EWI Thickness

Discussion in 'Building' started by jassdhali, 27 Oct 2021.

  1. jassdhali

    jassdhali

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    Hi,

    Just looking for some advice as to which thickness of insulation would be best for external walls.
    Not to sure of the U values required but the house was built in the 1930's & as such has no cavity.
    I was looking at 100mm, but perhaps that is to extreme.
    Thanks in advance for any advice.

    Jass
     
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  3. noseall

    noseall

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    Thicker the better whilst being practical i.e. fixing methods and soffit overhang, opening reveals, sills etc.
    I'm sure the accepted regulations minimum has been upped to 75mm for solid walls (was 50mm).
     
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  4. wgt52

    wgt52

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    Just had my 1930's house done - 90mm insulation plus 5mm slim plus 5mm render.
    can feel the benefit - not switched the heating on.
     
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  5. ^woody^

    ^woody^

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    Fire proof insulation is all the rage nowadays.

    Sod the efficiency and global warming.
     
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  6. Godwasaplasterer

    Godwasaplasterer

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    biggest scam since cwi.
     
  7. phatboy

    phatboy

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    We have 90mm of graphite EPS on our house, plus 10mm of render (3 coats). We had to have 90mm for Building Regs (Jersey).

    It's changed our lives, the house is lovely and warm and for not a huge amount of money. And the mould is 99.9% gone.
     
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  9. noseall

    noseall

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    What insulation?
     
  10. jassdhali

    jassdhali

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    Thanks for your replies :).
    Was hoping in some way to hide the soil pipe at the side of the house with EWI - but that may not work, if I take the soffit overhang into consideration.
    So 75mm may be the way forward.
    Luckily no mechanical fixings on side of house.
    Now the only decision is whether to use EPS or Rockwool.. any thoughts :whistle:
    Thanks

    Jass
     
  11. wgt52

    wgt52

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    As EWI affects the sale valuation of your property may I suggest you contact a local EPC assessor for advice. Building Control or Council Planning Office may want an input.

    When (or if) you have the work done take lots of photo's before, during and after to show to any assessor.
     
  12. phatboy

    phatboy

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    Hiding the pipe would create a void in the insulation, and so a cold spot, so best avoided.

    If you get Building Regs involved, with 75mm you are going to be needing XPS insulation to meet regs (same stuff as Kingspan you would use internally), and it's a lot more expensive.
     
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  13. jeds

    jeds

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    You've really got three alternatives and which you choose depends what thickness of EWI you want and how much you want to spend. Poly foam is the cheapest but you will need 100mm to get a decent thermal value. XPS comes next and with that you might get away with 75mm, but it will be more expensive. The best option - and the most expensive - will be phenolic or PIR foam. With that, 50mm is approximately equivalent to 100mm of polystyrene board.

    PS; XPS is not the same as Kingspan insulation. XPS typically has a thermal conductivity of 0.033 ish. PIR foam is 0.018. Much better - thus much more expensive.
     
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  14. phatboy

    phatboy

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    Ah my bad on the XPS/phenolic!
     
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