Basement Insulation


Old 01-18-01, 06:44 AM
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Hi all,

I will be ripping my 60's era panelled, uninsulated, unheated basement out this spring.

This is not the first basement I have done, but, I'm trying to avoid a problem I had experienced in the last basement refinish with moisture, and mildew.

Basement is 3-4' below grade. The last basement I refurbished was also 3-4' below grade, with NO leaks, or water problems. to do the job right, I Thoro-sealed the entire basement....all walls, and floor. This Thoro-seal is supposed to seal the concrete. It is applied with a big paint brush, and dries like a cement. Well, I sealed the walls and floor, then used steel studs (2X4) for the walls, and installed 2" thick foil faced foam boards between the studs 16"OC, and put 1/2" green board up (Water resistant sheetrock). The walls were built out from the concrete foundation approximately 3-4". I also installed a new heating zone, then, installed 14' of High Output baseboard (hot water). The floor had moisture resistant padding with carpeting install over it.

Then I put a drop ceiling in, good stuff, with foil backed 2X2 panels.

I still had a dampness, and mildew problem down there. I then proceeded to rip out the new basement window (1 of the two NEW windows), and installed an air conditioner. It helped the moisture and dampness problem during the summer, but in the spring and fall, when your not running the heat or AC, the moisture problem came back.

So, short of being relegated to running a de-humidifier (Which you probably guessed I am trying to avoid), what the heck can one do to insure this does not happen again? I went through considerable work and expense to insure the basement was well sealed and insulated, only to have it smell like damp, mildew. Yucch.

The one difference between my old basement, and the one I will be doing now is, this house has Central air. The basement has a duct coming down to the basement, which supplies cool air, but it does NOT have another duct to the return air (Which I will do, cause it aint' working right if the air is not being exchanged).

So, anybody out there see something I didnt do right to avoid this again? I'm certainly at a loss.

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Old 01-18-01, 11:59 AM
Join Date: Oct 2000
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Your Thoro seal not only keeps water out but it keeps moisture in.The previous owner of my house finished the basement a similar way. The problem comes when moisture gets past the insulation, it hits the cold, sealed wall, condenses and has no where to go, so it freezes in the winter and stays moist in the summer. In effect you have two vapor barriers. If there are no leaks from outside, it is better to leave the foundation unsealed so the moisture from the inside can penetrate it and evaporate to the outside.
The other problem that may arise is heat transfer from the ground to/from your slab and foundation. For example, in the summer the humid air will hit you cooler slab and or wall or other suface and the moisture will condense, into the carpet or wherever.
I am looking into insulating my foundation to eliminate the heat transfer and thus save on interior space. I have an older house with concrete block foundation that has minimal r-value.
The original builder installed homasote on the basement walls in some areas. I daresay this does not meet fire code but the benefit is that it does not trap moisture, it stores it and lets it evaporate, thus no mold problems and provides some insulation for the walls. I still need a dehumidifier as the slab is not insulated and I get some condensation on that.
Old 01-22-01, 05:06 AM
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Very good point....I believe your right. I effectively put two vapor barriers up by sealing the concrete. Never thought of that.

Maybe this time, I will insulate the walls, but forego the sealing of the concrete walls.

Hmmm, just when you thought you were doing the right thing.

Thanks for the reply,

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