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Polystyrene for underfloor insulation?

  • 04-06-2012 03:57PM
    #1
    nicecupotay
    Registered Users, Registered Users 2 Posts: 127 ✭✭


    I am about to move into an old farm house that needs some renovation,I will be putting insulated slabs on the walls,and the floors are going to have to be pulled up(timber floors),radon barrier and concrete put down.

    The thing is I have loads of sheets of polystyrene sheets left over from work packaging at my disposal(sheets are about 3 foot square and 3 inches thick)

    I know I cant use it for the walls,but can I use it underfloor?If so,what is the method for putting it down?


Comments

  • #2
    sydthebeat
    Subscribers Posts: 42,916 ✭✭✭✭sydthebeat


    make sure the substrate is level and "blinded" ie smooth and without pointy bits. Then lay a sheet of DPM over... good practise would also run this about 1.0 m up the walls as well.

    the lay the insulation so each layer is level and flat. If you had enough room, id lay in in two layers hick ie 150mm. The pour a min 100mm concrete slab over with A393 mesh incorporated. Preferably pour 150mm. Use 75mm vertical strips at the junction of all floors and walls.


  • #3
    nicecupotay
    Registered Users, Registered Users 2 Posts: 127 ✭✭nicecupotay


    Thanks sydthebeat,would it also need some sort of support between the sheets of polystyrene?just wondering if the concrete would compress it giving an uneven floor once it starts to settle over time?


  • #4
    sydthebeat
    Subscribers Posts: 42,916 ✭✭✭✭sydthebeat


    its hard to discuss the strength of the polystyrene without seeing it. Most packaging grades Ive seen have been comparable to the under floor type. The biggest fear would be the concrete pour pushing the smaller boards around... depending on the size of the room, i think your workmanship in laying the boards will be the biggest factor with this. If you can get the fit tight, then it should be fine.


  • #5
    martin46585
    Closed Accounts Posts: 342 ✭✭martin46585


    Try if you can, to put a layer of cheap 500g dpm between the insulation and the reinforced mesh, as it will stop the wet concrete getting between the joints in the insulation, as the concrete can tend to float the insulation, if it gets between and under them.....


  • #6
    [Deleted User]
    Posts: 31,118 ✭✭✭✭ [Deleted User]


    martin46585 wrote: »
    Try if you can, to put a layer of cheap 500g dpm between the insulation and the reinforced mesh, as it will stop the wet concrete getting between the joints in the insulation, as the concrete can tend to float the insulation, if it gets between and under them.....

    Yes, that's exactly what I did and have had no issues with settlement since, a drop of at most a couple of milimetres, that's all.


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  • #7
    NobodyImportant
    Registered Users, Registered Users 2 Posts: 585 ✭✭✭NobodyImportant


    Concrete floors on houses without a DPM ( IN THE WALL ) are a bad idea. The moisture which would normally evaporate into the room from the floor (which would be vented also underneath) ends up soaking into the wall and causing rising damp.


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