Storage area in basement under porch area is sweating.

tikamarieNovember 24, 2007

Our excavator excavated under our front porch so we can have a nice storage area in our walk-out basement. (Our builder does not excavate under the porch so we hired our own excavator). So the builder put steel pans down and then poured the concrete for the porch. Now when we go in the storage area in the basement, and look up, the pans are soaking wet with beads of water. (Sweating) We are not sure how to remedy this problem. The house won't be completely finished until about March 1, 2008, but we are afraid this will continue to be a problem and cause mold in time. And our builder will not give any advice because they don't excavate that area and because we hired our own excavator instead of using theirs, they are not very helpful. - Here is a picture of what I am talking about. -

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Think of the physics behind what you're seeing: it happens all the time on the outside of a glass of iced tea - water vapor in the air comes in contact with a cold surface and condenses.

Where is the moisture coming from? Is the concrete still curing? Are the outside walls sealed or protected from ground moisture contact? (Moisture wicks/passes right through concrete.) Does the floor have a vapor barrier below? Is there a moisture barrier between the walls and foundation? (Moisture can wick into walls from the foundation/soil contact also.) In regards to basements and water vapor, the rule of thumb is to plan on the fact that moisture will permeate through the walls as vapor and thus build so as to let the wall assemblies dry to the interior. Building science corp. has a lot of good info in regards to this subject. But, during the construction phase do all that you can to prevent water entry from the exterior.

Heating the pan surface temperature would stop the condensation but this is probably not an efficient long-term option; you would just lose the heat by conduction to the outside concrete. Probably better to insulate the pan surface with a non-permeable insulation. During the insulation stage of the house, I would have the contractor spray foam on the bottom side of the pans. This would insulate the ceiling and prevent water vapor contact with the cold surface.

Here is a link that might be useful: Building Science web site

    Bookmark   November 25, 2007 at 10:24AM
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This is a common problem in cold rooms. Those metal pans are the worst!

Sealing the cold room from the conditioned basement air may help.

But as formula1, says, the surest remedy is to insulate the bottom of the pan. However, to meet fire Codes, the insulation will usually have to be covered with a fire-rated covering--dyrwall, concrete board etc.

For an irregular pan, spray insulation works best, as it tightly covers the metal pan.

Before the fact, a knowledgeable former would place at least 1" of XPS at the bottom of the form, pour over it; when the form is stripped, the foam is adhered to the concrete.

If this wasn't done, you can attach the XPS with concrete screws through fender washers. Then install the drywall over the XPS.

    Bookmark   November 25, 2007 at 12:42PM
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Insulating is an important part of the solution. Reducing the humidity in the storage area is another part. Get a good meter and check the relative humidity. It probably is 70% or more, much too high for the benefit of most stored materials. Keep the humidity controlled to about 50%.

    Bookmark   November 26, 2007 at 8:21AM
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I had the same problem and I solved it by hanging some foam insulation board on the ceiling. I havent had a problem since.

    Bookmark   November 28, 2007 at 10:29PM
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my coworker had the same problem and he had a contractor come in and spray a foam type insulation on the walls and ceiling. It helped but he still struggles with condensation. I don't know what type or thickness insulation was used but apparently it wasn't enough.

    Bookmark   November 29, 2007 at 2:30PM
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he still struggles with condensation
In what way? On what surface is moisture condensing?

    Bookmark   November 29, 2007 at 4:33PM
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