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What Causes Dark Marks on Ceiling Where Attic Insulation Has Been Disturbed?

What causes dark marks on my livingroom ceiling? They appear anywhere the attic floor insulation has been disturbed. Also it marks the ceiling rafters where they meet the outside walls. I can paint over it using Kilz plus another finish coat, but it reappears in about eight months. It doesn't seem to be getting any worse.

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I have replaced all the soffits, moved the attic insulation away from the opening between the top of the outside wall and the roof to increase air flow. The roof ventilator is controlled by temperature and is working fine. I recently extended the bathroom exhaust fan duct to the area over the garage to reduce the moisture in the attic.

By Ron from Toms River, NJ 08757

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January 31, 20110 found this helpful

According to my published syndicated handy man it is dirt and some mold. Washing with water and bleach should remove it but it has to be cleaned when ever the dark marks reappear. According to him the dark material forms because the rafters are cool the the space in between the rafters are insulated and are not cool and that draws the dirt etc. Why not wash with some bleach and water to see if that removes the dark marks.

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February 1, 20110 found this helpful

What you have is called ghosting.

As mentioned earlier, its down to the difference between the drywall covered by insulation, where the water vapor in the air passes through and the joists that are colder touching on one side the warm air of your room and the cold air outside, these areas are colder and attract warm wet that condenses into the dry wall and the dirt thats carried in the air.

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Anonymous
February 1, 20110 found this helpful

Go to this link, scroll down to the bottom of the page and click on 'Ask Tim'. He's awesome!

http://www.askthebuilder.com/

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