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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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    • CommentAuthorandyman99
    • CommentTimeSep 25th 2018
     
    I appreciate there is lots on "breathability/permeability" on this forum and I have tried to read as much as I can, but I am needing to make decisions quite quickly and don't want to make a giant balls up. My extension build up is now most likely going to be single skin block work with EWI. Thicknesses and exact products still in discussion phase, but I am thinking of using Graphite EPS as the EWI product. On top of this will be an acrylic render. The renovations I've carried out to the existing house have been done with a view to allow breathability through the walls, should I be trying to do the same with this extension build up? Lets say the build up is

    Render - 150 EPS - 215 Block - Plaster (poss plaster board on battens).

    Will this be OK or do I need add a vapour control layer?

    Many thanks again

    Andy
  1.  
    I would use wet plaster rather than pb on battens (good air tightness where it belongs) and IMO no vcl needed
    •  
      CommentAuthorfostertom
    • CommentTimeSep 25th 2018
     
    Completely classic construction - no vapour barrier needed - indeed will be less robust with one.

    With 150 EPS outboard of it, the whole blockwork will be maintained at nearer to indoor than outdoor temp, well above averaged dewpoint.

    However, any transient condensation in it should be free to dry out inward as well as outward - hence no inboard VCL which would obstruct that.

    Put another way, an inboard VCL, unless superhumanly free of pinholes and hairlines forever, would act as a one-way pump sucking internal vapour into the wall under some transient conditions but not allowing it back out again inward.
    • CommentAuthortony
    • CommentTimeSep 25th 2018
     
    The dew point will be in the render , on it or in the last couple of mm of your EPS, the acrylic render should let it out OK, lime render would work better if you can handle it

    Well done with the good design
    • CommentAuthorandyman99
    • CommentTimeSep 26th 2018
     
    Thanks everyone for speedy help!
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