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Microbial in a vented attic


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I found microbial growths in a vented attic. The house was 21 years old, original roof. The venting appeared to be properly installed. The ridge vents had wide gaps at the top. The enclosed soffits were not blocked with insulation, but there was microbial growths on the sheathing. Normally its caused from lack of or blocked vents. Any suggestions.

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It depends on the house. I usually spend time figuring out the likely sources of moisture.

  • Most often, it's bathroom, laundry, or kitchen exhaust ducts that don't vent 100% outdoors (and I really mean 100%). Just pointing the duct toward a vent jack doesn't cut it.

Oftentimes it's wet crawlspaces, which are an epidemic in my area.

Sometimes it's skylight wells in bathrooms, which function like little shower steam chimneys to direct steamy air into the attic.

Frequently, it's just typical air bypasses: recessed ceiling lights, poorly sealed top plates, holes around light fixtures, etc.

Occasionally, it's sun-warmed steam from sidewalls rising up into soffit vents.

I've seen a few where the wrap around porch shares the same attic space as the house. Recessed lights there pump damp air into the attic.

You need to do some sleuthing.

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We're finding that with SPF applications, vapor drive is intense, more so than I'd have ever imagined. If the only way out is into the attic, that's where it goes.

That said, some of those black spotty areas look like sheets we pull off the bunk, like Raymond said. Was there additional "mold" beyond the black spotty areas?

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