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generalstads 11-01-2010 11:07 AM

Mold on insulation...I think?
I have an unfinished basement that I am in the process of finishing myself. I have a walk-out basement and live in Minnesota. In our frequently very-humid summers (I gets much more humid in other climates), my basement is nice and cool. On my exterior exposed 2X6 basement walls, here is the layering of materials as far as I can see(and maybe this is most typical):
vinyl siding
Tyvek wrap
Exterior OSB sheathing
2@6 Walls with fiberglass insulation
vapor barrier

On those summer days when it is very humid outside, I see moisture on the inside (insulation side) of the vapor barrier. Is that to be expected? That is in fact, the vapor barrier’s job, correct? Should I be concerned? The fiberglass insulation appears to have mold spot, but I am not sure if it is mold. I was told that mold really only occurs when you have constant moisture that does not dry up. Well, we have some instances where we have up to a week of humid weather. That might constitute constant moisture. I have talked to neighbors that have similar houses/basements and they don't get moisture like I do on their vapor barrier/insulation.

Would you recommend that I remove and discard all the insulation, install vapor barrier sealed tightly against the sheathing and then install new insulation before I finish the basement completely?


GBR 11-01-2010 08:08 PM

Study these, then ask questions, we will try to help you:

Building Science Consulting - Designs That Work - Cold Climate - The Basic House - Building Enclosure


nealtw 12-14-2010 10:33 PM

The bearier is to stop inside moisture from getting to the insulation.There should be no water on that side. You have a problem that needs to be inspected more.If your siding has a leak the tarpaper shoud keep it out. When water does get in it should vent out thru vent slots that are left between sheeting when the house was built. A common cause might be windows and no venting in the sheeting below it. I would suspect mold that should be removed and problem solved

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