# Cellulose Attic Insulation Question.



## WGFA (Nov 29, 2006)

I want to add some more insulation in my attic. I have FG blown in there now. It is just above the joist's. It's higher in some spots but not much. I would like to use blown in cellulose. Is this ok? TIA...


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## Gary in WA (Mar 11, 2009)

Check the thickness of drywall on ceiling, 1/2" at 24"oc framing = 1.6# per sq.ft. or R-49 minus the f.g. weight. 16"oc framing will take 2.2# per sq.ft. as will 5/8" drywall, or R-60; http://www.greenfiber.com/step_one_-_calculate_your_need_how_to_install.html

Insulation chart, Table 2; http://www.lafarge-na.com/GA-216-07_English.pdf

You will compress the f.g. with progressively more cellulose, degrading its R-value; http://www.greenbuildingadvisor.com/sites/default/files/Compressing fiberglass.JPG

Air seal the attic first and foremost; http://www.google.com/url?sa=t&sour...sg=AFQjCNHwd56o0AxLi8-V03E5cMUmwWATQw&cad=rja

I'll help you find them; http://www.finehomebuilding.com/PDF/Free/021105092.pdf

Gary

Some


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## WGFA (Nov 29, 2006)

Thanks for the info...


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## jklingel (Dec 21, 2008)

The cellulose will also "seal" the blown fiberglass. Blown fiberglass is best dense packed into walls. Loose in the attic I don't think it is quite as good as cellulose; too fluffy.


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## fstr (Dec 29, 2011)

I have a question regarding table 2 in the lined gypsum document. My interpretation is that the 1.6# per sq ft applies to wallboard. Further down in the table it specifically states ceiling board = 2.2# per sq ft. Please help me understand.


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## Gary in WA (Mar 11, 2009)

That would be special "ceiling board", rated as stiffer/stronger for ceiling insulation-framing spacing with insulation loads only. Sorry, no links now as continuing IP problems on my end. Sorry for the late answer. 

Gary


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