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Suspending ceiling from flat roof joists

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  • 03-08-2020 9:55pm
    #1
    briaineo
    Registered Users Posts: 152 ✭✭


    Hi

    Could any advise which is the normal way to hang a suspended ceiling from flat roof joists?

    We will have a Siga marjex airtight membrane on the underside of the joists and checked with siga rep and he said whether you drop it with timber or metal the same process applies to taping up the hanging angle.

    Is the method similar to underside of precast slab? Or is a different type of hanger / hanging angle used?

    Would I be right in saying there would be too much expansion and contraction in the roof to fix the hanging angle to the side of the joists? (Warm roof build up)

    I was thinking that using wire to hang from an eye screwed into underside of joist would make sealing the holes the penetrate the membrane easier to patch.

    Or a “U” shaped bracket fixed to the joist that would include an eye

    Will double check any suggestions with the engineer For structural approval.

    I have been googling to find a possible solution to run by the engineer but have not been able to find anything

    Thanks


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  • Options
    #2
    Dudda
    Registered Users Posts: 1,541 ✭✭✭Dudda


    My understanding is if you need it fire rated you need to fix into the side of the timber joists for strength and can't fix into the underside. You won't get anyone to sign off on it.

    If it isn't fire rated you could consider fixing into the underside of the joists similar to the way you fix to the underside of a concrete slab or hollowcore but using longer stronger screws.

    https://www.gyproc.ie/sites/default/files/CasoLine%20MF_2.pdf

    Gyproc who make or sell the MF suspended ceiling which I think everyone uses have a technical department you can ring. 1800 744480
    Ask for their technical department and they'll help you.

    How big a void in the suspended ceiling do you have? If it's only 100mm or less just fit timbers at 90 degrees to the joists and the plasterboard to that.


  • Options
    #3
    briaineo
    Registered Users Posts: 152 ✭✭briaineo


    Dudda wrote: »
    My understanding is if you need it fire rated you need to fix into the side of the timber joists for strength and can't fix into the underside. You won't get anyone to sign off on it.

    If it isn't fire rated you could consider fixing into the underside of the joists similar to the way you fix to the underside of a concrete slab or hollowcore but using longer stronger screws.

    https://www.gyproc.ie/sites/default/files/CasoLine%20MF_2.pdf

    Gyproc who make or sell the MF suspended ceiling which I think everyone uses have a technical department you can ring. 1800 744480
    Ask for their technical department and they'll help you.

    How big a void in the suspended ceiling do you have? If it's only 100mm or less just fit timbers at 90 degrees to the joists and the plasterboard to that.


    Hi Dudda

    Thanks for the reply.

    Ceiling drops more than 100mm at certain points as it follows the slope of the roof (long roof at 15m)

    The engineer said it would be alright to use these fixed into the underside of the joists with wire attached:

    https://www.ceilingtiles.ie/en/ceiling%20fixings/eye-anchors?search=Eye&description=true

    I’d imagine a similar type fixing attached to the side of joist would be better.

    I’ll look into the acoustic fixings mentioned in the pdf link you attached

    Thanks


  • Options
    #4
    mfceiling
    Registered Users Posts: 12,774 ✭✭✭✭mfceiling


    Those fixings you show are for "grid and tile" ceilings like you would see in shops etc. The wire is tied to them and also to the main runners which run underneath that.

    If it's a plasterboard ceiling then they are no use as you need a rigid hanger to screw to the main bar that the runners underneath that fix to.

    Fclauson used to post here and if I remember correctly he had a similar situation to yours. I installed an MF ceiling in his house and he *again I'm trying to remember* put a blob of sealant over the head of every screw in the rigid hangers.

    I've never seen or heard issue from any architect/engineer on any job about fixing the hangers straight to the underside of timber joists. The acoustic hangers you mentioned I've only ever used twice. They have a rubber grommet to stop the noise transfer from the floor above. Not sure on their effectiveness.


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