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Insulation under the floor

Post in 'DIY and General non-hearth advice' started by BrowningBAR, Jan 27, 2013.

  1. woodgeek

    woodgeek Minister of Fire

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    Might be a job for a fog machine and pressurizing the house.....find where the smoke exits to find the gaps.....then seal the stone to the slate with some appropriate material.

    Sealing the perimeter should be enough to allow comfort....temp-wise no different than slab on grade in the climate...cold but not freezing.

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  2. Highbeam

    Highbeam Minister of Fire

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    Where do you see slate? I agree that all this will take is sealing the edge to mimic a slab on grade setup. I wouldn't bother with spot sealing but would plan on sealing up the entire "edge" for a consistent look from the outside. Shotcrete or hand applied mortar. It would not preserve the exterior look but we don't know what that is anyway.
  3. BrowningBAR

    BrowningBAR Minister of Fire

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    The picture posted is of the third section, which is wood framed... in a very old way.

    The stone sections have the stone walls sunk into the ground to an unknown depth. Just stone. No sill. I do not have a photo of the flooring pulled up in those sections.
  4. woodgeek

    woodgeek Minister of Fire

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    BBAR--

    I get it. Stone house with walls going into the ground, perhaps resting on ledge/stone underneath the property. The joists supporting the floor are tied into the walls. Your complaint of freezing floors would seem to require a lot of air infiltration under the floor. If the (thin) airspace under the floor were tight, the floor would not get that cold. There has to be an opening to the outside to let the air in, maybe a few 10s of square inches total would do it. Could be a long crack running the perimeter of the house only 1/16" thick...like a crack under a sillplate, even though there is no sill.

    If you find and seal that sucka, you will have a much warmer floor. If the ground under the floor is dry, it will still be dry after the sealing.

    You might be concerned about soil gases, and that could indeed be hard to seal in your layout, but you could also put a little neg pressure under there (after sealing) like a radon abatement fan. Personally, I wouldn't worry about it.

    Are the walls double with rubble fill??
  5. G-rott

    G-rott Member

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    IF you can't get to the beam/sill/rim that the floor joist are attached to you will have a difficult time finding and sealing the leaks. One possible option would be low rise polyurethane foam. It is intended to be pumped into wall cavities in existing structures.

    I think a big part of your problem is that you have a huge (the earth) thermal mass in contact with your home that is likely below freezing this time of year. As well you have little or no thermal break(insulation or air space) between your framing and the cold mass. This transfers the heat in the room directly out to the heat sink of stone and earth. Thermodynamics tells us that heat moves to cold, seeking equilibrium.

    The polyurethane foam would fill and seal any voids eliminating air movement, your next step would be to add a thermal break to the flooring system and seal the walls to the floor, expanding foam and filler rod will be useful. A foam underlayment with the seams taped, then the flooring treatment of choice.

    The thicker the foam underlayment the better, the idea is to allow the room (warm) heat the floor faster than the earth sucks the heat away.

    On another note, where the earth is above the floor level any insulation you can add is a bonus, I have built miniature sips panels of foam and plywood and finished the top edge as a deep wainscot with a built up chair rail. You loose a little space but gain a lot of "r" value compared to what you have now.

    Good luck,
    Garett

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