ok, with a tagline like that, i'm sure everyone is thinking foam. i'm not. i wanted dense-pack cellulose, i know the limits of my budget.

let me start with a description of the house. i moved a rambler built in 1951(uninsulated 2x4 walls) with a 1976 addition (insulated w/ r7 foil faced batts) to my property, jacked it up, and built a daylight basement under it. then, i built the downstairs walls for superinsulation by building a 2x4 wall offset 2" from my foundation giving me a total wall thickness of 13.5"plus sheeting/sheetrock. my plan was to then spray in dense pack cellulose, for some great energy savings. then i could get the same folks to "drill and fill" the upstairs.

then the bidders showed up.

i got some blank stares, hemming and hawing. "well, we can't drill and fill the addition, because it already has r-7 faced insulation in the wall cavities" and "we can put up fabric, and fill the downstairs with cellulose, but the sheetrockers will hate it, because it will bulge out and make their work hell." and "all cellulose will settle" and " yeah, you should just use batts."

now, i would expect 1 or 2 contractors to just want to go with what they're used to, but this is all of them! is there some fault with damp spray cellulose i don't know about? the vids on the internet makes it seem doable, just make sure it dries before rocking, right?

so, now i'm starting to think i don't want any of these guys touching my house. i'm thinking of doing it myself, just put up the first 4' of sheetrock, blow in the cellulose as dense as i can, then put up the next 4' and repeat. btw, the walls are 9'4" so there would be a gap at the top to work with.

has anyone on here rented a blower from a box store, and tried their own dense pack? or will the consumer grade machines not get it tight enough, causing eventual settling issues?

or, maybe i should just pay someone to throw batts in and get this project done.

i'm a few weeks from pulling the trigger, but a decision needs to be made. what do you think?

Others will chime in with more up to date info but in the past I would do all the drywall, drill 2 holes at the top of each cavity and, putting the fill tube down the wall, fill the cavity till the cellulose pushes out the second hole. This allows a place for the air to come out. Just my 2 cents worth.

I've never dense packed a 13.5" wide space, but my guess would be to separate each bay with fabric, hang top and bottom drywall sheets leaving the middle open, install fabric and dense pack.
We have successfully dense packed old 2x4 construction with the thin batts, verified with IR, if its a fully fluffed bay it doesn't work or at least I cant get it to work with my machine. If you want to try it yourself you will need at least a Force 2 machine which some lumberyards have, the small machines at home depot cant generate enough pressure to dense pack.

Thanks, guys. greentree, are you saying a "force 2" machine would be necessary to dense pack a cavity with pre-existing fiberglass batts, or for dense packing in general? is force 2 a common industry term?

Force 2 is a make and model of insulation blowing machine. See link below for specs.

http://www.forceblowingmachines.com/

riggerjack-
I wonder where you are located that the insulation contractors seem to be behind the times. In my small Colorado town, they certainly know how to do wet-spray cellulose and the dense-pack cellulose with the fabric. (The insulations contractors may be out of Colorado Springs, but at any rate, both are common practice in this subdivision.) They used to do wet-spray cellulose, but now seem to be switching to the dense-pack with fabric, for whatever reason. The cellulose-filled fiber does bulge out from the studs, but the Sheetrock guys are certainly able to put up the interior walls over it. I don't know if they switch to a thicker Sheetrock or not with the dense-pack with fabric.

They do not put up any Sheetrock until the fabric has been filled with insulation. These comments all pertain to 2x6 wood stud walls.

Do not; repeat do not put cellulose insulation against a concrete foundation!!! Concrete passes moisture - it will be absorbed by the cellulose and you'll be dealing with mold. Either spray 2" closed cell foam against the concrete or install 2" of sheet foam, (wall and floor), air seal the assembly then fill the remaining bay with cellulose.

I'm not surprised you're getting pushback from old line contractors, but don't give up yet. Where are you building?

You can side stitch fabric, where you staple just inside the face of the stud to tighten the fabric, and you can face staple fabric and roll a glue mix over the studs, both methods we end up roll ing the cellulose flat because we get "pillowing" where the fabric bulges past the face of the studs. And yeah, don't blow it against concrete.

You need to have a sealed space, with the exception of where the hose enters, to dense pack. By sealed I mean it has to be blocked off somehow, you cant just fill 4', install another row of sheetrock and fill another 4'.

If you get an appropriate machine and do it yourself I would setup some practice bays so you can get the right density, if you dont know what it feels like to achieve proper density you run the risk of underblowing or popping drywall off the studs.

R7 batting is only 2.5" thick, and inserting the dense-packing hose is usually possible running just air. Once it's in you can dense-pack it just like any other 2x4 cavity. I know there aren't any rocket scientists wasting their careers as cellulose installers, but this isn't a very demanding process. If the batting has failed and is all bunched up forming an obstruction it may take more than one hole per bay to get there, but this kind of thing is done every day.

The box-store blowers are usually single-stage units and they don't generally rent them with dense-packing tubes either. But even with a single stage blower you can usually beat 3lbs density if the hose and blower aren't leaking. (I've done it even with a decrepit 40 year old antique of a single-stage blower.)

What Bob I and greentree said about cellulose against the foundation- ABSOLUTELY DON'T! Closed cell foam (either sheet or sprayed) is the only way to go there. If there's even a chance in 1000 of there being any bulk water incursion, use blown high density rock wool or high-density fiberglass in the wall cavities in the basement. But if the place is well drained, bone dry, never even a hint of moisture, sure cellulose is your friend.

Posted By greentree on 26 Oct 2012 03:16 PM


You need to have a sealed space, with the exception of where the hose enters, to dense pack.

Why just the one hole? does it need to build up air pressure to dense pack the cellulose? When we did a double stud cavities and normal 2x4 walls in the 90s, we always had a way for the air to escape. Maybe this is just old practice.....

You can do 2 hole if you want, we just do the one hole method per cavity since we usually are doing sidewall retrofits and its less siding off, less plugs we go through and more maneuverability with the hose since your drilling a bigger hole to let the air out.

Stabilized cellulose sprayed in before the drywall doesn't have any bulging or sagging issues.

so, the consensus is to not spray cellulose downstairs, because of potential water problem? i'm in the puget sound, washington, 8 months of rain each year. and that blowing the wall cavities upstairs with a box store rental should be fine if i'm careful.

Posted By MikeSolar on 26 Oct 2012 10:32 PM

Posted By greentree on 26 Oct 2012 03:16 PM


You need to have a sealed space, with the exception of where the hose enters, to dense pack.

Why just the one hole? does it need to build up air pressure to dense pack the cellulose? When we did a double stud cavities and normal 2x4 walls in the 90s, we always had a way for the air to escape. Maybe this is just old practice.....

With two hole method you never get sufficient packing pressure to hit 3+ lbs density- it'll be around 2-2.5lbs, and not nearly as tight, and will sag over seasonal moisture cycles.

An advantage to dense packing is that by relying on the random leakage for the back pressure, it drives the fiber into any & all cracks/seams/leaks that you missed, substantially sealing them up.  There's always space between the single drilled hole and the hose for the blowing air to escape, but you're looking for sufficient air-retardency in the fiber in the region surrounding the tip of the the hose to cause the blower to stall before pulling it back and filling some more.   (Dense-packing is da-BOM for retrofit tightening up house without ripping the walls apart.)

Since rental blowers don't come with dense packing hoses you'll have to fab up the reducers and hoses yourself.  If you google his name a guy named Karg has a lot of web-tips & info on dense-packing cellulose including some on how to set up & use the equipment.  You can find youtube instructional bits out there too.

Awesome! Googling now.

I know this is a pretty old thread, but I am curious about the "needing a sealed space" aspect. Since Insulweb is often used before sheetrock, air flow certainly isn't limited. Also, starting at the bottom of a cavity, the cellulose is still packed in lifts, well before the whole cavity has been filled. I don't see how this is any different than packing with the top fully open instead of a single hole. Granted I have not done this yet and this is just my impression from watching Bill Hulstrunk's demonstrations. Hoping to figure out if my perception is correct before learning to dense pack on a long, low-slope, larsen truss ceiling.

I was just rereading this thread and thinking I should have clarified that point and here you are asking about it. By sealed I meant enclosed as in by Insulweb or whatever fabric you have. The OP was talking about putting up a sheet of drywall and filling up 4' then going up another 4'. That would have made an insane mess with a machine setup for dense pack although you could do this with a long cavity like a rafter bay that has most of the drywall hung.

When you first start to fill a cavity fiber is flying inside the bay all over the place and will make its way up the stud bay like an initial light fluffy fill, the tube could really be anywhere, you are just getting material in the bay. Once it is filled up light you get the hose near the top or bottom and start to dense pack, you can hear it starting to pack and then it will stall out or plug, from a roar to silence. Back the tube out a foot and back in quickly and it starts to pack the next 6" and repeat. Can start fom the top down or bottom up, i stick the hose through at waist height for comfort. If you do this against drywall you can physically blow the sheetrock off the wall or ceiling if you overdid it.

You could not do this in an open bay very easily although its possible in certain situations like a long cavity with the hose entering from the far end but the cellulose needs something to pack against, thats why its hard to dense pack double stud walls and why you would install fabric "baffles" in a double stud or other open situation to enable a quality job. Thats why I dense pack into an onion bag in rim joist areas for instance. If I didnt use one I would waste an enormous amount of material waiting for the cellulose to catch. Instead of 12" deep in the onion bag it might take 6' down the floor joist cavity unrestrained by anything.

Also, its very easy to drill a hole, stick the hose in, start machine, stall it out, pull back, stall it again and repeat and think you've just dense packed your cavity when you did half of it or filled at half the required density. Machine settings, technique, type and model of machine, hose setup, cellulose used, weather all come into play. Thermal scan becomes necessary to check the siding installation, bag coverage guides your density.

A big box rental like a krendl 425 will drive you mad if you attempt to dense pack with it, mainly because they are so slow, but I guess if you havent done it before you wont know the difference. Lumberyards tend to carry the intec force 2 which alot of the low income weatherization groups use because its portable and may work better if its seals are decent. Nothing beats a truck mounted blower. Probably more info than you needed, I enjoy doing it so I get a little excited.

My machine is setup to get in and get out. So if there was a 8' tall cavity with an open top and I stuck the hose all the way to the bottom, my machine pressure would fill the bay and the cellulose would spill out the top like a popcorn machine until you give up or it ran out of fiber in the hopper, theres too much pressure, it wouldnt dense pack until you blocked the material from spilling out the top. As soon as you do that it starts to build on itself.

You may be able to back off on air and dial back material flow to slow it down and it might catch without being blocked off at the top but you run the risk of not hitting density. Hope that answers your question.

greentree, thank you for the analysis of the project. I tend to over-research projects, so really there is no such thing as too much info! I will be trying to find a Force 2 locally (or adding a 2HP inline blower to whatever machine I can get), so the possibility of the "popcorn machine effect" should be lower. However, if its a problem, I could add a face of insulweb between the larsen braces every 8' or so (in addition to the lengthwise web separating each bay), but then I would need a longer rigid section as I wouldn't be able to reach down as far. In any case, the first bay will teach me a lot.

No prob.
A big part of your success is conditioning the cellulose. It comes pressed in a bag, you will notice a premium regional cellulose suppliers bag will be bigger than the box store bag but have the same coverage. The machine needs to break it up and make it fluffy before it goes down the hose. Thats why the big machine specs will mention "aggitators" or shredders, basically a couple tine bars at the bottom of the hopper that chop the cellulose prior the cellulose entering the airlock. Better cellulose conditions faster since its not as compressed and allows a big machine to send it even faster than cheap stuff. Regional stuff is usually much cleaner, hand sorted. box store stuff will be full of plastic and chunks of crap.

If you add an inline blower to a machine that cant condition the cellulose fast enough youll get chunks and hose clogs that can be difficult to find and unclog when you are dense packing. Open blow doesnt matter as much, youll just use more bags than the bag says you will.