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Community and Q&A

Smart vapour barrier (MemBrain)

joan673 | Posted in General Questions on

I live in Toronto Canada Zone 5  I have installed rigid foam 1 1/2 inch on walls then 2x 4 studs with R 14 rock wool.  With the application of the rigid foam I have not been able to guarantee a 100 percent seal due to irregularities in the walls and  around the windows.  Probably 90 .  This is why I am thinking I need the vapour barrier (MemBrain).  Must the rim joist be totally insulated tight to stop the condensation as well   There will be a dry wall ceiling with safe and sound installed   I did not mention that this is a below ground basement installation
Hope to hear comments soon

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  1. Jon_R | | #1

    I would do a blower door test and find and fix any air leaks. I'd also follow the recommendations here (using MemBrain).

  2. Expert Member
    Peter Yost | | #2

    You can detail the MemBrain as both a vapor retarder and air barrier; there are two sets of installation instructions that reflect this.


  3. Expert Member
    Akos | | #3

    The smart vapor barrier in this case will not buy you anything especially if your foam's permeability is low.

    I would take the cost of the Membrane and get one of the smaller 2 part spray kits and seal up the remaining 10%. Important spots are around the rim joist, top of the foam and top plate of the interior wall.

    With basement insulation, the key is keeping air getting behind the insulation. The foundation is bellow room temperature most of the year, there is little opportunity for drying towards the inside.

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