Thread: Blackened insulation

Just wondering if anyone might know what causes this balckened insulation in attic...

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It is caused by warm indoor air leaking past that fixture.
I see it at the junctions of walls too, anywhere the vapour barrier is torn.

I think it is moldy dust, but I don't have scientific proof of that.

sounds good...thks

Any bathroom vents nearby? Two weeks ago I saw a bunch of blackened fiberglass insulation that was crammed right next to the exhaust on the bathroom fan in the attic. I suspect at one time it was vented perhaps to the exterior in the past (a short piece of metal vent nearby but not enough remaining to make it outside). No other signs of moisture there though and the owner is working on having the fan replaced and vented to the exterior.

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What does it mean if your fiberglass insulation is*black?
You might have noticed some black insulation in your attic or maybe around the perimeter of your basement, where the house rests on the foundation. What does this mean? Is it moldy? Wet? What is it?
In fact, black insulation is the energy auditor’s best friend because it tells us where the problems are. In just a few minutes of looking around the attic, you can find the most serious air leaks from the house. Here’s why…
When you have an air leak between the house and the attic, it is usually at an electrical wire or pipe that runs through the walls and into the attic. But sometimes, it’s at a bigger hole, like in the photo above.
The reason the fiberglass gets discolored is that it’s acting like an air filter. Over the years, that continuous air leaking from the house up to the attic turns the fiberglass black with dust. So any place you see black fiberglass, dig down and look for where the air is coming from. Once you find the source, use some good quality caulk or canned foam to fill in the holes. If it’s a big hole, you might need to cut a piece of sheet-metal or drywall to cover the hole. You then want to seal it with caulk or foam to ensure that it’s air tight.