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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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Products: Countersunk plastic screws for insulation fix?

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      CommentAuthorJustin
    • CommentTimeOct 21st 2010
     
    I've retro-fitted internal insulation 60mm PIR to a rubbish old cavity wall.

    Not able to cope with thickness for battens as well, I used 60PIR, initially foam glued in place, well sealed integral foil layer (fully taped including foam/tape at edges). 12.5mm plasterboard was fitted with a minimum number of 120mmx 6mm concrete screws sealed in with caulk to try and preserve the vapour barrier. Nice and solid and warm, but as I expected before I began, I might regret those significant cold spots! (the fat screws).

    Since the screws have made a (kind of) grip into the concrete blockwork. I was considering removing them expreimentally and carefully replacing with something less conductive. - But what? Would need very small countersunk head to loose in the PB finish and 6mm dia or thereabouts shank. Any product ideas? I find only Fischer fixings [url]http://www.screwfix.com/prods/81016/Fixings/Cavity-Fixings/Fischer-Insulation-Support-45-x-40-Pack-of-250[/url] but these have enormous heads not suitable for surface of PB.
    • CommentAuthorrhamdu
    • CommentTimeOct 21st 2010
     
    I sympathise. We've just had a flat warm roof put on our loft conversion, fixed with long stainless steel 'skewer' type fixings. According to Kingspan's calculations, the metal fixings add 8% to the heat loss through the roof.

    Those Fischer fasteners are used in external wall insulation, hammered into pre-drilled holes. The large flat heads are effectively covered by a render system which might have four layers of different materials.

    Maybe you could achieve the same effect internally if you put two coats of plaster over the board? Ask a good plasterer if this would work. Try a small experiment if necessary.
    • CommentAuthorjamesingram
    • CommentTimeOct 21st 2010 edited
     
    how about cut a hole in the end then knock them in giving them a good fwapp with a hammer to embed the head in the PB a bit, then fill them up with expanding foam , scrim and skim over the slightly recessed head , perhaps use a bit of 'bond it' ( pva with grit ) as an extra key on them if your worried about the skim popping of down the road .
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      CommentAuthorJustin
    • CommentTimeOct 21st 2010
     
    Hi rhamdu,

    Yep 8% might be likely. In my case I count 40 screws at 6mm dia over the whole wall. Assuming steel is 18W/M/K and they are effectively 70mm long, that gives me for all 40 screws 0.28W/K, or about 5.5 watts for 20C delta.

    I guess 20C delta is unlikely so I'll forget it in my case except I might get some condensation spots..

    For your roof assuming perhaps 100m Kingspan PIR, you get U = ~0.25? so one 3mm screw at 100mm is 0.00125W/K or the same as a square of your ceiling 70x70mm. Assuming 28 screws per board that's the same as 37x37cm of your ceiling. - which is 5%. perhaps your screws are fatter than 3mm (mine are sadly 6mm, thinnest I could find..)
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      CommentAuthorJustin
    • CommentTimeOct 21st 2010
     
    Hi James.
    I could try that, only breaking the PB paper too deeply I suspect my boards will fall off. Not many of these screws holding them on as it is.. Hmm. I'll try in corner..

    If I had any faith in gluing to the foil side of the foam I'd have done that...Only I don't. Kingspan/celotex seem to manage it with their foam+PB combo. Wonder what they use.
    • CommentAuthorjamesingram
    • CommentTimeOct 21st 2010 edited
     
    I've made my own PUR/PB lament for small areas using spray glue ( carpet tile stuff) seems to work OK , no call backs yet , though one was behind a rad so the long screw for the rad. bracket are probably doing the job and also back to the TB roblem . I bet that gorilla grip Pu glue might work also.
    had a link to a supplier of PU glue for insulation board , but cant find it , check Warren insulations product lists
    • CommentAuthoran02ew
    • CommentTimeOct 21st 2010
     
    not that it helps now you have drilled it but an ms polymer glue will stick it (like the type used for sticking wood floors to concrete) great stuff stick like s@@t to a blanket.

    as for the screw problem how about removing the screw drive in a wooden dowel and the screw into that as long as the screw head was biger than the dowel?

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