1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Cavity wall insulaation for new extension

Discussion in 'Building' started by Zehroni, 23 Jun 2019.

  1. Zehroni

    Zehroni

    Joined:
    25 Nov 2005
    Messages:
    275
    Thanks Received:
    0
    Country:
    United Kingdom
    the cavity of the walls on my new extension is 100mm,
    I have been looking for 95 or 90 mm celotex broads but unable to find on ebay. but there are plenty of 50mm. I appreciate help with the following :-

    what is the best cavity wall insulation ?
    is 50mm celotex is equivalent to 100mm knauf slabs
     
  2. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    5,609
    Thanks Received:
    750
    Country:
    United Kingdom
    you can't use 100mm celotex in a 100mm cavity, you need 50mm space on the cold side as standard. Or minimum 25mm at a push. You can use wool slabs and full fill though which would be the equivalent.
     
    • Thanks Thanks x 1
  3. Zehroni

    Zehroni

    Joined:
    25 Nov 2005
    Messages:
    275
    Thanks Received:
    0
    Country:
    United Kingdom
    is there any reason why I can not use 100mm celotex?
     
  4. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    5,609
    Thanks Received:
    750
    Country:
    United Kingdom
    the simple reason is because it's not approved for use in that way bt the manufacturer.
    The real reason I assume is both because celotex needs to be kept dry, and water could track across any joints to the inside leaf. The outer leaf of the caity needs to be able to drain, as it can get water penetration and possibly even condensation.
     
    • Thanks Thanks x 1
  5. ^woody^

    ^woody^

    Joined:
    3 Sep 2006
    Messages:
    26,031
    Thanks Received:
    3,196
    Location:
    West Mids
    Country:
    United Kingdom
    Ste you working to plans or just yoloing?
     
  6. stuart45

    stuart45

    Joined:
    13 Sep 2008
    Messages:
    2,797
    Thanks Received:
    370
    Location:
    Somerset
    Country:
    United Kingdom
    • Thanks Thanks x 1
  7. Leofric

    Leofric

    Joined:
    9 Nov 2018
    Messages:
    1,069
    Thanks Received:
    89
    Country:
    United Kingdom
    If you look at the websites of insulation companies they have technical data sheets giving their recommended types of insulation and 'U' values for different cavity wall situations. Your building regs application should specify the insulation required for your new extension.
     
  8. noseall

    noseall

    Joined:
    2 Feb 2006
    Messages:
    33,967
    Thanks Received:
    2,137
    Location:
    Staffordshire
    Country:
    United Kingdom
    Yes, every bricky will run a mile faced with having to use full fill rigid stuff. Bonkers.
     
    • Like Like x 1
  9. stuart45

    stuart45

    Joined:
    13 Sep 2008
    Messages:
    2,797
    Thanks Received:
    370
    Location:
    Somerset
    Country:
    United Kingdom
    Agree with that, although it's quite popular round here on Random rubble stonework of different thicknesses as it saves using a backing wall.
     
    • Like Like x 1
Loading...

Share This Page