dense pack cellulose & settling
Last Post 30 Jan 2010 11:22 PM by jerkylips. 17 Replies.
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jerkylipsUser is Offline
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21 Jan 2010 09:56 AM

Hi guys,

I meant to add this to a previous post but forgot.  I spoke at length with our builder about insulation options, & he prefers a combo of spray foam & fiberglass batts. 

I asked him about the dense pack cellulose, after learning more about it here.  He's very leary to use cellulose because of his experience with settling.  I understand that this "dense pack" process is supposed to eliminate settling, but wondering about real world testing/results. 

How long has this method been around?  How has it been proven that it won't settle?  We plan to be in this house a LONG time, so I don't want to find out 10-15 years later that it's settling.  I know that the r-value is better than fiberglass, but I'm concerned about long term performance..

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21 Jan 2010 11:16 AM
Dense packing has been around for decades. The only time settling occurs in dense-packed cavities iat 3.0lbs+/ft^3 density is when there is a water leak or condensation due to improper attention to vapor control and condensation occurs. Repeated wetting/drying eventually shrink it, but if it's just a vapor issue (as opposed to a leaking wall or plumbing leak) it's NOTHING so severe as the settling you can get with lower density 2-hole method.

The density required for dimensional stability under normal humidity cycling has has been well studied, and modeled:

http://www.nordicinnovation.net/nordtestfiler/rep565.pdf

http://www.en.sbi.dk/publications/with_en_summary/settling-of-loose-fill-insulation-materials-in-walls-1/

http://www.en.sbi.dk/download/pdf/dokumentation011.pdf (Lave jer læse Dansk?? or however you write that in Skandahoovian... :-) )

Basically, under normal conditions even lower density 2-hole method in wall cavities only drops to the performance of batt installations after a decade or two (and can be topped off if need be.) It's IMPOSSIBLE to install batts perfectly, but blown/sprayed insulation conforms perfectly to all imperfections & oddities to the framing, reducing or eliminating gaps,compressions & voids that are inevitable with batts. Blown fiberglass using finer wools than can be used in batts will have a slightly higher R-value (~7-10% higher under typical ASTM C518 delta-Ts) than blown cellulose on day-1, but it too has sag issues similar to low-density blown cellulose. Even lower density open blows in attics, etc have much larger fractional settling issues, but that too is a function of it's day-1 density and humidity cycling.

But if you dense pack with wet-spray, (cellulose or fiberglass) the adhesive keeps it from sagging even with moisture cycling & time. Blown fiberglass will outperform the cellulose in some conditions, but the cellulose outperforms fiberglass in others, but in general they'll be similar. Cellulose will wick condensation off of structural materials, reducing mold hazard, but will take much longer to dry out in an actual leak/bulk water incursion. Very high delta-Ts (hot or cold), blown cellulose retains it's R-value better, whereas fiberglass (blown or batt) loses some (primarily due to higher convection rates within the insulation). So while blown fiberglass outperforms cellulose slightly under low load (which is most of the hours in a heating season), it's steady state R may drop below that of cellulose when it's in negative-digits F outside. In the shoulder seasons with very light loads & high diurnal temperature swings, cellulose can sometimes outperform fiberglass due to the buffering provided by it's significantly higher thermal mass.

Bottom line, flash foam + wet-spray (cellulose or fiberglass) will generally outperform flash + batt, often for similar money. For even money, I'd personally go with wet-spray cellulose for it's hygric buffering capacity, thermal mass, and acoustic attenuation properties, but would opt for wet-spray fiberglass wherever the sheer weight of the cellulose becomes an issue. YMMV.

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21 Jan 2010 02:06 PM
Posted By Dana1 on 01/21/2010 11:16 AM
Dense packing has been around for decades. The only time settling occurs in dense-packed cavities iat 3.0lbs+/ft^3 density is when there is a water leak or condensation due to improper attention to vapor control and condensation occurs. Repeated wetting/drying eventually shrink it, but if it's just a vapor issue (as opposed to a leaking wall or plumbing leak) it's NOTHING so severe as the settling you can get with lower density 2-hole method.

The density required for dimensional stability under normal humidity cycling has has been well studied, and modeled:

http://www.nordicinnovation.net/nordtestfiler/rep565.pdf

http://www.en.sbi.dk/publications/with_en_summary/settling-of-loose-fill-insulation-materials-in-walls-1/

http://www.en.sbi.dk/download/pdf/dokumentation011.pdf (Lave jer læse Dansk?? or however you write that in Skandahoovian... :-) )

Basically, under normal conditions even lower density 2-hole method in wall cavities only drops to the performance of batt installations after a decade or two (and can be topped off if need be.) It's IMPOSSIBLE to install batts perfectly, but blown/sprayed insulation conforms perfectly to all imperfections & oddities to the framing, reducing or eliminating gaps,compressions & voids that are inevitable with batts. Blown fiberglass using finer wools than can be used in batts will have a slightly higher R-value (~7-10% higher under typical ASTM C518 delta-Ts) than blown cellulose on day-1, but it too has sag issues similar to low-density blown cellulose. Even lower density open blows in attics, etc have much larger fractional settling issues, but that too is a function of it's day-1 density and humidity cycling.

But if you dense pack with wet-spray, (cellulose or fiberglass) the adhesive keeps it from sagging even with moisture cycling & time. Blown fiberglass will outperform the cellulose in some conditions, but the cellulose outperforms fiberglass in others, but in general they'll be similar. Cellulose will wick condensation off of structural materials, reducing mold hazard, but will take much longer to dry out in an actual leak/bulk water incursion. Very high delta-Ts (hot or cold), blown cellulose retains it's R-value better, whereas fiberglass (blown or batt) loses some (primarily due to higher convection rates within the insulation). So while blown fiberglass outperforms cellulose slightly under low load (which is most of the hours in a heating season), it's steady state R may drop below that of cellulose when it's in negative-digits F outside. In the shoulder seasons with very light loads & high diurnal temperature swings, cellulose can sometimes outperform fiberglass due to the buffering provided by it's significantly higher thermal mass.

Bottom line, flash foam + wet-spray (cellulose or fiberglass) will generally outperform flash + batt, often for similar money. For even money, I'd personally go with wet-spray cellulose for it's hygric buffering capacity, thermal mass, and acoustic attenuation properties, but would opt for wet-spray fiberglass wherever the sheer weight of the cellulose becomes an issue. YMMV.


Excellent, thanks for the info.  You mentioned something that brings up another question.  Our builder said that he was using the blown in blanket fiberglass for a few years, but no longer recommends it.  He said that he was having a lot of callbacks for screw pops in the drywall, and that sometimes when looking down a wall, you could see a "wave" from the pressure exerted on the drywall from the blown in fiberglass.

Should I expect that there could be similar issues with the blown in cellulose?

The SipperUser is Offline
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21 Jan 2010 04:37 PM
jerkylips, trust me, I'm not trying to harass you. This is just for informational purposes, for others who are reading these threads, who have not made up their minds yet regarding their basic building envelope syatem: You just don't have these concerns with SIPs. I'll explain this statement in detail if anyone asks.
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21 Jan 2010 04:51 PM
Posted By The Sipper on 01/21/2010 4:37 PM
jerkylips, trust me, I'm not trying to harass you. This is just for informational purposes, for others who are reading these threads, who have not made up their minds yet regarding their basic building envelope syatem: You just don't have these concerns with SIPs. I'll explain this statement in detail if anyone asks.
STOP PICKING ON ME!!!  haha...

No concerns...  Like I just wrote in my other reply to you, I wish we could have used SIPs, I really do.  We just couldn't make it work within our budget.  So knowing that we can't, I'm trying to find the best alternative.  It may not give 100% of the performance of SIP construction, but I think we can get close.

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21 Jan 2010 05:30 PM
I appreciate the humor, JL, but, just to be clear, the "concerns" that I was referring to are "settling insulation" "screw pops in drywall", "wavy walls" etc etc etc

Cheers!
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22 Jan 2010 08:52 AM
I've seen a dry cellulose dense pack install where they overblew and the netting center was way passed the face of the studs. IF your drywaller would be dumb enough to install over that you would have problems. If your GC would let that slide you have problems. The solution on this job was to redo it right on the installers dime, no problems.
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22 Jan 2010 10:17 AM
Blow-in-bag and dense-packing always has some bulge & screw-popping issues, independent of the fiber used.  This is a bigger issue with 24" OC studs and thinner drywall though. Going to 5/8" or 3/4" drywall minimizes that, and adds thermal mass to the system.   Fastener-spacing also makes a difference- using 50% more screws than you would with an un-tensioned cavity would probably mitigate the popping (but not the bulge) issue.

It's more work/money, but a layer of 1/4"-3/8" OSB under the wallboard should easily handle dense-packed blow-in-bag stresses.  You could then go with thinner wallboard, and stagger the seams for air-tightness too.

Wet spray at lower density doesn't have bulge & screw popping issues at all, since it's not under tension, relying solely on the adhesive to keep it from sagging.  When it's installed the excess is trimmed flush with "stud scrubbers".  They usually work in crews of three- one running the spray gun, followed by someone with the stud-scrubber, and the third vacuuming up the excess to recycle into the sprayer's hopper. For a vidi explanation of open blow wet-spray (chosen at random from dozens of promotional videos) shows how that's done:

http://www.youtube.com/watch?v=K-tJjPHoG6w

Open wet-spray has slightly higher convection than dense-packed blow-in bag,  but far less than fiberglass batts.  Adhesives are not a new technology- the only way it can sag after going up is for the adhesives to fail (I wouldn't sweat that aspect much.)

This approach reliably fills micro-cavities as narrow as 1/4" or less, something that would be impossible with batts, difficult to do without voids even with spray foam (where the first droplet that hits the side of stud expands to block what follows.)

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22 Jan 2010 10:52 AM
FYI: We live in a large timberframe house where the walls were 2x6, 16OC around the timberframe. The insulation was dense pack cellulose. Bottom line: after 6 years we have seen no evidence of screw popping and the like. I might say that we had a very excellent Gen. Contractor who watched over everything like a hawk. Knowing him and his crew, they would have caught any problems. As an aside, after we sell our house, our new house plan design is to do 2x6 16OC with the same dense pack cellulose. Wall inside to out: drywall, 5.5" insulation cavity, 1/2" cdx, 1" XPS, stucco. Would love to have SIPs, but cannot find contractors that can do it locally at a decent cost. Since we are about 2 years away from a build, perhaps that could change. Regards, Steve
Eager to learn new things here in the foothills of the mountains of the Lincoln National Forest of New Mexico.
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22 Jan 2010 01:17 PM
Posted By altovintner on 01/22/2010 10:52 AM
FYI: We live in a large timberframe house where the walls were 2x6, 16OC around the timberframe. The insulation was dense pack cellulose. Bottom line: after 6 years we have seen no evidence of screw popping and the like. I might say that we had a very excellent Gen. Contractor who watched over everything like a hawk. Knowing him and his crew, they would have caught any problems. As an aside, after we sell our house, our new house plan design is to do 2x6 16OC with the same dense pack cellulose. Wall inside to out: drywall, 5.5" insulation cavity, 1/2" cdx, 1" XPS, stucco. Would love to have SIPs, but cannot find contractors that can do it locally at a decent cost. Since we are about 2 years away from a build, perhaps that could change. Regards, Steve

That's a decent amount of insulation for your location- I see lower R-values than that being built here in (much colder) New England all the time.

The 16" oc framing makes it less of an issue, but bulge & screw popping the can be controlled with 24" oc framing too. Specifying wallboard thickness & screw spacing should be enough.  But since this is a flash-foam + spray situation (?), it's already a very tight wall, and the additional benefits of dense packing aren't as large in comparison to open-spray cellulose as they would be were it the only cavity insulation installed.   (If the flash foam is out, I'd still dense-pack it wet-spray, and just make sure the interior wall could take the pressure.  This isn't rocket-science to get right.)
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22 Jan 2010 02:02 PM
Hello Dana1. Appreciate your thoughts. FYI, you kindly responded on another of my posts about vapor barriers and that was most helpful. As a matter of fact, I went back and read just about every article I could find online about vapor transmission, wall design, insulation choices, and so on. Probably have over 20mb of various articles on my PC. Moreover, I think I have now read over 15 of your posts. ....................... As a sidebar note, where I live, Alto, New Mexico, is located in an area that has just about the highest winds in the US. It is nothing for the winds to blow at > 70mph. We had a stretch last year where they blew continously over 100 mph for over 24 hours! So far, the winds have done nothing to our current house, thank goodness. Builders that I have spoken with around here hardly ever do 24" oc. Typically 16OC with 1/2" cdx or osb. ...... Keep on sharing! Thanks, Steve
Eager to learn new things here in the foothills of the mountains of the Lincoln National Forest of New Mexico.
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22 Jan 2010 03:02 PM
100mph winds are a SERIOUS design constraint! I can't imagine building 24" oc using somebody's structural insulating sheathing system in that kind of environment!

I CAN imagine putting up a small grid-attached wind turbine there though- sounds like you wouldn't need a tall tower to get a useful amount of power out of it.
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23 Jan 2010 08:20 AM
Hi Dana1: Yes, a turbine could work a bit. But, the problem is that the experts tell me they have to shut down at a certain wind speed, like 40mph. Otherwise they would spin too fast! Yesterday, the wind blew 70 mph for about 6 hrs.; it rained; it snowed 6 inches; and it was about 29 degrees. Nice day to be outside in shorts and t-shirt, heh, heh. .... But, I digress........ Another thing some, but certainly not all, local builders are telling me is that they prefer good cdx plywood instead of osb mainly because the screws and nails hold up pretty well. At least that is what I hear. Without getting into an OSB vs. Plywood range war, I think they may have a point. Stucco is very common here and the stucco lath has to be attached to something, and the plywood, with building paper to code, serves to do that. ......... Standing seam metal roofs are relatively common, too. In my case, it is a Mueller screwed down on plywood decking. Has not even budged, leaked, or anything, in the high winds. Plus rainwater harvesting is done more and more; hence, the metal roofs facilitate that. ....................... In spite of what appears to be a life in Hades out here for me, I love it. Scenery is tops. Mountain views everywhere. Just 50 yards behind our back deck, elk roam all the time. Check out this Youtube video of a huge bull that I got some footage of: http://www.youtube.com/watch?v=ZeJ4zo8dzNU Be Well, Steve
Eager to learn new things here in the foothills of the mountains of the Lincoln National Forest of New Mexico.
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25 Jan 2010 10:18 AM
One key technique the good installers use around here to prevent dense-packed cellulose from bulging out under pressure after filling is to staple the mesh up, then run another row of staples along the side of the stud. This gets the mesh very tight, and gives it room to expand out without putting pressure on the drywall.

If you don't side staple, you can indeed have problems getting drywall flat after the walls are packed.

Here's a video a builder we work with put together for JLC magazine: Installing Dense-Pack Cellulose in Fat Walls
Jesse Thompson<br>Kaplan Thompson Architects<br>http://www.kaplanthompson.com/<br>Portland, ME<br><br>Beautiful, Sustainable, Attainable
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30 Jan 2010 11:10 AM



Wet spray cellulose applications are just about the most mystifying construction practice I have ever heard of. How did the ICC approving board OK flinging wet newspaper into wall cavities?

Dense pack applications are kosher. Cellulose and/or foam is the way to go for cavity insulation needs. Batts (FG, cotton, etc, etc) are evil.

jb
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30 Jan 2010 04:18 PM
Posted By Johnny Boy on 01/30/2010 11:10 AM



Wet spray cellulose applications are just about the most mystifying construction practice I have ever heard of. How did the ICC approving board OK flinging wet newspaper into wall cavities?

Dense pack applications are kosher. Cellulose and/or foam is the way to go for cavity insulation needs. Batts (FG, cotton, etc, etc) are evil.

jb
Hmmm... flinging wads of soggy newspaper at the wall until it sticks- that's quite an image!

But it's a mistaken image.

The water content starts out ~30% water by weight, and tightly controlled by the spray settings to provide just what's sufficient to activate the adhesive, not saturate the material- it may feel damp, but never soggy, and you can't wad it up into a ball.  With 2-3 days of drying time it's humidity drops to under 15% as long as the relative humidity & temps are reasonable.  (It's best done in warmer temps than mid-winter, unless the building under construction is heated and humidity controlled.)

Wet spray cellulose been around for decades, and has a good track record.  The adhesives in wet-spray cellulose result in adding some structural strength & rigidity to the assembly as well. (More than half-pound foam, but not nearly as much as 2lb foam.)  The only caveats are that it needs to be allowed to dry before closing it in with vapor retardent materials (even semi-retardent paints) or it can take a very long time for it's humidity to stablize.  It's often closed in with sheet rock with a single-day's drying time, when it's humidity is still north of 20%, but I'd personally rather wait an extra 24hours just to be sure, or even an extra 48 or more if a class-I vapor retarder is going up before the sheet rock.
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30 Jan 2010 11:17 PM

Dense pack applications are kosher.

Hmmm. What makes dense pack Kosher? Perhaps this is some branch of Modern Orthodoxy of which I am not familiar.
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30 Jan 2010 11:22 PM
Posted By gregj on 01/30/2010 11:17 PM

Dense pack applications are kosher.
[/quote]
Hmmm. What makes dense pack Kosher? Perhaps this is some branch of Modern Orthodoxy of which I am not familiar.
[/quote]

It's much better than those pork-based insulation systems.......
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