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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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    • CommentAuthorRex
    • CommentTimeMar 2nd 2018
    What ho one and all,

    My house has a large roof overhang of around one meter. The roof is around 30cm deep and in the living areas, is fully insulated. The overhang has no insulation but is ventilated, top and bottom. The bargeboard is one of those horrible uPVC boards but it serves the purpose of not needing painting; the soffit is again, the horrible 'plank' look-alike uPVC which only occasionally needs a wipe. It is pinned to the rafters which are all Posi-Joist. So effectually, the entire overhand is an empty space.

    Today, while doing a wander around, I noticed some icicles hanging from the purlin (see photo) and it concerns me somewhat. I know that tiles are all OK so there can be no leaking from above, so where is the water coming from? Presumably condensation?

    This is the only section of roof where there are icicles.

    The only reason I can think it is happening is as follows. Most of my timber frame house is externally block and render so there is a 2" air gap which does ventilate into the empty overhang roof space. However where these icicles are, the wall is cedar board, and to build out to the depth of the ground floor block, we had to have a 6" gap. This side is south facing and the cedar probably warms faster than the white render. Is it likely this larger volume of air (warm? air) could be condensation on the inside of the soffit.

    If so, any ideas what I could do to resolve the issue?

    Thanks and toodle pip

      Icicle (Small).jpg
    • CommentAuthortony
    • CommentTimeMar 2nd 2018
    Don’t worry rare event
    • CommentAuthorRex
    • CommentTimeMar 2nd 2018
    Not so concerned about the icicle as such, more the fact that water is inside the space and will be blocked by the purlin. Don't recall if the purlin is painted inside, but I assume that water running to it is not the best idea.
    • CommentAuthortony
    • CommentTimeMar 2nd 2018
    Does it drip when it rains heavily?
    • CommentAuthorRex
    • CommentTimeMar 3rd 2018
    Have not noticed. I have noticed some very occasional water marks on the purlin but never an icicle in this position.

    Of course, it is better that it is dripping out rather than being trapped inside. Am wondering if some additional ventilation holes near the high point of the roof would assist with evaporation?
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