Humidity level in Attic

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Old 01-07-08, 11:02 AM
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Humidity level in Attic

What should the relative humidity level be inside of your attic? I put a hygrometer in the attic and was alarmed at what it read. Because you are ventilating your attic with outside air, would the RH level be about the same as outdoors?
 
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Old 01-07-08, 11:39 AM
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humidity

It should be the same as outside air. Just because its flowing thru the attic doesn't change the RH.
You didn't post what the level was. Why were you alarmed?
 
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Old 01-07-08, 01:33 PM
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Yesterday I did some work up in the attic as we have had moisture problems on an outside wall during a recent cold snap. The soffit chutes that were up there were 12", took out 3 of them and installed 8 24" chutes. So now the attic has more ventilation. Yesterday the RH was 70% and today is 82%! Currently, outside RH is 68%.
 
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Old 01-07-08, 01:45 PM
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Instead of adding more ventilation, which although important is more of a band aid, have you done some thorough airsealing of the attic space as well as beef up your attic insulation? What kind of attic access do you have and is it sealed and insulated? Where are you located and what levels and kind of attic insulation do you have? Could you describe the moisture problem on the wall more?
 
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Old 01-07-08, 01:58 PM
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humidity

Lemme think here...if the temp in the attic is higher than outside, then yes I believe the humidity could be higher, as warm air can retain more moisture than cold. Am I thinking right here, guys?

And as the earlier poster was stating, and I was going to ask, you probably have infiltration from the living area up there. Can lights, bath fans, wiring, plumbing, unsealed duct work can all contribute.

Thats one thing I've been doing here in my place in AZ. Sealing wall outlets, cauling between sheetrock and bath fan housings, putting dedicated vents for the bathfans w/insulated duct, foaming penetrations, etc etc.

Yer doing good things, just keep going!!!
 
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Old 01-07-08, 03:17 PM
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My "To Do" list is quite lengthy. We live in Central Illinois and had a recent cold snap. Got down to about zero. Noticed half-dollar sized wet spots on an outer ceiling wall of attached garage at every truss location. Attic access is through hatch in garage. Fiberglass blown-in insulation was not close enough to outer wall and got cold spots. Found an excellent web-site on sealing attic air leaks:

http://www.rd.com/familyhandyman/content/18158/

Going to follow it to a "T", as well as add some gable vents to air out a cubby-hole dead-zone.
 

Last edited by Don W; 01-07-08 at 03:47 PM.
  #7  
Old 01-07-08, 04:38 PM
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Bathroom Fan

Here is one to test the air flow of your bathroom fan. (Provided it is exhausted to the exterior of your home.) Just because you turn it on and you hear it running, doesn't mean it's working. The test is on page 5.

http://emergencypreparedness.cce.cor...ndensation.pdf
 
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Old 01-08-08, 08:03 AM
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Originally Posted by Don W View Post
http://www.rd.com/familyhandyman/content/18158/

Going to follow it to a "T", as well as add some gable vents to air out a cubby-hole dead-zone.
I've read this article before too. Its good but the only thing I would change here is to use pink 2 inch foamboard and sprayfoam for closing off big holes they mention. The batt in a bag method can sometimes work, but i found that the foamboard with sprayfoam still seals way better.
 
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