Condensation on above grade basement wall

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Old 07-08-09, 04:14 AM
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Condensation on above grade basement wall

Hello.. I started the project of finishing my basement. The house is on a hillside so 2 exterior walls are basically above grade. My plan has been to cover the inside walls with plastic then build the framing 1-2" from the wall so there is an air space around the walls. Now that I have the plastic up I am getting condensation inside the plastic, against the wall. I am assuming it may be from the changing outside temperature of the exterior wall and the constant cooler temperature of the basement?? Now I don't really want to leave trapped moisture behind these finished walls. Should I just remove the plastic and let the walls air naturally? (I don't like the thought of that moisture dissipating into the basement) Or should I paint them with a waterproofing product to create a water tight seal? The walls are standard concrete block. Thanks for any insight / suggestions.
 
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Old 07-08-09, 05:16 AM
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Hi aa and welcome to the board and welcome to the challenge of finishing a basement, perhaps the toughest remodel for a home. There are a lot of related links and posts on this board and I will list a couple of my favorites below.

The concept is to ensure that moisture has a place to escape. That can be inside, but you will have to deal with it, or outside. That moisture can come from: plumbing leaks; rain leaking in; condensation as you have with cooler temps inside and warm moist air outside; condensation from cold temps outside and warm humid air inside; ground water; or poor drainage around the house. And I am sure I missed a few. But if you miss one, the results can be stinky and disastrous.

I'll let you do some reading and get out of the way so others can post and wait for more questions.

My preference is for closed cell rigid foam sprayed or glued to the interior of above grade walls with no air gap. Insulates to avoid condensation and allows (forces) the moisture to dry to the outside.

http://www.eere.energy.gov/buildings...s/db/35017.pdf

RR-0509c: Renovating Existing Basements —

Bud
 
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Old 07-08-09, 05:33 AM
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I think you are on the right track. Rip that barrier down, paint with drylock, frame walls away from concrete and install insulation facing in. And then, go get the best dehumidifier you can afford and run it 24/7 during the summer. IMO, no matter how well you finish a basement, if you don't condition it, it'll be a mildew garden in a couple of years.
 
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Old 07-08-09, 08:24 AM
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Provided you have good drainage (i'd recommend a good system with a sump pump system that includes battery backup pump for a finished basement) and took all the precautions on the outside to keep the soil around your foundation walls you should provide a way for the basement walls to dry into the inside of the basement.

A vapor plastic sheet will cause exactly the problem you experienced. Moisture will be trapped and build up around it, the water will run down and eventually find its way into the basement, unless you have an internal drain tile or a baseboard system.

You did not mention what kind of insulation you are using, but US EPS, US Department od Energy - EERE Building America and Building Science Corp.all recommend that you avoid fiberglass in the basement and go with rigid foam board insulation instead.

Fiberglass soaks up moisture like a sponge and as it does, looses all its R-Value. And because it is usually held together with an urea based compound, also supports mold growth.

Insulation for basement need to be 199% inorganic, waterproof and non absorbent, which is why they recommend the rigid foam boards.
They are a bit more expensive than fiberglass, but a safer option for basements.

Alternatively, you might want to look at "all-in-one" basement wall systems that include rigid foam board insulation and a waterproof cement core that unlike drywall, will give you usable walls you can have shelves, flat screens and fixtures from.

After your basement is finished, if the RH levels read at or above 60% (which you can check with an inexpensive hygrometer sold in hardware stores) you might want to consider a good dehumidifier.

I am including the PDF from the US Department of Energy - EERE with a lot of useful information.


Basement Insulation Systems
 
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Old 07-09-09, 04:01 AM
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Condensation inside walls

Thanks so much for the quick replies. You are confirming my thoughts. By "Rigid Closed Cell Foam", are you referring to the 4' x 8' sheets that are typically light blue and come in various thicknesses at the Big Box stores? What thickness would be appropriate for an inside wall and you tape them to make them airtight?

Sounds like I need to shift gears a little. A dehumidifier is definitely in the plan, my outside grades are all good (that was one of last years projects that has been very successful)

Thanks Guys.
 
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Old 07-09-09, 12:18 PM
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Hi, and welcome to the forum!
Yes, the box store blue foams are extruded poly. Use a mastic or glue to get a thermal break from the concrete. Foil tape (not duct) any joints and gaps.

I would not use Dryloc as it would waterproof the wall with the water collecting and seeping through the slab or the slab/wall joint. The idea of foam board (which is not waterproof or a vapor barrier) is to allow the moisture to slowly release into the room as the article brought out. It will allow some moisture through as it is a vapor retarded.

1" or less thickness board is recommended: In new construction the interior insulation and finishing approach must take into account the moisture migrating up through the footing. This is best accomplished by installing vapor semi-permeable rigid foam insulation on the interior of the assembly to protect the interior finishes and to release the capillary water to the interior in a controlled manner at a rate that does not damage interior finishes or lead to mold.
The best foams to use have a perm rating of greater than 1 perm for the thickness used. This means limiting extruded polystyrene insulation to less than 1-inch thickness for walls (more than 1 inch thick and they do not breathe sufficiently) and making sure that the rigid insulation is not faced with polypropylene skins or foil facings. Additionally, since foams need to be protected from fire, and this is often done with gypsum board only latex paint should be used on interior gypsum finishes (since it breathes). Here: BSD-012: Moisture Control for New Residential Buildings —

Use fiber batt insulation (with a kraft face only above grade portion) in the wood stud wall spaced 1", as mentioned, if at all. Be safe, G
 
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Old 07-09-09, 07:02 PM
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Thanks again so much for the excellent info. I think I have a plan now. All the input is much appreciated and has saved me from going down a bad path.
 
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