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    • CommentAuthorjwd
    • CommentTimeJul 19th 2010
     
    I am about to let builders loose on my extension /renovation project. Our architect has specified 70mm of kingspan/ celotex polyisocyanurate insulation under a 75mm concrete layer with UFH but I am a bit worried having read that these kind of products off gas a and lose some of their insulating properties over time.

    a) is there any truth in the loss of insulating qualities via off gassing idea and does the same issue effect polystyrene as well?
    b) can I substitute expanded polystyrene floor grade insulation without affecting the structural make up of the floor?
    c) if yes to b) how much more polystyrene do I need to get equivilent Uvalues?
    d) is it likely to cost more?

    I can dig deeper into existing subfloor to put the insulation in without too much grief.

    Thanks

    Jwd
  1.  
    If you can dig deeper then there's no reason to use polyisocyanurate insulation. Expanded polystyrene is much cheaper. Extruded polystyrene is not as cheap, but has a lower k value & can be used below the damp proof membrane as it's not affected by moisture.

    The thickness depends upon the properties of the particular polystyrene. However, to achieve the same U values as polyisocyanurate insulation you're likely to need 65% more expanded polystyrene or 25% more extruded polystyrene.

    Depending upon the perimeter to area ratio, 70mm of Kingspan/Celotex is little better than the minimum required by Building Regulations. If I was paying the heating bills I would go for 200-300mm of extruded polystyrene with aerated concrete block to the perimeter walls where they bridge the floor insulation.

    David
    • CommentAuthorCWatters
    • CommentTimeJul 19th 2010 edited
     
    Posted By: jwdI am about to let builders loose on my extension /renovation project. Our architect has specified 70mm of kingspan/ celotex polyisocyanurate insulation under a 75mm concrete layer with UFH but I am a bit worried having read that these kind of products off gas a and lose some of their insulating properties over time.


    a) As I recall the loss of performance is modest and it's taken into account in the performance figures provided by most manufacturers. eg it's still better than polystyrene even after the outgassing is done.

    b) Yes but it depends what's going on top. Polystyrene isn't suitable for use directly under thin laminates in high traffic areas.

    c) It would have to be thicker to achieve same U-Value.

    d) I believe polystyrene is cheaper.
  2.  
    Hi jwd
    If you are going to use EPS under your floor I'd recommend EPS 100 with a density of 20kg/m3, Page 28 (or pdf page 30) of BSEN 13163 the British Standard http://www.viking-house.ie/downloads/BS%20EN%2013163%20-%202001.pdf gives it a Lambda of 0.035W/m.K, so I would guess you will need 20% more EPS to get the same lambda as PUR's eventual U-value.
    Put a 100mm anti capillary layer of 18-35mm compacted stone under the EPS to keep it dry, the lambda of EPS drops by 2% I'm told if its immersed in water for 28 days but it can allow your floor to sweat as its quite breathable.
    • CommentAuthorpmusgrove
    • CommentTimeJul 20th 2010
     
    Is Jabfloor extruded or expanded polystyrene? I am trying to get some prices for their product that has a reflective surface (and also something to stick the UFH pipe clips into) but it seems that no-one wants to sell it to me! Need 50 sheets.
  3.  
    eps easy to buy ask springvale www.springvale.com for a distributer then lay concrete square re bar mesh over the lot and cable tye pipe to mesh concrete over the lot do pressure test first though and if it is a high trafic are dont be tight get eps 150
    • CommentAuthorpmusgrove
    • CommentTimeJul 25th 2010
     
    Thanks; will take a look.
    • CommentAuthorMikeRumney
    • CommentTimeJul 26th 2010
     
    Posted By: pmusgroveIs Jabfloor extruded or expanded polystyrene? I am trying to get some prices for their product that has a reflective surface (and also something to stick the UFH pipe clips into) but it seems that no-one wants to sell it to me! Need 50 sheets.


    Have found this site very useful ...
    This page is re Jablite
    http://www.greenspec.co.uk/html/product-pages/jablitejabfoor70.php
    •  
      CommentAuthorfostertom
    • CommentTimeJul 26th 2010
     
    Springvale 'platinum' (grey tinged) EPS is the only kind to consider - its lamda is .031 against .038 for standard EPS e.g. Jablite. At that, it matches XPS, at much lower cost.
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