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gma2rjc 11-19-2012 03:12 PM

How many bags of cellulose to buy
I'm hoping to get my mom's attic insulated this weekend and would like it if someone could look over my math and tell me if I'm in the ballpark as far as how many bags of cellulose to buy.

The attic is "T" shaped. One section is 26' x 11.5'. The other section is 29' x 11.5'.

I came up with a total of 632.5 sq. ft. of space.

I want to get it deep enough to to be R-60.

According to the chart at -
would I need about 68 bags to do the job?

(Thanks for posting that link in another thread, Gary.)

I left some of the older fiberglass batt insulation up there when I was sealing things up, but plan to take it out of the bays just before blowing in the cellulose. Is it alright to lay the fiberglass batts on top of the cellulose when we're all done?

joecaption 11-19-2012 03:18 PM

Why would you not just blow in the new over the batts?
Has everything been air sealed?
Has baffles been added so the soffit vents do not get blocked up?

DexterII 11-19-2012 03:57 PM

You're math looks good to me. However, and I'm certainly not the expert that Gary or others are, so some may disagree, but even recognizing that they are not going to be as effective once they are compressed by what you blow in, unless the layout is is such that the bats could very easily be rolled up and laid out of the way, or if you are concerned that animals may have been in the attic, I would probably leave them where they are.

gma2rjc 11-19-2012 05:30 PM


Originally Posted by joecaption (Post 1056165)
Why would you not just blow in the new over the batts?
Has everything been air sealed?
Has baffles been added so the soffit vents do not get blocked up?

Everything has been air sealed - I'm embarrassed to say that I've been working on this project off-and-on for a couple years.

The baffles have been added and insulation pushed in between the bottom of the baffle and the top plate to keep insulation from going down into the soffit. The top of the baffles are up high enough that nothing should get down into them. Some bays don't have baffles because they don't lead down to an exterior soffit.

I thought about pulling the fiberglass out of some of the bays so that the cellulose can get down into any gaps or air spaces that may be under or alongside the batts.

I also thought that the fiberglass should be pulled away from the floor near the soffit openings so that more cellulose will fit between the sheathing and the attic floor. But maybe that's the wrong way to do it (?).

It's an old farmhouse that was gutted a few years back and a large addition built on to it. The ceilings in the upstairs bedrooms were not level, so the old ceiling joists were left in place and new joists were put in to level everything off. So there are two sets of joists to insulate between and under. Some of them are side by side, but an inch or two from each other - old and new.

In the other end of the attic, the ceilings below were dropped about 6" or so with new joists, leveled and drywalled. But those joists crisscross each other - one set 6" above the other. I'll try to post a couple pictures.

Fix'n it 11-19-2012 08:40 PM

my advice is to buy 50% more than you think you need. wish i did. chances are that you will use it. and if you don't , just take it back.

fstr 11-20-2012 09:08 AM

My "wisdom" from my project this past weekend:
I estimated 60-70 bags based on greenfiber . com chart. I ended up using 72.
The Home Depot blower crapped out after ~25 bags. Around 1pm on a Saturday it was tough finding a different HD that had a machine in stock. Luckily I have many stores around me and found another. At the second store I got into an argument because they wanted me to buy at least 10 bags. They could care less if I already bought a truckload of bags from store #1.
Machine 2 clogged continuously until I took the time to pull everything out and properly inspect it - to find it clogged with pieces of cardboard!
If I had to do it again today, here is what I would do: Buy some of the bags from one store and some from another, and rent 2 machines. This may sound like more work, but doing the calculation this additional upfront effort would have saved me about 5hrs. Keep in mind the stores will be busy this coming weekend and not in the mood to provide customer service!

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