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Musings of an Energy Nerd

Borrowing a Cellulose Blower From a Big Box Store

Put on a dust mask and get ready to lay down a deep blanket of cellulose on your attic floor

The insulation blowers lent out by stores like Home Depot and Lowe's are low-power models that are easy to transport. While these insulation blowers aren't powerful enough to easily dense-pack walls, they work fine for insulating attic floors.
Image Credit: Images #1, #5, and #6: Karyn Patno
View Gallery 8 images
The insulation blowers lent out by stores like Home Depot and Lowe's are low-power models that are easy to transport. While these insulation blowers aren't powerful enough to easily dense-pack walls, they work fine for insulating attic floors.
Image Credit: Images #1, #5, and #6: Karyn Patno
Before any insulation work starts, it's important to perform air sealing work at the ceiling and to complete ventilation and insulation dam details at the perimeter of the attic. After this photo was taken, Clark installed rectangles of rigid foam to cover the kraft-faced batts visible between the floor joists. The edges of these rectangles were sealed with canned spray foam.
Image Credit: Images #2, #3, #4, and #7: Martin Holladay
Karyn was in charge of feeding the insulation into the hopper. She was careful to keep her fingers clear of any moving parts. It's safe to put your hands into the hopper to break up clumps of insulation, as long as you keep your hands above the red grate. Once cellulose starts to come out of the hose, it's hard to photograph the work. The light from the camera's flash tends to bounce off the suspended cellulose particles. By the end of the day, we were pretty dusty. When working, it's important to wear a dust mask. A deep layer of cellulose is a pretty sight. This table shows how many bags of cellulose you will need to buy. The Green Fiber web site, where this table is posted, states that the figures are based on bags weighing 19.05 pounds. Mysteriously, the same table was printed on the bags of cellulose I bought at Home Depot, even though the labels on the Home Depot bags read 18.1 pounds. According to Green Fiber, the manufacturer aims to fill each bag with 19.05 pounds of cellulose, but some bags are lighter; 18.1 pounds is the minimum weight.
Image Credit: Image #8: Green Fiber

Back in the early 1990s, I worked for a nonprofit agency, overseeing renovation work at several old wood-framed buildings in St. Johnsbury, Vermont. Each of these century-old buildings had between two and five apartments; after renovation, they were rented to low-income families at subsidized rents.

Almost all of these buildings received similar weatherization measures: empty stud bays were filled with dense-packed cellulose; attic floors received a new layer of deep cellulose; and air leaks were reduced with blower-door-directed air sealing. These retrofit jobs convinced me that cellulose insulation was versatile, affordable, and effective.

In 2000, while serving on our local school board, I helped develop the scope of work for energy improvements at our town’s elementary school. The floor of the school’s attic had a thin layer of fiberglass insulation, so I made sure that the retrofit specs called for the installation of a layer of thick cellulose on top of the fiberglass. Once the job was complete, I climbed into the attic to verify that the cellulose met specifications. (Unfortunately, it didn’t — the layer was too thin — so the contractor had to come back and add more.)

Although I’ve been involved with many construction projects that specified cellulose, I haven’t installed any of the stuff myself. (Most of my construction experience dates back to the 1970s and 1980s — the bad old days when fiberglass batts ruled the roost.)

Last year, with the help of friends and family, I built a garage. The garage has a second floor which I am gradually transforming into a guest room. This summer, my brothers and sons finished drywalling the ceiling and walls of the second floor, so the next step was to blow cellulose in the attic. This was an easy one-day job, and there were three willing workers on the crew: my wife Karyn, my brother Clark, and me.

I don’t own a cellulose blower, so I did what most homeowners do: I bought my cellulose from a big box store, which lent me a blower for 24 hours at no charge.

A homeowner’s guide to cellulose insulation

Cellulose contractors usually show up at a job site with a large truck equipped with a cellulose blower that can deliver up to 3,000 pounds of cellulose an hour. Because these blowers often draw 30 amps, the typical truck is equipped with a 10,000-watt gasoline-powered generator.

If you want to install dense-packed cellulose in your walls, and you are aiming to achieve a density of 3.5 to 4.0 pounds per cubic foot, it’s usually best to call up an insulation contractor who owns a big truck-mounted blower. (For more information on this issue, see Eric Habegger’s advice in Comment #3, below. For a better understanding of how insulation contractors do their work, see How to Install Cellulose Insulation.)

However, if all you want to do is blow cellulose on your attic floor, you won’t be dense packing — so all you really need is one of the wimpy blowing machines that are available at Home Depot and Lowe’s. These machines are rated for about 450 pounds of cellulose per hour.

There are at least two advantages to these wimpy machines: they aren’t very heavy, so they’re easy to load into a pickup truck; and their relatively small motors won’t trip your 15-amp breaker.

Air sealing comes first

Before you drive out to the store to pick up your insulation blower, your attic needs to have been properly air-sealed. Don’t leave this work until the last moment. Give yourself plenty of time to inspect the attic carefully. Use as many cans of canned foam and caulk as you need to make sure that your ceiling is as airtight as possible.

Don’t forget to build a plywood insulation dam around the perimeter of your attic hatch. If you plan to install 16 inches of cellulose, make sure that your dam extends at least 18 inches higher than the drywall ceiling.

For more information on this work, see Air Sealing an Attic.

If you are insulating the attic of an old house, remember that installing insulation on top of knob-and-tube wiring is a code violation and a possible fire hazard. If you have knob-and-tube wiring in your attic, you can only insulate on top of the knob-and-tube if you are sure that it has been permanently disconnected. When in doubt, call an electrician to have your wiring evaluated before proceeding.

One person feeds the blower, and one person aims the hose

Two people can lift one of these blowers up and load it into a pickup truck. The machine should come with 100 feet (two 50-foot lengths) of 2½-inch diameter hose.

If it’s not raining, you’ll probably be setting your blower up outdoors. A rental blower can easily blow insulation onto the floor of an attic above a second or third story.

You’ll need at least two people to operate an insulation blower. One worker opens the bales of insulation and feeds the insulation into the hopper of the blower. The other worker is in the attic, aiming the hose.

How many bags should you buy?

Cellulose bags usually include a table to help you calculate how many bags you need to buy (see Image #8, below). For example, the brand of cellulose I bought comes with a table that explains that an R-60 installation requires an initial installed thickness of 18.4 inches. Each 18.1-pound bag is adequate to insulate 9.3 square feet of attic floor to R-60. Such an installation would require 2.06 pounds of cellulose per square foot.

For R-49, you want an initial installed thickness of 15.2 inches. An 18.1-pound bag will cover 12 square feet to R-49; this results in an installation with 1.6 pounds of cellulose per square foot.

If you live in a warm climate, you might be satisfied with only R-38 insulation; that would require an initial installed thickness of 12 inches. An 18.1-pound bag will cover 16.4 square feet to R-38; this results in an installation with 1.16 pounds of cellulose per square foot.

You should probably buy more cellulose than you think you need. When you return the blower to the store, you can return any unused bags for credit. (This approach is easier than running out of insulation halfway through the job.)

To insulate our 25 foot by 20 foot attic, I bought 70 bales; that’s 1,267 pounds of insulation.

If the blowing machine were truly capable of delivering 450 pounds per hour, it should have taken about 3 hours to deliver that much insulation. It actually took us more like 5 hours.

Feeding the hopper

The blower grinds up the cellulose insulation and blows a mixture of air and cellulose out the cylindrical steel fitting that extends horizontally from the bottom of the hopper. The rate of insulation delivery is controlled a simple sliding sheet-metal gate. The instructions advise adjusting the gate so that it is about 3/4 open, and that advice makes sense. If you try to open the gate all the way, the hose will probably clog, and delivery will stall.

If you can’t find the coupling used to connect the two lengths of hose, they can be easily connected with ordinary duct tape.

Blowing cellulose is dusty work, so wear a dust mask. If you are filling the hopper, don’t try to cram in too much at once. If you overfill the hopper, the cellulose can jam at the top, creating a bridge that hides an invisible void below; if this happens, the hose will deliver nothing but air. You want to be able to see the safety grate about halfway down the hopper. Break up the cellulose near the top of the hopper with your fingers or a short 2×4, but make sure you don’t stick your fingers where they don’t belong. If an object other than cellulose falls into the hopper, hit the “off” switch immediately.

Watching the drifting snow

If you’re holding the hose in the attic, you’ll probably get bored. The insulation comes out like snow, and it can take a while for drifts to form. If you have a big spring clamp, you may want to fasten the end of the hose to a rafter or truss chord, and let the insulation pile up for later raking.

You don’t want the hose to get away from you and disappear through the attic hatch to the floor below. One way to prevent this is to pull a few extra feet of hose into the attic, and wrap the hose around a framing member to provide friction on the hose. (Don’t wrap it in a full circle, of course — tight corners impede airflow.)

Do you need a set of walkie-talkies to communicate with the operator below? Not really. The insulation comes out slowly. If you have a way to secure the hose safely in the attic, you can even climb down the ladder and chat with your co-worker feeding the hopper.

When do we quit?

The difference between “almost enough cellulose” and “a bit more than you need” is subtle. You can expect cellulose to settle at least 13%. If you want a settled thickness of 16 inches of insulation, you should aim to install at least 18 inches. To me, that means at least 19 inches. Blow as much as you think you need, and then blow some more.

Don’t skimp. Aim the hose at the corners and edges of your attic; look for crannies that may need special attention; and be generous. A little too much does no harm at all. Remember: if you have the blower on site and the hose in your attic, it’s never going to be easier to add a little extra cellulose than it is right now.

Once you are all done, rake the high spots smooth and admire your work.

Martin Holladay’s previous blog: “Martin’s Pretty Good House Manifesto.”

Click here to follow Martin Holladay on Twitter.


  1. User avater
    Robert Swinburne | | #1

    super satisfying
    super satisfying, huh? Like finishing the woodpile before it snows.

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to Robert Swinburne
    Yes, it is super satisfying.

    And you're right about wood piles, too. I just finished putting metal roofing and rocks on my outdoor wood piles last weekend -- and now it is snowing. So everything is good.

  3. Eric Habegger | | #3

    Hi Martin,
    Actually, you CAN

    Hi Martin,
    Actually, you CAN dense pack with the machine you are showing in the picture, it looks like the Cyclone. I was having trouble locating a machine to rent that I trusted to dense pack cellulose. I called the manufacturer representative and he told me that the Cyclone you are showing will do it, but just barely. You can depend on getting about 3.2lbs/cubic foot packing and with proper technique more than that. 3.2 is probably sufficient for a 2x4 wall.

    The trick is to almost close the slide gate. I left it only two positions from the closed position. This is necessary to avoid bogging the machine down when dense packing. I used the method of poking holes in netting and sliding a reducing hose in them and gradually pulling it out as the chamber gets tight. If you do it correctly you will get a belly on the netting. Don't skimp on the bellying out. You then use a roller to compress it back to original shape prior to it bellying out.

    I very carefully measured the cubic feet of space that was filled using a 20% framing factor and also carefully counted the number of bags of cellulose used. It came out to slightly above 3.5 pounds per cubic feet. I'm quite sure that was accurate as it ended up similar to semi hard mattress density after it was all done.

    The two tricks to getting that density was closing the slide gate way down and belly out the netting and then compressing it with a roller. It can be done but you have to be careful and methodical. And its slooooow. I was lucky enough to go to a lumber yard where they let me borrow the cyclone for up to a week, no charge, as long as I bought the cellulose from them. The name of that lumber yard also came from that manufacturer representative for the cyclone. Give them a call.

  4. User avater GBA Editor
    Martin Holladay | | #4

    Response to Eric Habegger
    Thanks very much for your helpful comments.

    I was aware of the technique you describe, but was reluctant to advise readers to follow the technique, because I was unsure of how much care and experience it takes to get the density we all seek. You've done a good job explaining how you did it.

    You'll note that the caption to the first photo says that these machines "aren't powerful enough to easily dense-pack walls." I chose the word "easily" to convey what you have described in more detail in your comments.

    Again, thanks for sharing your experience. Needless to say, 2x6 walls take longer to insulate than 2x4 walls, and double-stud walls are a whole 'nuther kettle of fish. As far as I know, double-stud walls still require a big truck-mounted blower.

  5. Eric Habegger | | #5

    Yeah, I wouldn't trust it for a double stud wall and not have it slump in the future. My wall is 2x6 so I think 3.5 lbs per cubic foot is fine for that.

  6. Richard Beyer | | #6

    Great Video
    Blown in -v- dense pack tutorial...

  7. Nathan Spriegel | | #7

    Knob and tube wiring
    What irritates me about the big-box stores is that they do not reliably inform the people buying cellulose insulation that it is not acceptable to install over (in attics) or against (for walls) knob and tube wiring. Even the "professional" installers will do so, despite the codes (and manufacturer instructions) prohibiting it.

  8. James Howison | | #8

    Prepping attic with old insulation in it?
    Looks like good times :)

    Any advice for prepping an attic with existing insulation in it? Say your standard poorly installed fibreglass with a touch of rock wool around the place? Or existing loose fill? Or a combination? :) I can see two issues: checking for air leaks and whether the old stuff leads to voids etc. I suppose that one could try to check for air-leaks from underneath, but that seems likely to be a problem.

    Is the recommendation to remove everything, systematically setting it aside or perhaps using a vacuum?

    Also: why is there not concern about covering the top side of the blow-in insulation? I've heard it said around here a few times, cover insulation on all six sides to avoid wind-washing. Is it just that the attic, even with venting, is sufficiently covered?

  9. User avater GBA Editor
    Martin Holladay | | #9

    Response to Nathan Spriegel
    Thanks for your comments. You wrote, "The big-box stores ... do not reliably inform the people buying cellulose insulation that it is not acceptable to install over (in attics) or against (for walls) knob and tube wiring."

    You're right. Since GBA tries to do better than the average big-box store, I have added a warning about knob-and-tube wiring to my article. Your suggestion was a good one; thanks.

    Concerning the big-box stories: If every rental tool outfit tried to anticipate all the stupidity out there, the rental guys would have to set up a classroom and spend two hours with every idiot before a tool could go out the door.

    What's the bottom line?

    1. There are a lot of ways to screw up any type of construction work. Some mistakes can kill you. Other mistakes can kill your clients.

    2. If you want to do construction work, do your homework.

    3. If you are timid and ill-informed, hire a contractor.

  10. User avater GBA Editor
    Martin Holladay | | #10

    Response to James Howison
    Most of your questions are answered in this article: Air Sealing an Attic.

    If you are air sealing an attic with some existing insulation, you'll have to remove some -- but usually not all -- of the insulation, at least temporarily.

    Concerning the need for a top-side air barrier: In theory, you could install Tyvek on top of your attic cellulose. In practice, this work is (a) awkward and difficult to do well, and (b) expensive.

    Researchers have learned that adding a little more cellulose (increasing the depth of the cellulose) has the same positive effects that a top-side air barrier would have, at a lower cost and for less hassle. So if you feel that your insulation might be subject to thermal degradation due to the lack of a top-side air barrier -- and frankly, with cellulose this really isn't much of an issue -- then just install another few inches of cellulose so that you can sleep better at night.

  11. User avater
    Dana Dorsett | | #11

    The knob & tube wiring thing... a purely theoretical fire risk for poor twisted wiring connections becoming hot enough to ignite wood (or celulose insulation) from the resistance if buried inside a layer of thermal insulation. While I'm sure it's possible to create such a fire in a laboratory, SFAIK there has still never been a house fire traced to insulation over knob & tube wiring.

    There was a quiet movement afoot more than a decade ago to remove that clause from the code. There are far more fires caused by decrepit many decades old BX wiring, which unlike insulation knob & tube, has myriad documented real world fires. Some states now DO allow retrofit insulation over knob & tube, provided it has been inspected (presumably to verify that the connections aren't all corroded.) See the next to last paragraph (and references) in the Wiki entry:

    I'm not suggesting that one willfully violate the code on that, but don't sweat it if you happened to have insulated over knob & tube in a stated of ignorant bliss. Your odds of getting killed (or having your your house burned down) by eco-terrorists are higher than your odds of suffering injury in a house fire caused by insulating over knob & tube. There are at least existences proofs of the eco-terrorists causing death & property damage, while the risk from insulation over knob & tube is still only a theoretical possibility.

  12. Rob Wotzak | | #12

    Thanks, Martin!
    I'm about to tackle this same project this winter in the unfinished attic of my 1871 CT home, Martin. This is a perfect primer for the process. Thanks!

  13. User avater GBA Editor
    Martin Holladay | | #13

    Response to Rob Wotzak
    I'm glad to hear that this article was well-timed for you.

    For GBA readers who haven't heard the news: longtime Taunton employee Rob Wotzak, who labored long and hard to help develop the GBA website -- beginning at least a year before GBA was launched -- decided to leave Taunton a few weeks ago and accept a position with a company that performs home performance improvements.

    We all wish you the best in your new career, Rob. And good luck with the cellulose job on your house.

  14. Bill Rose | | #14

    made my day
    You said four things that registered. 1) The hose guy's job is boring, 2) Raking is easy, 3) Secure the hose so it doesn't slide down from the attic, and 4) no need to communicate. I'd put off blowing this attic until I found someone to help and this morning, after reading the post, I decided to do it myself. A one-man job, and a 67-year-old man at that. Piece of cake. Took two men only to load and unload the blower. Tie off the hose with duct tape, blow 2 or 3 bags, rake and move the hose. Thanks.

  15. Andrew C | | #15

    Removing loose insulation before air sealing.
    I just went thru this in my own attic. There was fiberglass batt with loose fiberglass blown on top (but not much). Trying to do air sealing work without first removing the insulation was very frustrating. The existing insulation sticks to the end of your caulk gun (permanently gooey acoustical sealant) or your Great Stuff Pro gun tip. What a mess. Grrr. At the very least, pull the insulation 'way back from the area you're trying to seal.

    I guess like many things, air sealing and insulating a horizontal surface is not hard, but you can make it difficult for yourself. If you can, avoid trying to air seal with loose insulation in the immediate vicinity. You'll cuss less.

  16. Bill Rose | | #16

    Response to Dana Dorsett
    You say "While I'm sure it's possible to create such a fire in a laboratory..." Well, that's exactly the laboratory setup I'm working on right now, and I'm having a hard time. I'd like to create a 1 to 10 ohm resistance using copper only, in as close to a point source as possible. Not easy. A foot of 40 ga copper has a 1 ohm resistance. Ideally it would be a loose spiral splice that would enlarge with heat, but even so the contact resistance seems to be in milliohms. Anybody have any experience with actual benchtop setups that would replicate burning cellulose with copper resistance? Any ideas are welcome.

    Also, we may be putting out a call for actual knob and tube junctures removed from houses, to measure the resistance in each. Not yet, but we may do that.

    Anyone out there familiar with fire investigations? I heard scuttlebut to the effect that when a fire investigator cannot pin down a cause, "electrical fire" is a default conclusion. I'd like to hear from investigators who can say that that's not the way it's done.

  17. Malcolm Taylor | | #17

    Response to Bill Rose
    I'm the president of our local fire department. It's small enough that the chief decides the causes of fires, not a dedicated investigator, so things may be a bit different here, but the default conclusion if we don't know what happened is "cause unknown".

  18. User avater GBA Editor
    Martin Holladay | | #18

    Response to Bill Rose (Comment #14)
    Thanks for you comments. Yesterday, your attic wasn't insulated -- and now it is. I'm glad that my article arrived at the right time.

    And it's good to know that one person is all you need to blow cellulose into an attic.

  19. User avater GBA Editor
    Martin Holladay | | #19

    Response to Andrew C. (Comment #15)
    You're not the first person who has been frustrated by the stickiness of canned spray foam. It's not a particularly fun product to use.

    Your suggestion -- to move insulation far away from the area when air-sealing an attic -- is a good one.

  20. User avater GBA Editor
    Martin Holladay | | #20

    Response to Bill Rose (Comment #16)
    You wrote, "I heard scuttlebutt to the effect that when a fire investigator cannot pin down a cause, 'electrical fire' is a default conclusion."

    Here in Vermont, when a hunting camp burns down -- most hunting camps are off the grid -- a fire of undetermined origin can't be blamed on the electrical wiring. The scuttlebutt I've heard (and this may have originated with journalists rather than fire investigators) is that the usual way to describe the cause of a fire in such a case is, "mice were chewing on a box of matches."

    So that's the next scenario to investigate in your lab. Don't most labs keep a few cages of mice around for experiments?

  21. Ken Chester | | #21

    Knob and Tube and insulation
    We just bought a house in Coos County NH the entire attic is knob and tube wiring. Looking at the work I must say it had to have taken forever to install. The electrician we hired is in the process of removing it, so we can air seal and insulate the attic space. The ceiling rafters are 8 inch, there's plenty of space to put a set of 2x6 the opposite way to add more insulation while still having use of the attic for walking and storage after the job is done. What do you think?

  22. Rick Van Handel | | #22

    Box store blowers and Spider fg for walls?
    A few questions for those in the know:

    Do the box store blowers have enough power to get the high end fiberglass blowing wools to a 2.0 lb density or better? I have 2x8 stud cavities to fill that are 14' high, so I'm worried about future settling with cellulose. Otherwise, do you think I can do the primary filling and then have a pro come in the finish getting the "high" density?

    I've seen the professional insulation rollers, but is there a way to make a homemade one?

  23. Rick Van Handel | | #23

    Typar instead of insulweb?
    Also, anyone see any issues with using typar septic fabric (looks like typar house wrap without plastic facer) instead of insulweb? I can get it in much wider rolls and at a lower cost.

  24. Bill Rose | | #24

    Response to Ken Chester #21
    If the house has knob and tube, it probably also has plaster ceilings, which are heavy. You might consider running new 2x6s in the same direction as the joists, with ends supported on walls, if possible, and independent of the 2x8s. This isolates the plaster load from the live and storage loads.

    I think of storage as providing some thermal resistance, and have wondered what is the R-value of a 16" thickness of Barbie dolls.

  25. Dan Kolbert | | #25

    Speaking of Barbie's
    Paul Eldrenkamp talks about attic retrofits, where the insulation is provided by shredding its contents.

    And one more piece of advice - don't do it in August. I speak from experience.

  26. User avater GBA Editor
    Martin Holladay | | #26

    Response to Rick Van Handel (Comment #23)
    Q. "Anyone see any issues with using Typar septic fabric (looks like Typar housewrap without plastic facer) instead of Insulweb?"

    A. I'm not familiar with the product you describe. Ordinary Typar certainly wouldn't work, because ordinary Typar is an air barrier. The point of using InsulWeb is that you want to use an air-permeable membrane, not an air barrier, so all the air that comes out the blower hose has somewhere to go.

    If the product you are thinking about leaks air like a sieve (unlike Typar), it might work.

  27. User avater GBA Editor
    Martin Holladay | | #27

    Response to Dan Kolbert (Comment #25)
    The best tool for transforming attic contents (Barbies, plastic Christmas ornaments, and children's rocking chairs) into shredded insulation is a brush chipper. You can't get one from Home Depot for free, unfortunately; you have to rent one. The good ones have gasoline engines, so make sure that your attic is well-ventilated.

  28. Rick Van Handel | | #28

    Yes, typar will leak air like
    Yes, typar will leak air like crazy. It's a filtration media over the gravel beds in septic systems. If you've ever looked at the backside of typar house wrap, it looks just like it. Random layers of webbing...somewhat see through.

  29. Eric Habegger | | #29

    Response to Rick Van Handel (comment 22)
    Most of the blowers for the big box stores are made by Intec. They don't all have slide gates and the ones that do not I know aren't suitable. As far as fiberglass dense packing goes I would just google Intec and then call them and see what they say. You are going to have a lot of weight bearing on the bottom portion with a 14 foot wall. Instead of doing it in two stages with two groups of people (good luck with that!) I would just consider putting in fireblocks at 3.5 foot intervals. That way you would only have 3.5 feet of insulation bearing down and compressing the lower part. You then just have to find out from Intec if one of their common blowers at big box stores will handle fiberglass 8" thick.

    I should add that if you are trying to avoid thermal bridging you could cut back the fire blocks maybe an inch or so. It should still serve the purpose of holding up the fiberglass. You could even get fancy and cut them back two inches or more and alternate them being flush with the inner wall and the outer wall.

  30. Keith H | | #30

    DIY post-mortem
    I blew insulation into my dad's converted garage attic a few years back. Here's a few DIY takeaways for anyone who read this far:

    Buy more bags than you need. It's a lot easier to return extra bags when you take the machine back than run for more
    Get a N95 dust mask or N100, especially if the attic is poorly ventilated. Don't cheap out; you only get one set of lungs.
    If your ceiling joists are 24" o.c. and the drywall is not well screwed, the weight of the cellulose may cause cracking. Something to be prepared for
    If you are going to air seal with foam and need more than a couple cans, get a pro gun via the local real lumberyard or mail order. Buy aiming tips and straws as well. SO worth the few bucks.


  31. User avater GBA Editor
    Martin Holladay | | #31

    Response to Keith H
    Thanks for sharing your suggestions and experience.

    I like your suggestion about buying more bags of cellulose than you think you'll need. I have edited the article to include your suggestion.

    I'm guessing that the main reason that you had problems with drywall ceiling cracks had very little to do with the cellulose, and more to do with the other issue you mentioned: the drywall was not well screwed.

    When I spoke to Bill Hulstrunk (an expert on cellulose insulation) on this issue, here's what he said: "We have never seen a sagging issue due to the weight of the cellulose installed above a ceiling. That may be because some of the weight of the cellulose is being redistributed onto the ceiling joists. We have blown very high R-values, up to R-100, and never had any issues with the ceiling sagging."

    Of course, "sagging" is different from "cracking." Nevertheless, I think it's true to say that if your drywall ceiling is properly installed, cellulose isn't going to cause any ceiling problems.

  32. Daniel Beideck | | #32

    Don't block attic ventilation
    Be aware of the ventilation design of your attic. I've added cellulose in a couple of attics that had venting at the eaves. There was blocking in place to prevent the cellulose that was initially installed from clogging up the vent and prevent air from entering the attic. However, the blocking was only high enough to do the job for the initial depth of insulation but wasn't high enough for the new depth with the added insulation. You need to add to the blocking before adding more cellulose or the new stuff is going to spill over the old blocking and cover the vents.

  33. User avater GBA Editor
    Martin Holladay | | #33

    Response to Daniel Beideck
    Thanks for your comments. Here are links to a GBA video and a GBA article that provide more information on the issue you brought up:

    Video: How to Ventilate Rafter Bays When Adding Insulation

    Air Sealing an Attic
    ("If your attic has soffit vents and ridge vents, you'll need a ventilation gap under the roof sheathing at the perimeter of your attic — a clear channel that allows air to flow from your soffit vents to your attic. In some attics, this area is blocked by insulation. The solution is to install ventilation baffles — either commercially available baffles or site-built baffles. If you need to install these baffles, you’ll also need to install insulation dams from the top plates of your exterior walls to the underside of the ventilation baffles.")

  34. Brian Driscoll | | #34

    Kob and tube and Cellulose
    Bought my 1920's house in 1988. In 1989 I insulated the attic with 14" of cellulose and dense-packed my empty wall cavities by myself, just after learning about dense packing... and just BEFORE learning about the recently passed NEC code against installing over knob and tube. I slightly worried for a year or so but then started to think about the physics of it all. All the wiring connections are twisted AND soldered. I also borrowed a plug-in circuit tester a few years later. The only border-line performing connection was a newer, non-knob and tube circuit, circa 1970's!
    All the knob &tube wire is 12, not 14 gauge. I had my electrician/father look at the wiring many years ago and he wasn't worried. The only spots of concern were immediately above light fixtures where the heat over the years had made the wiring insulation brittle. So I just remove the brittle part, and install electrical heat-shrink insulation sleeves over the bare wire on the last 2 inches. I no longer worry, except convincing any future buyer that it's OK.
    As a side note, I did a blower door test on this house before any air sealing or insulating in 1988 and had a 2000 cfm 50 value. Did one the other day, after many years' retrofit work . It's 750 cfm 50.

  35. Jason Peacock | | #35

    Borate only cellulose is healthier
    I did the same thing on my house with the same material and had lung issues afterward for three months. I found out after talking with Bill Hulstrunk (from National Fiber - borate only cellulose) that less quality cellulose has ammonium sulfate added, which can react with humidity and create ammonia, which is a known lung irritant. I noticed that GreenFiber now sells an "premium All Borate" version of their cellulose. Can you get the All Borate version at big box stores? Is it special order? Why don't they just get ride of the one that creates ammonia. Ammonium Sulfate costs less than Borate.

    I think wearing a good double ventilator is a really good idea when working with cellulose. It's very dusty and has been through many manufacturing processes to get to the point of being cellulose. I'm sure your lungs would agree.

  36. User avater
    Tristan Roberts | | #36

    question on double-stud walls
    On units similar to this that I have rented, the controller for the machine is on a very long power cord. As the person directing the hose I also hold the controller so that I can shut it off as needed to adjust the spray.

    Question #1 -- does anyone know if the Force 2 blower is similar in power to these boxy units? This is the unit that can be rented at the local lumberyard and I have gotten mixed messages about what densities it is capable of.

    Question #2 -- can someone explain to me how dense-packing a 12" double stud wall is a different animal when it comes to a machine like this? Is it basically that the cellulose has a lot more places to go, so achieving density is more challenging? I am asking from the point of view of wanting to do it myself.

    Thanks for sharing your experiences, Martin. No one does it better.

  37. User avater GBA Editor
    Martin Holladay | | #37

    Response to Tristan Roberts
    There are many brands of cellulose blowers. Some (like the one you rented) can be controlled from the attic with a switch on a long cord. Others (like the one I borrowed) have a simple toggle switch on the blower, with no provision for turning the blower on and off from the attic.

    Q. "Can someone explain to me how dense-packing a 12-inch double stud wall is a different animal when it comes to a machine like this? Is it basically that the cellulose has a lot more places to go, so achieving density is more challenging?"

    A. That's part of it -- and that factor can be somewhat controlled by compartmentalizing your wall with vertical dividers made of InsulWeb or Tyvek -- a step that some, but not all, builders use.

    There is another issue, however: insulation installers have learned that cellulose insulation installed in thick double-stud walls needs to be installed at a greater density to prevent settling than cellulose installed in a 2x4 or 2x6 wall. In a recent article, I quoted cellulose expert Bill Hulstunk on this issue. Hulstrunk said, “Deep cavities require that cellulose be installed at higher densities. I recommend 3.7 pounds per cubic foot for a 12-inch cavity or 4 pounds per cubic feet for an 18-inch cavity. Deeper cavities require more experienced installers, since multiple hose passes are required.”

    It's difficult for a small machine to achieve these densities.

  38. Mike Cartwright | | #38

    I have remodeled two home's
    I have remodeled two home's on my own, blowing insulation into the attic is one of the only job's I promised my wife we would never do again on our own. The house was much more comfortable though after we finished :)

  39. Mike Strevell | | #39

    Cellulose touch roof decking?
    For those of us who have no soffit or ridge vents, is it OK for the cellulose insulation to touch the underside of the plywood roof decking at the edges of the attic? Can I just blow the insulation into the edges with wild abandon?

    Will the cellulose get wet from condensation if it touches the underside of the plywood roof decking? (I live in the Rocky Mountains and the outside temperature gets down in the single digits in the winter.)

    So even if I don't have soffit vents, will I still need to create some kind of dam all the way around the edge, or attach a piece of foam to the underside of the roof decking?

    This would be nasty work since I already have fiberglass batts in the attic, and the work space out at the edge is not high, so I would be scrunching down on my knees amidst the fiberglass. So if a dam or break is needed, any tips on the easiest way to do it? Again, I do not have soffit vents. (The house was originally built with no attic vents, but the local building official made me add several mushroom vents when I put on a new roof.)

  40. User avater GBA Editor
    Martin Holladay | | #40

    Response to Mike Strevell
    There is no simple answer to your question. I'll make a few observations.

    1. If your attic is unconditioned, most building codes require that the attic be vented. This is usually accomplished with a combination of soffit vents and a ridge vent. In your case, you have mushroom vents; although these meet code, they are not the preferred method for ventilating an attic.

    2. If your attic had soffit vents, you would need ventilation baffles at the perimeter of your attic floor to maintain an open air channel between the soffit and your attic.

    3. Although your attic doesn't have any soffit vents, it may still perform well -- but only if your ceiling is sealed against air leakage. Most ceilings have a lot of air leaks, but your ceiling may be one of the rare ones that is relatively airtight.

    4. Your roof sheathing can get wet during the winter and spring, especially if your ceiling has air leaks. This occurs when escaping interior air, heavy with moisture, encounters cold roof sheathing. If cellulose is touching the roof sheathing, the cellulose can get damp. This problem can be avoided by either (a) sealing the air leaks in your ceiling, or (b) installing ventilation baffles to keep the cellulose away from the roof sheathing.

    5. If you haven't noticed any signs of damp roof sheathing or mold, your attic may be fine the way it is. Most attics are dry.

    For more information on these issues, see All About Attic Venting.

  41. Robert Connor | | #41

    You are getting a little chubby there - Time to put on your Speedo and get back in the water and get swimming with your big hands a feet again! Lets see you jump in a lake this time of year!

  42. Darren Finch | | #42

    Been there done that
    I added a 6" layer to the R38 batts in my attic (after I had sealed the airleaks of course) and added some to fill the voids where the batts had dropped in my garage ceiling, under the spare bedroom.
    I found that when I did the attic, taping a broom handle to the end made even distribution far easier, especially when hanging off the rafters with my other hand.
    The energy bill dropped by 50% once it was done so is it worth it, the local utility certainly has felt it

  43. Robert Hallenbeck | | #43

    Installing cellulse insulation on small job without a blower?
    A small section of my attic floor lacks cellulose insulation. I calculate I'll only need to install 6 bags & is easily-accessible from the 2nd floor. I'd rather avoid having to rent a truck (& again to return it) & rent the blower (6 bags is below the store's minimum for a free blower rental). Wondering if it's possible to manually loose-fill a few bags of cellulose insulation without a blower?

  44. User avater GBA Editor
    Martin Holladay | | #44

    Response to Robert Hallenbeck
    Yes, you can insulate a portion of an attic floor by just dumping the cellulose out of the bag. The main disadvantage of this approach is that the cellulose is compressed when it is packed for shipping, so you won't get the advantage of the fluffing that a blowing machine provides. It will clump.

    Use your fingers to break up the clumps as much as possible. It's a little like integrating cold butter into biscuit dough when you make biscuits. If you are worried that your manual fluffing method was imperfect, just buy a few more bags to make the cellulose layer a little thicker.

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