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Insulating flat roof on extension

Discussion in 'Roofing and Guttering' started by TargetDummy, 24 Apr 2019.

  1. TargetDummy

    TargetDummy

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    All, I'm currently working on my daughters house making it fit to live in. It has a 2 storey flat roof extension at the rear which was in a pretty poor state and leaking:


    On the inside, there was evidence of moisture leaking in from outside and possibly more due to condensation as there was no insulation between the plasterboard ceiling and roof deck:


    We've now repaired the roof and it's water tight:


    On the inside, the timbers are now fully dried out and mould free.

    I have a load of 100mm Celotex left over from a previous project and I wanted to check what steps I should take before putting up the new ceiling. My thinking is that I put the Celotex between the joists, pushing it tight up to the deck, add a vapour barrier and then cover with plasterboard.

    Does this sound right? If the vapour barrier is required, what should I use?

    Advice welcome, thanks.
     
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  3. You can use Visqueen 1000 sheet as a vapour barrier ,or use foil backed plasterboard as the ceiling.
     
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  4. TargetDummy

    TargetDummy

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    Thanks Leofric, I'm sure I've got some visqueen 1000 somewhere, so I'll use that.
     
  5. It has to be a continuous membrane of course.
     
  6. TargetDummy

    TargetDummy

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    Absolutely. I've got an unused 4m x 4m sheet which is plenty big enough
     
  7. Londoner2

    Londoner2

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    Should have made into into a warm roof and used grp as covering.
     
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