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  1. #1
    OK, here's another problem for all the experts out there. Another dilemma caused by my having a builder use materials he was new to. Our attic in Boston has reached as high as 130 degrees on mid 80's days. The humidity is low like 15% at that point and I haven't seen it above 70% on the wettest of days yet. It cools down nice at night. This can't be a good situation, esp for ice dams in the winter.

    We insulated the attic floor of our house with icynene foam. Baffles were used to allow air flow to the soffits in this cape style house with a 3rd gable wing off the back. Ridge and soffit venting were used. Problem is I think the soffits may be blocked in many spots since a smoke pen's smoke isn't getting sucked into the attic at the soffits at several spots I tried. We have continuous ridge venting and the AC/heat ducting is is in the attic but insulated.

    So if the soffits are blocked, how do I introduce more air into the attic without messing up the air flow even more causing a different problem?

    1. Roof power fan
    2. Gable vents
    3. Vents low to the floor at the gable end
    4. Gable fan
    5. Other....

    Thanks...

  2. #2

    You're on the right track

    I am not an HVAC contractor, but I am a Mechanical Engineer. I think all of what you said could work; my recommendation is a temperature controlled gable vent fan. Should only open up and run when the attic is above a set temp. This is what I am planning for my house.

    By the way are the areas that don't vent small less than 4 feet or large more than 4 feet? Are you sure insulation isn't blocking the vent?

    Also to reduce heat gain in the summer you can buy metal paint (yes metal paint) and spray it on the roof sheeting underside. This reduces heat gain from radiation. People with metal roofing will have cooler attics then people with asphalt shingles.

    Heat transfer from your home can occur by conduction, convection and radiation. It is typically modeled in terms of conduction, although infiltration through walls and around windows can contribute a significant additional loss if they are not well sealed. Radiation loss can be minimized by using foil-backed insulation as a radiation barrier.

    Hope this helped.


  3. #3
    Join Date
    Aug 2003
    Posts
    144
    If the soffit vents blocked un block them and then put in some kind of high vents. in the gable or on the roof.Or put in some big cable vents on each and every gable.
    Another problem with no venting in the attic is the warm air will go into the attic and then frezz on the underside of your roff sheeting. when it gets a little warm it will melt and leak into your house also causing rot.

  4. #4
    Some of the baffled areas are maybe 10 feet long over the kneewall of the crawlspace where they blew the insulation up against the rafters. If I do some power venting of any kind, I'll need a manual override switch since winter temperatures are just as problematic for ice dams as high heat in the summer for condensation (which we haven't seen yet - knock on wood) or just shingle/plywood life deterioration.

    I have not been able to check visually most of the soffits as the stupid insulation contractor blew in foam so much that walking in the attic is like a moon scape and I need to get some boards to move around up there so as not to fall through the ceiling. I have seen a few from the area I can stand and they are clear to the eave but I have my doubts on those over the kneewall where I did the smoke pen test and the smoke went up over the roof rather than into the soffit vent under the eave....not a good sign.


  5. #5
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,287

    Lightbulb Attic Ceiling is correct

    Originally posted by newhomeboston

    We insulated the attic floor of our house with icynene foam.
    Why wasn't the foam insulation put on the Attic Ceiling! ?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  6. #6
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,275
    There is a HUGE difference in quality of ridge vents. Many designs are quite restrictive allowing minimal airflow. Personally I'm a big fan of the wind turbines, especially for Oklahoma

  7. #7
    Dan, the house was designed for a vented attic so when we switched to foam insulation I didn't want to try and design an unvented attic on the fly so we used it in place of batts in the attic floor.

    Any idea how to figure out which ridge vent was installed easily?

  8. #8
    Join Date
    Aug 2003
    Posts
    626
    Newhomeboston--I don't understand why you think you have a problem. What does the temperature and humidity levels in summer have to do with ice dams in the winter?

    [Edited by uktra on 06-16-2005 at 11:27 PM]

  9. #9
    Uktra,

    They don't directly, but 130 degrees is going to shorten the life of my roof, make the ac less efficient, and maybe cause condensation to develop in the summer.

    If its heating up this much with solar gain in the summer, then it will do the same in the winter and the attic will be above 30 when its less than 30 outside so snow will melt and ice dams develop.

    Two different problems, same cause - not enough ventilation - right?

  10. #10
    Join Date
    Aug 2003
    Posts
    626
    Shingle life is dependant on sheathing temperature rather than air temperature. Even if you had been really smart and insulated under the sheathing to create a non-ventilated attic the difference in shingle life is only about 5-7 %. In terms of A/C effeciency, what you should be concerned about is the duct/air handler tightness and insulation level. While it probably is impracticle to reinsulate your ducts, they need to be as air tight as possible. High humididty in the attic is not a problem as long as there is no dew point. The ducts and air handler are again the problem areas. Ice dams in winter are usually caused by air leaks from the rooms below the attic that bypass insulation to melt the ice at the eves. Your foam should prevent that problem.

  11. #11
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,287

    Lightbulb Clarify

    Originally posted by uktra
    High humididty in the attic is not a problem as long as there is no dew point.
    Could you repeat that ?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  12. #12
    Join Date
    Jun 2004
    Location
    Dallas
    Posts
    179
    Originally posted by uktra
    Shingle life is dependant on sheathing temperature rather than air temperature. Even if you had been really smart and insulated under the sheathing to create a non-ventilated attic the difference in shingle life is only about 5-7 %. In terms of A/C effeciency, what you should be concerned about is the duct/air handler tightness and insulation level. While it probably is impracticle to reinsulate your ducts, they need to be as air tight as possible. High humididty in the attic is not a problem as long as there is no dew point. The ducts and air handler are again the problem areas. Ice dams in winter are usually caused by air leaks from the rooms below the attic that bypass insulation to melt the ice at the eves. Your foam should prevent that problem.
    I'm agreeing with what you are saying, but did you mean to say the melted water would FREEZE at the eves? The eve is the overhang, correct?

    If his icynene was applied correctly in this fashion, which I agree was not the best way, ice dams shouldn't be too much of a problem. Air leaking from the HVAC is still an issue, though- I agree with that completely. If that were leaking anought it could melt some ice and cause a dam.

    Just my opinion- your fine- don't do anything.

  13. #13
    The ducts are well sealed to my knowledge...mastic and wrapped with foil tape. Have a little leakage that needs to be address around the air handler/acquacoil unit still.

    Old Yeller, still not sure why I wouldn't get the attic heating up in the winter from solar gain and melting snow that will freeze over the eaves and cause an ice dam. Its a low slope roof. I've been thinking roof heaters might alleviate this possibly though.

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