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mears 08-18-2012 12:47 PM

Batt insulation on top of cellulose in attic?
My attic has an inadequate amount of some type of blow-in insulation. I'm in the process of re-siding my home and am removing the old r-11 bats in the walls and replacing with r-15. Rather than throwing away the old insulation, I'm considering laying layers of it on top of the loose insulation in my attic. Is this ok? I figure worse case scenario I may compress the existing insulation a very small amount.

hand drive 08-18-2012 01:11 PM

if you have enough insulation lay some in the joist bay over top the old and if you get the the insulation up level with the top edge of the joist then lay more insualtion crossways on top of that...

The idea with insulation is you do not want to compress it, it looses its r value if compressed

Gary in WA 08-19-2012 11:14 PM

If you have cellulose up there the additional batts on top will be fine. Cellulose gets denser as it is compressed, raising the R-value per inch. This would also help with wind-washing of the cellulose near the intake (soffit) vents. Though any wind will only slow when going through fiberglass....

If blown-in fiberglass, compressing it will help make it denser also, raising the R-value per inch and helping to slow air infiltration/exfiltration and convective loops inherent with low-density insulation.. Better still, is to air-seal the attic then rake the loose-fill back--- if fiberglass or cellulose. Fiberglass batts lose R-value for their rated thickness when compressed but the density increases per inch.

Remove any paper-facing from the batts first, not just "slashing" them which does slightly more than nothing (unlike an air barrier) to the vapor retarder as a whole.

Check your ceiling drywall thickness before adding any more weight up there, what is the on-center spacing, material (Plaster/lath) and thickness?

P.S. Welcome to the forums!

dleaoh 08-22-2012 08:12 AM

Good Advice From GBR
The reply from GBR in WA tells you about all you need to know :thumbsup: but I want to reinforce his comment about removing backing from the batts before you put them in the attic. It's absolutely essential that you do this, or you will risk serious moisture problems.

Gary in WA 08-23-2012 12:45 AM

Thank you for the compliment, dleaoh! Few and far between..... LOL. I many times end a thread with a following dead silence. Start answering all the cellulose threads with us, you sound pro from your other answers. There are a few other insulation pros here, myself not included, I'm a remodel (contractor no more) carpenter now. Partake!


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