Humidity in finished basement vs 'upstairs'

bcrawfo2July 9, 2007

I'm almost done with my basement finishing. I still don't have my drop ceiling installed.

Carpet was installed on Friday and the installer used a watering can to spread water on the backing of the carpet to aide in stretching. I saw at least two watering cans (gallons) go onto the 22x22 room. How long til you think that should dry out?

I noticed it was pretty humid down there, so I ran the de-humidifier for a while. I was able to get it down to 44%. When I turned it off for today (Monday), it went up to 53%. Upstairs is 46% at the same temperature.

I have a large return and pretty good sized supply. I plan on adding another supply.

The walls of my basement have 1" rigid foam insulation with taped joints, then R13 in the walls. I have delta-fl and OSB under the carpet. This is in a basement that has never been wet.

I need to insulate the rim joists, but that's my last step. I wouldn't think that would add significant moisture.

Should I expect my insulated basement to be very different humidity-wise than the rest of my living space (when using the same hvac system)?

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Even with the board insulation--I hope it's extruded polystyrene--you need mechanical dehumidification to keep humidity below 50%. Especially as you have carpet, which is partial to mould growth. (BTW, I never heard of carpet layers using water.) See Building Science.

The finished basement in my current home is insulated the same as yours, but with open cell in the rims. In the summer I pull out at least 20 pints a day from about 1650 sf.

    Bookmark   July 9, 2007 at 11:31PM
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Our basement is always at least 10% more humid than the house, sometimes more. The only time it hits 50% without a dehumidifier is in winter.

My understanding is that AC is inadequate to remove humidity from a basement because basements are typically cool and the AC can't run long enough to remove the humidity. We have a bone-dry basement and run the dehumidifier from May until early October. I'm surprised you even need AC in the basement, ours is only 60-65 degrees in the summer.

    Bookmark   July 10, 2007 at 1:15PM
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