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Green Building Bible, Fourth Edition
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Housing - Renovation: Floor VCL to walls

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  1.  
    • CommentAuthorlngn2
    • CommentTimeFeb 7th 2023
     
    I'm stuck on a floor related detail and have been procrastinating about doing anything else in the affected area so time to work out what I should be doing.

    Context:

    New concrete slabs with DPM underneath.
    PIR on top
    Slip membrane/VCL
    Anhydrite Screed.

    I understand that the DPM should be joined to the DPC in the wall (but can't as the builders didn't leave enough membrane free and I wasn't aware at the time). Seems I can mitigate with a paint-on DPM such as BlackJack or Synthaprufe).

    How does one deal with the floor VCL though? Should that also be joined to the wall? I'm tempted to trim it back to floor level and then use blower-proof paint over the junction? Alternatively I could use some sort of tape - Contega Solido?

    As an aside, does anyone know how long a concrete floor should be left before covering with PIR? Our builder said it would be OK after a few days (which is what we did) but subsequent digging suggests otherwise and I've had to pull him up on a number of technical points he got wrong and I suspect this may be one?
    • CommentAuthortony
    • CommentTimeFeb 8th 2023
     
    Drying of concrete slab - 1mm per day with good ventilation or 25mm per month

    VCL is controversial, I prefer a combined VCL and DPM on top of the concrete and insulation (On the warm side of the insulation) it is possible though unlikely for it to collect condensation if on the cold side.

    I trap membranes behind the skirtings.

    If dpm overlaps dpc in practical terms ok if not black the gap
    • CommentAuthorlngn2
    • CommentTimeFeb 8th 2023
     
    Tony - thanks - fingers crossed it'll still dry when trapped under all the build-up. I suspect not, God help us...

    VCL is in the right place at least. Thanks for confirmation on membranes - black & blower-proof (or similar) it is then!
    • CommentAuthorGreenPaddy
    • CommentTimeFeb 10th 2023
     
    Is that really a VCL over the insulation, or simply a slip plane for the screed and to hold the water in the screed till it cures? What would you be trying to prevent vapour from transferring into - the concrete?

    Jointing the DPM to the DPC level, I suspect the only option is a Liquid Membrane, as you described.
    • CommentAuthorlngn2
    • CommentTimeFeb 10th 2023
     
    Back-up to the foil-faced vapour barrier on the PIR I think? Albeit both were punctured when stapling down the underfloor pipes.

    I was thinking that there's a possibility of moisture-laden air getting behind the PIR upstands at the floor/wall junction and then condensing on the concrete slab?

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