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Cold Corner Insulation

Post in 'DIY and General non-hearth advice' started by dougstove, Jul 24, 2012.

  1. dougstove

    dougstove Member

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    Hi;
    I have a north, upper corner of a room that is a cold spot that suffers condensation, and I am wondering how to fix it.

    Complicated story:
    1968, 2x4" frame house with ~R12 batt insulation in the walls.
    Soffit level under the eaves about ~3" below the level of the inside ceiling.
    Soffits were not properly vented.
    Attic had fiber glass batt insulation, ~R20

    So, last year:
    -added ~R30 cellulose insulation to the attic and did significant improvements to lower air infiltration from the living space to the attic (although still more to do).
    -resided exterior; the contractors added 1.5" foil backed insulation board to the exterior, seam taped under the new siding...
    But: The new layer of insulation only extends up to the level of the old soffits, so the top ~3" of wall is less insulated than the rest.
    And, the contractors added ventilation to the soffits.

    So now:
    -cold air can flow in through the soffit to the attic (as is proper), but it flows past the top 3" of wall, which is now a cold corner.

    Does anyone have ideas or pointers?
    I know this a stupid sequence of events.
    I am wondering about injecting foam insulation from the inside, into the top of the walls?

    Getting to the corner of the attic is almost impossible.
    cheers, Doug

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  2. semipro

    semipro Minister of Fire

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    Where do you see the condensation?
  3. dougstove

    dougstove Member

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    The condensation is on the surface of the paint, in the top corner of the room, mainly at the junction of the wall and the ceiling.
  4. woodgeek

    woodgeek Minister of Fire

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    Crown molding with spray foam behind it??
  5. Hogwildz

    Hogwildz Minister of Fire

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    Take the soffit down and add insulation to the top portion of the wall that is not insulated. Reinstall soffit with screws to make it easier if you need to take it back down. And see what happens.
  6. semipro

    semipro Minister of Fire

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    What Hog said.
    Injecting foam won't help with the thermal bridging that seems to be occuring through the top plates.
    If the condenstaion is only occuring below the level of the top plates then the foam in the wall might do it.

    If you had it to do over I would have recommended you consider spray foam between the roof rafters and closing off any connections between attic and soffits; basically bringng the attic withiin the thermal shell of the building.
  7. woodgeek

    woodgeek Minister of Fire

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    On the interior!
  8. semipro

    semipro Minister of Fire

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    I got that. I was talking about the OPs plan to inject foam in the wall.
  9. woodgeek

    woodgeek Minister of Fire

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    S'cool. When retrofitting there are best practices that should be adhered to when possible, but of course there are no end of odd little problems and challenges....then it is necessary to get creative.
  10. dougstove

    dougstove Member

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    Thanks everyone.
    I am dreading the soffit removal/wall insulation/soffit re-installation.

    "If you had it to do over I would have recommended you consider spray foam between the roof rafters and closing off any connections between attic and soffits; basically bringng the attic withiin the thermal shell of the building."

    I thought seriously about taking out all the old insulation and putting in spray foam.
    But I was cheap and did the blow-in cellulose myself.
    In my area the advice is that cold air should flow up from the soffits to the roof vents, to keep the roof surface cold in winter. This supposed to limit ice dam formation.
  11. save$

    save$ Minister of Fire

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    What Hog said is right. If you don't, you will see some very dirty walls. Ghosting will occure. All the particals of dust in the home will settle out in the condensation and leave a gray deposite on the wall. Usually you see this on outside wall as outlines of the studs that are behind the sheetrock. usually need to wash the wall, prime with kills it, then paint again. If you are installing a stove in that corner, and that is the only cold area, maybe you could install some sort of hearth backing behind the stove that would allow you to add insulation in the process.
  12. woodgeek

    woodgeek Minister of Fire

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    Could there be a gap in the wall cellulose near the top of the cavity? This might not be a thermal bridging issue, so much as a need to top up the cavity (somehow).
  13. semipro

    semipro Minister of Fire

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    Good catch. I think you may be onto something here WG.
  14. begreen

    begreen Mooderator Staff Member

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    Cellulose does have a tendency to settle, especially the low pressure stuff.
  15. dougstove

    dougstove Member

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    If the wall insulation has settled, is there a practical means to top it up from inside?
    Drill in and fill with foam from the top corner of the wall, between each pair of studs?

    The condensation only manifest when:
    -the soffit ventilation was opened up
    -the outside walls were insulated up to the level of the soffit (but below the level of the room ceiling.

    So I think/hope that either:
    -cold air is now moving more over the top corner, making it colder
    -insulating the wall has generally made it warmer but created a relative cold spot.

    Thanks everyone. I really wish I had thought to insist that the old soffits were removed before the exterior wall insulation was put on. But I was away at the time of the job.
    cheers, Doug
  16. semipro

    semipro Minister of Fire

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    If the cellulose has settled then I think you could drill a small hole and inject foam between the studs right below the top plate. Normally I'd be worried that the swelling foam might expand the wall somehow. In your case it seems that it would just compress the cellulose further instead.
    The trick will be to figure out how much open space there is and how much foam (how long?) to inject to fill that open space.
    Maybe you could just drill a small hole and then feel around with a small piece of wire?
  17. save$

    save$ Minister of Fire

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    Might also be able to use one of those digital thermal scanners. Cost under $50. Can use it to find any other cold spots.
  18. dougstove

    dougstove Member

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    Hi again;
    Thanks for all the advice.
    I did some more googling and found a study from North Dakota that identified the design flaw, common in houses of my vintage, that leads to thermal bridging above the soffits, causing cold corners and condensation.

    They found the best fix is to:
    -control interior humidity (working on that)
    -install insulated crown mouldings. So I am doing that. The insulated crown moulding keeps the warm room air away from the cold corners.

    The study found that the crown mouldings worked better than attempts to insulate from outside or from the attic.
    cheers, Doug
  19. semipro

    semipro Minister of Fire

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    Could you provide a link to the study?

    There are crown moldings made of structural foam I think.
  20. dougstove

    dougstove Member

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    Hello;
    I found the study under:
    best1.thebestconference.org; it was a .pdf down load.
    If you google the following text you should get it:
    "A common site of moisture damage, discoloration and mold growth, usually found in
    houses with truss construction and low-slope roofs in heating climates, is located at the juncture
    where the ceiling meets the exterior wall. The aim of this research was to determine if insulation
    retrofits could improve the thermal conditions at the wall-ceiling juncture and thereby reduce the
    likelihood of mold growth or other discoloration."

    There are indeed solid foam insulation crown mouldings, but the delivered cost was high.
    So I used 6" MDF crown molding from Home Depot, drilled access holes and filled behind with GreatStuff.
    I messed around trying to cut solid insulation boards into shape to fill the void, but it made mounting the crown moulding too difficult, and it turns out that is only takes about 1 can of GreatStuff to do each of my rooms.
    cheers, Doug

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