Thread: attic spots- mold or stain?

possible mold

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Originally Posted by Heather Smith

Buying our first house. Inspector found "blackened surfaces" that he says are rust stains. After looking on this site and internet I'm afraid it could be mold. Would love to know what experts here think!! thanks!

I would guess that your inspector is correct and this is rust from exposed nails and limited ventilation in the attic. If an attic is not adequately vented, or if moisture is being vented into the attic from a bathroom fan, dryer exhaust or other source, moisture will condense on the cold areas. Often nails are colder than any other part of the attic.

I do alot of consultations for contractors regarding this exact issue and condition. During the winter all the openings in your ceilings especially your attic hatch or pull down stairs allow excessive air/heat to escape into the cold attic. The coldest thing in the attic is the metal nails.
They are typically at the brink of frosting, and adding the heat from the interior allows them to "sweat" and drip, causing the rusting and stains on the sheathing.
Along with proper ventilation, sealing or at least insulating the openings is required. An insulation panel over the attic hatch, proper insulation at the other openings in the ceilings (ie, exhaust fans, lights, fans, etc) will help reduce the heat escaping into the attic.
Make sure the exhaust fan connections are sealed properly at pipe seams and at the perimeter of the fan enclosure between drywall and fan housing.

A good test for these condition is to go into the attic and push up on the plywood looking for any loose or separation of the plywood and the rafters. This condition can be a costly one to correct...

Poor ventilation and excessive moisture conditions are among a your homes top priority for correction and repairs.

Best

Ron Bibler
Excellence Exterminating Co. Inc.
Excellence Home/Building Inspection Services
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