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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    • CommentAuthordelprado
    • CommentTimeMar 6th 2018
     
    It is said time and again that external insulation is best, and I understand many of the reasons given.

    However, in a retrofit context isnt a significant benefit of IWI that you can entirely remove thermal bridging through the foundations, whereas with EWI you cannot?
    • CommentAuthortony
    • CommentTimeMar 6th 2018
     
    Leaves the thermal bridge at all internal walls and partitions, should go down into the ground to mitigate the thermal bridge of the below ground walls.
    • CommentAuthordelprado
    • CommentTimeMar 6th 2018
     
    I dont think it has to go below ground if it hits a solid insulated floor (like mine with geocell?)

    No meaningful internal thermal bridge if its a cavity built house at the internal wall partitions
  1.  
    One of the issues is what U value target you are aiming to hit, linked to the cooling of the walls and the interstitial condensation and timber decay risk.

    ''No meaningful internal thermal bridge if its a cavity built house at the internal wall partitions''
    Surely that is only the case if the cavity is insulated? Otherwise the inner skin, which is attached to the internal walls, is likely to be at a similar temp to that of the external skin.

    In your case, Delprado, what will the IWI 'hit'? The insulation, or a screed/board over that?
    • CommentAuthordelprado
    • CommentTimeMar 6th 2018
     
    Hi Nick

    Yeah sorry assuming cavity is insulated, which in my case it is, 70mm eps beads.

    I am putting an internal wall plate to load joists on, and am obviously being very careful with air tightness in that area (and everywhere).

    My original plan was adding 80mm of wood fibre board on the inside, but now I think I am going to do that and add another 60mm on the outside
    • CommentAuthorgravelld
    • CommentTimeMar 6th 2018 edited
     
    If you have gables (not a fully hipped roof) and a cold loft then the internal leaf gable is a TB.

    Then there's the windows...

    Posted By: delprado
    My original plan was adding 80mm of wood fibre board on the inside, but now I think I am going to do that and add another 60mm on the outside
    I know you're using wood fibre, but does that really give you a totally "free pass" wrt moisture? I'd worry if you weren't using something that breathable.

    Where's the AT layer?
    • CommentAuthordelprado
    • CommentTimeMar 11th 2018
     
    AT layer is on the inside, wet plaster, but I'd also make the outside the same too.

    Does anyone know that presumably that thermal bridge effect through foundations is less on internal walls than it in on the external ones?
    • CommentAuthorjfb
    • CommentTimeMar 11th 2018
     
    are you suggesting wood fibre IWI, cavity with 70mm EPS beads and then 60mm (eps?) EWI on the outer cavity?
    just trying to understand what you are saying because if that is what you are suggesting it don't make sense to me!
    • CommentAuthordelprado
    • CommentTimeMar 11th 2018
     
    not sure what is on the outside yet, but one option is a wet render which has eps in it, made by Baumit, called dp85, but yes my proposal is to have the build up you describe. The stuff in the cavity is already there
    • CommentAuthorjfb
    • CommentTimeMar 11th 2018
     
    Surely save yourself a lot of time/ money and just go for ewi
    • CommentAuthorgyrogear
    • CommentTimeMar 11th 2018 edited
     
    In renovations, IWI can = big-time disruption and also reduces your livable area.

    Not to mention negating potential effects of thermal mass...

    gg
    • CommentAuthordelprado
    • CommentTimeMar 11th 2018
     
    On masonry construction though using iwi is an easy way to get an airtight area - you wet parge behind it and chase into the insulation (in my case wood fibre), without worrying about penetrating air tight layer

    How does it negate potential effects of thermal mass?
  2.  
    Chase what into the insulation? Wiring? I'd rather not chase into it. It is in the less effective range of insulants anyway (but good to use for other reasons), so I'd rather not diminish it. You could either batten and pl'bd and use a service void, or surface mount. But maybe I am being too picky!

    ''How does it negate potential effects of thermal mass?''

    It isolates it, though it does have better decrement delay than Pu, for example.
    • CommentAuthordelprado
    • CommentTimeMar 11th 2018
     
    My proposed 80mm board internally would have a 20mm chase into it, from the ground, thats not very much.
    •  
      CommentAuthordjh
    • CommentTimeMar 11th 2018 edited
     
    Posted By: delpradoDoes anyone know that presumably that thermal bridge effect through foundations is less on internal walls than it in on the external ones?

    Yes, it's less but it's still a thermal bridge.
    •  
      CommentAuthordjh
    • CommentTimeMar 11th 2018
     
    Posted By: delpradoOn masonry construction though using iwi is an easy way to get an airtight area - you wet parge behind it and chase into the insulation (in my case wood fibre), without worrying about penetrating air tight layer

    No, that's a very good way to build in a condensation and mould problem. What you probably meant to say was that in your case where you have CWI outboard of the inner wythe and perhaps some EWI outboard of the outer wythe then it's OK. But it's best to be explicit about what you mean if you want sensible responses.
    • CommentAuthordelprado
    • CommentTimeMar 11th 2018
     
    djh, why do you say that? IWI has been used in thousands of properties using the woodfibre systems (the ones I know most about) for 30 years, without issue in the way described?
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