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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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Housing - Renovation: Between rafter ventilation with PIR roof insulation

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    • CommentAuthorblubb
    • CommentTimeNov 17th 2023
     
    I am planning to create a warm loft by adding PIR insulation between the rafters. To give the rafters enough ventilation, I am planning to install 70mm PIR boards, leaving a 30mm between the PIR boards and the sarking felt. The problem is that the installed sarking felt is not permeable to air or humidity. Hence I was thinking of installing felt lap vents between each pair of rafters, one on the bottom and one on the top. My worry is if this will give enough ventilation -- I am worried about the rafters rotting away.

    Related question: I was thinking of installing another 70mm PIR board on top of the rafters. Is that a good idea in terms of ventilation/condensation/dew point?

    Many thanks!
    •  
      CommentAuthordjh
    • CommentTimeNov 18th 2023
     
    Posted By: blubbon top of the rafters
    Do you mean on top or underneath?
    • CommentAuthortony
    • CommentTimeNov 18th 2023
     
    Why not insulate at ceiling level?
    •  
      CommentAuthordjh
    • CommentTimeNov 19th 2023
     
    Posted By: blubbI am planning to create a warm loft

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