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Insulating on top of the cavity closing block in roof?

  • 26-01-2021 2:52pm
    #1
    Cluedo Monopoly
    Registered Users, Registered Users 2 Posts: 9,627 ✭✭✭


    I probably will not explain this very well. I am putting more rockwool insulation into the attic floor. There is already 150mm in between the joists but it only runs out to the edge of the inner block wall.

    At the eaves I see the block that closes the cavity and running on top of that block is a long wooden beam (is this the wall plate?) which I guess is the platform for the rafters.

    Should I insulate above the 'wall plate' and to the other side of the 'closing block' so that I am essentially covering the outer block wall too? This would mean the insulation is almost touching the soffit. Or is it dangerous to cover the timber? Obviously I will ensure the soffit vents are uncovered. The question is how far out into the eaves should my insulation go?

    What are they doing in the Hyacinth House?



Comments

  • #2
    Ginger83
    Registered Users Posts: 3,553 ✭✭✭Ginger83


    Cluedo Monopoly wrote: »
    I probably will not explain this very well. I am putting more rockwool insulation into the attic floor. There is already 150mm in between the joists but it only runs out to the edge of the inner block wall.

    At the eaves I see the block that closes the cavity and running on top of that block is a long wooden beam (is this the wall plate?) which I guess is the platform for the rafters.

    Should I insulate above the 'wall plate' and to the other side of the 'closing block' so that I am essentially covering the outer block wall too? This would mean the insulation is almost touching the soffit. Or is it dangerous to cover the timber? Obviously I will ensure the soffit vents are uncovered. The question is how far out into the eaves should my insulation go?

    Does this help?
    https://www.xtratherm.ie/app/uploads/2020/09/XT-XWP-1.09-1.10-Eaves-Rev-4.pdf


  • #3
    Cluedo Monopoly
    Registered Users, Registered Users 2 Posts: 9,627 ✭✭✭Cluedo Monopoly


    Ginger83 wrote: »
    Does this help?
    https://www.xtratherm.ie/app/uploads/2020/09/XT-XWP-1.09-1.10-Eaves-Rev-4.pdf

    Yes it does. That cavity doesn't seem to have a closing block though.
    I never realised you could have the insulation touching the eaves.
    It looks as though I should cover the outer leaf and stuff the insulation right up to the rafters in the eaves. Thanks.

    What are they doing in the Hyacinth House?



  • #4
    headtheball14
    Registered Users Posts: 234 ✭✭headtheball14


    That looks very tight to eaves in the diagram. I thought you had to leave a decent gap and pull back from the edge so the ventilation is unimpeded.


  • #5
    Biker1
    Registered Users, Registered Users 2 Posts: 395 ✭✭Biker1


    headtheball14 wrote: »
    That looks very tight to eaves in the diagram. I thought you had to leave a decent gap and pull back from the edge so the ventilation is unimpeded.

    That diagram shows counter battens and a ventilation tray. Under these conditions the insulation can go out further than normally would be the case.


  • #6
    MicktheMan
    Registered Users, Registered Users 2 Posts: 2,856 ✭✭✭MicktheMan


    Cluedo Monopoly wrote: »
    I probably will not explain this very well. I am putting more rockwool insulation into the attic floor. There is already 150mm in between the joists but it only runs out to the edge of the inner block wall.

    At the eaves I see the block that closes the cavity and running on top of that block is a long wooden beam (is this the wall plate?) which I guess is the platform for the rafters.

    Should I insulate above the 'wall plate' and to the other side of the 'closing block' so that I am essentially covering the outer block wall too? This would mean the insulation is almost touching the soffit. Or is it dangerous to cover the timber? Obviously I will ensure the soffit vents are uncovered. The question is how far out into the eaves should my insulation go?

    Nothwithstanding the ventilation question, unless you are also going to externally insulate the wall there is no point doing this. This cavity closing block as described is ultimately a thermal bridge and therefore putting insulation on top only is as useful as an astray on a motorbike.


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