Replies

1. Expert Member
   Zephyr7|Dec 12, 2018 11:56am|#1

   Yep, reduced humidity is a good result. Chances are you sealed up ingress paths that were letting in excess humidity (although this doesn’t do as much in the winter), and the insulation on the walls will stop vapor from migrating inward. I’m working to seal and insulate my own basement the same way, although right now it’s too cold for me to spray foam the rim joist.

   Bill

2. Expert Member
   Dana Dorsett|Dec 12, 2018 01:16pm|#2

   >"Is this to be expected? This would be a nice ancillary benefit. I’ve also noticed a 15% increase in average temperature as well, notwithstanding the unusually cold weather we’re experiencing in New England this December."

   Raising the temperature lowers the relative humidity. I'm not sure what means "...15% increase in average temperature..." in 'merican dialect- is that 15% higher relative to absolute zero? Or did you really mean 15 degrees F (use to be 50F, now it's 65F)?

   Temperature is what the humidity is RELATIVE to in "relative humidity". At the same absolute humidity air that was 45% RH @ 50F would be only 26% RH @ 65F and conversely, without removing or adding any moisture. That air has a dew point (= the temperature at which it hits 100%RH) of about 30F- the only thing that changed was the temperature, and thus the relative (but not absolute) humidity.

3. GBA Editor
   Martin Holladay|Dec 13, 2018 06:41am|#3

   Jason,
   It's possible that moisture was evaporating from your foundation walls before they were insulated, and that inward evaporation was introducing moisture into your home. Installing closed-cell spray foam on the interior of your foundation walls would have eliminated the evaporation.

4. Expert Member
   Dana Dorsett|Dec 13, 2018 09:03am|#4

   I'm sure some moisture was evaporating from the foundation, but not enough to make a radical a shift in the indoor relative humidity over a short period of time.

   The primary factor here is still the rise in room temperature.