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Partially filled cavity wall with EWI = Thermal Looping

  • 23-10-2014 11:03am
    #1
    CPS84
    Registered Users Posts: 28 ✭


    I’ve come across this discussed before on these boards, but I’m trying to obtain more technical information on this type of Thermal Looping. Nearly all of the literature I’ve found online for Thermal Looping relates to normal traditional partially filled cavity walls where the insulation has been loosely fitted.

    However I want to get more of an understanding of how it occurs in cavity voids between insulation layers. If for example, say an existing house has a 300mm wall makeup comprising of 100mm external block, 40mm cavity, 60mm insulation, 100mm internal block. If EWI is applied this will result in thermal looping in the cavity.

    My question is what are the effects of this thermal looping? What is the science of it?

    Will the actual U-Value performance of the wall be considerably less than the calculated/ predicted U-Value because of this thermal looping and if so why?

    Will the air looping between the warm and cool air in the cavity void cause other issues i.e. condensation, mold etc?

    Cheers
    CPS84


Comments

  • #2
    BryanF
    Moderators, Home & Garden Moderators Posts: 10,140 Mod ✭✭✭✭BryanF


    If the cavity is not sealed then cold air can enter it, reducing the effectiveness of any insulation outside it.i fail to see how this can be measured in the field other than by testing the internal air-leakage to estimate general air change rates.
    I haven't any thermal looping studies to hand, but if you consider the above, what more is there to it?
    If you can Pump the cavity


  • #3
    galwaytt
    Registered Users Posts: 12,751 ✭✭✭✭galwaytt


    My understanding would be if there is a cavity, I suspect it would need ventilation. In which case I wonder if EWI does anything at all.

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  • #4
    MicktheMan
    Registered Users Posts: 2,823 ✭✭✭MicktheMan


    CPS84 wrote: »
    However I want to get more of an understanding of how it occurs in cavity voids between insulation layers. If for example, say an existing house has a 300mm wall makeup comprising of 100mm external block, 40mm cavity, 60mm insulation, 100mm internal block. If EWI is applied this will result in thermal looping in the cavity.

    My question is what are the effects of this thermal looping? What is the science of it?
    The science of it is that any material outside a ventilated air space should be ignored when calculating the u-value. This is why a detailed inspection of the cavity followed by pumping it is essential for ewi to be effective.
    BryanF wrote: »
    If the cavity is not sealed then cold air can enter it, reducing the effectiveness of any insulation outside it.i fail to see how this can be measured in the field other than by testing the internal air-leakage to estimate general air change rates.
    I haven't any thermal looping studies to hand, but if you consider the above, what more is there to it?

    An insitu approximate u-value can be determined but it requires steady state conditions on both sides of the wall over a decent period of time. This can then be compared to the designed / calculated u-value.

    Another consideration with ewi is to ensure that each insulation board is buttered at the edges to prevent thermal looping between the back of the ewi and the face of the external wall


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