Q.) are you sure you don't have a leak into the cavity space and that you aren't seeing water leakage into the wall and not condensation?

Dehumidifier in the basement should minimize that problem if it is only due to the heat differential and basement humidity..

There is one other thing than can cause the moisture---if a cooling/heating register is close to that area and cool/warm air is directed at the area. If that is happening, simply add a deflector to prevent the air from blowing directly on that wall.

A poly sheet is not enough over any insulation in any wall cavity.

First, poly sheets (as are paper faced 'vapor retarders') fully flammable.

Building codes require that any flammable paper or poly materials be covered with at minimum 1/2" gypsum board.

Hang and finish your insulation and exposed vapor retarder with the rwquired 1/2" minimumgypsum board and your problems will be resolved.

The moisture is coming from the outside and condensing in the cooler insulation and on the exterior side of the vapor barrier.

For cooling season the vapor barrier is on the wrong side.

Since you are in NH, you have predominately a heating season and the barrier is towards the warm (interior side) of the insulation.
In predominately cooling areas, the vapor barrier goes on the outside (the side that is warm most often).

Since there is no practical way to move the vapor barrier for the seasons, the longer season is used to decide the vapor barrier location.

In the off season there may be limited condensation.
Running a dehumidifier inside the house is not going to remove moisture that is on the other side of a vapor barrier.

Be SURE there are no leaks from anything.
The small amount of condensation on the outside of the vapor barrier should dry to the outside.

I have same issue in our 6 years old house which we bought 2 months ago. First I noticed small (5 cm in diameter) paddle of water close to one of the walls, water was dripping from the bottom edge of vapor barrier sheet. This wall is facing south and backyard. Insulation was wet inside along whole wall, but only this wall, others were dry. I pulled it out in few places - it was wet only where it touches plastic vapor barrier sheet. Wall behind insulation was warm and dry. No leaking pipes. I think it's condensation, because it's quite cool in the basement.

brickeyee, thanks for the explanation. I'm curious if there is a way to minimize amount of condensation. Has anyone solved this problem?

"I'm curious if there is a way to minimize amount of condensation. "

Control the indoor humidity.
For residential use this generally means a dehumidifier.

brickeyee, as you have noted "The moisture is coming from the outside and condensing in the cooler insulation and on the exterior side of the vapor barrier." therefore controlling indoor moisture won't make any difference. Again, I interpret this as moisture is coming through the ground, then basement wall, then fiberglass insulation and then it condenses on the poly VB sheet because air temperature inside basement is cooler than air temperature inside fiberglass insulation covered by VB sheet. Out of 4 walls in the basement only south facing one has the most condensation, some condensation also exists on the adjoining 2 walls, about half way through. South facing wall is a lot warmer, therefore air inside fiberglass insulation is warmer too and can hold more moisture.

We recently noticed that our basement walls are 90 % wet behind the plastic, this seems to only happen when the air conditioner is on and it is very cold in the basement. If we open the vents the piping sweats so we keep the vents closed. We have stripped the walls to check for leaks and found nothing, replaced all new insulation and plastic and again are walls are soaking wet..

Is it because the air conditioning is running, we have one of those air purifiers not sure if that is working, see no water in the plastic tubing.

Any suggestions greatly appreciated. We are in Windsor, Ontario.

To much moisture would be my guess, run a dehumidifier.

Not much can be done with this problem as the vapor barrier is on the wrong side during summer but the correct side during winter. The only thing you can do is replace it with XPS insulation, which is technically a vapor barrier on both sides. Fiberglass batt on the basement walls always seem to have problems one way or another. Rule of thumb in my opinion is fiberglass shouldn't touch concrete unless you want problems.

Ah missed that Vith, good catch.

I run a dehumidifier in my basement during the summer. It keeps the air a bit drier down there when the AC is not running. When the AC is running, I do leave the basement registers open to circulate air throughout the house. It seems to work pretty well overall. We have heat and humidity here in MO in the summer. I had musty odors down there before using the dehumidifier. I set it at about 55%. When it's very humid out, it pulls 5 gal of water out in 24 hrs. from a 3000 sf house. More if we empty it. And we're pretty good at keeping the doors shut!