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Thread: Roof sweating

  1. #1
    Join Date
    Oct 2010
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    Default Roof sweating

    I have a question and I don't know were to turn for the answer. I have a Georgian (25' X 25' Square two story) in Chicago and last fall installed blow-in insulation in my attic. The house has a hipped roof with two vents on the south and north sides. Last winter I noticed that inside the attic the roof was sweating and dripping on the container inside the attic. I was told that problem is because of ventilation and I need to add more roof vents. The roof has no soffit vents and where I purchased the blow-in insulation, the guy told me that I could place the insulation into all the ends of the roof. Can anyone give me any ideas how to fix the problem?

  2. #2
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    Mar 2008
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    nova scotia, canada
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    Default Re: Roof sweating

    you can pull back the blown in fro where the soffits would be, install through vents then from there stuff fibreglass back in between the top plate and through vent.

    depending on what your soffit detail is, you may have to drill large holes in wooden soffit then install perforated vinyl soffit and metal fascia cladding. this will increase air flow up to the attic which will relieve the moisture problem.

    i should mention though, the big thing is to find the source of hte moisture. do you have a bathroom ceiling fan and if so where is it vented. if you dont this could be a source of the moisture, its migrating up through the ceiling into the attic
    fire up the saw and make some dust

  3. #3
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    Oct 2010
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    Question Re: Roof sweating

    There's a bathroom on the second floor but we don't use it's shower because it doesn't have a exhaust fan.

  4. #4
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    Default Re: Roof sweating

    Having roof vents without lower intakes aren't doing much good --- which is part of your problem.

    The other thing is as jkirk mentioned -- find any penetrations into the attic and seal those preventing warm moist air into the attic.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  5. #5
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    Oct 2010
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    Default Re: Roof sweating

    I didn't have the problem until I installed the blown insulation. I'm going to install a exhaust fan in the second floor bathroom.

  6. #6
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    Default Re: Roof sweating

    blown in insulation is known for causing sweating especially in older homes. the big thing is to get more ventilation in the attic space and making sure you have adequate insulation in the ceiling space to help reduce cold surfaces on the ceiling which allows condensation to form
    fire up the saw and make some dust

  7. #7
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    Oct 2010
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    Question Re: Roof sweating

    The thing is that I can only add vents in the two other hips of the roof. Should I install them lower on the roof to act as intakes?

  8. #8
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    Default Re: Roof sweating

    Normally with a hip roof you expect to have roof vents on all 4 sides or at least 3 sides.

    Installing vents lower down wouldn't be advisable if you live in an area with snow.
    Those lower surface mounts will suck snow inside the attic.
    Secondly if there is enough snow accumulation that covers the vents they won't intake air.
    "" an ounce of perception -- a pound of obscure "
    - Rush

  9. #9
    Join Date
    Mar 2009
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    Default Re: Roof sweating

    Howdy . What type of blown in insulation? If cellulose it restricts air flow. If you have not added soffit vents add 1 sqft for every 300 sqft of attic floor . You want cross ventilation - some on opposite sides of the roof slope. Are there roof vents at the top of the roof for the air to exhaust out of the attic? If not agian there are needed. The same sqft vent for every 300 sqft of attic floor space. Installing the vent for the bath is great idea be sure to vent the exhaust out side of the dwg either threw the attic and roof or out threw a wall.... Another item is to caulk around the ceiling lights to seal them to the ceiling so air infiltration is retarded so warm moist air is not entering the attic....
    Do you have a humidifier on the furnace if so turn it off and see if attic issues abate.
    If crawls space if dirt is exposed install 6 mill plastic on it to retard moisture infiltration into the home. So inotherwords reduce the humidity in the house and make the attic have air flow in an out ...

  10. #10
    Join Date
    Jan 2011
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    1

    Default Re: Roof sweating

    Block houses are notorious for sweating... this is most often due to the fact that they are not insulated very well, and the cold transmits through the block, to the interior of the home, where the humidity condenses on the cold block surface, just as a cold drink will sweat around the outside of the glass.

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