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insulation above flat roof on 1930s house

Discussion in 'Roofing and Guttering' started by essex123456, 25 May 2021.

  1. essex123456

    essex123456

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    I have a draft from above a bay window, its an upper floor bay with a flat felt roof. I have striped the lath and plaster to reveal the wood. Can I just fill this with rock wool? or do I need ventilation ?

    I have looked on here but the posts I have found are for bays with tiles or ground floor with another bay above.

    Thanks
     
  2. Alastairreid

    Alastairreid

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    Better with rigid insulation, full filled hard against the deck...tape the joins with foil tape and install a vapour barrier...need to stop moisture from the room getting to the underside of the cold deck.
    Proper way is insulation on top of decking...warm roof.
     
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  4. essex123456

    essex123456

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    Thanks for the reply, would I be best half filling with rigid insulation to leave ventelation at the top like a cold roof construction? Just done a 29sqm warm roof on our extension my brains frazzled not sure why I hadn't thought of it being like a cold roof construction.
     
  5. Alastairreid

    Alastairreid

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    That would only work if you had ventilation in the gap you left, ie eave and wall abutment.
     
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  7. essex123456

    essex123456

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    Thanks for your help.
     
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