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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
    • CommentTimeFeb 16th 2021
    What ho one and all,

    The recent very cold spell brought up an issue that i have ignored every year, but thought I would run it past the minds on this forum.

    The poor quality photo shows some icicles hanging off the purlin. Whilst not a big deal, it does concern me where the water is coming from and whether that dampness can percolate into the purlin itself. The house is timber frame.

    The roof has a 1m overhang; the sofits and fascia are Upvc, the purlin is obviously wood and the soffit just butts up to it. The roof is 300mm deep of Posijoist and where it covers the house, it fully filled with Warmcel; obviously the section outside the shell has no insulation but is fully ventilated. The roof itself has sarking broads, covered with breather paper and cross batterns, so there is unlikely to be any water ingress from above.

    The first floor has regular rendered thermolite block with a 2 inch cavity. But the f/f timber section here, is battened out so the cavity is around 6 inches.

    Thee are some other timber clad parts to the house, but they are all battened to the timber frame with 2 inch timber, so the cavity is considerably smaller, and most importantly, these other area where the timber cladding goes up to the soffit, show no signs of water drainage.

    So is this condensation and if so, what can I do about it? Or, alternatively how can I allow the condensate to escape?
    • CommentAuthortony
    • CommentTimeFeb 16th 2021
    most likely condensation on the underside of the sarking - possibly exacerbated by airleakage from inside the house running down and leaking out at the purlin

    likely to be too intermittent to be a problem
    • CommentAuthorRex
    • CommentTimeFeb 16th 2021
    Thanks for your thoughts. Underside of the sarking; would it not be on the inside of the Upvc soffit?

    Since the sarking is PanelVent board, and although not fully water resistant, surely there would be some absorption rather than the amount that obviously is dropping to the soffit?

    You may be correct, but everything was pretty well sealed during the build and although not designed as a passive house, the air test was close to passive standards. The same sort of detailing was done everywhere but this is the only part where I get iciles and/or sometimes, obvious water dripping.
    • CommentAuthortony
    • CommentTimeFeb 16th 2021
    condensation goes for the coldest place so yea, back of soffit possible but i would expect dripping on the way down too
    • CommentAuthorRex
    • CommentTimeFeb 16th 2021
    I know you don't know the answer, but why this overhang and none of the other three similar sections of roof?
    • CommentAuthortony
    • CommentTimeFeb 16th 2021
    North facing?
    • CommentAuthorRex
    • CommentTimeFeb 17th 2021 edited
    No, south and the roof if more or less east, albeit protected by the neighbour's annoyingly tall leylandii.

    So winter mornings it does not get a lot of sun.

    I agree it is condensation, but why there and no-where else? I do wonder if it is due to the cavity behind the cladding, which is around 6" and hence thee is considerably more air.
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