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

Insulation behind uPVC cladding

Discussion in 'Building' started by djheath, 20 Sep 2021.

  1. djheath

    djheath

    Joined:
    25 Jul 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    My 70s house is part clad in uPVC shiplap. This is mounted to wooden batterns which are mounted to the breezeblock, and then internally this is plastered. I'd like to insulate behind the uPVC as the wall is facing north and north east and is very cold.

    Can I fix the celotex type insulation direct to the external breeze block wall, then the cladding over that, or do I need a vapour barrier or ventilation somewhere? To my knowlegde, the cold side will be the exterior of the celotex, directly behind the uPVC so any condensation will be there rather than close to the block work, so this method should be ok.

    Also, will I be able to remove the uPVC and refit it, or will it break/weaken etc. so that I'll have to fit new cladding.
    Thanks.
     
  2. Sponsored Links
  3. motorbiking

    motorbiking

    Joined:
    31 May 2016
    Messages:
    6,798
    Thanks Received:
    770
    Country:
    United Kingdom
    Do you like the UPVC? I have something similar on a house I am working on. I plan to replace the UPVC with external insulation and smooth render.

    e.g.
     
    Last edited: 20 Sep 2021
  4. djheath

    djheath

    Joined:
    25 Jul 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    It's not great, but I don't mind it really. Every house in the street has it, so it would look very odd if we had something different.
     
  5. motorbiking

    motorbiking

    Joined:
    31 May 2016
    Messages:
    6,798
    Thanks Received:
    770
    Country:
    United Kingdom
    • Thanks Thanks x 1
  6. djheath

    djheath

    Joined:
    25 Jul 2007
    Messages:
    94
    Thanks Received:
    0
    Country:
    United Kingdom
    If anyone has any other info about this it would be great, as I've been doing a lot of reading and still not got the perfect answer. Some cladding manufacturers say there should be an air gap behind the cladding of 25 mm, but my existing installation seems to be blockwork, 19mm battens, then cladding. I reckon I can fit some Kingspan K5 type insulation which is 20mm https://www.kingspan.com/gb/en-gb/p...ds/kooltherm/kooltherm-k5-external-wall-board between the battens. This seems to be external grade, so shouldn't need a vapour barrier, but it would mean the cladding is touching the insulation. What I don't know is if this matters? If condensation forms, wouldn't this be on the back of the cladding, or on the insulation face behind the cladding? Is this a problem?
     
  7. IT Minion

    IT Minion

    Joined:
    28 Jul 2018
    Messages:
    4,412
    Thanks Received:
    297
    Country:
    United Kingdom
    20mm of PIR isn't worth the trouble of pulling the cladding off.

    If you don't have an air gap then the battens won't be able to breathe, which isn't ideal. The PIR and UPVC cladding should be fine though.
     
  8. motorbiking

    motorbiking

    Joined:
    31 May 2016
    Messages:
    6,798
    Thanks Received:
    770
    Country:
    United Kingdom
    Is there any reason you can't have another 2-3cm when you reattach the cladding? 20mm will halve the U-value but its not going to be noticeable. 50mm is really the minimum you should be thinking about. It will bring the wall up to 1990s standards.
     
  9. Sponsored Links
Loading...

Share This Page