Michael writes from Severna Park, Maryland: "I installed miraflex insulation blankets in my attic in 2002. I've noticed in the winter that water vapor can get trapped in the perforated plastic leading to some black staining from mild mold growth in the fibers. It isn't soaked, but putting your hand under the plastic feels moist and some. I plan on locating holes in the ceiling and foaming them so I get less moisture penetration. The insulation does dry out when the weather is warmer (50-60 degrees). Can I remove the perforated plastic from the blanket rolls? Do you think this will solve my problem?"

Answer: If you have mold growth, I recommend removing and discarding the insulation. Check to make sure your attic ventilation is not blocked and that there is an equal amount in the soffit as there is in the roof. You will need to do some math to calculate your ventilation requirement. The minimum ratio is 1/300. That means you need one square foot of ventilation for every 300 square feet of attic space. We recommend a ratio of 1/150.

You may also have excess warm air infiltrating into the attic from the house via cracks or gaps around electrical and plumbing fixtures. For example, any a pipe, electrical wire or junction box that penetrates the ceiling should be sealed with spray foam or caulk.