gaps between attic ceiling and insulation batts

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Old 02-08-10, 10:32 AM
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gaps between attic ceiling and insulation batts

I am going to have insulation blown into my attic and in the process discovered that the existing insulation (1" +/-batts) were place perpindicular to the joist resulting in a 3-4 inch gap between the ceiling and the insulation. How important is it to correct this problem?? Some people say as long as they blow enough insulation in on top it will not matter, but I was also told that I should take the insulation and place it correctly before they start the work. The house is a 1950 2 story cape in MA
Thanks, Mike
 
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Old 02-08-10, 01:41 PM
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Hi Mike, good question. Yes it should be down inside the cavities as that air gap promotes air circulation and reduces the insulating properties of what is there. Now, is there a vapor barrier, Kraft facing or foil facing on the existing insulation and is it facing up or down? And where are you, warm or cold climate?

A Kraft or foil facing is a poor vapor barrier floating in the air. To be of any value, it needs to be in direct contact with an air barrier, ie your drywall ceiling. Adding more insulation over this would create a space where moist air could accumulate with the potential for mold. If you are in very warm country with air conditioning, different arrangement.

My advice, since you have the opportunity to correct two problems at the same time, pull the existing insulation and air seal all penetrations from below. It is a long list, but easy to do when the insulation is out of the way. Link below for details.
Then we have to decide on the need and placement of a vapor barrier and that will depend upon your location, tbd.

http://www.efficiencyvermont.com/ste...ide_062507.pdf

ps, air sealing is one of the best energy improvements you can make, a good payback.

Bud
 
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