAug 28th 2021
    Thanks everyone!
    A surveyor thought the rising damp was being caused by some cracks in the front paving, causing water to come through the ground and then up the brick, so we were planning to fix that. But it would be good to ensure that is the only cause, and nothing else... @Nick, what do you mean by 'softening the surface'?

    Right now, there is what's believed to be a cement render from the floor to the window (and then just painted brick above that). I will try to get a photo when I'm there next (started renovations so not living there atm). We did wonder if it's better to remove that cement render, and replace with lime, however we've also read that cement is not actually that impermeable, compared to lime, so not sure if that is worth the cost..

    We're only planning 40mm or 60mm IWI - its just to improve what is. Building regs said because it's a Victorian flat, and a ton of insulation would take up a lot of internal space, we don't have to meet building regs (as long as we're not making things worse). I also believe that would help limit the chance of interstitial condensation?
    'Softening the surface' - using gravel in a French Drain, for example, so that rain falling on it tends to permeate directly in (and into the perforated pipe at the bottom of the French drain and away to a soakaway or other drainage destination) rather than bouncing off a hard surface and onto your wall.

    Yes, 40-60mm would have less chance of interstitial condensation than 80-100mm.
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