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Insulated plasterboard up to hollow core ceiling or not?

  • 30-06-2021 11:53pm
    #1
    Registered Users Posts: 15 PC00123424


    Hi All,

    Am at stage house build now when plasterboard is about to be put on the walls after a sand cement air tightness layer has been done. There will be a 150mm suspended ceiling drop from the hollow core.

    It seems that the trades involved are happy now to have the suspended ceiling put in at this stage and then insulated plasterboard will be put on the external walls, or this is the plan now anyway.

    I was just wondering if it would be better to install the insulated plasterboard before the suspended ceiling goes in, so it runs all the way up to the hollow core? The way it's being planned at the moment, there will obviously be a 150mm strip around the house above the suspended ceiling level which will not have this internal insulation from the insulation backed plasterboard.

    Thanks.


Comments

  • Registered Users Posts: 252 ✭✭ Biker1


    PC00123424 wrote: »
    Hi All,

    Am at stage house build now when plasterboard is about to be put on the walls after a sand cement air tightness layer has been done. There will be a 150mm suspended ceiling drop from the hollow core.

    It seems that the trades involved are happy now to have the suspended ceiling put in at this stage and then insulated plasterboard will be put on the external walls, or this is the plan now anyway.

    I was just wondering if it would be better to install the insulated plasterboard before the suspended ceiling goes in, so it runs all the way up to the hollow core? The way it's being planned at the moment, there will obviously be a 150mm strip around the house above the suspended ceiling level which will not have this internal insulation from the insulation backed plasterboard.

    Thanks.

    I would have assumed your engineer whoever done your Part L would have highlighted that the slabs must go up to the hollowcore.


  • Registered Users Posts: 10,926 ✭✭✭✭ Calahonda52


    Biker1 wrote: »
    I would have assumed your engineer whoever done your Part L would have highlighted that the slabs must go up to the hollowcore.

    I agree 100% with the detail, is it specified in Part L as a compliance requirement, just curious and too lazy to look :)


  • Registered Users Posts: 252 ✭✭ Biker1


    I agree 100% with the detail, is it specified in Part L as a compliance requirement, just curious and too lazy to look :)

    No specific mention in Part L. I guess they cannot cover all scenarios and just provide the basics.


  • Registered Users Posts: 15 PC00123424


    Thanks for this. The engineer has advised nothing about this specifically, I'll talk to him.

    I also can't see it in Part L. But you are advising that this definitely should be done?

    The trade installing the suspended ceiling has said he's never seen it done or heard about it in his 20 years of work.


  • Registered Users Posts: 525 ✭✭✭ Fine Cheers


    So you are talking about running the wall slabs up 150mm further to meet underside of slab. Very surprised to hear from your ceiling guy that this is not the norm but as already mentioned I would insist on it. I trust you have cavity insulation also ?


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  • Registered Users Posts: 15 PC00123424


    Yes there is cavity insulation also.

    Do you know of any documentation I can see online which shows this recommended method, running the slabs all the way up to the hollow core?


  • Registered Users Posts: 30,654 ✭✭✭✭ listermint


    It makes no sense if there is 150 mm of block that can wick cold from above into this suspended space to leave that uninsulated. It will just conduct the cold into that area making the gap cooler than you'd want it


  • Registered Users Posts: 525 ✭✭✭ Fine Cheers


    Your certifying engineer will advise and will probably say that it is not required to comply.
    Are your finished ceiling heights the standard 8 foot or 2.4m ?
    Just wondering if it is not usually done for convenience or cost as the insulated plaster board sheets are probably 8' x 4' ?
    I assume the insulated board has been specified by the engineer and is needed to provide the relevant u value.
    To be honest, I would just to do it because it can be done and is a better detail.
    Are you skimming the boards or tape and joint ? A compromise might be to continue the board up, then put in the ceiling so the the 150mm doesn't need to be plastered but you are getting the insulation benefit.

    As a matter of interest, why the 150mm void - presume for services etc. Do you provide access hatches for maintenance ?
    I am sure you are already but one tip is to take plenty of photos of where all your pipe runs go just in case !!


  • Registered Users Posts: 149 ✭✭ landcrzr


    PC00123424 wrote: »
    Yes there is cavity insulation also.

    Do you know of any documentation I can see online which shows this recommended method, running the slabs all the way up to the hollow core?

    Your plasterboard manufacturer will have standard details.
    From what you're describing, I'd run the cosy board all the way up and then board out the ceiling.
    If you were dealing with non load bearing internal stud partitions and they are not fire rated studs, then you could do the ceiling first. Sound could be an issue though.


  • Registered Users Posts: 688 ✭✭✭ keno-daytrader


    Its your house, its your money, you are paying the trades, dont let them take the lazy way out.

    This space is also overlooked for making it airtight, but I see that you have plastered right to the hollowcore which is the correct method, or airtight paint on the block in the 150mm void.

    So you should follow the correct method for insulated plasterboard also.


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  • Registered Users Posts: 1,892 ✭✭✭ chooseusername


    Will the suspended ceiling be insulated?


  • Registered Users Posts: 252 ✭✭ Biker1


    Will the suspended ceiling be insulated?

    No. It is an internal ground floor ceiling with void above for services therefore no insulation necessary.


  • Registered Users Posts: 10,926 ✭✭✭✭ Calahonda52


    PC00123424 wrote: »
    Thanks for this. The engineer has advised nothing about this specifically, I'll talk to him.

    I also can't see it in Part L. But you are advising that this definitely should be done?

    The trade installing the suspended ceiling has said he's never seen it done or heard about it in his 20 years of work.

    This because they cant be orsed, this is the way we have always done it blah blah

    The 150, as noted by others will be a thermal bridge as iy has different U value from the wall below.
    Extreme case you will get condensation and mould, extreme case yes but possible


  • Registered Users Posts: 15 PC00123424


    As said, no insulation on pb on downstairs ceiling, no point I've been told, which seems to make sense.


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


    PC00123424 wrote: »
    Yes there is cavity insulation also.

    Do you know of any documentation I can see online which shows this recommended method, running the slabs all the way up to the hollow core?
    What’s the cavity thickness & what insulation are you putting in it?
    And What’s the drylining thickness ?


  • Registered Users Posts: 2,095 ✭✭✭ Yellow_Fern


    Hi, you asked about the 150mm void between a hollowcore and ceiling. Is 150mm considered unusual? What would be typical? Is it just as deep enough for services? Where would you have an access panel?



  • Registered Users Posts: 525 ✭✭✭ Fine Cheers


    From my own house experience it is useful to know where pipe runs of shower and bath wastes, heating pipes etc. Say you have leaks or blockages and need to access. My knowledge of this type of construction is limited so not going to bluff re ceiling void. I guess if you have 100mm pipe runs in there then 150mm is perfect.



  • Registered Users Posts: 185 ✭✭ 2018na


    This is a very tricky chicken and egg situation in the real world of building. Ceiling grid has to go up for services.insulated slab has to go on after services. Ceiling grid is installed using a Chanel fixed to the wall all around the room.Recently involved in a house build like this and I fully agree that the airtite render and insulation should definitely meet the hollow core and it's something that we did but it is a very difficult thing to achieve if you're not installing these items yourself



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