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Contractor says don't use dehumidifier

Posted by gina_w (My Page) on
Mon, Jun 11, 07 at 12:25

Hi all! I'm in dry, warm Southern California and I've just had a basement area finished. It was an unfinished open room off the garage, with one concrete block wall.

My contractor closed it off from the garage, added insulation to the ceiling (under my living room), can lights, and Drylocked then insulated/drywalled the concrete wall.

The concrete wall side is underground.

I ordered a dehumidifier for another purpose, but told my contractor I would use it in the new basement room too. He said it wasn't necessary, and not only that - it would draw moisture from outside INTO the concrete wall, new insulation, etc.

We've not had any moisture issues there previously, and this is a 30-y.o. townhome.

Any experiences? Do these dehumidifiers work so well that they draw moisture in from the outside like that?

I will listen to my contractor, since he's a smart cookie, but I am curious.


Follow-Up Postings:

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RE: Contractor says don't use dehumidifier

"He said it wasn't necessary, and not only that - it would draw moisture from outside INTO the concrete wall, new insulation, etc." BALONEY!!! My suggestion is to buy a humidity meter. Radio Shack has a small combo meter/clock for about $20.00. Overpriced, China, but it seems to work well. I keep my basement at 50% relative humidity. Use the dehumidifer if necessary. Over 60% RH encourages fungus growth, less than 40% causes breathing problems. A dehumidifer can add to the electric bill.


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RE: Contractor says don't use dehumidifier

I'm not so sure your contractor realizes that all a dehumidifier does is removes moisture out of the air. It's not going to draw any in. But, why run one if it's not humid down there? You are probably running A/C anyway, right? The air that leaves an A/C is dehumidified air. Use the space for a while, and if it feels clammy and damp, get the meter like what bas driver said and go from there.


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RE: Contractor says don't use dehumidifier

I'm near the ocean and don't need AC. I'm not sure how this room will feel since I've never used it yet - it's just been a junk storage space till now. I got the dehumidifier for a large, closed storage room near the basement room. I noticed some mold in there. I keep shoes, tools, holiday stuff, etc.
in there.

Since I saw that, I wanted to head off any such issue in this new room, since we just closed it off. The contractor did put a small ventilation cutout near the floor on one wall.


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RE: Contractor says don't use dehumidifier

One of the things the contractor obviously does not understand is that as air gets cooler, the relative humidity of that air rises, with no change at all in moisture content. Basements are typically cooler than the outdoor ambient temperature. My basement has no water intrusion at all. 4 layers of 7.5 mil poly under the floor slab. But Summer humidity there will rise to about 75% due to it being so cool in the basement. Your basement possibly may be too humid. I have two dehumidifiers so that the whole area is covered for effectiveness. I have them controlled by Honeywell humidistats for rather precise humidity levels. One of them dump into a floor drain, so no bucket to empty. The other will soon be to a drain.


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RE: Contractor says don't use dehumidifier

Thanks bus_driver - I'll definitely get a meter and check it out.


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