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Housing - Renovation: fixing insulated plasterboard

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  1.  
    I have purchased a load of insulated plasterboard... it arrived today and I have only just realised I am unsure how to fix it!

    Its 100mm insulation plus 12.5mm plasterboard, going on to a skeiling. I assume screwing it on is better than dot and dab, but am unable to find long enough screws (150mm probably required to allow the end to get into the rafter).

    Any ideas? Surely someone else has come across this before?
    Ta!
    • CommentAuthortony
    • CommentTimeMar 13th 2008
     
    What is the point of using metal fixings they will thermally bridge the insulation and you will get little spots on the paint highlighting every one

    Screws are made long enough but they are expensive. I use plastic nails:smile:
  3.  
    Where would you get said plastic nails from? I am only able to find plastic head nails, and not of long enough length.
    • CommentAuthorfuncrusher
    • CommentTimeMar 13th 2008
     
    You need 135 - 140mm bugle head phosphate coated screws - if you can get them. I assume you intend to skim with plaster. If not, make sure the screwheads are 2mm below the surface and fill with ready-mixed Gyproc joint compound (used for plasterbooard joints). I suspect the boards you have purchased are normally used on walls with dot and dab.
    • CommentAuthorMike George
    • CommentTimeMar 14th 2008 edited
     
    Hi Phil. I would not use such heavy boards in the application you propose - they are not intended for ceilings. They are normally stuck on with adhesive and where mechanical fixings are used -they are nailable plugs. See http://www.british-gypsum.com/products/plasterboard___accessories/gyproc_fixings/gyproc_nailable_plugs.aspx As you can see these ones are not long enough nor suitable as a timber fixing.

    The thickest boards I have fixed to rafters were 40mm PUR with a 12.5mm laminated plasterboard- I used 100mm drywall screw as they are treated so as to avoid the staining Tony mentions. I don't think they make drywall screws longer than 100mm

    I would consider taking down your existing ceiling and cutting the insulation you have bought between the rafters, leaving a clear 50mm ventilation gap on the cold side of the insulation. Don't try and cut them tight- instead leave a 5-10mm gap either side of each board, temporarilly wedge, and then fill the gaps with expanding PUR foam. Then put a polythene sheet fixed underneath and then plasterboard over and skim.

    EDIT: My final paragraph assumes the existing rafters are deep enough to allow the full thickness of the boards plus a 50mm airgap. If not you may need to 'plant on' timbers to the existing rafters to make up the difference.

    Hope this helps
  6.  
    Tony , with thses plastic nails would I need to use something like a glass hammer or perhap sky hooks

    Jim
    • CommentAuthortony
    • CommentTimeMar 15th 2008
     
    A normal hammer works fine though I usually place nails with a pneumatic nailer.

    Never seen a glass hammer. Or was it a hammerfur?
  8.  
    I thought plastic nails were only any good in aircrete blocks...? pneumatic nailer with plastic nails...? ...'am I missing something tony...?

    J
    • CommentAuthorjamesingram
    • CommentTimeMar 16th 2008 edited
     
    sorry for my poor attempt at humour
    were you never sent to get a long weight in your apprentice days Tony

    But Plastic nails? never used them , unless you mean the external insulation fixings
    , got a supplier/manifatures name

    I've been using long screw with washers and 3mm ply strips to fix thick PUR/pb board on to the rafter, I realise the thermal bridging problem
    but I've yet to come up with a better idea,
    contact glue could work If you could get some level rafter ( loft conversions so retrofit mainly)
    but I cant help sticking screws in everywhere ,belt and braces approach


    cheers Jim
  10.  
    External insulation fixings look like they would do the job - huge plastic head on the end. Any idea of a supplier, I can't find one - tried two local builders yards to no effect.
    • CommentAuthorJeff B
    • CommentTimeMar 17th 2008
     
    Try www.techmarkets.co.uk - they seem to have what you need.

    Jeff B
  12.  
    Maybe too late but screwfix do them as well
  13.  
    Have had problems fixing it up (probably due to my incompetance) - very tricky getting the angles right and getting sheets to match well together. In the end I got the plasterer to do it as he is experienced! A cop out I know, but 100mm insulation is hard to fix up!
    •  
      CommentAuthorMartian
    • CommentTimeMar 28th 2008
     
    I wonder if the sort of fixings used to fix external insulation to walls would also work in this application.
    Have a look at some of the fixings here:
    http://www.wbs-ltd.co.uk/renders_beads.htm
    look at the "SBH-T 65/25" and TERMOFIX 6H
    • CommentAuthorJoinerbird
    • CommentTimeMar 28th 2008
     
    Just wondering why 100mm for a ceilling?

    I went off to buy a "fixed bubble level" back in the days, but was too quick for the skyhooks and glasshammer
  16.  
    See the thread titled "loft insulation - u values?" for background on insulating the skeiling - I basically went for as large insulation as I could get, which happened to be 100mm.
    • CommentAuthordachaidh
    • CommentTimeApr 29th 2008
     
    I was sent for a short weight with a long stand. So took off into town and had the day off. Boss asked me the next day where I had got to, so told him that they sent me to their other factory and by the time I had finished it was going home time. He just laughed with the lads about it. I got paid for having day off..!
    • CommentAuthorMike George
    • CommentTimeMay 2nd 2008 edited
     
    Posted By: MartianI wonder if the sort of fixings used to fix external insulation to walls would also work in this application.
    Have a look at some of the fixings here:
    http://www.wbs-ltd.co.uk/renders_beads.htm" rel="nofollow" >http://www.wbs-ltd.co.uk/renders_beads.htm
    look at the "SBH-T 65/25" and TERMOFIX 6H


    They would work to fix the boards, but I am not confident that plaster would remain adhered to them. They would also have to be flush finished with the face of any plasterboards and doing this would likely damage the boards in a way that defeats the objective.

    I have considered using these in the past, but have dismissed them because of the above risks, They are also a bit on the expensive side.
  19.  
    Evolution Fasteners manufacture 150mm long drywall screws. See www.evolutionfasteners.co.uk they will let you know who their local distributor is but I know that Evolution's screws are available from many specialist tool and fastener dealers in the UK
    • CommentAuthorMike George
    • CommentTimeSep 16th 2008 edited
     
    Hi Michael. Thanks for that. Only seem to go up to 135mm in the catalogue [p42] http://www.evolutionfasteners.co.uk/pdfs/downloads/catalogue08.pdf Says will fix up to 90mm of material so longer than those I have used previously. Are there other ones that I have missed?

    My only other query would be whether they are designed to be plastered over, as some fixings leave surface staining. Will contact their technical department
    • CommentAuthorabomb1969
    • CommentTimeSep 16th 2008
     
    Mike, I have a warm roof.

    Why "leaving a clear 50mm" airgap? I have just got some 150mm Kingspan from seconds&co. My rafters have 125mm and my architect specced 25mm airgap under the membrane. When I told him I had got this insulation cheap he said I could reduce the airgap to 10mm to get more of the insulation in the rafters, leaving 35mm under the rafters. Any input appreciated, I was going to put a 10mm batten behind the roof membrane to hold the insulation off the membrane a bit.

    Adding battens to beef up the rafters will create a cold bridge, my architect suggested filleting in a 35mm deep strip of board and screwing through this with the board held off the screws.

    The comment about adding a layer of polythene sheet over the insulation is a good one.
  22.  
    Hi abomb, that's not a warm roof. A warm roof is where the insulation is outside the structural timbers. Where the insulation is placed between the rafters you need a ventilated airgap of 50mm to vent away any moisture which permeates through the structure below - otherwise it may condense on the cold underside of the sarking felt. Some will say this is not required where a breather mambrane is used but I prefer to do it anyway. The polythene sheet also reduces the risk of moisture permeating through as well as improving airtightness - Belt and braces approach

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