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Flat roof problems...Watertight....but still leaking....

Discussion in 'Roofing and Guttering' started by k13wjd, 25 Mar 2020.

  1. k13wjd

    k13wjd

    Joined:
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    Location:
    West Lothian
    Country:
    United Kingdom
    Hey chaps. Hope you are all safe!

    I own a 1950's(ish) pre-fab concrete house, with a flat roof. Appears to be Jesperson block type

    Flat roof, last replaced around 15 years ago. During October, a leak developed, with water coming through the joint in the concrete panel ceiling/roof. I went up and had a look, Nothing major, no pooling or lifting of the felt etc. Spotted some cracks where the roof falls into the central downpipe. Temp patched with primer and flashing, then called out my friendly roofer to clean it all up, 1m2 torchon applied.

    Huge rain storm a week later - no leak. Nada. Nothing. waited a few weeks, replaced ceiling covering etc. No issues.

    January....during a nice try spell.....THE LEAK RETURNS. a few drips per hour.

    The leak has gone and come back many times, but does not appear to be an immediate leak. We had torrential rain for a week, and it didn't even drip once. Recently been having a spell of warm dry weather, and the leak is at its worse for the last month.

    Now, I have to assume the actual roof covering is waterproof.

    I'm not sure of the construction under the felt, but there is clearly going to be insulation/plyboard of some type.

    Is it safe to assume that the roof is indeed watertight, and the leak i have is residual water from the insulation being sodden/plyboard being sodden/rotten? The fact it is worse when it is sunny would suggest that - With the black( the silver paint has worn off) roof warming up, the moisture in the insulation venting off, and with nowhere to go, its pushing the remaining water into the cracks?

    Or is it my nextdoor neighbour who has a huge puddle on her roof? I think that there is a barrier, but haven't been able to get that checked.....
     
    Last edited: 26 Mar 2020
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  3. KenGMac

    KenGMac

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  4. k13wjd

    k13wjd

    Joined:
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    Location:
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    I have no idea how I came up with that. must have been a copy/paste.

    Its Jesperson concrete. The 5m's are steel framed, this is most certainly concrete, floors, walls and roof.
     
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    DIYnot Local

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