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Best way to cut roof insulation around these little dormers...?

Discussion in 'Roofing and Guttering' started by Dannyboyski, 9 Sep 2020.

  1. Dannyboyski

    Dannyboyski

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    We're having a new roof on our renovation.

    building control are onboard etc. Replacement roof will have a u value of 0.16.

    I'm using superfoil sf40BB which is insulation foil and breather membrane in one.

    this should be a simple job but for my little dormers.

    Ive laid a couple of sheets on the roof with clamps for now, while I decide whether its best to cut or fold the bottom sheet where it goes up the little dormers...

    any advice please....?

    looks like a straight cut in the membrane at the top of each dormer then put a fill piece over the top of each dormer ridge.

    Many thanks

    Dan
     

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  2. ^woody^

    ^woody^

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    Is there a manufacturer's guide for cutting and sealing? I would suspect that it needs to be cut centrally to the valley, and then both pieces sealed with tape on both sides of the insulation. Alternatively cut a little longer than the centre line and lap the insulation on a central batten.

    Running insulation in this way over the valley means that the valley boards themselves need to be raised (replicated) above the insulation.
     
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  4. datarebal

    datarebal

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    cut tight at the top no gaps, tape all cut edges.tape all joins then a strip of underlay to weather the ridge as you suggest. avoid double thickness of the insulation content it will cause slight humps in the battens.
    A problem if you are having a slate roof
     
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  5. Dannyboyski

    Dannyboyski

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    Yes I suspected this. It is being slated.
     
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