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  1. #1

    Attic temperature/ventilation - smart ideas needed

    Hi guys, while not quite HVAC - it is heat and ventilation related...

    I've been in this new home now for going on 3 winters and so far it hasn't been a big problem but we got hit with ice dams this year. The attic just stays way too warm.

    Here is the situation, the contractor used Icynene open cell foam on the attic floor to insulate (my choice) but apparently looks like they didn't put in enough depth to get a good R value. The attic has ridge vents (sort of a mesh stuff) and soffits but a lot of the soffits are partially blocked by the foam and given the design of the house we don't have 2:1 soffit to ridge ratio even if they were all wide open (its a cape with a perpendicular wing off the back). So I had a gable vent put in to see if a little more air flow might help and it didn't really. And its the only ventilation when a lot of snow is on the roof as the rear roof is low pitch so the ridge vent is useless. When there is snow on the roof, the attic stays a pretty constant 45 degrees (the ductwork is up there but R6 insulated and pretty tight).

    Just after the ice dams last week when I broke down and put in a gable fan in the other gable (god they are loud) to help control temperature. It has helped some when its on but only gets the attic down to 38 or 39 degrees with snow on top insulating things when its even in the low 20's outside.

    Even if I turn off the upstairs heat to rule out duct leakage/radiant heat, the temperature is still elevated with and without the fan on. So I need more insulation - I'm going to put in fiberglass batts on top of the foam and have them try to free up some soffits if they can.

    But here is the dilemma, the attic also stays relatively humid, sort of a dewpoint between the inside and outside roughly - I'm not even running my inside humidifier - and only having the fan on brings that dewpoint down to the outside level. I'm afraid if the insulation works and I get it colder in the attic that it'll start to condense the atmosphere up there and get wet.

    Is it that the open cell foam allows not only the temperature but the vapor to migrate into the attic? I guess if we'd gone low tech and used kraft faced batts it would have a vapor retarder. The other possibility is that my ceilings were just primed not painted...I hear just latex paint can be a vapor retarder - might painting the ceilings help?

    Any ideas how you would deal with an attic like this? Thanks....

  2. #2
    Join Date
    Jan 2007
    Location
    Minneapolis, MN
    Posts
    415
    It sounds like you have a large air bypass from the inside to the attic. A blower door and chemical smoke can be used to try to find the bypass. More fiberglass insulation will not help if you don't seal the air leaks. The Icynene is a good air barrier so I believe something was missed. An energy rater or home performance contractor should be able to help diagnose the problem. De-pressurizing the attic with a fan is not a good way to ventilate.

  3. #3
    Join Date
    Oct 2006
    Location
    So. NH
    Posts
    745
    Like was mentioned make sure everything is airsealed including ductwork and insulate well. I would use blown in, batts are difficult to install tightly with ductwork etc.

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,743
    Instead of blowing out the heat you paid for.
    Add more insulation to the attic.
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    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  5. #5
    we actually had a blower door test on the house at one point and it was tight by building science standards, so I don't think there is a void that was missed...i don't get any negative pressure noticed in the house when fan is on

  6. #6
    Join Date
    Apr 2007
    Location
    Derwood, Md
    Posts
    142
    Also make sure that your bathroom vents and/or dryer vents are not venting into your attic. Could be the source of your problem.

  7. #7
    Join Date
    Dec 2007
    Location
    oregon
    Posts
    885
    After you insulate the attic, and humidity is still a concern, You can put in an attic fan with a humidistat. Have you done a duct blaster test to ensure the integrity of the duct work? Just curious, how deep(thick) is the spray foam insulation?
    Genius = The guy who can do anything...except make a living!

  8. #8
    Bathroom vents being used don't seem to affect the humidity up there so I think they are tight. We had a duct blaster done on the original ductwork that was here - but we replaced it and they apparently did a very careful job - humidity is affected even if I turn off the upstairs heat for a good part of the day so I doubt its leakage there either.

    As far as the foam thickness...it was a sloppy job that I should have had them totally redo during construction. They blew in a few inches in places, full depth of 9 inch joist in other places...then to compensate they blew in randomly on top of the Tyvek backing they had used to blow against up in the attic - so depth in any place is completely random.

  9. #9
    Join Date
    Dec 2007
    Location
    oregon
    Posts
    885
    The reason I asked about the foam is we did a job 7 years ago ( geothermal install) and the home owner wanted icynene foam for the building insulation and the insulation contractor only put down 5" in the attic and told the home owner that was all he needed. The same situation occured,(as you are experiencing) and after investgating the thermal loss; it was discovered the foam that was used was only rated R 1.7 per inch! it also had begun shrinking away from the attic joists. The reason we were called back was his energy bills were higher then predicted based on load calcs done before the install. After blowing in the attic with 12" of fiberglass his bills on the coldest month dropped 60 -80 dollars! (The foam contractor has gone out of business.) The home was a new construction project, 2800 sq ft single level, in Oregon.
    Genius = The guy who can do anything...except make a living!

  10. #10
    sounds like the same song and dance - "you only needed x inches" not the 9 inches to achieve R30 code...Icynene is definitely >1.7/inch though...I guess the contractor didn't use Icynene? Was there a humidity issue in that customer's attic?

  11. #11
    Join Date
    Dec 2007
    Location
    oregon
    Posts
    885
    Before, yes. There was frost on the plywood IN the attic. After the insulation was added, it has not reappeared. The home also has an ERV installed as the bath exaust system. There is also an attic fan.The frost and snow now do not melt off of the roof. The contractor "called" it icynene I did not see the insulation go in.
    Genius = The guy who can do anything...except make a living!

  12. #12
    Join Date
    Jul 2006
    Location
    Connecticut
    Posts
    271
    Are there channels (or chases?) in the eaves to keep the insulation from blocking the soffits?
    Seen them in both plastic and aluminum.
    Tom D. - Long-time Journeyman from CT.

    On account of being a democracy and run by the people, we are the only nation in the world that has to keep a government four years, no matter what it does.

  13. #13
    they do have styrofoam baffles but foam has seeped in and blocked quite a few, mostly those over the kneewall since it was such a long run.

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