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Soffit moisture

6grgUkTcQQ | Posted in General Questions on

I built a new house in a suburb of Chicago this past spring and moved in, in August. I had Icynene sprayed in the walls and Gaco firestop 550 on the underside of the roof . Now that we have had some cold weather under 30 degrees I am seeeing moisture dripping from some spots on my exterior soffits and fascia. I had the insulator back to look in the attic, it looks like it was sprayed well and we can’t see any areas missing insulation. Any ideas, could humidity be able to pass through the Gaco insulation? Any ideas?

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  1. user-723121 | | #1


    What is the humidity level inside the house and do you have mechanical ventilation? Is condensation forming on the windows on the colder mornings? I live in Minneapolis and we really have not had winter yet.

  2. 6grgUkTcQQ | | #2

    The humidity is about 46%, I shut the humidifiers off and I am running a dehumidifier in the basement. I have 3 levels of finished living space above the basement and I am thinking about adding a second dehumidifier on the 3rd floor.I noticed some condensation on the windows a week ago when I first noticed the moisture dripping from the soffits. I do not have mechanical ventilation.

  3. GBA Editor
    Martin Holladay | | #3

    The moisture you observe dripping from the soffits has to come from somewhere. If you have eliminated the possibility of a roof leak, and if you observe the dripping in cold weather, presumably you are seeing condensation. That means that warm, humid air is leaking from somewhere and condensing in your cold soffit. Obviously, the most likely source of the air is the interior of your house.

    1. You need to find the leak and seal it.

    2. If you have a brand-new Icynene-insulated house near Chicago, you made a big mistake to forget the mechanical ventilation system.

    3. In cold weather, it is far cheaper to lower indoor humidity by ventilating than by running one or two dehumidifiers, as you propose.

    4. A brand-new Icynene-insulated house does not need humidifiers. (Plural, even!) Who put those in? Obviously, turning them off makes sense.

  4. homedesign | | #4

    foam in the stud and rafter bays does not create a complete Air Barrier System.
    The air control layer should be continuous.
    Spray foam does not address the wood to wood cracks and crevices(the cracks between top-plates and the cracks between rafters and plates,cracks between stud and plate,cracks between dbl-studs...etc)
    Mike, did your contractor also do a complete "caulk & seal" job ?

  5. homedesign | | #5

    Here is an extreme example....
    This is from a Habitat for Humanity project in Dallas
    I took this photo a few minutes before the wall was covered with drywall.

  6. homedesign | | #6

    Mike, if you have bathroom exhaust fans that discharge outdoors ... then you do have a primative ventilation system.... running the exhaust fans longer should help reduce the humidity during the heating season(unless they leak )

  7. 6grgUkTcQQ | | #7

    I have 2 furnaces with fresh air intakes, does running them with the fan in the on position constantly circulate fresh air in the house? The moisture is coming from from more than one soffit area, it is definitley not a roof leak. Can a mechanical ventilation still be added? Do I need to have the checked for attic leaks ? I went through some of the attic areas that are accessible and it looks well sealed.

  8. homedesign | | #8

    Are your furnaces sealed combustion (hopefully they are)?

  9. user-716970 | | #9

    Could it be that the bath fans are discharging into the soffit space?

  10. 6grgUkTcQQ | | #10

    The furnaces ar Trane 95% efficient furaces, Some of the drips are nowhere near an exhaust fan.

  11. homedesign | | #11

    So, it sounds like you have Supply ventilation
    this might be working against you ...

  12. user-723121 | | #12

    John is right, you can ventilate your house with a bath fan (exhaust only). Make sure it is an efficient unit.

  13. 6grgUkTcQQ | | #13

    How might it be working against me?

  14. Boro | | #14

    Mike, Do you have insulation on the attic floor in addition to the rafter bays being spray foamed?

  15. 6grgUkTcQQ | | #15

    No insulation on the floors, I have dormer over one area of the attic and there is even some drips from that soffit. The drips are in many areas the insulation rep says he has never seen thiis before. I don't want to have to rip apart my attic in my brand new house This is extremely frustrating. Should I have an energy audiy Co come out and do an audit. I am very confused. Today the attic temp is 67 with 42% humidity in the attic and outside air is 26 degrees and i see a few drips around. I know brand new houses have high humidity the first year, but this is still odd. i hope there is a simple solution without having to rip drywall down and switch to a vented attic with different insulation.I paid good money to have spray foam and right now am very disappointed with the outcome.

  16. user-723121 | | #16


    There must be some attic bypasses at work here, I would not push the panic button quite yet. New homes do have a lot of moisture until the concrete cures. This has been an unusual winter in that it has been warmer than normal. The outside air is still holding a lot of moisture and is not drying the air (and surfaces) inside the house as it normally would. The humidity in our house in Minneapolis dropped to 34% about a week ago but is now back up to 38%. In the middle of a normal winter it will drop into the mid 20% range.

    Quit relying on the insulation rep. for answers to your questions, these guys are salespeople and not building scientists. I would hire a qualified energy auditor to take a look. A blower test and infrared scan will show you where the air leakage is.
    This what I could find on the product you specified, looks to be an open cell spray foam. In MN I believe an air barrier is required for some of the open cell spray foams but I can't be specific.

  17. user-716970 | | #17

    This quote is from the Gaco website...
    "When required, a vapor barrier shall be applied to the warm side of the Gaco Western insulation. In low temperature applications, or in high humidity conditions, consult Gaco Western for specific instructions."

    A coat of vapor retarding latex primer is probably called for in this situation...Icynene can be an excellent air barrier, but it is very vapor permeable..

  18. homedesign | | #18

    The reason that I say the supply ventilation might be "working against you" is that it is probably pressurizing certain rooms(or all the rooms)....and pushing warm moist air thru those cracks and crevices that I mentioned earlier.
    Balanced ventilation or exhaust ventilation is better for Cold Climate Homes

    Do you have dedicated returns or jump ducts in all rooms?

    your only "exhaust ports" may be the accidental openings (flaws,cracks crevices) and the bathroom fans.

  19. 6grgUkTcQQ | | #19

    I do have return ducts thoughout the house in just about every room.
    The insulator is supposed to come back and spray more foam in the areas we can get to. Some areas are unaccessible so I'm not sure if it will be easier to remove some of the soffits and spray from the outside or remove drywall on the inside, hopefull we can spray the accesssible areas and then see what happens after that. What I decided to do for now is to keep a fexhaust fans running and crack open the window in the finished room in the attic, this seems to have brought the humidity down to about 42% and made it a little cooler in the unfinished attic areas.

  20. wjrobinson | | #20

    Mike, your new home is not like homes of before sprayfoam. Run bath fans long after showers. Lowes carries nice electronic switches with delay off settings. If you have many houseplants.... Bad idea till your moisture level drops. If you have an outside vented range hood use it. If not, trouble. Bath fans must properly vent outside, if not, trouble. And you can sell the humidifiers, you don't need them.

    Get your moisture level down. Two years from now the home will be mostly done with it's share of your moisture problem.

    New homes can be the cause of moisture issues, and so can some homeowners.

  21. Foamer | | #21


    What you describe is a head-scratcher and your insulation contractor should be as interested in finding the source as you are.

    Your first step should be to run a blower door test on your house. Find out how leaky it is, then have your auditor locate any trouble spots (I would be suspicious of the wall top plate to rafter area). If your contractors did a good job, you should be well below 2 ACH at 50 pascal. Foam alone does not get you there and I hope your insulator provided proper caulk and seal work.

    Second, with a tight house, balanced mechanical ventilation is NOT optional. As pointed out by John Brooks, your current system is pressurizing the house and making any problem you may have worse. Bite the bullet and install an HRV or ERV.

    Third, don't panic. Let your house dry out and then evaluate before you take any drastic steps.

    Fourth. The Gaco foam is an open cell material with high vapor permeability. In your climate, the foam in your attic should be covered with a vapor retarding paint. This is most likely unrelated to your problem.

    (Full disclosure: I am a spray foam contractor in the Cleveland, OH area and in the years we have been in business, I have never seen what you describe. I would be most interested in your findings as you investigate your problem)

  22. user-626934 | | #22


    Do you have pictures of the areas and/or drips that you could upload to the GBA site?

    A couple of weeks ago I stepped outside my back door on a cold, clear morning, and was met with a drip of water on my head. Frost had developed on the fascia over night, and was now melting as the sun came up. It had nothing to do with insulation or airtightness.

  23. GBA Editor
    Martin Holladay | | #23

    There are a lot of unknowns here. You wrote, "I have 2 furnaces with fresh air intakes," and John Brooks concluded from that statement that you have a supply ventilation system, but I still don't know whether you do. Are you talking about the combustion air intake vents for your sealed-combustion furnaces, or are you talking about a passive duct that introduces outdoor ventilation air into your return-air plenum?

    If you actually had a central-fan-integrated supply ventilation system, your indoor humidity level shouldn't be at 46% during the winter in Chicago.

  24. homedesign | | #24

    Martin, you are right.
    we can't be sure
    There are still many possibilities(including John Semmelhack's)
    Mike may also have a supply side ventilation system that was never calibrated
    That happened on my house....
    I decided to read the controller instructions and realized that my contractor had not measured the flow to set the controller.
    When they came back... we discovered that a flap was stuck closed.

  25. 6grgUkTcQQ | | #25

    Let me give a little description of my house. Perhaps this will help, regarding some of the comments. We built it new and moved into it in Augut. We have two Trane 95Xl. gas furnaces One in the basement, which is unfinished and one in the attic on the 3rd floor. The house is about 3400 sq feet with a full basement ,roughly 1500 sq feet on the 1st floor and 1500 sq ft on the 2nd floor and 400 sq ft finished in tha 3rd floor, with the balance of the attic left unfiished. The furnace room is finished and located in the 3rd floor.I had obviously made a mistake by having humidifiers installed. I was never told by the insulator or the HVAC contractor, that they would not be needed. The 2nd obvious mistake is that I ran the humidifiers when the heating season started, thinking that it would help my woodwork and hardwood floors from shrinking and leaving gaps in betwen the boards, which is what I saw happen in other homes. A couple of weeks ago I noticed some moisture on the interior of my windows when the outside air was around 15 to 20 degrees, i figured the humidity was too high, so I turned of the humidifiers. I also have two masonry gas fireppalces in my house, one in the first floor family room and one in the basement. When it got cold outside and you sit near the fireplace,you can fell the temperature differnce in the family room which is a bit colder. I then might have made another mistake by turning both of my furnace fans to "on" instead of '"auto". I thought I could make the house more comfortable throughout by constantly circulating the air. From some of the comments I've read i think I may have been pressurizing the house. So for now i have shut off the humidifiers, put the furnace fans back to auto, left two exhaust fans running on my 2nd floor, one in a bathroom and one in my laundry room and I have left the attic window open about an inch. Humidity is down to about 38%.
    Thanks to all who have left comments.

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