Dormer window insulation

Discussion in 'Building' started by melross, 16 May 2018.

  1. melross

    melross

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    Hoping someone can give me some advice please. A builder has installed a dormer into our house which I need to finish internally. He has used OSB board with a timber frame supporting this inside. The timbers are 93mm deep and 43mm wide. I wish to put Celotex insulation boards between these timber members, do I need to put an insulation board as close as possible to the 93mm depth of the timber members or is advisable for example to use a 50mm deep insulation board pushing it flush between the members but retaining an air void of 43mm behind. I intend to then place insulated plasterboard over the top to eliminate cold bridging of the cross members. Can anyone advise. Thanks
     
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  3. ^woody^

    ^woody^

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    Fill it completely, flush against the OSB and leaving no gaps against the timber. Then a layer of 25mm or 10mm if space is tight or your insualted plasterboard across the internal face. Tape the celotex joints with foil tape.
     
  4. Ian H

    Ian H

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    I put 75mm between mine then 50mm over the top. Timber is the same size.

    The temperature is always constant but the PIR boards do nothing for sound. If I did it again I'd maybe try and get some sound proofing in the void.
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    DIYnot Local

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