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Thermal looping in gables

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  • 27-11-2022 7:16pm
    #1
    Registered Users Posts: 2,585 ✭✭✭


    Hi all,

    In my diagram A, I show what I think is a rather typical gable detail in Ireland in a semi-cavity build, based on UK literature. In situations where PIR/ EPS boards have been used, there is a tendency for drips of mortar to prevent a snug fit, creating a unwanted void leading to thermal looping, so in theory, is scenario B common in Ireland? In such a case, is it worthwhile parging the attic gable at point C to prevent infiltration into the unintended cavity?


    Also, how far is the cavity insulation taken above attic insulation in Irish new builds? It is 200 mm in this UK design.



Comments

  • Registered Users Posts: 2,827 ✭✭✭MicktheMan


    Imo, no there is little point in parging the attic gable because there will be ample other gaps between the boards themselves to allows air flow. This is the number one disadvantage of rigid board cavity insulation (fine on paper but rather difficult to execute on site).

    IMO, in order to kill the thermal bridge above ceiling level on the gable wall, the cavity insulation should be taken 1000mm above the ceiling level in addition to insulation on the inner leaf in the attic to the same level.

    As an aside, that wall detail in your example has a much larger heat loss issue than the thermal looping mentioned. Because of the dabbed on plasterboard, it is lacking an air tight barrier and therefore convection heat loss will dwarf any thermal looping losses.



  • Registered Users Posts: 39,138 ✭✭✭✭Mellor


    Thermal looping is the cavity is a major issue with rigid insulation. I don’t see on treating the inner face of the attic helps.

    Insulation should go as high as possible in the cavity imo. Ideal inner face too.



  • Registered Users Posts: 2,585 ✭✭✭Yellow_Fern


    Thanks for the feedback



  • Moderators, Home & Garden Moderators, Science, Health & Environment Moderators Posts: 17,786 Mod ✭✭✭✭DOCARCH


    'Also, how far is the cavity insulation taken above attic insulation in Irish new builds? It is 200 mm in this UK design.'

    My understanding is 600mm (above top of insulation to attic/over ceiling). Not sure where I got that from, but that's what I allow for.



  • Moderators, Home & Garden Moderators, Science, Health & Environment Moderators Posts: 17,786 Mod ✭✭✭✭DOCARCH


    Curiosity got the better of me! There is an Irish ACD.

    Indicates insulation to cavity carried up min. 1000mm above ceiling level. 



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  • Registered Users Posts: 2,585 ✭✭✭Yellow_Fern


    Brilliant, thanks.

    In this build, the gable at attic level had some big gaps in the pointing so you could even see the unwanted void between the PIR and the inner face.

    That ACD shows the insulation being packed to higher than normal level on the inner side. I think to 45cm. At the least I can implement this with the fibreglass. Not sure if it would stay in place though



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