very high house humidity

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Old 05-29-20, 06:28 AM
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very high house humidity

I live in a modular cape style home. I am the second owner. I believe when the first owners had the house shipped, the second story was just attic space and they have completed the upstairs into bedrooms themselves. The main floor (ground floor) is very very humid in the summer months (I live in upstate NY). It is about 80% humidity. I have done lots of research and nothing seems to fit our issue. I've read it could be leaky pipes, which we show no signs of, could be leaky roof, which we had a new roof put on, incorrect ventilation on second story, we redid all of this the correct way, and we are still at 80% humidity. Very very uncomfortable living conditions. I am running the dehumidifier 24/7. My next and only guess for the humidity would be that we have insulation in the ceiling of the first floor, which is the floor of the second story. I have looked at diagrams that show you need to block of in between the joists of the second story floor where the knee walls start that way air cannot come in through the soffits and sit in this space. Currently we do not have this blocked off. Does anyone know if this would fix the humidity issue in the house, if we blocked off the air flow between every joist?
 
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Old 05-29-20, 06:40 AM
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Doubtful. The only way fresh air from outside would increase humidity inside would be in the summer when your AC is on and its dripping wet outside. More than likely you have a high water table and possibly no vapor barrier under the cement pad. The cement could be the source of your high humidity.

I'd say that all you can do is try to ventilate through fresh air exchange. Talk to HVAC experts and see what they can do. You might need to add a mechanical exchange.
 
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Old 05-29-20, 06:47 AM
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I do not think blocking will help a humidity problem.
But they should be blocked off.
The upstairs floor must be very cold in the winter.
It is probably costing you a fortune to heat.
Also there are probably condensation problems.
The above is if I understand you correctly that cold air can get in through soffit vents on one side of the house then travel above the insulation in the floor and out the other side of the house.

You say the humidity is high on the first floor (80%)
What is it on the second floor?
What is the outside humidity?
What are possible humidity sources on the first floor re: showers, stove top etc?
Is the bathroom vented?
Do you have a range hood?
Is this on a slab or a basement?

 
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Old 05-29-20, 07:24 AM
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With time the temp and humidity levels will equalize between the interior of the house and the outside weather.

Anything you do, insulation, blocking, vapor barriers will slow the equalization but not stop.

You either need additional de- humidification or addition of AC to more effectively control humidity levels!
 
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Old 06-01-20, 05:46 AM
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Yes, the air can go from one soffit, travel through the upstairs floor and go out the other soffit. But the floor of second story and ceiling of first story is insulated. I do think our house costs higher to heat on average than others. So you think we should block these off and we should save money on heat, even if it is currently insulated? And there are a few spots on our first ceiling floor that are now brown. I always thought it was from our roof leaking, but after you say this, i think it was probably just condensation.

I have checked humidity in basement, outside, main floor and upstairs. It seems the humidity isn't coming from outside or the basement, based on another response I received on another forum website.

Let me know what you think about blocking the soffits. Thanks.
 
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Old 06-01-20, 07:21 AM
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Yes I would block off the soffits so that cold air cannot get in.
I would actually remove them and stuff some insulation in, and then seal the holes.
Otherwise you will still have cold spots at the vent locations,

 
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Old 07-10-20, 02:39 AM
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Your AC could be oversized. How often does your AC cycle on the hottest summer days? It should run nearly continuously during the late afternoon when temperature exceeds your design (88F or 90F - Not sure of your location). Today's homes only need 1,000 SF/Ton or so, can go as high as 3,000. Depending on when yours was built it might be as low as 600+ if there've been no upgrades.

A "Blower Door Test" will quickly identify any building envelope issues. $400+/-.
 
 

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