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IWI on redbrick, waterproofing methods?

  • 19-12-2022 2:13pm
    Registered Users Posts: 6,214 ✭✭✭

    Looking for some advice here, please.

    I have a two storey detached house where the main body is constructed with double-leaf blocks, 100mm cavity and 50mm PIR in the cavity. The PIR seems to be well adhered to the inner leaf (used a borescope to check), etc. Around two sides of the house we have a single story extension in redbrick, double-leaf, 100mm cavity with 50mm PIR. EWI isn't an option due to cost and complexity of the job (non-standard layout).

    The main body of the house could really benefit from IWI due to leakage at joists, cavities for supporting beams and the usual losses just below the top-plate. I can go get that pumped with open-cell IWI and I'd be happy enough as none of the main body of the house has redbrick within the lower parts of those walls, but the part which is concerning is the redbrick on the 'wrap-around' extension.

    I have researched on this site a lot and also elsewhere to see what are my options for IWI on the redbrick extension. Am I correct in saying that there is no approved (Agrément cert) IWI method for redbrick at all, neither open or closed cell, or bonded beads? What then would the opinions be on open-cell insulation with the redbrick treated with a hydrophobic cream (example: Would/could this lead to trapped interstitial condensation or is there remedial venting for between the bricks available to prevent this?

    Need a solution as my feet are freezing. Many thanks all.


  • Registered Users Posts: 2,810 ✭✭✭MicktheMan

    Hi 10-10-20, not sure if I understand your query properly but are you trying to upgrade your wall insulation (install IWI) to address an air leakage issue?

  • Registered Users Posts: 6,214 ✭✭✭10-10-20

    Not exactly Mick. I want IWI to insulate the cavity and fill in some of the voids from a time when voids didn't seem to matter. That's pretty clear-cut on the double-leaf block portion of the house, but it's the red-brick portion which I'm asking about.

    Can I have comfort in avoiding trapped moisture within the bricks and open-cell insulation if I treat the external face of the red bricks with a hydrophobic sealer to prevent wicking/porosity, or do I need to avoid IWI completely?

  • Registered Users Posts: 2,810 ✭✭✭MicktheMan

    Apologies 10-10-20 but am still confused. Using IWI (internal wall insulation) to insulate a cavity makes no sense to me. Do you mean CWI (Cavity wall insulation)?

  • Registered Users Posts: 6,214 ✭✭✭10-10-20

    Flippin-hell - you're right Mick - Cavity wall insulation (CWI). And I can't even edit it now. 😫

    I fitted IWI on one room recently - I had that on my brain.

  • Registered Users Posts: 2,810 ✭✭✭MicktheMan

    Ah, okay. Now it makes sense :)

    By open cell do you mean a foam product? I wouldn't be pumping any foam product into my cavity if it was my house. Too difficult to remove if something was to go wrong.

    I am generally not a fan of trying to seal up the outermost layer of an element, be it brick, cement render etc. If there is no certification for the use of the product then I would proceed with extreme caution.

    You mentioned your feet being freezing, can you elaborate on this a bit ... maybe more insulation is not the answer.

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