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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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    Recommended washer to hold PIR to timber?

    I have seen ones specific for concrete and masonry but nothing for timber specifically? Is it just the screws that are different? Something like this okay:

    I only need say two washers per board to hold my PIR boards in place while I screw the PB on top of it. I could just use screws and no washers but I have found it rips through the foil an doesn't give a firm hold...

    • CommentAuthortony
    • CommentTimeNov 26th 2017
    Ordered. Thanks Tony

    Would you use 2 per sheet and allow the PB screws to take the main weight combined? Or use quite a few per board?

    • CommentAuthortony
    • CommentTimeNov 27th 2017
    4 or 6 per board, have done it with Just careful screws
    • CommentAuthorslow
    • CommentTimeMar 14th 2018
    Hi Victorianeco & Tony

    Could I ask, would you consider using these washers to fix insulation in a warm flat roof build-up? I've got an osb deck, then 150mm PIR insulation, then a 2nd osb deck. I'm planning at the moment to use 220mm Insofast twist fixings, as I'm thinking these washers would sit too proud, and sow through the epdm or felt (that decision's not been made yet either).

    Many thanks for any tips from your eperiences
    • CommentAuthorTimSmall
    • CommentTimeMar 15th 2018 edited
    Timber at the top of the build-up you describe (the second OSB deck) won't survive very long due to high winter/spring moisture content (OSB lower down below in the build-up is fine).

    I'd fix the insulation to a single OSB deck (I've used Soudatherm Roof 250, and other similar fixing foams), and then bond the EPDM or felt directly to the insulation.

    Bonding the insulation is several times stronger than mechanically fixing it (but you could mechanically fix if you prefer).

    You can often pick up "non-foil" Kingspan PIR boards (the type with fibreglass "tissue" or grey/dimpled fibreglass surface) which are intended for this type of build-up cheaply from "Seconds and Co" - which is what I've usually been able to use (but make sure you get PIR, not the pink phenolic "kooltherm" etc. boards).
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