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rovers1973 05-14-2010 03:42 PM

Condensation inside wall on vapour barrier
I am in the middle of re-insulating my outside wood frame walls. I got a bit done the other day and noticed when I came back to it the next day, there was condensation on the vapour barrier inside the wall where the insulation is? The following day it was gone??? Is it because the whole wall isn't finished yet? Or is it a normal cycle for some moisture to condense and dry back out in the wall.
Its wood frame, with OSB sheathing, building paper and cedar siding. Fibreglass insulation with 6mil poly inside. Test area was a south facing wall and it has been sunny and warm during the day. I want to sort this out before I finish the whole thing off.

xxPaulCPxx 05-14-2010 10:00 PM

So you are seeing water from the inside of the wall, contained within the insulated cavity through the clear plastic, right?

Congrats, you are seeing thermally driven vapor. Normal water vapor gets into the surface of the structure, then it gets heated up by the sun. This actually drives the vapor deeper into the structure. What should not be happening is actual condensation on the inside of the plastic. There should be enough insulation so that any vapor is gently warmed before it hits a condensing surface... where it will drip down, collect, cause rot and mold and attract termites.

You've got your walls open, might be time to thing about GOOD insulation. Fiberglass batts is not under that heading.

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