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I live in Northern CA.

  • For over 2 weeks, outside humidity is 90% (night) to 60% (4pm).
  • I use fans when cooking and bathing.
  • I keep the house temperature at 60-66 deg (night-day) and probably may drop to 57 when not at home during the day.
  • I try to open windows and ventilate, but that is hard since when I am home, I want to heat on and it tends to be night time so outside humidity is higher anyway
  • I have no basement
  • house is old, so I don't think it is "too air tight"
  • windows (about half) are old, single pan (not drafty though) and they get TONS of condensation every morning

Why is it that other houses I went to seem dry and maintain humidity at 40-50% while I have such a big problem lowering it?

Am I doing something wrong, like, should I heat the house to a higher temperature, will that help? Is getting a dehumidifier a (only) solution?

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2 Answers 2

up vote 4 down vote accepted

If you have a crawlspace with an earth bottom, it's possible the humidity is coming up through that--check whether you have a vapor barrier below your house. You probably don't, given the age of the house.

Getting a dehumidifier is definitely a possibility. Or a 'swamp cooler' arrangement, where cold water is used to make condensate that you then pipe out of the house, but that really only works in higher temperature air.

(edit) You may find some of this writeup really helpful.

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wonder if cost of that vapor barrier is reasonable for the problem. Also, maybe insulation of floor takes care of that as well since some of the insulation comes with vapor barrier? –  csmba Jan 6 '11 at 17:35
    
Adding insulation to the underside of your floors might help. I think you can staple a vapor barrier right to the joists from below, if you want double protection. –  Alex Feinman Jan 6 '11 at 18:02
    
Don't staple vapor barrier below as @AlexFeinman suggests: you'll get mold and trapped water. –  Bryce Mar 9 at 18:32

we have a similar problem with our house. so far we have found it has helped a little to get fully-vented soffit and roof ridge vents. this allows the outside air to move through your attic to vent the humid air.

condensation is a problem of insulation. the cold from outside is allowed to cool (either windows or poorly insulated sections of walls/roof) and the warm humid air inside condenses on the cool sections. if you have condensation on windows, you need new windows. if you have condensation on walls, you may need better insulation at those points.

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Condensation forms where the temperature of the air decreases below its dew point. I think that adding additional insulation by itself may not prevent the condensation, it may just move the dew point. If your walls are permeable by the damp air adding insulation may move the dew point inside the wall where you can't see it but it is still causing damage. You may need a combination of additional insulation, vapour barriers and ventilation/dehumidification to prevent the condensation. –  flamingpenguin Mar 2 '11 at 11:41

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