Mold and ice behind my insulation

[mamamew]

Need your help! I'm a contractor working on my own house and I've run into a strange problem with my insulation. I used some extra Roxul insulation in my garage and when an electrician tore a piece out, I found mold on the OSB sheathing.

I started pulling out the rest of the insulation in the garage and found more mold. It was only at the very top of the wall. When I checked the rest of the house, all the insulation was frozen to the sheathing. I live in northeast Pennsylvania so it's cold outside but where there's no insulation, there's no ice or mold. I called the company and they said I need to put R-10 insulation on the outside of the house. The house used to have faced batt insulation and fan fold on the outside. Why would my new insulation be freezing and getting moldy? Has anyone else had this happen with Roxul?

 

[Passionfru1t]

@mamamew yeah, the company's advice to add R10 on the outside is the right solution.
That R10 insulation is what's called continuous insulation. It moves the temperature of the OSB sheathing to a warmer point, so the moisture never gets a chance to condense on it.
The dew point is now safely on the outside of your sheathing, where it belongs.
It's a much better way to build in a cold climate than relying on a vapor barrier on the inside

 

[itsrainingtac0s]

I had the same problem last winter when I fixed up my workshop walls. I used extra Roxul and saw frost and mold near the top of the wall. The issue was no outside insulation. Warm air inside hit the cold wall and made water build up. Roxul doesn't block vapor, so the water got stuck and froze. The old insulation had a face that helped stop that. You might need to add foam on the outside or seal things better to keep the wall warm enough. A lot of people in cold areas deal with this too.

 

[RosalieGomez03]

Need your help! I'm a contractor working on my own house and I've run into a strange problem with my insulation. I used some extra Roxul insulation in my garage and when an electrician tore a piece out, I found mold on the OSB sheathing.

I started pulling out the rest of the insulation in the garage and found more mold. It was only at the very top of the wall. When I checked the rest of the house, all the insulation was frozen to the sheathing. I live in northeast Pennsylvania so it's cold outside but where there's no insulation, there's no ice or mold. I called the company and they said I need to put R-10 insulation on the outside of the house. The house used to have faced batt insulation and fan fold on the outside. Why would my new insulation be freezing and getting moldy? Has anyone else had this happen with Roxul?

Switching from faced batts to unfaced Roxul? That's probably why you're seeing mold and ice. It sounds like the moisture's condensing in a different spot now that the Roxul lets more vapor through to the cold sheathing.

 

[hotriot]

Looks like the build could be because the heat is escaping the building, Chack that out. There's mold inhibitor now available, get one to avoid the growth then reinstall the insulation when it;s dry. Best if you can add a vapor barrier sheet.