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Community and Q&A

Extreme Humidity Fluctuations

exhaustedandventing | Posted in General Questions on

Hello (and thank you for reading)! Built 2005, I purchased a 925 sf home with 1 car attached garage in the northeast (MA).
First spring I noticed higher humidity levels, worse going into summer, even Fall. Went up to mid 70% and up a bit at times. AC brings it down in summer but my master closet (all the closets) smell not moldy but musty. Clothes have a dampness. Damp Rid hanging bags in the closets fill in 3 weeks.
In winter however, the RH drops to 28, and down to 24 at times. So uncomfortable.

The main roof covering the house itself, has a hip roof.  4 contractors have all said the same. “You have an 8 ft ridge, and the ridge actual vent space is possibly only 2-3 feet”.  I do have soffits/soffit venting.
Crawl space (just over 4 ft in height) with concrete flooring, has had a stand-alone Aprilaire dehumidifier installed.last summer that I keep at 45%.
Attic insulation is only 6-8″ we’ve noticed. I live at the back end of the development, in a corner, surrounded by trees and wet conservation land.
Home seems to not have the ability to or does not have natural stack effect, it isn’t allowing humidity in the home to purge out. Little windows over the garage freeze in winter, and my vehicle door has been hard to open, frosted over. The other homes facing how mine does, do not have any of this.
The house does pop on occasion when seasons change, less since the crawl space dehumidifier was installed.
Is there anything you think could be the issue, please and thank you!?

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  1. Expert Member

    To me it sounds like the house is not very air tight, for a few reasons

    1. Very humid in the summer months, when the outside air is humid
    2. Very low humidity in the winter months, when the air is dry.
    3. The crawlspace is dehumidified, but the house is overwhelmed by air infiltration in the walls or roof.
    4. The Damp rid fills up, but the humidity stays the same. The moisture must be coming from somewhere.

    The only real way to test this theory is with a blower door test, or some time of home brew test using a few fans and an IR camera, possibly a smoke test as well. If confirmed, the solution is to attempt to air seal as best you can.

    1. exhaustedandventing | | #2

      Thank you so much KBentley for your thoughts and reply. I will have that test done!
      I've been told by neighbors "You need to open your house up more!" But if I do that on a humid day, I feel it just makes it worse bringing in more moist air to be trapped.
      I also failed to mention that when the humidity drops outside, I do open the windows and the inside RH lowers. But the problem is within say a half hour of closing the windows the RH climbs and is back up higher again even tho it remains the same lower outside. That is the BIG conundrum!

      Suggestions have been:
      1) GC suggested a replacing the current bath exhaust fan with a low cfm continuous (dual) fan w/humidistat. Said it would run at a constant and bump for higher humidity. Should help overall in such a small home.
      2) A roofer suggested an attic fan, but that doesn't solve the winter very low humidity inside.
      Thank you again!!

  2. Expert Member
    BILL WICHERS | | #3

    I also suspect general air-leakiness, and possibly also moisture seeping in through the crawlspace walls and possibly also the slab. Since you said you're in a wet area, there is a good chance the crawl space is bringing in a lot of moisture. Encapsulate the crawlspace (install a complete liner on the walls and floor) to help with that.

    The air leaks are probably lots of places, since lots of little leaks all add up. I would check the worst offenders first, which are usually the rim joist area and attic access hatches. Seal those and you're likely to see a lot of improvement. Other things to check are especially double hung windows (which tend not to seal very well), and any other windows/doors since seals can wear out over time or get damaged.

    It may be helpful to you to rig up a box fan as a "blower door", then get some smoke pencils (sometimes incense sticks can work too, you just need visible smoke), which will help you find all the air leaks.

    BTW, I don't like to use the "smoke in a bottle" products for use indoors due to the material used for the "smoke". Use one of the flammable-type smoke pencils or incense sticks.


    1. Deleted | | #5


    2. exhaustedandventing | | #7

      Thank you so much for your thoughts and input!

  3. Expert Member
    PETER G ENGLE PE | | #4

    With that much indoor humidity, and with such a quick humidity rise after shutting the windows, there could be a combustion gas leak from one of your appliance vents. This could be dangerous (carbon monoxide) as well as depositing lots of humidity in the air. If you have an energy audit that meets BPI and/or HERS standards, they generally include a combustion safety review along with the blower door test. If you have carbon monoxide alarms, make sure they have new batteries and that they work when tested. This is important.

    Aside from that possibility, I agree that it sounds like the house is relatively leaky. The energy audit can help you figure out where the air leaks are and where your dollars are best spent on improvements. I also agree with the recommendation for sealing the crawl space. Otherwise, the dehumidifier down there is just trying to dehumidify the great outdoors. Damp Rid is mostly useless - it removes a pint of water in a few weeks. Your crawlspace dehumidifier removes pints per hour. Some houses require dehumidifiers in the main living space, especially in the shoulder seasons when the HVAC is not running, but these are primarily very tight houses, not leaky ones. A good energy auditor can provide specific recommendations for your home.

    1. exhaustedandventing | | #6

      Thank you for your reply and input!
      I will definitely have someone in for the proper physical air leak testing. The prior in Oct 2021 was a general audit and done virtual due to covid.

      No gas appliances, but do have an oil-runned furnace. Purchased a new CO detector in January (thank you for the tip, tho!).

    2. exhaustedandventing | | #8

      And I agree about the dehumidifier. Ugh.

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