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Attic insulation and vapour barrier(again)

  • 22-11-2016 3:18pm
    #1
    whosedaddy?
    Registered Users, Registered Users 2 Posts: 937 ✭✭✭


    Hi,

    I understand the common approach to the vapour control layer between the between rafter (say TP10) insulation layer and the below rafter insulated plasterboard say (K18) layer.

    Does the same recommendation apply if you have two equally thick TP10 between rafter and TP10 below the rafter? (and no PB finish).
    Would the staggered seams (assuming all taped and sealed) of the two TP10 layers be ok? Or would that cause concern re condensation between the the layers and therefore extra vapour barrier is a must?

    Its a typical 50s house (extremely windy attic, but no actual sofit or ridge vents.
    I can fit 75mm insulation into the rafters whilst keeping min vent gap.

    Taking the tiles, battens and the felt off might be on the cards at a later stage...

    /WD


Comments

  • #2
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    2/3 outside VB 1/3 inside is the rule of thumb


  • #3
    whosedaddy?
    Registered Users, Registered Users 2 Posts: 937 ✭✭✭whosedaddy?


    Ok. Thanks. More work to make that happen


  • #4
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,146 Mod ✭✭✭✭BryanF


    whosedaddy? wrote: »
    Hi,

    I understand the common approach to the vapour control layer between the between rafter (say TP10) insulation layer and the below rafter insulated plasterboard say (K18) layer.

    Does the same recommendation apply if you have two equally thick TP10 between rafter and TP10 below the rafter? (and no PB finish).
    Would the staggered seams (assuming all taped and sealed) of the two TP10............

    /WD
    Please don't read the Kingspan catalogue and expect a meaningful response


  • #5
    whosedaddy?
    Registered Users, Registered Users 2 Posts: 937 ✭✭✭whosedaddy?


    Not sure I got the last comment.
    anyway, running the risk not asking meaningful questions.... still trying to get my head around the "right" way..

    I found some older posts here on the forum, where comments where made my forum Mod that a Vapour membrane does not serve much purpose with rigid/foil insulation. (in context of badly fitted foil backed xtratherm boards), as the insulation is impermeable once taped and sealed.

    OP of that topic was using Intello plus, which was questioned to be waste of money, due to the foil backed boards.

    Which adds to confusion what to do. Happy to spent the money and time to put vapour barrier in place, if it serves a purpose and isn't counter productive.
    Not wanting to "waste" money, would you use the likes of Intello plus or would cheaper option do just same?

    /WD


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