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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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    Hi All,

    Just looking at options for a 30m2 garden building/workshop.

    Decided against SIPs as I have quite a bit of PIR and timbers already. When it comes to the walls I want to explore my options rather than cutting PIR to fit between and over studwork as I have done elsewhere.

    With that said, would there be any foreseen issues with the following? Stud walls,OSB, then the full PIR boards before battening for cladding. So almost like a deconstructed SIP with no second layer of OSB. (This would also allow PIR to carry on down beyond outside of any exposed slab.) Would there be any reason for a membrane under battens if foiled boards are all taped up anyway?

    As the workshop will be running power tools, i then have the option to put soft insulation between studs for additional sound insulation, before VCL and internal wall. PIR may cut enough noise out anyway.

    Any thoughts on the above?
    • CommentAuthordereke
    • CommentTimeJan 23rd 2019
    I did something similar to this for my office.
    Timber frame, PIR glued to frame, tyvek, battens fixed at roof and floor, cladding.
    Seems to work OK.

    I'm thinking about using a slightly different build up for my next project
    Timber frame, OSB, Rockwool EWI, membrane, battens, cladding.
    • CommentTimeJan 23rd 2019
    The latter every time, for me. No VCL anywhere - let it breathe. Glue and screw or otherwise make all joints of the OSB into an airtight 'tea cosy'.
    • CommentAuthorgravelld
    • CommentTimeJan 23rd 2019
    What about a closed frame with twin or I studs and filling it with cellulose or EPS bead?

    E.g.. https://mbctimberframe.co.uk/passive-wall/
    Thanks for replies.

    I could go a brethable route but like I say, with the fact that many of the materials are on hand I need to keep to PIR. Is OSB3 that breathable anyway?

    So I guess what I am asking is, will the external application of a PIR envelope around the OSB be better or worse than between studs? It would remove need for PIR layer on inside of stud walls and be a much quicker install using full sheets. What purpose does the tyvek memnbrane dereke used have in this application?
    • CommentAuthordereke
    • CommentTimeJan 24th 2019
    > What purpose does the tyvek memnbrane dereke used have in this application?

    If any water gets past the cladding then it will just run down the tyvek. It is breathable I believe but I don't think that really does anything with the PIR behind it.
    Would the taped foil not be a durable enough back up barrier for any water that got past clading? There would be no horizontal joins so as membrane not needed for breathable properties I figured the foil would be suficient on the off chance water got through cladding.

    I guess the only othe risk is the consistancy of the over battening, i.e making sure that the PIR does not compress more in some areas than others when screwed tight, something SIPs would prevent. But then with sawn cladding I can't imagine it being too notcible.
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