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Green Building Bible, Fourth Edition
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  1.  
    I'd appreciate your views on whether Rockwool or similar is likely to 'wick' and/or hold water if continued down to the top of DPC level in a rainscreen.

    I've used it in this arrangement for brickwork cavity walls before and then placed something like XPS in the below DPC area. My current timber rainscreen detail (below) therefore swaps out the lowest band of Rockwool for a 350mm plinth of XPS in the knowledge this is less permeable.

    How paranoid am I being, though? It would be far simpler to take the same insulation all the way to ground, but clearly I'm keen to not build in a recipe for damp further down the line. Particularly with a timber internal structure.

    NB. external ground levels will slope away from the building more than is shown here...
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      CommentAuthordjh
    • CommentTime6 days ago
     
    Rockwool will certainly hold water; I don't know about wicking - I don't think so. I have some foamed glass (Technopor) at the bottom to form a capillary break.

    I would think you want the DPM/DPC under the floor level, otherwise how does an indoor flood escape?
    • CommentAuthorTimSmall
    • CommentTime6 days ago
     
    EPS is as good as XPS for that purpose I think.
  2.  
    Thanks guys,

    Posted By: djh
    I would think you want the DPM/DPC under the floor level, otherwise how does an indoor flood escape?


    I've got a Radon barrier membrane below the concrete structural slab (admittedly not as shown on the drawing as I subsequently moved it from above slab to below) to stop rising water. Had been planning just a bonded screed on top of the slab but you're implying another thin membrane below the screed may not be a bad idea.

    The thing is there's now grout below the CLT wall around the perimeter so any substantial water build-up internally would be fairly well contained anyway - I've been more concerned about keeping air from leaking out than how to get rid of internal water.

    Externally, anything that got through the breather membrane (blue) & 400mm of Rockwool should hit the airtight vapour-check membrane wrap (dashed red layer) outside the CLT and be directed down to the concrete (we are butyl sealing the membrane down to the slab). My concern was that once it gets to the concrete it could be 'held' by the rockwool whereas XPS might be more hydrophobic and thus the water would be shed.
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