I built a new garage in Oct 2011. It is heating buy radiant in floor. Today I had to pull beck a peice of insulation, the sheeting was pretty wet. Yu could see the water, I have since checked all over the garage. There are place where it's wet and more places that are bone dry. I can not figure this out. There is only house wrap on the exterior. 2x6 walls with paper face R19 in the walls. The garge is 30x40 with 16' ceilings. Can any one give me some advice as to why this occured????? Thanks A very frustrated guy!!!!

Where are you located? For condensation to occur, warm moist air must pass a cold surface. Cold air cannot hold as much moisture as warm air, so it simply condenses on the surface. So, what do you have in your situation? Air leaks/currents pulling warm air through the wall? If the temperature of your wall is colder than the dew point outside, condensation will occur. How cold do you keep the garage?

Is it possible that you have leaks or improper flashing diverting water into the wall? What kind of exterior do you have. Synthetic Stucco (Dryvit) that extends below grade can cause ground moisture to wick up and get to the sheathing. Same holds true with stone veneer. Is the OSB on the inside as well as outside of the walls?

"pull back a piece of insulation"? It sounds like there is no air barrier between the garage and the exterior sheathing AND the insulation is fiberglass batt. I'm sure the insulation experts will chime in, but that is not an ideal situation. Warm, moist air has free access to the cold sheathing as typical batt installation is not an effective air barrier.

Pretty simple. Concrete is drying out and you have high humidity. Bigrig hit the nail on the head about the lack of an air barrier. kraft facing makes it easy to install but is not a very effective at stopping air leaks. It will also trap the moisture in the wall. Now that the moisture is in there you need to pull all the insulation and let the structure dry.

If you are serious about insualtion you should pitch the batts and get blown in cellulose and then detail the drywall to be air tight. I would not use plastic.

What are all of the layers in the wall - inside to outside?

jonr: According to the description it's:

housewrap/(sheathing- type unspecified)/fiberglass/kraft facer

..with no exterior siding or interior finish materials specified.

I suspect the wet bays may be where the facer leaks lots of air, the dry areas are where it's tighter, but there's a lot more going on here.

One factor is how much direct sun the siding gets- a north side wall will run substantially lower on average, accumulating more moisture, and taking longer to dry out. Shaded vs. sunny sections, same story.

Another is the lack of siding. Housewrap is referred to as "weather resistive barrier", but it's not functionally capable of behaving like siding. If it gets any wind-driven rain, roof-eave drip splashback, or piled up snowdrift it's getting literally hundreds (or thousands) of times more liquid water on it than it's designed for, so in some wet areas the moisture drives may be primarily from the exterior.

Since it's heated-conditioned space it will probably make financial sense to put at least 1" of exterior foam over the housewrap and leave a ventilation gap between the foam and siding so that the siding can't trap moisture in the wall. The type and thickness of foam that makes the most sense is climate and use dependent. If it's only heated intermittently the economics of foam may not always work, but even 3/8" fan-fold XPS siding underlayment does a lot for reducing moisture drives from the exterior, and adds ~R2 of thermal break over the framing.