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Housing - Renovation: Insulating a concrete floor

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    We are refurbishing a bungalow to a high thermal standard (min. aecb silver) with additional extern. insulation (100mm phenolic), triple glazed windows and doors, probably 125mm sprayfoam under felt, and airtight barriers around window and door frames plus fitted to the ceiling.
    The tricky bit is the existing floorslab, which we don't want to dig up and which in 2 areas also has parquet fitted. Due to this we also don't want to raise the floor level too much.
    Is it worth fitting 12mm Kingspan floor insulation plus a 12mm or 18mm ply on top?
    • CommentAuthortony
    • CommentTimeJul 6th 2010
     
    You could do wing or perimeter insulation instead -- this would use the mass of stuff under the house as insulation/thermal mass. -- no flowing water though but remarkably with a high water table it is OK to go this route
    • CommentAuthorSaint
    • CommentTimeJul 7th 2010 edited
     
    This is exactly the situation where if the budget allows you'd go for aerogel. 12mm Kingspan does not for instance perform at half the level of 24mm Kingspan. The blowing agent finds it much easier to escape from thinner foams and so the thermal conductivity gets progressively worse as the insulant gets thinner. To be fair Kingspan doesn't produce a 12mm product as it would contribute very little thermally. Aerogel is not reliant on blowing agents, 5mm performs half as well as 10mm aerogel and a 10mm layer's performance is pretty impressive
  4.  
    Hi Saint, is there an Aerogel product for floors now then?
    • CommentAuthorSaint
    • CommentTimeJul 7th 2010 edited
     
    Hi Mike, not really although you can buy it bonded to T&G chipboard or plywood. In fact you can buy it bonded to most types of building board now. It can of course also be rolled out onto the floor and have a screed laid over it but no room for that in clippyclaus' case
  6.  
    I'd agree with Tony. Forget floor insulation & continue the external wall insulation down below ground level, ideally down to the level of the strip foundation. Use insulation that is not affected by moisture, e.g. 200mm extruded polystyrene, & protect the insulation from rodents with a paving slab on edge.

    David
    • CommentAuthorSaint
    • CommentTimeJul 7th 2010 edited
     
    Yes David, I'd agree on that as an alternative. Years ago the C&CA did a test where XPS boards were laid just below ground level horizontally around the perimeter of a house rather than vertically. Can't remember exact details but think they went for 1m wide. Worked well, breaks the "isotherms" radiating through the ground around the edge of slab to the external air
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      CommentAuthordjh
    • CommentTimeJul 7th 2010 edited
     
    Posted By: Saintbreaks the "isotherms" radiating through the ground around the edge of slab to the external air

    Are broken isotherms classified as waste? Do you need a licence to dispose of them? :bigsmile: :bigsmile:
  9.  
    thanks for all your input. I had planned to insualte externally down to soil level, material below dpc not decided yet.
    Initially the plan was to insulate below ground level vertically along foundations until I discovered the bungalow was built on a raft foundation protruding about 250mm away from the house and about the same in depth.
    I don't particularly want to insulate horizontally on top of the raft, since this would come above the ground level with more 30mm thickness.
    • CommentAuthortony
    • CommentTimeJul 8th 2010
     
    OK then how will you mitigate the thermal bridge down the inside skin and through the raft and up again to the ground/air?
    • CommentAuthorSaint
    • CommentTimeJul 8th 2010 edited
     
    Aerogel based cold bridge strips laid on top of the protuding raft edge (10mm or 20mm thick) and then XPS again vertically
    • CommentAuthorjms452
    • CommentTimeJul 8th 2010
     
    Going through the same dilema at the mo. as our foundations are only about 300mm deep!

    If you work out how much the EWI and triple glazing is costing (a small fortune I'd imagine) it might be worth rethinking the imposed limitation of not taking up the existing floorslab. Taking up the floor slab is probably small fry compared to these large costs (even if you factor in a two week holiday in while its done!). If you took up the parquet carefully you could relay this, put underfloor heating under the lot and end up with a near perfect solution.

    Then again there is thick carpet and thick underlay...

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