Hi all!

Been a while since I've posted anything - been getting settled into the new house & also have a new baby.  I have been reading this site, & saw something recently that reminded me of a question I had wanted to ask..  When we were planning our build, I talked to the builder about doiing dense pack cellulose.  He said that the insulation company he normally works with didn't offer it, because they didn't trust that it wouldn't settle over time.  We were on a really tight timeline to get the homebuyer tax credit, so I just couldn't fight that fight.  Anyway, I looked at that insulation company's website & noticed that they offered blown fiberglass "BIB" systems.  I thought it was odd that they had concerns about dense packed cellulose settling, but not dense-packed fiberglass.  Is there ANY reason to think that one would settle more than the other, or is this just a case of selling what they had to sell?

Certainteed Optima will settle if blown at 1lbs density, and is less air-retardent at that density, which leads to lower performance at the temperature extremes due to convection within the fiber..  But if they dense-pack it to 1.8lbs min it won't settle, and will be about as air-retardent as cellulose, and somewhat higher R.

JM Spider can be wet-sprayed in mesh at any density, and if wet-sprayed settling is minimal. But at 1lbs density it isn't as air-retardent as cellulose.  But like Optima, if blown at 1.8lbs or denser it's very air-retardent and performs well.

Settling of other fiberglass or mineral blowing wools is probably a function of blown density too, but the density required for sufficient air-retardency will likely differ from Spider or Optima or dense-packed cellulose.

The settling of dry-blown cellulose is a function of it's installed density and the amount of seasonal moisture changes it experiences, which is both local-climate and stackup dependent.  In most of the US 3.2lbs density will be sufficient to prevent settling in a no-foam wood-clad building, but 3.5lbs might still be necessary in parts of the US. If it's a foam-sheathed studwall it's seasonal cycling will be far less a no-foam stackup, but under a brick or stucco cladding without exterior foam or exterior vapor retarder it'll be higher.  Rainscreened wood or vinyl sided it would be less humidity cycling than with un-vented siding, and can probably get away with 2.5lbs in most places, but I'd still hold the line at 3lbs for dry-blown even with backvented siding. (Dense-packers worth their salt usually shoot for 3.5lbs and take core samples to verify density.)  Wet-sprayed cellulose can be installed in walls at any density with minimal settling, but at low density in open blow attics it can still settle in higher summer humidity vented attic environments (=most of the eastern US.)

The Bible on dense-pack cellulose settling an minimum density required to eliminate it relative to the season humidity cycles was written by a Skandahoovian researcher named Torben Rasmussen. SFAIK his model is still the definitive and best authority on the subject:

http://www.nordicinnovation.net/nor...rep565.pdf

I'll give you a reason since I've blown both products. Very simply when you open a bag of cellulose before you dump it a machine it just sits there until the machine rips it apart and fluffs it. When you open a bag of fiberglass it's like pulling the pin on a grenade. My machine holds 3 bags of fiberglass or 18 bags of cellulose. Even with the most powerfull gas driven insulation blower you could not get the fiberglass insulation back in that bag but you could come pretty close under the right conditions of compressing that cellulose back into it's original package. I've been installing insulation for over thirty years and if I was going to install sidewall insulation in new construction it would be one of the short strand fiberglass products definitely not OC cube wool that product is a joke. Now to totally confuse you I would install cellulose in the attic on that same new construction project.

I a lots of information in your thread and also in replies i really enjoy it.

Posted By smartwall on 17 Sep 2011 10:29 AM
I'll give you a reason since I've blown both products. Very simply when you open a bag of cellulose before you dump it a machine it just sits there until the machine rips it apart and fluffs it. When you open a bag of fiberglass it's like pulling the pin on a grenade. My machine holds 3 bags of fiberglass or 18 bags of cellulose. Even with the most powerfull gas driven insulation blower you could not get the fiberglass insulation back in that bag but you could come pretty close under the right conditions of compressing that cellulose back into it's original package. I've been installing insulation for over thirty years and if I was going to install sidewall insulation in new construction it would be one of the short strand fiberglass products definitely not OC cube wool that product is a joke. Now to totally confuse you I would install cellulose in the attic on that same new construction project.

The installed density of any of these fibers won't be anything like the shipped density- that's not a guiding factor on performance or anything else.

The fact that the micro-fiber f.g. is compressible to much higher density than cellulose for shipment has little bearing on it's installed performance or air retardency.  Yes, it's good stuff, but not ncessarily a better price/performance than cellulose.  At 1lb density may not be as good in "typical" retrofits despite higher ASTM C 518 test performance.  At 1.8lbs+ it's very good- and will thermally outperform cellulose slightly, but with low density installations the quality/integrity of the interior & exterior air-barriers become critical. (I'd take open-sprayed wet cellulose over 1lb Spider, and spend the difference on thicker exterior foam. YMMV.)

Micro-fiber fiberglass also counts on  lower permeance vapor retarders than cellulose in some climates, which can interfere with it's otherwise excellent rapid-drying capabilities, whereas cellulose will buffer and release seasonal moisture.

Dana, you make my point . I can install cellulose at it's original packed density or close to it,but I can't with fberglass. As far as wet cellulose, it can become a problem as far as drying time . When you have a construction timeline, waitng a week for the wall to dry before drywall is not an option for most builders. Plus the problem for what is really in the cellulose.

I have been talking with some very good local installers of all insulating products. My planned build of a double stud wall however has a few scratching their heads around here. Not so much blowing 12" thick (they do pole barns and stuff all the time with that thickness) but they are asking....why do you want to do that. However back to the point, all of them have said they would rather blow fiberglass then cellulose any day of the week. They do all installs, wet, netted, dense, etc. All of them hated dense, most push some sort of open cell foam, etc.
They are pricing the fiberglass pretty much the same as the dense packed cellulose around here. I am sort of in a limbo stage of deciding which product to use. They both have their pros and cons.

Posted By smartwall on 20 Sep 2011 08:05 AM
Dana, you make my point . I can install cellulose at it's original packed density or close to it,but I can't with fberglass. As far as wet cellulose, it can become a problem as far as drying time . When you have a construction timeline, waitng a week for the wall to dry before drywall is not an option for most builders. Plus the problem for what is really in the cellulose.

The fact you can't pack fiberglass at the same density as it's shipped is truly meaningless.  The air-retardency at the INSTALLED density is everything in terms of it's real-world performance.  With noo-skool fiberglass at 1lb it's not so good (about as good as a well-installed batt) but, dense-packed to 1.8lbs it's getting to be almost as good as low density cellulose. At 2.5lbs it's as-good or better than dense-packed cellulose, but SFAIK nobody other than the manufacturers ever install it at that density (for marketing purposes.)  I wouldn't use it at low density, but would at 1.8lbs or better. YMMV.

Drying time on wet-sprayed cellulose isn't much of an issue for 2x4 constuction, but very much is for double-walls & Larsen Trusses.  Dense-packing is a viable option there, or on 2x6 construction in situations where the "time is money" factor  dominates.  There's not much labor difference between installing 3lbs cellulose vs. 1.8lbs Optima, eh?
 

Expanding on it a bit:

The fact that the fiberglass can be compressed more tightly in a press than cellulose means only that it has more air per unit volume when shipped. The fibers in cellulose are tubular/hollow,and could be compressed more, but it would break the tubular structures reducing it's insulating effectiveness as well lowering it's ability to safely wick & store moisture. The fact that cellulose is shredded paper- essentially flakes of bonded fiber rather than individual strands contributes to it's comparatively better air retardency even at low density. To achieve similar air retardency with discrete fibers requires packing them more closely together.

The less air-retardent a fiber insulation is, the greater the performance losses will be at the temperature extremes due to loops of air flow within the insulation layer. This is a serious performance drawback for old-school blowing wools, and even for the new stuff at lower installed densities, but barely measurable in low-density cellulose.

The other issue with cellulose is how the product is made and what the customer receives as an installed product.

Dana,

Forgive me if this question has an obvious answer, but if both Spider and Optima have recommended densities of 1.0/1.8 and 1.8 respectively, how would you go about having them shoot it at greater densities (or is it simply another product that you haven't mentioned)?

You can under blow a product or over blow it in a closed cavity. All products have an optimal density at which they give the best results. It is much harder to over blow fiberglass, much easier to over blow cellulose.

Izerac, your insulation contractor is right . I would do fiberglass for a 12" wall not cellulose. The only way the celly won't settle in a 12" cavity is if you use adhesive spayed cellulose. This would have to be done in repeated layers so it is more labor intensive.

Posted By MikeG on 21 Sep 2011 09:24 AM
Dana,

Forgive me if this question has an obvious answer, but if both Spider and Optima have recommended densities of 1.0/1.8 and 1.8 respectively, how would you go about having them shoot it at greater densities (or is it simply another product that you haven't mentioned)?

John's Manville published a nice set of test data results comparing it's air retardency of Spider to cellulose a couple of years back touting it's superior air-retardency. However all of the installed densities tested were considerably higher than the 1.8 lbs recommended.  IIRC 2.2lbs was the lowest tested, and it performed quite well relative to 3.5lb cellulose (40% better but not 2x better) and it doesn't actually need to be that air-retardent to stabilize R value across the typical temperature ranges seen for the vast majority of housing in N. America.  The air-redardency of even 2lb cellulose is good enough for stabilizing performance, but 3-3.5lbs will measurably tighten a house in a blower door test.

See:

http://www.specjm.com/files/pdf/Den...lulose.pdf

http://www.specjm.com/files/pdf/JMS...esults.pdf

If you look at the ASTM C 522 air resistance curves on the left side graph on page 8, you'll see that 1.8lbs Spider is about as air-retardent at 3.5lb cellulose, both of which are standard "dense-pack" densities.  But if you project the Spider curve down to 1.0lb you can easily infer that it'll be significantly lower than 2-2.5lb low-density cellulose.  I can only assume the reason 1lbs goods tested against low-density cellulose weren't included is that those data do not favor Spider.

The ~R3 difference in center-cavity R value seems more signficant than it turns out to be in a timber framed structure.  The thermal bridging of the studs reduces that apparent advantage to about R1 for a whole-wall number, (R11 instead of R10 in a 2x4 studwall, a 10% reduction in heat loss). Installed costs will vary, but usually increasing the thickness of exterior insulating sheathing by 1/4-1/2" raises the whole-wall R by a greater amount than switching from low-density cellulose to 1.8lb Spider, at a lower increase in total cost.

So while I'm convinced that dense-packed noo-skool fiberglass is indeed very good stuff, where & when it's actually worth the upcharge over usually-cheaper cellulose will vary.

How to go about verifying the actual dense-packed density of fiberglass may require a bit of geometry and a scale.  Taking core samples of known volume and weighing them is a standard method for better cellulose dense-packers. I'd assume the same would be true for f.g. installers as well.  The steepness of the air retardency curve for Spider means it's less forgiving for under-packing than cellulose. It may well be that the 2.2lbs density prevalent in those documents reflects the average installed density if the installer follows the manufacturers' dense-packing instructions to the letter, crossing all t-s and dotting all i-s but I don't know this to be the case.  The spec sheet says 1.8lbs.

Posted By smartwall on 22 Sep 2011 07:46 AM
You can under blow a product or over blow it in a closed cavity. All products have an optimal density at which they give the best results. It is much harder to over blow fiberglass, much easier to over blow cellulose.

All products are more air retardent at higher density, but at some point the R begins to drop. In practice overblowing cellulose to 4 or 4.5lbs would not reduce the whole-wall R value by even R0.5, even though the center-cavity R would fall by slightly more than R1.

The air-retardency costs of UNDERBLOWING are far more severe with fiberglass than with cellulose.

See the curves on p.8:  http://www.specjm.com/files/pdf/JMS...esults.pdf

And dense packing cellulose in a 12" cavity rather than wet-spray is sufficient to prevent settling. The required minimum density will vary by climate and wall stackup though, but for most double-wall construction in most of the US, 3.2-3.5lbs is just fine. 

See:  http://www.nordicinnovation.net/nor...rep565.pdf

Underblowig cellulose means settling while undeblowing fibergalss will not have the same result. The problem with trying to blow a 12" cavity especially a double wall is the fact that you don't have a defined space to pack the cellulose in thereby creating areas where the celly won't be packed as evenly. Dana everything is great in theory and formulas. I've installed millions of pounds of celly and fiberglass and I'd use fiberglass every time if I had the choice. I go by the joke about if you saw sausage made you would'nt eat it. Well i've seen the celulose made and when they switch from sulfate to borate and the only difference is the bag, that doesn't give me great confidence in the material. I have a large townhouse job coming up and we are using celly blown behind Insulpac from the only reliable manufacturer that I know of in the northeast

I hear what you're saying, but I've yet to see a wet-sprayed low-density cellulose wall or a dense-packed wall that showed signs of settling years later when opening up walls for additions/renovations/repairs. With a fluffed dry-blown 2-hole method sub- 2lb stuff that should have been 2.5lbs+, yep, it' settles a ton, but even in a junk-install it's still more air-retardent than low-density Spider. I haven't had the experience of breaking open an Optima or Spider wall a decade later, but I'll take JM's air-retardency vs. density curves at face value. At 1.8lbs+ it's great stuff. At 1.0lbs, not so much- even if it might not settle at that low density (TBD) it's performance is bound to suffer at the temperature extremes due to convection within the material.

With the better fiberglass it's dense-packed or nuthin' for me. With cellulose I'm still OK with wet-sprayed low density on open studs. I've never been thrilled with 2-hole dry-blown in walls, but even 3lbs dense packed seems to hang in there, even if the density is inconsistent within the stud bay.

It's good (but not surprising) to hear that the noo-skool f.g. installs very consistently- it's light-years ahead of the junk they were selling back in the '80s (but then the quality of cellulose has improved since then too, if only incrementally.)

Using cellulose vendors that don't even buy the sulfate is one easy way to avoid the corrosion & stinky-when-wet issues. Field tests for sulfate using NaOH (Drano) are pretty easy to perform too, if you're into lowering the risk with Brand-X goods. IIRC Australia and a few other countries have banned sulfated fire retardents in insulation (the right move, IMHO.)