What is best to insulate with over existing blown in fiberglass insulation?
gat
| Posted in General Questions on
I have about 9inches of blown in fiberglass already and would like to add more.
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Replies
Gerard,
Assuming that we are talking about an attic floor, the answer is cellulose. As much as you can afford.
x2!!
Even if the weight of the cellulose compresses the lower density fiberglass it's the total depth that counts. Compressing the fiberglass layer slightly makes it more air-redardent and more R/inch, but lower inches, lower total R for that layer, but you want at least a foot, and preferably more of overall initial depth. The cellulose will lose about 10-15% of it's loft to settling over the next decade. To hit ~R50 at the settled depth needs to be about 14", which means installing it at 15.5-16", etc. The higher density and infra-red (radiated heat) opacity of cellulose make it a superior performer in this application. It's pretty cheap stuff, and an easy DIY with a rental blower even for newbies if you read up on how to do it.