adding insulation to the attic

I would like to add insulation to my attic. I currently have about 3 inches of 40 year old rockwool insulation between the joists. I do not think there is a vapor barrier anywhere in the attic. My plan was too leave the old rockwool (or whatever it is) alone and roll out new bats of fiberglass insulation perpendicular to the joists (covering the wood joists for maximum effect). Should I get faced or unfaced insulation?
Thanks, Jason
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The vapor barrier ( face ) should be between the ceiling and the insulation. <rj>
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I agree but if your current insulation does not come to the top of the existing joists you may want to reconsider your direction or add some fill to bring it to the top of the joists.
Colbyt
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How do I add additional layers of attic insulation to a joist cavity that is only half full?
If joist cavity is only half full and the recommended insulation level in your area is R-38, fill the joist cavity flush with the top with the appropriate thickness of fiber glass insulation. Then lay a second layer of unfaced insulation perpendicular to the existing layer to give a total of 12" (or an R-value of 38) in the joist cavity. Covering the attic joists with the second layer will reduce heat loss through the wood. as it says at: http://www.owenscorning.com/around/insulation/faq_attic.asp
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Or, you could just blow in cellulose.
Bob
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I highly recommend the cellulose. It's a little dusty going in, but it does the job very well once it's there. Either way you go, make sure your soffit vents aren't covered when you're done or you'll have moisture problems.
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Thank you to everyone who responded. I will look at cellulose and fiberglass.
Jason
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with the top of the joists. Added 6" unfaced fiberglass perpendicular to the joists.
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It's my understanding that kraft faced (or vapor barrier), that the VB should be the closest to the heated area of the building. Since you have insulation, you'd want non vapor barrier fiberglass.
Rolling across the joists sounds like exactly the way to go.
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Christopher A. Young
Do good work.
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