Warm roof construction

Discussion in 'Roofing and Guttering' started by Sdfuk, 20 May 2017.

  1. Sdfuk

    Sdfuk

    Joined:
    27 Feb 2011
    Messages:
    45
    Thanks Received:
    1
    Location:
    Essex
    Country:
    United Kingdom
    Hi

    Instead of a vapour barrier over the decking is it ok to use foiled backed PIR instead and tape the joins?

    Cheers
    S
     
  2. Sponsored Links
  3. chappers

    chappers

    Joined:
    27 Aug 2004
    Messages:
    3,254
    Thanks Received:
    357
    Country:
    United Kingdom
    not entirely sure how you would tape the joints before laying the insulation. The VCL is to prevent vapour entering the insulation layer
     
  4. ^woody^

    ^woody^

    Joined:
    3 Sep 2006
    Messages:
    34,693
    Thanks Received:
    4,699
    Location:
    West Mids
    Country:
    United Kingdom
    The vapour check goes on the back of the plasterboard, not above the deck
     
  5. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    6,408
    Thanks Received:
    887
    Country:
    United Kingdom
    Usually it would go on the warm side of insulation that's more vapour permeable than it's insulating. And ideally no air movement between it and the insulation, but that's for other reasons.
     
  6. Sdfuk

    Sdfuk

    Joined:
    27 Feb 2011
    Messages:
    45
    Thanks Received:
    1
    Location:
    Essex
    Country:
    United Kingdom
    Thanks
     
  7. chappers

    chappers

    Joined:
    27 Aug 2004
    Messages:
    3,254
    Thanks Received:
    357
    Country:
    United Kingdom
    that's a bit old school now, the preferred place with modern VCLs is over the deck on a flatty.
    Would still put VCL under plasterboard on a cold unvented, breather membrane pitched roof with insulation at loft level.
     
  8. Sponsored Links
  9. ^woody^

    ^woody^

    Joined:
    3 Sep 2006
    Messages:
    34,693
    Thanks Received:
    4,699
    Location:
    West Mids
    Country:
    United Kingdom
    That makes no sense at all, and will be doing jack.
     
  10. chappers

    chappers

    Joined:
    27 Aug 2004
    Messages:
    3,254
    Thanks Received:
    357
    Country:
    United Kingdom
    does everything it's supposed to which is keeping vapour from penetrating the insulation layer, the issues of protecting at ceiling level nowadays are the amount of penetrations of the ceiling in modern construction.
     
  11. Sdfuk

    Sdfuk

    Joined:
    27 Feb 2011
    Messages:
    45
    Thanks Received:
    1
    Location:
    Essex
    Country:
    United Kingdom
    Initially building control wanted a VCL at ceiling level. The builder said this was impractical due to spot lights being fitted etc. They then agreed to use foiled PIR to act as a vapour barrier. The building control guy has been round twice to confirm this after I raised my concerns. All the literature I've read is to have a continuous VCL after boarding and before the insulation. I have 1200mm of insulation. 200mm runs vertically and then 1000mm runs horizontally. As far as I'm concerned warm air can still escape through the gaps between the insulation. I have seen examples where expanding foam is used to 1) glue the PIR to the boarding and 2) fills any gaps in the joints. The roof is on now and Time will tell I guess.

    Cheers
    S
     
  12. chappers

    chappers

    Joined:
    27 Aug 2004
    Messages:
    3,254
    Thanks Received:
    357
    Country:
    United Kingdom
    yep your reading is correct and your BCO isn't really fully up to speed, don't quite understand what you're saying about the arrangement of your insulation, but yes your concerns are correct, warm air could in deed escape between your insulation, but the reality is you will almost certainly be fine.
    I hope you insulated, in your rafter end voids too, letting cold air in there could cause condensation to form in your ceiling void
     
  13. Sdfuk

    Sdfuk

    Joined:
    27 Feb 2011
    Messages:
    45
    Thanks Received:
    1
    Location:
    Essex
    Country:
    United Kingdom
    Hi
    Yes, I've talked to the builder about putting insulation at the ends and he's doing that.

    Cheers
    S
     
  14. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
Loading...

Share This Page