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Rim joist question

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Billbill84

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IMG_0780.JPG IMG_0781.JPG IMG_0792.PNG IMG_0818.PNG IMG_0819.PNG IMG_0820.PNG Hi all. The other day I posted about my fully finished basement having barely any insulation in the rim area (saw this while removing dummy vents to winterize hose bibs). In winter winter my basement is the coziest place in the whole house so warm. Actually the colder it is out side, the warmer it is down there, which is nice.
But back to my rim question, after my theory (in last thread about house), of why my copper pipes never froze near the very poorly insulated rim, sort of contradicts what happens to exposed rim joists having condensation issues which I do NOT have. It seems what I am able to see of the rim is pretty clean. It's all drywall in basement and ceilings and it's dry down there too, I sometimes run the dehumidifier in winter as well. The rim is above a drywalled ceiling which acts as it's own pocket of warm beneficial air to the surrounding area.
Wouldn't there still be some condensation on the rim joist even if it's sandwich between sub floor and drywall ceiling?? Is the warm air so dry that it will not condense to the cold rim? Air flow seems to be helping me in some way I don't fully understand yet. I did however carefully stuff some R30 behind the copper pipes just incase but then I started to worry about a potential condensation issue behind the R30 that, technically should already be going on with a sort of exposed rim. Any scientific thoughts are appreciated haha.
 
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nealtw

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Not enough moisture in the air to condense?
The inside of the rim is so warm the cold never gets to the inside?
There is so much warm air leaking around the pipes helping to keep that rim warm?
All guesses.
See the picture with the yellow fibreglass, that is a lot of dirt being dropped off while air is leaking passed it.
 

Billbill84

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Not enough moisture in the air to condense?
The inside of the rim is so warm the cold never gets to the inside?
There is so much warm air leaking around the pipes helping to keep that rim warm?
All guesses.
See the picture with the yellow fibreglass, that is a lot of dirt being dropped off while air is leaking passed it.
Ok so just warm and cold colliding on a surface doesn't necessarily mean condensation then? That warm air has to be warm moist air, right? Can a rim joist have condensation in summer when the AC is on and the outside is 96 degrees out? All I ever hear about is condensation on rims but no one ever mentions the actual humidity levels in the air. If my dehumidifier reads 30% humidity in a warm basement in winter then there shouldn't be any condensation issues even if it's insulated or not right?
 

nealtw

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Ok so just warm and cold colliding on a surface doesn't necessarily mean condensation then? That warm air has to be warm moist air, right? Can a rim joist have condensation in summer when the AC is on and the outside is 96 degrees out? All I ever hear about is condensation on rims but no one ever mentions the actual humidity levels in the air. If my dehumidifier reads 30% humidity in a warm basement in winter then there shouldn't be any condensation issues even if it's insulated or not right?
We do everything to stop mold and moisture, it is just stabbing in the dark to figure why you are not getting it.
Even if you have high moisture in the house does it circulate enough to get to the cold rim joist.
Dew point is the subject you can study for when moisture condenses. In the summer it would be on the outside but only where the moist are come in contact so at most it would be the outside of the house wrap or siding. But even the rim joist has some insulation value.
But you house breaks some rules. We make a great effort to fire stop from basement to floor and from floor to upstairs. So the fake vent should be at least backed up with 1/2" plywood or drywall, that would also stop air movement into that area. . If some of the basement is finished with insulation and drywall the end of the finished wall should be sealed to the foundation so moist air can't get behind the insulation.
 

Billbill84

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Even if you have high moisture in the house does it circulate enough to get to the cold rim joist.
Probably not my house has pretty dry air so any air leaks from my ductwork that runs between the basement ceiling and subfloor is from the furnace's warm dry air. That's probably the only air floating around in that closed off area so I'm sure it's near the rim as well. This is also why I'm very hesitant to fire up the whole house humidifier in winter but that's probably another issue because unless everything was built/finished properly to accommodate a whole house humidifier, it can wreak havoc in the area I just mentioned as parts of the rim are completely exposed up there when I peak in that dummy vent
 

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