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  1. #1

    Confused

    I am posting this here, because of what I learned here on another thread. I am experiencing heavy condensation on attic ducts and have decided I either have to reinsulate the ducts or, as has been suggested, foam the attic roof. I either have to raise the skin temp of the ducts or lower the attic temp & humidity to stop the condensation.

    The foam contractor wants to foam the rafters and seal all the penetrations, including power vent and soffit vents. It is 1900 sq feet and it is very hot and humid here at the coast in SC. I have always believed in attic ventilation, but here you just bring in more hot humid air.

    Does anyone have any experience with this process or foam type?
    Wouldn't we need to ventilate this area some how?

    I am concerned about other potential ramifications, such as roof sheathing or shingle problems. There are also two types of foams: Icynene, which is water based and open cell and polyurethane, which I believe is closed cell, but I have concerns about the chemical smell and toxicity if there should be a fire.

    Contractor claims attic will stabilize at 4 or 5 degrees above the second floor temp.
    Wouldn't this affect manual J calculations for the rooms below?

    Don't mean to offend anyone, so if you know of a better forum on which to post this question, please let me know. This forum has many responders who promptly reply and try to help. Thanks.

  2. #2
    Join Date
    Feb 2002
    Location
    Houston Tx
    Posts
    344
    yes this will changes your design paramiters for sure, I am located on the gulf coast and am going to Iceneye my new home. this stuff is the future.

    no attic ventalation needed it is a sealed attic, no humidity ducts dont sweat..

  3. #3
    Join Date
    Jun 2005
    Posts
    23
    I have used Iceynene in our walls and am tempted to use it in our attic. However, they have not concluded the long term effects of the insulation to the roof shingles. It will make the shingles hotter and will possibly decrease the lifespan but again, there have been no long term studies available.

  4. #4
    Join Date
    Feb 2002
    Location
    Houston Tx
    Posts
    344
    Stevio, you are correct but I wonder in our hot climate the effects of tec shield kicking the heat off the roofs ? again no long term studies on either,,,

  5. #5
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,642
    The condensation problem is most severe during the evening when the attic cools below outside temperature and the exterior of the cooling ducts is below the dew point of the outside air . Daytime hot attics keeps the exterior of the ducts above the dew point of the air. Several a/c coastal contractors are closing the attic vents and installing 100 pints of dehumidification per 2,500 sq.ft. of attic. The dehumidification is not needed when the attic is hot. The dehus are connected to a t-stat/dehumidistat to not operate when the temperature/RH is above 100^F or 50%RH. Data logging the attic temp shows a +10^F rise in daytime temp. during the day with low dew points during the evening.

    Foam on the bottom of the roof deck works and decreases the cooling load of the home. Air infiltration from duct leaks decreases. The need for mechancial fresh air increases. These combinations increase the advantage of a whole house ventilating dehumidifier to provide fresh filtered air, control the relative humidity during low sensible cooling loads. Whole house dehumidifiers can be connected to control attic humidity during the night and the home during the night. TB

  6. #6
    Join Date
    Feb 2003
    Posts
    1,996
    Maybe insulating the ductwork is the answer?

  7. #7
    Join Date
    Jul 2004
    Posts
    253
    I have an unventilated attic with sprayfoam (closed cell) insulation on the underside of the roof sheathing. The attic gets up to about 85F on the hottest summer afternoons. I havent done any humidity measurements but I suspect the absolute humidity (dew point) is the same as in the rest of the house. The house is pretty tight (new construction, ICF walls). I dont have any mechamical ventilation (except shower fans) and havent had any problems. I have a two speed compressor on the heatpump which runs most of the time so the humidty control is pretty good. I used Elk shingles which are warranteed with an unventilated attic. It is becoming more popular here ( southeast GA ) - I have 3 other friends with the sprayfoam roofs. All are pretty happy with them. I dont think it is reasonable to expect the attic to stabilize at 4-5F above the second floor temperatures - 10F maybe.

    Originally posted by beachwalker
    I am posting this here, because of what I learned here on another thread. I am experiencing heavy condensation on attic ducts and have decided I either have to reinsulate the ducts or, as has been suggested, foam the attic roof. I either have to raise the skin temp of the ducts or lower the attic temp & humidity to stop the condensation.

    The foam contractor wants to foam the rafters and seal all the penetrations, including power vent and soffit vents. It is 1900 sq feet and it is very hot and humid here at the coast in SC. I have always believed in attic ventilation, but here you just bring in more hot humid air.

    Does anyone have any experience with this process or foam type?
    Wouldn't we need to ventilate this area some how?

    I am concerned about other potential ramifications, such as roof sheathing or shingle problems. There are also two types of foams: Icynene, which is water based and open cell and polyurethane, which I believe is closed cell, but I have concerns about the chemical smell and toxicity if there should be a fire.

    Contractor claims attic will stabilize at 4 or 5 degrees above the second floor temp.
    Wouldn't this affect manual J calculations for the rooms below?

    Don't mean to offend anyone, so if you know of a better forum on which to post this question, please let me know. This forum has many responders who promptly reply and try to help. Thanks.

  8. #8
    Join Date
    Aug 2003
    Posts
    626
    Have you had your ducts pressure tested for leakage? Leakage is one of the main causes for sweaty ducts. It also causes higher utility bills. Have those checked first before spending all that money. I am a great believer in sealed attics for new construction, but to spend the money now would produce a long pay back time. As far as shingle life, test have shown only a 3-5% lowering of shingle life.

  9. #9
    Join Date
    Nov 2004
    Location
    Atlanta, Ga. burbs
    Posts
    281

    From a HO

    Yes it works. We are looking to sell and buy another house. We were looking at one closely to buy. The attic had insulation and no foam. I got out of the attic and the realtor said to examine the knee wall spaces. Man it was really cool in there. Reason: foam on the rafters. I could not believe it.

  10. #10
    Join Date
    Jun 2001
    Posts
    3,917
    Foam on attic rafters sounds like a good idea. This may be off topic but for those who foam in the walls, " Doesn't that nullify ever running any electrical or any wiring forever?"

  11. #11
    Join Date
    Feb 2005
    Posts
    3
    Yes and no. We foamed our family room walls when I replaced the wood planks and ran new electrical. What I think would happen is that the electrical contractor would come in and rip through where they needed to run the wires and leave you with some gaps. As we are in the middle of a 600 ft addition, I've discovered that a lot of the workers feel that it is always some one else's problem. Painters screw up wood work and vice versa.

  12. #12
    Don't you just love it when the subs begin blaming each other? Especially the pieceworkers, who just want to get in and get out.

    On the matter of the foam, I have it on good authority that foaming the roof was tried on a number of the homes in the Las Vegas area and resulted in roof sheathing delamination. Don't have the details, but we have decided to install a new trunk line with new insulation. I just want to solve this problem and go on with my retirement. Not going to risk it.

  13. #13
    Join Date
    Aug 2003
    Posts
    626
    could you share with us the "good authority" on this alledged delamination problem?

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