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Install Phenolic (or other PIR) thicker than studs?

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  • 11-11-2019 9:17pm
    #1
    johnnyboy08
    Registered Users Posts: 149 ✭✭


    Hi, could I install PIR thicker than studs? For example, install 150mm board between 100mm studs?
    Thanks


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    #2
    listermint
    Registered Users Posts: 33,687 ✭✭✭✭listermint


    How or why would you do this....


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    #3
    johnnyboy08
    Registered Users Posts: 149 ✭✭johnnyboy08


    listermint wrote: »
    How or why would you do this....
    Easily done, there's a 380mm gap between the studs so fillable with any thickness of PIR. Question is should it be done? You could potentially for example put 150mm PIR between 100mm studs and batten out the studs so they're flush with the PIR surface for restraining battens or to run more insulation perpendicularly to PIR.


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    #4
    listermint
    Registered Users Posts: 33,687 ✭✭✭✭listermint


    johnnyboy08 wrote: »
    Easily done, there's a 380mm gap between the studs so fillable with any thickness of PIR. Question is should it be done? You could potentially for example put 150mm PIR between 100mm studs and batten out the studs so they're flush with the PIR surface for restraining battens or to run more insulation perpendicularly to PIR.

    You didn't suggest making the studs wider in your opening post though...

    What exactly is your question and what are you hoping to achieve with the additional insulation? Where is the wall what's either side.


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    #5
    whizbang
    Registered Users Posts: 1,924 ✭✭✭whizbang


    When fitting PIR insulation between studs, theres a lot of difficulty in making it airtight.
    To mitigate this issue, you fit a continous sheet of 50mm over the whole lot.
    Hence the 150mm recommendation.

    If you really wanted to overdo it, fit 50mm front and back.!


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    #6
    Idbatterim
    Registered Users Posts: 17,841 ✭✭✭✭Idbatterim


    Is there an issue with screwing the pir board into the studs ? The board will be covered by timber cladding ... surely it saves a lot of time and the only downside is a minor loss of space ?


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    #7
    Lumen
    Registered Users Posts: 31,014 ✭✭✭✭Lumen


    whizbang wrote: »
    When fitting PIR insulation between studs, theres a lot of difficulty in making it airtight. To mitigate this issue, you fit a continous sheet of 50mm over the whole lot. Hence the 150mm recommendation.!
    I think in that scenario the extra layer of insulation is to combat cold bridging, not provide air tightness.

    You get air tightness by taping the joints (of a product which is air impermeable) or using a continuous sheet barrier (over a product which is air permeable).


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