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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.

PLEASE NOTE: A download link for Volume 1 will be sent to you by email and Volume 2 will be sent to you by post as a book.

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    Beginner here

    Bedrooms are ‘in the roof’ of our conversion. We have prefab attic trusses and 150 celotex between rafters. We want to put some insulation under the rafters. Head height is an issue so we are looking to minimise that loss.

    1) One decision is whether to use insulated plasterboard . Expensive material but less labour cost
    2) Or whether we should use separate PIR board with ordinary plasterboard over the top, which may be cheaper materials, but more labour cost as not fitting ourselves. What would you suggest to be a good method to fix these separate layers to the rafters ?

    Thanks for you help
    The joiners doing our roof lining were not keen on insulated plasterboard because the long screws don't fit in their auto feed drivers. They preferred to fix long horizontal battens along the slope below the rafters, fit insulation between, plasterboard screwed to the battens. We had unproductive conversation about thermal bridges or foam glue but eventually it came to the fitter doing the way they felt comfortable.
    • CommentAuthortony
    • CommentTimeDec 22nd 2017
    wastes an inch

    go for composite p board with insulation.
    If you use separate insulation and plasterboard you get much better air- and vapour-tightness. I try not to use composite boards any more. I do not agree with the manuf's who say a taped and joint-filled joint is all the VCL you need at the joint.
    • CommentAuthorcjard
    • CommentTimeDec 22nd 2017
    Will, you still have to fix insulation backed boards to the rafters with thermally conductive screws. I'm not sure the counterbatten vs long screws thermal bridging argument has significant legs..
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