Welcome to the AECB Forums Building Refurbishment and Retrofit External Wall insulation on existing cavity wall dwelling

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  • #31966

    Hello AECB Forum

    This is my first post, and I look forward to what comes back 😉

    I have a situation where I am keen to apply a hygroscopic insulation material (e.g. woodfibre) with an appropriately suited render or facing externally to an early 20C property. Except – it has a vented cavity which breaches the insulation. I am therefore keen to fill the cavity, ideally also with a hygroscopic insulation material – and wondering if any AECB forum members have any experience or recommendations for this situation??

    I have read in a recent paper by the UCL moisture group that the combination of highly hygroscopic materials with less hygroscopic materials that have greater potential for capillary movement (e.g. fired brick) can work well together for the passage of moisture, though I imagine this must depend on occurrence of dewpoint.

    Helen Richards
    Powered Living Ltd


    Great to hear from you Mark and I am glad you think filling the cavity could be the wise thing to do….. or another option could be sealing off air vents? Though the cavity may still be connected to sub floor or roof spaces and the overall result wouldn’t of course achieve such a good U value.

    Surely hygroscopic infill insulation material would be OK if the external weather screen on EWI is performing adequately? I am keen on using a detail recommended by Natural Building Technologies http://www.natural-building.co.uk/sites/natural-building.co.uk/files/pdf/8/retro-ewi-clad-system-sheet-may-16_0.pdf

    Link to the paper I mentioned:


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