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Help - Floored Attic - Cracks on Ceiling and where Ceiling meets Wall?

  • 14-12-2021 5:56pm
    Registered Users Posts: 2,391 ✭✭✭ FGR

    Hi all,

    I hope this is the correct forum, apologies if not ! I hope you can help.

    We bought a new build house (3 bed semi detached) and, during construction, ensured that the appropriate strengthened trusses were put in to allow for a full attic conversion in the future. The builder installed those and left the attic with an access door and nothing up there bar insulation.

    A few months back we got the builder back whose carpenters floored the attic with timber boards. I don't know what type of timber but they're the kind that I was told could have laminate put on top of them when I do go about to getting the full conversion done with walls, ceiling etc. From what I can see the carpenters compressed the insulation down to allow them to screw the boards onto the joists. We put up a few bits such as suitcases and the Christmas decorations etc. Nothing that to me was heavy and left it be.

    Anyway onto my question - a week or two after this big cracks started forming on the ceiling - we have a good few which run opposite to the joists upstairs but the worst ones are where the ceiling meets the walls where they continue on from the back of the house to the front, through the rooms as if there were no partitions.

    Is this a result of the insulation being compressed down, the joists being screwed in, the weight of us being up there walking around or all of it? Someone suggested to me it could be the huge temperature difference between the attic and the downstairs as the houses are A rated which makes the joists expand/contract much more.

    If so I hope someone can help as those cracks are ghastly. The builder filled some of the cracks but they came back within days - despite no one being in the attic. They're looking into it but I haven't been given a concrete answer.

    How can this be fixed? Do I need to take up the flooring and remove the compressed insulation? Hopefully in a way where the problem won't be recurring.

    Thanks all - hoping you can help :)


  • Moderators, Social & Fun Moderators, Society & Culture Moderators Posts: 25,729 Mod ✭✭✭✭ looksee

    Look, I am no builder, but even I know that compressing insulation renders it pretty much useless, and what is the point in insulating between two habitable (even if one is not yet habited) areas? The insulation should have gone under the roof.

  • Registered Users Posts: 2,387 ✭✭✭ standardg60

    I've no problem with the insulation being left in situ but i'm curious to know what size the 'strengthened trusses' are. The joists should be 9inch x 2inch for a proper conversion, in which case the insulation shouldn't need to be compressed.

    It sounds like the ceiling is cracking along the plasterboard joins due to movement of the joists.

  • Registered Users Posts: 3,367 ✭✭✭ 10-10-20

    I'm not structural engineer, but... You'd also need to look at how's the first-floor is supported.

    We had cracking at the ceiling level on internal walls in our house and it was caused by settling of the partitions as the wood in the 1st floor joists (and probably everywhere else) shrunk over the first years. The partitions have now been shimmed at the bottom to support them and this has prevented the ceiling plasterboard from being pulled downwards causing the parallel cracking.

    I'm not saying that this is your issue, but I'm adding it in to help. :)

  • Registered Users Posts: 32 docst

    Google 'Truss uplift'

  • Moderators, Home & Garden Moderators Posts: 10,101 Mod ✭✭✭✭ BryanF

    Op we can’t offer structural advice. Get a carpenter that’s used to doing this type of work to take a look, if your altering the roof structure, or if ceiling joists spans are excessive they should recommend a structural engineer.

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