# Attic Insulation & Sealing planning



## Windows on Wash (Aug 30, 2011)

You are certainly on the right track.

I personally like a cellulose cap over the blown in fiberglass as it makes that stuff work better. Stops most of the convective air movement.

If you combine the two, you can mitigate the weight of the installed cellulose and still get relatively the same R-Value.

R-60 is probably overkill but you could get there with about 6" of additional cellulose on top of the FG.


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## Gary in WA (Mar 11, 2009)

"I'm also a teeny bit worried about ceiling sagging under the cellulose. I plan to be @ R60 which is about 18" for cellulose and 24" for fb."--------

http://www.diychatroom.com/f103/cellulose-attic-insulation-question-162875/

Gary


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## fstr (Dec 29, 2011)

Windows on Wash said:


> R-60 is probably overkill but you could get there with about 6" of additional cellulose on top of the FG.


My calculation is as follows: FB = R2.5/" and cellulose = R3.7/"
So 12 FB = R30 and compressed would be somewhat less. That would require another R30+ of cellulose to get to R60.
30/3.7 = ~8+ inches of cellulose.
How do you get 6?


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## fstr (Dec 29, 2011)

GBR in WA said:


> "I'm also a teeny bit worried about ceiling sagging under the cellulose. I plan to be @ R60 which is about 18" for cellulose and 24" for fb."--------
> 
> http://www.diychatroom.com/f103/cellulose-attic-insulation-question-162875/
> 
> Gary


Thanks for the link - The document on the gypsum was new for me. I posted a question in that thread as my interpretation of table 2 is different in that 1.6# applies to wallboard and 2.2# applies to ceiling board.

Regardless my calculation is as follows (assuming I blow the cellulose over the FB):
12" FB = ~0.5# per sq ft (per Atticat spec sheet) and at R2.5/inch = ~R30
To get to R60 I need Cellulose of R30-38. 
R38 weighs 1.16# per sq ft

1.16 + 0.5 = 1.66.
So I can safely blow 8-10" cellulose over the FB


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## Gary in WA (Mar 11, 2009)

3" minimum of cellulose will stop any convective loops. 1# of weight is similar to a small water bottle every square foot = compressing the f.g., losing R-value. 

Gary


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## fstr (Dec 29, 2011)

Just to close the loop - I finished my project.
First I sealed the attic over the Veterans day long weekend. This was a misrable project! Crawling through fb with a respirator and coveralls (get Tyvek 2sizes too large - others dont last). I installed accuvents in the eaves. My eaves are really small (due to very minimal soffit overhang) and I ended with only about 3-4" at the narrowest over the top plate. I also sealed the outside top plate as best I could prior to - and after installing the accuvent. The accuvent only got me up to ~16" above the ceiling, so I cut addition accuvents in 1/3rds and added the 1/3rds above to get to ~22". Additionally I systematically worked my way through the attic, moving fb out of my way as I go, and sealed all interior top plates and other penetrations.
Next up was the build walls around the access hole and a new catwalk 20" up. 
This past weekend I blew in cellulose. I raked the fb away from the eaves. The logic was that seeing as the eaves are down to 3-4" I would rather put a material with R3.7/inch into that space than to go with 2.5/inch. Then I blew in the cellulose over the fb to a total of 18".
Keeping in mind that the fb was not quite evenly distributed (raked away from the eaves), and based on greenfiber numbers, I blew in an average of 12" of cellulose. A rough estimate puts me at about 2" compressed out of the fb and about R50 overall with combined weight of about 1.5# /sq ft.

Lessons learned:
-crawling in an attic sucks
-fb itch sucks ( I knew both these already)
-cellulose makes a LOT of dust
-accuvent is a great product except it is too short in shallow locations
-Home Depot and the blowers they rent is the weakest link in an otherwise easy job of blowing cellulose.

Thanks for all the valuable responses!


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## Windows on Wash (Aug 30, 2011)

fstr said:


> Lessons learned:
> -crawling in an attic sucks
> -fb itch sucks ( I knew both these already)
> -cellulose makes a LOT of dust
> ...


Good job and good feedback.

This is why most folks say to not skimp on the blowers. 

Congrats on getting it done though!!

:thumbup:


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