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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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    Dear Illustrious community,

    we're building our second, lower impact/lower cost strawbale cottage with intentions to build with reused materials where possible. We have window frames which we'll need to glaze. Please would anyone who knows offer some advice about ensuring appropriate U values for the technically challenged - I remember a paer given at an AECB conference on exactly this topic which was dizying in its technical complexity and. I think, biled down to the secret being in the care with which the window is set into the building…I guess you can have the windows glazed by glass companies but don't know how the U value is then calculated…..???
    Dizying, biled, paer…….apols for carless ness/typos!
    • CommentAuthorDarylP
    • CommentTimeJul 2nd 2015
    Carol, the std. for Part L compliance is the 'BFRC' window.
    See the centre-pane values attached below...
    Add on 'a little' for uPVC frames, and 'a little more' for timber frames.

    Good luck... :smile:
    Thank you DarylP. not sure whether this relates to particular "makes"? Still not quite clear how we calculate the whole window U value unless the glass has it's own U value regardless of the frame….?
    • CommentAuthorDarylP
    • CommentTimeJul 3rd 2015
    The problem you will have is the s/w that window mfr's use applies to their windows....
    Use the centre-pane U-values in the spreadsheet, then add on 33% for uPVC and 50% for timber frames. (bigger areas of glass compared to frame area will perform better)
    This will give you a ball park U-value.

    The centre-pane U-values are not related to a particular mfr of glazing.

    Good luck
    • CommentAuthorgravelld
    • CommentTimeJul 3rd 2015
    Sorry, why add more for timber? If timber allows for larger areas of glazing surely they should be lower if anything? Or does it assume insulated frames?
    • CommentAuthorDarylP
    • CommentTimeJul 3rd 2015
    ..because timber frame has a higher thermal conductivity than uPVC frame. The OP is fixed with the size of frames already?

    • CommentAuthorgravelld
    • CommentTimeJul 3rd 2015
    'Kay, thanks.
    DarylP, you said: ''..because timber frame has a higher thermal conductivity than uPVC frame. The OP is fixed with the size of frames already?''

    Does this apply to uPVC frames which are reinforced with galv steel, as I understand many to be? That sounds counter-intuitive.
    • CommentAuthorDarylP
    • CommentTimeJul 6th 2015

    Steel reinforcement has a significant effect, that is why I compared just uPVC and timber.
    This is why U-values for windows are produced by the window/profile mfr's themselves, as they know what goes into the frames. I am sure you 'could' buy the s/w or something similar, but would it be worth it for the OP....?

    Cheers :smile:
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