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Basement Knee Wall Insulation

The upper part of the walls for my walkout basement/workshop is 2x6 construction, insulated with un-faced fiberglass insulation. I noticed last winter that the outside wall under the insulation had frost on it. My builder says you shouldn't put poly on the walls in a basement. I think that poly on this part of the walls is required to prevent moisture migration to the cold surface and then freezing. What is your recommendation??????

Re: Basement Knee Wall Insulation

My builder says you shouldn't put poly on the walls in a basement.

Bob ...
I would have to disagree in part with that statement.

That's exactly the role of the vapor barrier ... to provide a barrier from warm moist air from contacting the cold zone and condensing.

The frost is evidence that moisture is present in the area behind the insulation .... which is the coldest point ... and freezing.

Some clarification is needed ...... how new is this construction?

The reason I ask how recent is the structure is ..... new lumber and concrete will expell moisture as it cures and dries. This could be as long as a year or so after construction. However ... if this new structure is immediately filled with insulation and covered over with a plastic vapor barrier this will trap that moisture from the new materials as they dry and cure .... and may prolong the time the moisture can be evacuated .

If it isn't recent construction then it's very possible the vapor barrier wasn't properly installed. It needs to be completely sealed and air tight as possible ... otherwise it's a waste of time and money ... also can cause more harm than good.

Just a thought. :)

Re: Basement Knee Wall Insulation

To answer you question, the house is 2 years old. Also, these is currently no vapor barrier, I'm planning on installing one hopefully to prevent moist migration and frost. That's the reason for the question.

Re: Basement Knee Wall Insulation

My mistake ... it wasn't clear to me if there was vapor barrier before.

Yes .... properly apply vapor barrier and don't leave any gap between the insulation and exterior wall.

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