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Using Damp proof membrane as vapour barrier

Discussion in 'General DIY' started by MattFinish, 20 Feb 2021.

  1. MattFinish

    MattFinish

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    Have a good amount of damp proof membrane left which my builder previously used when laying down concrete. Really heavy duty stuff this:

    https://www.screwfix.com/p/capital-...amp-proof-membrane-blue-1200ga-15-x-4m/98181#

    I'm fixing insulated plasterboards with built in vapour control to a solid wall.

    I'm probably being extra but can I attach this damp prrof membrane behind the timber battens all across the solid wall as like a backup vapour control layer?

    Wall doesn't have any damp but I'm just worried about condensation if the vapour control in the insulation fails...
     
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  3. Swwils

    Swwils

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    Depends what your condensation risk analysis calculation says.

    Also not all insulated plasterboard "vapour control" is equal, some has barley any vapour control and can be totally unsuitable for the application.
     
  4. MattFinish

    MattFinish

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    Haven't done a condensation risk analysis. To be honest most people upgrading internal wall insulation don't especially if it's a DIY project.

    And I've been looking at the spec sheets for various insulated pb manufacturers. Most are well over 100 MNs/g. In comparison a standard knauf or British gypsum vapour foil backed plasterboard is around 60-70 MNs/g.
     
  5. foxhole

    foxhole

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    Would make fixing plasterboard more difficult and achieve little .
     
  6. Swwils

    Swwils

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    And actual vapour check boards give give like 1300@85% on a 13950 test.

    Hence why it's important, the boards you end up using can be totally unsuitable depending on what's going on.

    Depending on your construction and needs it might be advisable to dpm just to cover behind the battens and not the whole wall, if at all.
     
  7. MattFinish

    MattFinish

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    I plan on using Kingspan k118 phenolic foam insulated plasterboard. Read the spec for this and it says vapour resistance at well over 100MNs/g if that means anything...

    Yes I did consider buying 100mm dpm strips you can get from screwfix, about 30m. It's only around £5 but will this blue damp proof membrane do the job if I cut into strips and staple behind battens?

    I'm using 2x1 battens btw...
     
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