04:13PM | 01/29/03
Member Since: 01/28/03
1 lifetime posts
During some few warmer days of last week all of my concrete walls in the basement of my newly built house started to “sweat”. I had water almost everywhere on the whole perimeter between basement floor and the walls. At first I thought it’s the water coming from under the concrete floor. But after further examination I took out some of the fiberglass wall insulation and what saw was the water flowing down from melting ice as a result of moisture condensation. In the air pockets between the subflooring and the concrete basement walls I have not only moisture and icing but also mold growing all over the places.
I do not agree with opinion of my builder that it happens during the first year when the concrete is still curing because the condensation would appear on the whole area of concrete wall rather than showing up only at the area – top of the concrete wall and the level of the ground. The level below is fine and dried up.
In my opinion I will have the same problem every year not just this year.
I do not know what to do with the mold which already started to grow in the pockets mentioned above. I also would like to mention the level of relative humidity in a house is approx. 30-35% and I can not go lower than that as I’ve been instructed to maintain it at this level because of hardwood flooring I have in half of the area of the house. I would appreciate any advice I could get from anyone. Forgot to mention I live in Winnipeg, Manitoba where temp now is -25C
Thanks a lot


02:34PM | 01/30/03
Member Since: 01/28/03
693 lifetime posts
Actually, your builder is correct. There is an excess of moisture the first year in any new construction. Masonry products outgas water vapor. So do wood products.

And what you are exeperiencing is completely in line with the physics of your basement.

But even at a 'normal' 30-35% relative winter humidty, the fact that your basement walls below grade will remain at a relatively constant 55degrees F but the upper portions of your wall can and will drop to nearly the -25C you are experiencing only goes to support the fact that the upper walls are cooling the air below the dew point while the lower walls are not.

For example, at an interior temperature of 70 degrees F and a relative humidty of 35%, the dew point (Condensation point) is only 40 degrees F. Any surface that cools below this level has the potential to create condensation and icing.

Obviously your upper walls are well below 32F or 0C since the condensation is freezing only above ground, and not below.

If you have open web concrete blocks for your basement walls and the webs remain open at the top, this will only add to your existing problem.

The reason is that ground water vapor will enter the block cavities, move up and out of the block cavities at the top of the wall thru convection, increase the relative humidty in these pockets below the subfloor and the top of the block wall, and increase condensation and the dew point.

The only ways you can reduce this problem is to dehumidify the basement, add foam insulation on the outside of the house foundation above the ground, and to fill the webs in the block at the top of the wall to block moisturef rom entering the basement.

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