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Cold flat roof help

Discussion in 'Roofing and Guttering' started by Roystone, 22 Aug 2021.

  1. Roystone

    Roystone

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    We're in the middle of building a cold dormer (added a couple of posts about it) and wondered if

    a) Is a vapour control barrier is required (contractor says not) - there will be a house bathroom and an en-suite in the dormers.

    b) We want to put some 5mm or 10mm thick Acoustic / Soundproofing Resilient Tape between the lower layer of PIR (or VCL if we're having one) and soundbloc F plasterboard - to isolate some sound (like the noise of rain - appreciate we can't get rid of it - but lowering it a little will help) - Does this make sense?

    We had to go with soundbloc F as BCO required high fire rated plasterboard because of the closeness of neighbouring properties.

    The picture is an example - ours is two layers of OSB, GRP finish.

    upload_2021-8-22_17-15-55.png
     
  2. ^woody^

    ^woody^

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    All flat roofs require a vapour check layer, it just alters as to where it goes.

    Wet rooms certainly need it as there is increased moisture risk
     
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  4. Roystone

    Roystone

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    @woody, is the VCL not needed behind the plasterboard if using 25mm sheet of PIR on the underside of the joist (there will be 100mm Kingspan between the joists).
     
  5. ^woody^

    ^woody^

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    As per your other thread, a vapour check layer can be the PIR if it is foil faced and taped
     
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