Home Improvement → Cellulose v Fiberglass for the attic

I remember last winter there was thread here talking about cellulose v fiberglass and if I'm remembering correctly I don't think there a conclusion. But I'm wondering if anyone knows of an impartial resource comparing the two? The fiberglass people say cellulose will make your house dusty then burn it down. The cellulose people say fiberglass is bad for the environment and extremely toxic. Basically a bunch of claims but I can't find any data on either side to back it up.

I need to add some more insulation to the attic and there's blown in fiberglass now, just not enough. I'm looking at the diy and pro costs of both and they're just all over the map. Most of the pros I've called don't do blown in fiberglass, just cellulose and spray-foam(which would be nice but removing all the fiberglass then respaying is astronomically out of the budget.) In-fact only one does fiberglass and the salesman said I could have either one for the same price; and they have no preference.

I'm confident they both insulate well I guess the secondary properties is where the conclusion lays. Even if there's no data anyone have any anecdotal experiences to share?

cellulose won't make you itch if you have to work in the attic! my attic is divided in three parts, 1 has cellulose blown over the roll in fiberglass, teh other 2 just the roll FG. i can work in teh cellulose side no problems, but if i put something in the other sides or need to run cabling in them, i itch like crazy.

I haven't looked at cellulose for years, I did look in to it years ago and went with FG but I can tell you that if I go into the attic with fiberglass insulation I have to wear a respirator or I'm dying the rest of the day.

Let me sum it up for you.

Thermal insulating value: Both about the same
Sound insulating value: Cellulose is better than fiberglass
Comfort working in attic: Cellulose is better than fiberglass
Increased dust in the house: Fiberglass is better than Cellulose

I too, have "blown in" fiberglass from the 60's. It wasn't nearly enough, so I blew in cellulose right on top of it (it's ok to do that).

The answer was simple for me. Cellulose and the blower equipment were readily available for me to do it myself.

It's much nicer to work up there now with the fiberglass covered. I don't get nearly as itchy. You should still wear a mask with cellulose. It's pretty gross when airborne.

As a professional who must access attics fairly often, I can say that my least favorite is blown in fiberglass insulation. Yuk.
There is some new insulation, it's usually white, that isn't nearly as bad as the old fiberglass. I do believe it is still fiberglass, but much softer.

fiberglass insulation derives it's insulation properties from the air it entraps, putting heavy cellulose insulation over it will cause it to compress, and not allow the air pockets to form, how much it's affected depends on how much it's compressed. there is one other thing better about cellulose, it stops air infiltration, wind will blow right through fiberglass, but not cellulose.

The cellulose isn't heavy at all. There is no noticeable compaction. Although, I only added 5-6 inches.

Even if the current fiberglass were to be compressed it's already badly compressed due to settling. According to the chart left up there R-32 was put in and in some areas it's settled to about R-12 I don't use the attic for storage, and other then once or twice to pull wire and occasionally poking my head up there to check on things I don't use the attic. Even if I wanted to the way the roof is framed leaves very little space for much of anything. I'm planning on bringing it up to R-50 or R-60 so that's at least 10 inches(but probably closer to 20) that has to be blown in.

I'm wondering about the dust; how dusty does it get? Nunya I'm doing exactly what you did. Did you notice an increase in dust or anything after the cellulose went in?

I've got the pink fiberglass now, that's what they sell at lowes and that's what the contractor that does fg uses. I think the white fg is certainteed but no one around here sells it or installs it.

you can get low dust or stabilized cellulose, although the dust is only created during insulation, if you had a crack in the ceiling or some other way for the insulation to get in the living space, some could get in, but it MUST be a lot better than breathing in tiny GLASS particles from fiberglass!.

The dust is mainly in the installation. There's lots of it. A particle mask and goggles are a must. When I am up there crawling around, I do kick up some dust.
It's like that in every cellulose attic I've ever been in. As far as in the house, there isn't any infiltration.

Ah ok I usually throw on a particle mask even if I'm just poking my head upinto the attic now. For the install; mask, goggles and coveralls no matter which product I choose.

There's nothing really connecting the attic to the living space other then the hatches and I guess space around the ceiling light fixtures. I guess the dust isn't a problem. I was googling earlier and found some blog posts about a fine layer of dust in the house that never goes away after putting in cellulose; I'm a little skeptical of that.

Sounds like they have a hole somewhere in thier HVAC supply / return lines.

That's kind of what I figured too. Since I don't have any hvac in the attic, seems like dust shouldn't be an issue.

You can't touch fiberglass with your bare hands safely, it will trigger a reaction if it gets in your eye etc, the color (naturally clear) comes from an adhesive (varies in heat rating), which off-gases formaldehyde (carcinogenic VOC). Cellulose is mainly newsprint & corrugated, attic spray-in usually has a water based adhesive to keep it from settling. No dust is involved after installation.

I would go with the cellulose, because it's safe, clean, non-toxic, easier to work with, and diverts paper from landfills, also takes less energy to make.

- A

Have you looked into spray foam?

I was thinking the same thing. I did my entire office with it. 4 inches on the walls and 6 in the celling. I have small water heater for the in floor radiant heat, and my "heat" bill is about $25.00 per month for a 1000sf office. It is not cheap but it pays for its self over time.

any air ducts in the attic (including heat) will need to be well sealed - I am certain my ducts are not sealed well - the house is incredibly dusty. I would LOVE to rip out the blown insulation and do foam.

The idiots that blew in the insulation also put 1 bundle (all wrapped up) in the middle of 2 joists - 8 feet or so from the middle of the attic.

I did look into sprayfoam but the lowest bid for the foam + the removal of what's up there now is double the highest bid for new blown in. The payback over-time is good; but I don't have that kind of cash to do it.

My entire hvac system is in the basement. There's no ducts or returns in the attic, all the registers are floor registers and the returns in the wall cavity don't open into the attic.

I've read that fiberglass does very poorly in cold weather. For that reason alone, I suggest cellulose if you've already ruled out closed-cell insulation (the best).

It's very prevalent in Canada where it has been known to get a little cold.
I prefer Roxol as it doesn't itch as much and is water and fire resistant.

No offense, but just because people do something doesn't mean it's the best or better choice.

I'll try to dig up the research and post it here.

None taken, but as fiberglass is so pervasive I doubt millions of homes in Canada were insulated with it if it were not a good product to use in the cold.
I await your research.

I've used roxul in the past, I think it's mineral wool not fiberglass. In my reading I did find this:

quote:

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When attic temperatures drop below 0°F, some low-density, fiberglass, loose-fill insulation installations may allow air to circulate between the top of your ceiling and the attic, decreasing the effectiveness of the insulation. You can eliminate this air circulation by covering the low-density, loose-fill insulation with a blanket insulation product or with a higher density loose-fill insulation.

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from the U.S. DOE and Oak Ridge lab. But I'd also be interested in seeing some actual data. I bet I have that low-density loose-fill fg they're talking about...

Still looking for the scientific research links. I will pass along this image I found. Take with a grain of salt for now.