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  1. #14
    Join Date
    Jan 2007
    Location
    Minneapolis, MN
    Posts
    415
    You state that your attic is humid. The attic should be at the same humidity as the outside unless it is getting moisture from the interior (or water getting in from the roof). The attic cannot create humidity. You state the house is "tight" but that is relative, do you have the CFM50 for leakage? I still believe a blower door check used for diagnostics with smoke and probably infrared scanning would be more telling for air leakage. Adding insulation is easy enough but if air is moving though it the r value will be compromised. Knee walls are tricky areas, the floor cavities under them need to be sealed. Turning off the heat does not stop stack effect. Blown cellulose is better than fiberglass IMO. Good luck and let us know what the final fix is.

  2. #15
    Join Date
    Oct 2006
    Location
    So. NH
    Posts
    795
    Quote Originally Posted by mbarson View Post
    You state that your attic is humid. The attic should be at the same humidity as the outside unless it is getting moisture from the interior (or water getting in from the roof). The attic cannot create humidity. You state the house is "tight" but that is relative, do you have the CFM50 for leakage? I still believe a blower door check used for diagnostics with smoke and probably infrared scanning would be more telling for air leakage. Adding insulation is easy enough but if air is moving though it the r value will be compromised. Knee walls are tricky areas, the floor cavities under them need to be sealed. Turning off the heat does not stop stack effect. Blown cellulose is better than fiberglass IMO. Good luck and let us know what the final fix is.
    I agree, I have seen others post that they had a blower door test done and it was "tight by building standards". What does that mean???
    It seems that many are not getting CFM50, ACH50 or more important ACHn numbers, CFM means nothing without volume in the calculation.
    I also like cellulose over fiberglass, but different climates may change the best product. 20" of cellulose over my house in the Northeast.

  3. #16
    I don't remember how tight the house was but the guys from Building Science who know it all tested it with their seal of approval. The ducts haven't been tested since being replaced though. I will look into cellulose, I like the ability to go into the attic without the mess of fiberglass everywhere. Will let you know how it goes.

  4. #17
    Join Date
    Oct 2006
    Location
    So. NH
    Posts
    795
    Cellulose is every bit as messy as blown fiberglass but without the itch!
    Point is that it keeps the heat where it belongs, in your house.

  5. #18
    If you are in NE, who did your blown in cellulose? Anyone near Boston? Not a lot of contractors use cellulose it seems.

  6. #19
    Join Date
    Oct 2006
    Location
    So. NH
    Posts
    795
    I am in So. NH. I did it and I don't know of any insulation contractors who do blown in that don't do cellulose. It's a product thats been around for a very long time and is not going away any time soon as far as I know. Check the yellow pages and if you come up blank let me know.

  7. #20
    well got the cellulose...still a bit too warm. Even with a gable fan running all night it only got down to 6 degrees warmer than the outside temp when I got up at 6am today. I guess the R6 (or 8 I forget) flex duct and wrapped plenum and the Trane TWE just radiate too much heat up in my attic. How do most other new homes get by since many have similar complicated roofs with ducts up in the attic.

  8. #21
    Join Date
    Aug 2007
    Location
    Northern VA 38 degrees N by 76 degrees W
    Posts
    5,062
    Quote Originally Posted by newhomeboston View Post
    well got the cellulose...still a bit too warm. Even with a gable fan running all night it only got down to 6 degrees warmer than the outside temp when I got up at 6am today. I guess the R6 (or 8 I forget) flex duct and wrapped plenum and the Trane TWE just radiate too much heat up in my attic. How do most other new homes get by since many have similar complicated roofs with ducts up in the attic.
    I would be cautious running the gable vent fan while checking temperature rise in the atic.
    If you have any air leakage in the wall cavities, chases, drilled holes from plumbing vents, wiring, air handler, register boots, etc., you may be creating a negative pressure in the atic and drawing the heated air from the conditioned space and giving you the warmer atic.

    There was another mention of humid atic that would point to the negative pressure.

    In the summer time if all is not sealed you will loose cooling also.

  9. #22
    Join Date
    Jul 2005
    Posts
    717
    Newhomeboston; It would seem as if your ceiling is lacking a "vapor " barrier on the warm side(just under the insulation. Also, inadequate insulation R value can be a cause of this ice damming too. Also the soffit and the high (near the peak) ridge vents need to be sized to allow enough air flow thru-out the attic.

    For every 300 sq ft of attic floor area there should be 1 sq ft of 'free' area venting, divided 50/50 between the soffit and the ridge vents.
    As long as you have adequate insulation within an attic it can NEVER have too much ventilation. and even with roof snow coverage an attic will still breathe.
    note; a properly vented attic, using just soffit and near the peak (continuous ridge vent is best) vents, needs no gable or other fan type vents.

  10. #23
    Join Date
    Oct 2006
    Location
    So. NH
    Posts
    795
    I think I would leave that fan off and see how the house performs now that is better insulated. We have had alot of snow, rain, cold and warm patterns that also can cause ice build up, even on my shed roof.
    I'm also not so sure it is completely unusual that it is slightly warmer in your attic than outside, I might experiment with that a little.

  11. #24
    Join Date
    Oct 2006
    Location
    So. NH
    Posts
    795
    I was curious so I put a thermometer in my shed that has a vented roof and is mostly shaded. The outdoor temp was 31 and it was 44 in the shed.
    So like I was thinking before you might be too worried and what you are seeing is quite normal.

  12. #25
    Join Date
    Jul 2005
    Posts
    717
    A PROPERLY vented (via soffit/ridge) and well INSULATED attic should be at least within 20% -30% of that outside temp.
    in other words if it's 30 f outside, ideally it should be approx 36-39F within the attic. The closer to the outside temp the better.

  13. #26
    What if your attic is finished. My sister lives in New England and is considering finishing off a very large attic space atop a colonial-style house. Presumably the house has soffits and a ridge vent. What do you have to do in this case to prevent the ice dams? You still have to maintain close to outside air temp in the winter on the backside of the roof decking, right? How is this done?

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