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Question concerning condensation

budweiserbb | Posted in General Questions on

I just moved into a newly constructed house in zone 5A this past October. It has SIP walls, slab on grade (stained & sealed) with radiant and cellulose in the ceiling at R-42.

I know this is a new house and there will be a lot of moisture from the 2x’s and drywall that will eventually go away, but it seems that I have a more than average amount. My Pella Proline windows have 20-30% condensation that is dripping all over place. The Therma Tru doors are fine (front and patio), but the brass hardware is dripping wet.

Now the house is comfortable as hell and maintains a constant 68 degrees, but the condensation is killing me. My builder said that it will all go away in a couple of years as everything dries out in the house, but I am not sure.

Any advice? – Thanks –

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  1. GBA Editor
    Martin Holladay | | #1

    You didn't describe your mechanical ventilation system. You do have one, don't you? Or did your builder forget to install one?

    Here's an article that explains mechanical ventilation: Designing a Good Ventilation System.

  2. user-974347 | | #2

    I do not have a mechanical ventilation system because the builder insisted I did not need one. The house is one level and has 14' vaulted ceilings throughout. He claimed that the ceiling height would provide more than enough air circulation and a ventilation system was not needed. The humidity inside right now is at 65% and the condensation is almost not existent during the is mainly at night/early morning that it happens.

  3. GBA Editor
    Martin Holladay | | #3

    Step one would be to run your bathroom exhaust fans all night long, and see if that helps.

    A year from now, you'll have a better idea of whether this is a construction-moisture problem or something else.

    You may eventually want to install a ventilation system. In the meantime, I hope you don't have a humidifier.

  4. davidmeiland | | #4

    Second the motion to run the bath fan(s) continuously, or at least for long periods. Of course, make sure you are running them during and after showers (~one hour) and using the range hood during and after cooking. We have a very quiet range hood that runs about 100CFM at low speed, and I often run that while cleaning up the kitchen after cooking.

    Sounds like you have a thermo-hygrometer, so just watch it over a period of time and see if the RH% drops as you ventilate more. You want it closer to 40%.

    Your slab may be a significant source of moisture as it slowly cures. Is there a vapor barrier under it?

  5. user-974347 | | #5

    No...I do not have a humidifier :-) How long does it take for a slab to cure? Also, it has been stained and sealed so will it cure properly or is the moisture trapped? There is 2" of ridged board and 2" of Crete-Heat on top of that (Crete-Heat has built-in vapor barrier) then the pex tubing. I will not be a happy camper if I have to install a ventilation system...I have no duct work and may only be able to install one at the end of the house as I have all vaulted ceilings. This guy assured me that he had built several houses like this and was up to snuff on the latest technologies...he also came highly recommended as well. I did a ton of research myself and specifically asked him about a ventilation system because once it was done, I have no way of putting one in post-build. Again he assured me that it would NOT be needed. Maybe I should have gone with my gut...

  6. GBA Editor
    Martin Holladay | | #6

    As I wrote in the opening paragraph of my blog on ventilation, "Since green buildings usually have very low levels of air leakage, mechanical ventilation is usually essential." This has been the mantra of energy-efficient home builders for at least 30 years: "Build tight and ventilate right."

    So your builder made a mistake. However, don't despair. If at least one of your bathroom exhaust fans is a quiet model (like a Panasonic), you can install a 24-hour timer to control the operation of that fan. Bingo -- now you have a ventilation system.

    It's not as good as an HRV, but it may solve your problem.

  7. user-974347 | | #7

    Thanks Martin. I didn't mean to go off like that but I just knew what I was reading and then I let this guy give me a false sense of security in his knowledge. Just makes me so aggravated... Anyway, another question if I may - I do have Panasonic Whispers in both bathrooms (they are side by side). The electricians installed a 4" flexible pipe from each fan into a Y-connector. Then they ran a 4" flexible pipe from the Y to a soffit vent (spring loaded to close when not in use). Should they have gone through the roof instead? Now I am reading about water getting trapped in the pipe as hot, moist air from the bathrooms is cooled off in the cold attic space during the winter. I don't have any problems (I think) now, but I have only been here a short amount of time.

  8. GBA Editor
    Martin Holladay | | #8

    A soffit termination isn't ideal. Sometimes, icicles can build on on these terminations in cold weather. But in a warmer climate, they often work just fine.

    If you have any problems, you can always re-duct the exhaust to a roof termination or (best of all) a gable termination.

  9. user-974347 | | #9

    So the flexible piping is fine? Do I have to worry about water forming inside of the pipe? It is lying underneath the cellulose insulation and I wouldn't want it to leak water into it.

  10. GBA Editor
    Martin Holladay | | #10

    Here's my standard recommendation: run your ductwork straight up from the exhaust fan until you reach a height above the termination; install an elbow; then run rigid galvanized ductwork, sloping downward to the termination. Support the ductwork so that it has an even slope with no dips. Ideally, you terminate at the gable wall.

    In a cold climate, insulate as much of the duct as possible.

    There are too many variables to know whether or not you'll get condensation. If your duct has a low point, the water can collect there. I have seen bath exhaust ducts with gallons of water in them.

  11. user-974347 | | #11

    Thank you very, very much. Your help is greatly appreciated!

  12. Expert Member
    Dana Dorsett | | #12

    During the heating season purging all that moisture by running exhaust fans gets to be expensive & uncomfortable. A couple of 70 pint room dehumidifiers will convert that moisture to sensible-heat, taking some load off the heating system with that power use rather than adding to the heat load. Keep it under 35% RH in mid-winter if you can, to limit the amount of condensation along any exfiltration paths. In the late spring/summer/early-fall ~50% RH is healthy for both house & humans.

  13. wjrobinson | | #13

    Dehumidify. Your new home is drying. Your builder is right. Also run bath fans more.

  14. user-1022459 | | #14

    Reduce indoor moisture by ventilating or operating a dehumidifier? The answer depends on a number of factors:

    The difference between the indoor air dew point and the outdoor air dew point
    The difference between indoor and outdoor ambient temperatures
    The cost of electricity
    The cost of (your) heating fuel

    If the outdoor dew point is considerably lower than your indoor dew point (which is usually the case when you experience the condensation problems you describe) and you have an efficient affordable (to operate) heating system, ventilating the house (exchanging indoor air with outdoor air) is the most cost efficient way to reduce indoor moisture. Since you have installed good bath fans, you can invest in a handy timer/controller that will fit into your existing switch box to automate your ventilation. The negatives to this method are that you can not (completely) control the source of your make up air which can be somewhat poor if it infiltrates from an attached garage where you idle your car to warm it up each winter morning. This method will depend on you setting up the system to maintain your desired humidity level and it will not work year round. If the outdoor air is really cold, you may create uncomfortable areas where the outdoor air infiltrates into your house.

    If the outdoor air dew point is only marginally below or above your desired indoor air dew point, you will need to dehumidify mechanically. A refrigerant dehumidifier will consume electricity, remove water from the air, and deliver heat in your house. The cost of operating a dehumidifier can vary substantially depending on your desired indoor temperature and humidity level, the moisture load on your house, and the efficiency of the dehumidifier. The most efficient Energy Star dehumidifiers are more than three times as efficient at removing moisture (pints of water removed per kWh consumed) than lower cost dehumidifiers found in retail outlets. You should consider the life cycle cost (including the operation cost) of HVAC equipment including dehumidifiers. Run your bath fans when bathing and kitchen hood when cooking to remove moisture at the source. Maintaining the indoor temperature as high as you can stand during the cooling season (summertime) will increase the amount of moisture that may remain in your indoor air at a given relative humidity and will reduce the amount of dehumidification required.

    If you believe your house has excess moisture in the materials and you want it dried quickly, you can contract a fire & flood restoration contractor to dry it. There is a cost involved in this, but you will get a contractor that knows how to dry buildings and has all of the required equipment to dry your house for your money. These contractors also have the skills and instruments to assess the moisture content of the materials in your house.

  15. wjrobinson | | #15

    Tim, great post, great information. Stick around.

  16. toddoskin | | #16

    I know this is a little late in the game, but you could also install a dehumidistat
    ( to control your exhaust fan so you don't have to run it 24/7.....

    This is also considering what Tim O'Brien said of course (this would work if the outside RH is less than the interior RH... i think).

    If the outdoor RH is worse than the interior RH, a dehumidifier is probably best....

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