Ventilation Techniques

darcar

I am receiving 2 types of feedback about this topic / Contractors vs. Inspectors

I am finishing a basement of a home with concrete exterior walls. Framing 2x4 walls, insulated, and planned to add plastic to the walls. At first I was going to put the plastic on the cold side of the insulation mainly b/c that is how I was taught to do it as an employee of a former boss. Now that I'm getting into doing my own jobs, it is my name on the line if anything happens down the road so I want to be cautious.
Inspectors tell me to put the moisture barrier, as req'd by code, on the warm side of the insulation.
Contractors say it will lock the moisture in and cause mold.
Here is the code section from the 2006 IRC

Section R318 of the 2006 IRC

In all framed walls, floors and roof/ceilings comprising elements of the thermal envelope, a vapor retarder should be installed on the warm-in-winter side of the insulation.
Exceptions:
1. In construction where moisture or freezing will not damage the materials
2. Where the framed cavity or space is ventilated to allow moisture to escape
3. In counties identified as in climate zones 1 thru 4 in table N1101.2 (Linn county Iowa is zone 5)

The only true way I see to avoid mold and moisture issues is to vent the area and allow moisture to escape as stated in ex 2. That would let cold air into a conditioned room though wouldn't it? Do any of you actually do this method or do most of you just frame the wall without a barrier and/or ventilation?

Also, what does the phrase "comprising elements of the thermal envelope" refering to? Does this mean if the wall etc. is an exterior wall? If so, wouldn't the framed wall still be considered to be on the cold side since between the foundation wall and the framed wall is not conditioned area?

reveivl

If you put the vb on the outside moisture will migrate into the insulation, hit it's dew point and condense inside the insulation. The contractor you were taught by is wrong.

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darcar

Since the plastic is already applied to the cold side of the insul, and the wall is framed, it is ok to leave like it is and add another barrier to the warm side of the insul right?
Is using paper faced insulation batts a sufficient barrier?
If left like this, should a vent be cut in high and low in the wall to vent the space behind?

mighty anvil

None of these code and moisture control issues should apply to the finishing of a basement foundation wall. This is not a "framed wall", it is a concrete foundation wall. The thermal barrier should be on the outside of the wall so that water vapor from inside the house will not condense on the concrete. You should be able to add interior walls any way you want. Whatever the design, I would recommend metal strapping and rigid insulation on the concrete in order to avoid the problems of fiberglass, wood, vapor retarders, and condensation in a basement.

darcar

Since the house was built in the 1930's, I don't think there is insulation on the exterior side of the "concrete foundation wall". The concrete wall is dry, we are trying to address mold and moisture before they become an issue.

Dustball

Here in St. Paul, we're required to put up a moisture barrier on both the warm side and the cold side of framed walls along the exterior basement walls.