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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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    • CommentAuthorRex
    • CommentTimeAug 17th 2019
    What ho one and all,

    My timber frame house generally has a thermolite exterior with Alumasc thin render applied. However, there are a few areas where the render is applied to cement particle board.

    Two of these areas are below the kitchen and office windows, the board is only around 1.3m wide and 700 mm high. The board was on 2x2 battens and the board touched the outer brick base, so the cavity from the ring beam, was clear up to the window itself. For unknown reasons, this area was never ventilated; this may or may not have been the problem.

    The problem was the thin render, 'bubbling' near where the render board was in contact with the blockwork and possibly caused by poor detailing in that area.

    An Alumasc approved contractor is doing the repair, new battens, ventilated strip at the base and the top will be open (previously sealed) to allow air flow; it will be covered by the window sill.

    There will be a 20mm gap at the base where the boards sits in a ventilated strip to allow air flow, but this will be apparently be 'open' to the cavity, allowing all kinds of creepy crawlers to gain access.

    My question relates to what happens below the ventilated board support? Is the cavity usually closed or should it be open but have some kind of bug restraint mesh?

    Trust my description is clear and thanks,

    • CommentTimeAug 17th 2019
    Sorry, not clear to me; hopefully it is to others. The bits that confuse me are:
    - the 'blockwork'; where is this?
    - if the ventilated strip is at the base, presumably on the brick plinth, how is there below?
    - why is the ventilated strip open, shouldn't it have an insect mesh?
    - Thermolite appears to be clothing???

    Perhaps a diagram or picture would help.
    • CommentAuthorRex
    • CommentTimeSep 6th 2019 edited
    What ho one and all,

    My question was based upon ;what was thought to be the construction and until the board was removed, only guessing.

    Once the render board was removed, it was obvious that during the original build, there was a 'lack of dampproof' detailing by the original installer. Fortunately, the dampness had not encroached on the timber frame itself.

    By changing the 'detailing' of the construction at the lower edge, there is now ventilation between the renderboard base where it was touching the outer brickwork, and the sill below the window. As a result, the renderboard is no longer in contact with the outer brickwork. And all supports for the replaced renderboard have been isolated with DPM.

    So I think everything is good.
      _RAB4496 (Medium).jpg
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