Insulation requirements new wall

Discussion in 'Building Regulations and Planning Permission' started by adwt2004, 13 Feb 2018.

  1. adwt2004

    adwt2004

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    If I build an extension wall to spec with 100mm cavity do building regs require that I insulate the existing wall too or is a wall that already exists allowed to stay as is? It's around 65mm cavity.

    I'm not exposing the cavity, just using wall starters on it with vertical dpc
     
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  3. ^woody^

    ^woody^

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    Yes if it is an external wall and forms part of the extended area.
     
  4. adwt2004

    adwt2004

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    Well it forms part of the current kitchen and is already there. I am then adding an extension to the end of it.
     
  5. Aeron Rees

    Aeron Rees

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    Hello

    It sounds like the wall between your new extension will simply become an internal wall. I therefore do not think that you are required to place insulation between that wall.

    Your are inevitably increasing the thermal performance of that part of the wall anyway, by building insulated walls around it as part of the extension.

    Probably best to ring your local building control officer to get an absolute response.
     
  6. garyo

    garyo

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    It sounds like he means the existing external side wall to me, which will be extended in length by the new extension wall.

    I've never upgraded this on the few extensions I've done and building control seem happy.

    You may find you dislike the step in thickness though so want to batten it out anyway.
     
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  8. adwt2004

    adwt2004

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    Yes that’s right. I will see what it looks like first before considering making it flat.

    Thanks guys, just wanted a good idea of what’s expected.
     
  9. lt8480

    lt8480

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    You could use a higher spec insulation and making the cavity slimmer. to match the wall thickness to existing.

    Or as others have said you could board the wall out (or even insulate on internal face then board).

    Insulating the existing walls is probably worth doing even if you don't have - its pretty cheap and the long term cost saving and general comfort in the property will be improved.
     
  10. adwt2004

    adwt2004

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    100mm full fill dritherm 32 has been specced for my build, is there something thinner which achieves the same heat loss rating? Cost is not an issue.
     
  11. lt8480

    lt8480

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    I've never specified Dritherm 32 but a quick search shows it has a thermal conductivity / lambda of 0.032 W/mK.

    Kingspan Kooltherm 106 is one of the current best on the market and gets down to 0.018 lambda - although think its thinnest availability is 80mm with a 10mm residual clear cavity so your wall is still 300mm overall - its generally used/designed to perform better in normal thickness (rather than thinning walls down). However for reference this gives a 0.17 overall wall u-value which is much better than the minimum required for building regs for extensions which is a max u-value 0.28.

    A quick look I think Xtratherm Thin-R might work at 40mm with a 25mm residual cavity (required). As long as your blockwork has a lambda of 0.14 or less (look for lightweight aerated blocks, which should be fine in this instance):

    http://www.xtratherm.com/wp-content/uploads/2012/06/Thin-R-XT-CW-4pp-web.pdf
     
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  12. lt8480

    lt8480

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    A quick check using this calculator (https://www.cba-blocks.org.uk/u-value-calculator/) confirms the following meets 0.28:

    Brick externally, 25mm residual cavity, 40mm Thin-R (0.022 lambda), Lightweight Block (0.14), plasterboard on dabs.

    If you want a fully filled 65mm cavity, with brick externally and again block internally (0.14) with plasterboard on dabs then you will need insulation with a lambda of 0.026.

    Xtratherm also do something for this (0.021 lambda, which should also work with any blockwork): http://www.xtratherm.com/applications/cavity-walls-full-fill
     
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  13. DIYnot Local

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