Older home with high Humidity in spring/summer/early fall How to find source?

Ever since Ive moved into this house in 2010, Ive become obsessed with trying to find out how humid air gets in so easily. After getting tiny dark spots on bathroom ceiling, papers I leave out around the house get warped due to moisture/humidity, and just plain uncomfortable air in the house, its driving me crazy.

I have already added a Santa Fe Classic Dehumidifier to my unfinished basement, so now levels are kept between 45-55%. But the main living area, always gets nearly as humid as the air outside. Often times, Ive run my a/c unit, not because its hot since temperatures are usually fine inside, but due to it being so humid. I usually give up though because as soon as I turn the a/c off, I can watch the hygrometer and the humidity levels slowly climb right back up.

I also have a bathroom exhaust fan that I run after a shower. Regardless, the bathroom will usually be even more humid than the rest of the house. Regardless if I shower or not. I have have not found any leaky pipes either.

So what can I do to find the source of humid air getting into house? I immediately think its coming up some how from the basement, but if I have a dehumidifier running down there keeping levels low, how could that happen?

Should I just wait for the cold winter, and rent one of those expensive thermal cameras to find leaks that way, and hope those are the sources?

Im sure most obvious answer might just be to get a whole house dehumidifier, which Ive thought about. But it would be great to know the source of it, regardless. That and I just dont have that kind of money to get one installed.

 

Hi BucSox,
First, a new tool for your search (if you aren't already using one):
Temperature, Dewpoint, and Relative Humidity Calculator

Since relative humidity is "relative" you need to compare it at the same temperature. That basement 45 to 55% is a different number if the temperature is different upstairs. Somehow I suspect you are aware of this, but the calculator makes it easy.

Next, all homes leak air to the outside which gets replaced by air leaking in. An average home would be 1/3 of all inside air is exchanges every hour. Leaky homes worse and tight homes are better. Thus conditioning the air inside your home can be a very temporary fix, as you discovered.

Take a bunch of RH and temperature readings, inside, outside, basement, bathroom, and any other suspect areas and convert them all 70°. Now compare and look for the high numbers.

A prime suspect in the summer is, as you stated, warm outside "humid" air. Once it leaks in and cools down, its RH goes up. A large ac unit that cools quickly will often not run long enough to remove a lot of moisture.

Basement moisture is another concern, especially if you are having to run the dehumidifier that much. Dirt floor or any moisture problems down there?

Bud

 

This about explains it all. The humidity in your home will not be less than the outside unless you condition the air in the home. So you need to run the A/C or a dehumidifier constantly to change the environment.

Some of the things that will help reduce the exchange of humidity between the outside and inside is to properly insulate and air seal your home. Controlling moisture is a part of this process. You say your home is old, so chances are your house is under insulated and air sealed. The dehumidifier in your basement is only part of the solution.

 

I get what you're saying, but to be honest, the temperature in the basement, isnt always far off from the house temperature.
I do believe under the home, there must be a steady source of water somewhere, because in my sump pit, there has always been a slow steady stream of water that goes out this big white pipe that drains out somewhere. I dont know where this pipe goes, or when it was put in. Never could find info on it.
I have older windows in the basement too, that seem to be just plexiglass. Since I dont have money to change them out right now, and i dont use them, im thinking of using some sealer around them to make them more sealed.

 

Then I suppose the best thing I can do, is rent one of those thermal cameras this winter, and look for biggest source of leaks. Ive heard I should check the sill plate as well, so Ill do that.

I dont like to use my a/c, because a lot of the times, like now, I dont need the house cooled. Temperature is perfect, but humidity is high. Sometimes, temperature is in the 60s even, and if its humid outside, it will be humid inside. It isnt really equal to the outside air, except maybe in my bathroom for some reason, but itll be about 5 to 10 % higher inside than out if i leave all windows closed.

 

Bathing, cooking, and breathing will add moisture to your home.

 

What level of humidity do you find to be uncomfortable?

Do you have central air conditioning or window units?

Do you run your bathroom exhaust fan during your showers? For how long after your shower do run it? How much air does the exhaust fan move?

Since you have a dehumidifier in the basement, I find it difficult to blame the basement on this humidity problem in the upper floors. How long have you been running the dehumidifier in the basement?

 

What really makes this interesting to me is the curling of papers around the house. I grew up without a/c and I don't think I have ever seen this before. The spots in the bathroom do not seem out of the ordinary to me. Your exhaust fan can be undersized and you may not be running it long enough. The paint is also probably not mildew resistant.

What year was the house built and what do you know about the insulation in the home? Does it have any? Was it installed as a retrofit?

 

I have central air, but the system is a single speed system that does not work well at all for actually cooling the home when I need it. So if I use it anymore, its just remove humidity.

The walls I know are not well insulated. There is some Styrofoam type insulation on the outside the home under neath the vinyl siding.

I always run the exhaust in the bathroom during/after shower.

Home was built in the early to mid 1950's. As far as the papers thing goes, its not extremely noticeable, but it does happen.
Ive also noticed the paint on walls is a bit funny. Not sure if its humidity related, nor do I know when they were painted though it doesnt seem that recent. But if I lean a solid object up against a wall for a while, then pull it away after a long period, you can almost hear the object try to stick to the wall or sometimes a little paint will come off. Again, may just be a poor paint job by who ever did it. Not sure.