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  1. #27
    Join Date
    Sep 2007
    Location
    Balto, MD.
    Posts
    200
    Quote Originally Posted by Colt Hero View Post
    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?
    I forget what they are called, but panels are placed against the roof deck. Insulation is placed inside the roof joist, then dry wall as normal. The panels allow for ventilation between the insulation and roof deck with out blocking air flow to a from all the vents. This is the same practice when doing a vaulted ceilings in homes.

  2. #28
    Join Date
    Jan 2007
    Location
    Coloma MI
    Posts
    214
    I'm suddenly having issues with Ice Dams since replacement of my roof. Attic is insulated to R-38. Full Soffit ventilation and previously had a Hard Plastic Ridgevent. When we replaced the roof the roofing supplier recommended Cobra Vent in place of the rigid plastic. Now I have Icicles and Ice Dams. You guys think the cobra isn't allowing as much air to flow as the rigid plastic? Previous 9 years of winters never had a single icicle. Now they're everywhere.

    I'm not looking forward to climbing up there in middle of the winter to peel off the ridge cap/cobra vent and replace it.

  3. #29
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    No ice damn issues,but we have high humidity issues with Cobra vents several times causing mold/mildew on the ceilings.

  4. #30
    Quote Originally Posted by stvc View Post
    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.
    Sorry for taking a while to get back to you guys...no big snow till now and I was out of town too. We got almost a foot of snow in the Boston area and without running the fan last night the attic was 41 degrees this morning after it had reached 25 outside as the low for a while. If I recall, the last big snow before the fan/cellulose it reached 45 but I had run the fan a bit yesterday on its timer.

    Sounds like the insulation may or forced ventilation may have helped some but not dramatically as we were getting big ice dams with the attic at 45 during the last heavy snow.

    I've got a guy coming in two weeks to do a blower door test and also use a thermographic camera to see if we have any cold spots in the walls/ceiling.

    But from what this other guy was saying about Cobra mesh vent which is essentially what I have, it does sound like I need a better ridge like Shingle Vent II that some people swear by. Still not sure how the attic breaths when the ridge is covered with snow though.

    Test results in two weeks. I assume enough attics have lesser insulated ductwork in the attic up North and don't have problems so this has to be fixable.

  5. #31
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,451
    To stop the moist air from moving from the house into the attic when ventilating the attic, reverse the attic fan to blow outside air into the attic. This reduce moisture and air temperature. Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  6. #32
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,347
    Newhomeboston,

    Do the upstairs portions of your home have recessed "can" lights? If so, are they sealed? Can lights are notorious leakers if not sealed/rated IC for insulation contact. Unsealed, they can be a large contributer to setting up a stack effect in the home.

    Your indoor humidity levels...what do they normally run? Do you use an indoor humidifier? If you've been leaving it off, lately, what do your indoor humidity levels typically run?

  7. #33
    Quote Originally Posted by shophound View Post
    Newhomeboston,

    Do the upstairs portions of your home have recessed "can" lights? If so, are they sealed? Can lights are notorious leakers if not sealed/rated IC for insulation contact. Unsealed, they can be a large contributer to setting up a stack effect in the home.

    Your indoor humidity levels...what do they normally run? Do you use an indoor humidifier? If you've been leaving it off, lately, what do your indoor humidity levels typically run?
    No cans, etc...ceiling upstairs is sealed with blown in foam. BUT Icynene now says that it needs a vapor retarder and my builder just primed the ceilings (cheapskate and I didn't notice the difference). So RH migrates through the ceiling into the attic where it generally should be dispersed with good ventilation but ours isn't that good. So I think I need to paint the ceiling with some latex paint which I guess has been shown to be an effective vapor retarder, not a barrier, but slows the migration down.

    When the humdifier is on in the house we keep it 35% in the winter about as it adjusts based on outside temp but without it the RH is 25-30%.

  8. #34
    Join Date
    Jul 2006
    Location
    Connecticut
    Posts
    271
    I have heard of a special paint that acts as a vapor barrier in this situation, but I'm not sure of the composition. It could be sort of a rubber/latex type. But regular primer won't do it, not even KILZ.
    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.

  9. #35
    well the results are in and the energy audit showed there was plenty of insulation in the attic but there was some leakage in the ductwork noticed during the blower door test....

    I guess the poor attic ventilation combined with slight air leakage and the R8 insulated ductwork still radiating a lot of heat just is too much to overcome. I had the duct system installed very carefully with a solid trunk line and flex runs to the rooms so I'm not sure where the leakage could be to try and fix that. And the R8 insulation was the best the contractor said was possible. So I'm not sure I can really affect those two issues much.

    I guess I can try and improve ventilation which may help or the other suggestion the auditor had was to use foam and create a closed attic by insulating the underside of the roof. Does anyone have any preference?

    And if I go for the closed attic, is there a problem that I might cause somehow? I still have the attic floor insulated with foam already...will insulating the roof underside create a situation where the attic doesn't have any air movement, or excess humidity/condensation somehow?

    THanks.

  10. #36
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    visit BUILDINGSCIENCE.com
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  11. #37
    Join Date
    Mar 2008
    Location
    florida
    Posts
    21

    attic vent

    insatall an attic fan to work on attic temp common problen in florida attic temp 140 degrees,,,like putting duct work over a campfire,,,heat is penetrating the duct even if it is r-6.
    i fix many customer problems with attic fans use the right cfm for square footage.

  12. #38
    Join Date
    Feb 2008
    Location
    Waffleville
    Posts
    10,339
    seal it up and install a dehumidifier thats what we are doing here, but our humidity is in the summer months, so thick you can cut it with a knife
    If Guns Kill People, Do Pencils Misspell Words?

    http://www.youtube.com/watch?v=An2a1...eature=related

    Before we work on artificial intelligence why don't we do something about natural stupidity?

  13. #39
    Join Date
    Jul 2006
    Location
    NJ
    Posts
    356
    Quote Originally Posted by valerioac View Post
    insatall an attic fan to work on attic temp common problen in florida attic temp 140 degrees,,,like putting duct work over a campfire,,,heat is penetrating the duct even if it is r-6.
    i fix many customer problems with attic fans use the right cfm for square footage.
    And it's official, The can has been opened!

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