First let me say there's a lot of competing information on which is better, fiberglass or cellulose insulation. Both can be blown into existing walls and attics without significant demolition. The people who mainly sell and install cellulose insulation think it's worlds better than fiberglass and those that manufacture and install fiberglass insulation think that's the best choice. I'm still trying to make up my mind what to believe but both options can be DIY projects and both choices offer a free blower rental with a minimum purchase from Home Depot.
Insulation recommendations changed a few years ago. If your home was built before 1990 there's a good chance you don't have enough attic insulation. If the level of insulation in your attic is at or below the floor joists, you don't have enough. If you can't see your floor joists in the attic because they're covered with insulation you're probably good.
If your home was built before 1980 you may not have any insulation in your walls. If your home was built before 1960 you more than likely don't have insulation in your walls. There's really no way to tell without making a small inspection hole in an exterior wall and visually checking.
To add insulation to existing walls without having to tear down all the drywall the only two affordable choices are blown-in fiberglass or cellulose insulation. Foam is way too expensive for me right now.
Here's what cellulose and fiberglass insulation is currently selling for at Home Depot in my area:
$11.48 for GreenFiber Blown-In Cellulose Insulation
$29.68 for Owens Corning AttiCat Fiberglass Expanding Blown-In Insulation System
When I first saw those numbers I got excited and thought I could blow in cellulose for a lot cheaper than I previously priced fiberglass. Unfortunately you need a lot more cellulose packages than you do fiberglass because the fiberglass is compressed. When it comes to walls it gets even worse which I'll explain after we look at the numbers for attics. Let's say we have a 1,000 sq ft attic we want to insulate by adding an additional R-30 worth of insulation. Here's what the numbers look like.
Attic Insulation Cost Comparison
| Insulation | Pkgs Needed | Price/Pkg | Total | Savings |
|---|---|---|---|---|
| GreenFiber R-30 | 44 | $11.48 | $505.12 | |
| AttiCat R-30 | 16 | $29.68 | $474.88 | $30.24 (5.99%) |
| OC Fiberglass R-30 Batts | 29 | $15.98 | $463.42 | $41.70 (8.26%) |
| GreenFiber R-38 | 59 | $11.48 | $677.32 | |
| AttiCat R-38 | 20 | $29.68 | $593.60 | $83.72 (12.36%) |
| GreenFiber R-49 | 81 | $11.48 | $929.88 | |
| AttiCat R-49 | 26 | $29.68 | $771.68 | $158.20 (17.01%) |
The costs above only reflect the cost of the insulation. You get a free 24 hour blower rental if you buy 20 bags of GreenFiber or 10 bags of AttiCat and we're above both of those and I assumed you'd need to rent a truck for either if you don't already have one. Although you're getting a lot more packages of GreenFiber so for some people, that may mean having to rent the HD truck instead of using their own truck.
R-30
If you're only adding an additional R-30's worth of insulation the cheapest option is to use Unfaced R-30 Batts that you just roll over your existing installation (perpendicular to your joists.) if you don't mind crawling around cutting insulation.If you'd rather blow insulation, AttiCat is slightly less than GreenFiber and not much more than R-30 rolls. Not a big enough difference to choose one over the other if you have a certain preference for either fiberglass or cellulose in my opinion.
R-38 and R-49
If you want to add an additional R-38 worth of insulation or more you really start to see significant savings with AttiCat. For some reason, GreenFiber's recommendations aren't linear. You need proportionally more insulation as you increase R-Value.
At R-30 you need about 2.75 times as many GreenFiber bags as you need AttiCat. At R-38 it's 2.95 times more and at R-49 it's over 3.1 times as many packages.
I think the labor will become an issue as well with cellulose. You have to load, unload, carry and feed about 3 times as many bags of GreenFiber as you do AttiCat.
At R-30 you need about 2.75 times as many GreenFiber bags as you need AttiCat. At R-38 it's 2.95 times more and at R-49 it's over 3.1 times as many packages.
I think the labor will become an issue as well with cellulose. You have to load, unload, carry and feed about 3 times as many bags of GreenFiber as you do AttiCat.
Wall Insulation Cost Comparison
The following table compares the price for 2,000 square feet of 2x4 framed exterior walls.
| Insulation | Pkgs Needed | Price/Pkg | Total | Savings |
|---|---|---|---|---|
| GreenFiber R-13 | 98 | $11.48 | $1,125.04 | |
| AttiCat R-13 | 27 | $29.68 | $801.68 | $323.68 (28.77%) |
| AttiCat R-15 | 31 | $29.68 | $920.08 | $204.96 (25.58%) |
Things get a lot worse for cellulose insulation when it comes to blowing into existing walls. When installing blown-in insulation in walls you have to blow it in at a higher density than you do for attic installations.
This is true for both cellulose and fiberglass but fiberglass only needs double the amount while cellulose needs triple the amount. With AttiCat you also have the option to add a little more to get a higher R-15 insulation rating. With cellulose you'd probably start busting through your drywall?
Cellulose insulation settles a little bit compared to fiberglass so you really have to pack it in. When you do that, the settling is minimal. I'm guessing that's why it takes much more cellulose insulation compared to fiberglass.
Cellulose insulation settles a little bit compared to fiberglass so you really have to pack it in. When you do that, the settling is minimal. I'm guessing that's why it takes much more cellulose insulation compared to fiberglass.
You're saving a lot more money on material cost with fiberglass than with cellulose insulation even if you choose to go with the R-15 installation option of AttiCat. You're also dealing with about 1/3rd as many packages of insulation.
Conclusion
There are pros and cons to each but it's a bit difficult to discern what's truth and what's marketing. For example fiberglass is more affordable and provides good insulation but is itchy. Cellulose is treated with borates which makes it fire retardant and may repel pests and mold. It can be as much as three times heavier than fiberglass which could be an issue in some structures and if not installed to the correct density it can slump over the years leaving an uninsulated void at the top of the wall cavity.
Either GreenFiber or AttiCat is going to be better than not having enough attic insulation or any insulation in your walls if you live in a colder climate. Both can be installed by DIY'ers who spend time reading the instructions and preparing beforehand.
Either GreenFiber or AttiCat is going to be better than not having enough attic insulation or any insulation in your walls if you live in a colder climate. Both can be installed by DIY'ers who spend time reading the instructions and preparing beforehand.
For adding insulation to your attic at R-30 they're similar in cost but as you go deeper you realize more savings with AtticCat.
For adding insulation to existing walls you can save close to 30% with AtticCat versus GreenFiber and you'll need to deal with about 1/3rd as many packages of insulation. They're similar in size but the AtticCat is heavier because it's compressed. Still I think having to open and load that many more packages into the blower is going to get tiring and possibly slow things down.
You can get a free blower rental with either so other costs should be similar.
The numbers I calculated are from current prices in my area. Check to see what GreenFiber
and AttiCat is selling for in your area before you make any decisions.
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